Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Nov Mon 11, 2019 9:24 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 47 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 1:15 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4273
Location: Boston, MA USA
Another PA amplifier.

-David


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 1:23 am 
Member
User avatar

Joined: Sep Sat 29, 2018 8:42 pm
Posts: 480
Location: Hamilton, Ontario, Canada. L8R 3H4
dberman51 wrote:
Another PA amplifier.

-David

It has mic inputs, but the frequency response seems high-fidelity. How can you tell it is a PA amp?

_________________
51' Crosley Alarm Clock Radio–D-25MN
57' Heathkit EA-2 Amplifier
58' DuMont–Sound Stage 200


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 2:28 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5352
Location: Rochester NY USA
It's a PA amp, one of the better ones. I've measured the output transformer, and it's better than anything Dynaco made. But the output tubes are 8417s, made of unobtanium.

Bogen made some really good amplifiers for sound reproduction, and some like the Challenger series that were NOT so great. Unfortunately their best amps often used tubes like 8417 and 7868 that are hard to find and expensive if you DO find them.

_________________
My web page: https://bit.ly/2rxq4qx


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 2:38 am 
Member
User avatar

Joined: Sep Sat 29, 2018 8:42 pm
Posts: 480
Location: Hamilton, Ontario, Canada. L8R 3H4
Tom Bavis wrote:
It's a PA amp, one of the better ones. I've measured the output transformer, and it's better than anything Dynaco made. But the output tubes are 8417s, made of unobtanium.

Bogen made some really good amplifiers for sound reproduction, and some like the Challenger series that were NOT so great. Unfortunately their best amps often used tubes like 8417 and 7868 that are hard to find and expensive if you DO find them.

When you say 'output' was better than any Dynaco, do you mean the wattage or the frequency range or both?

How does the sound compare to a regular (non-PA) Dynaco or Eico? Could it be run as a regular amp and give high-fidelity output?

The seller will sell to me for 70 USD + 60 USD shipping = 130 USD. This is by far the best deal I've seen for a tube amp shipping to Canada. It's not a pretty amp, but I imagine I can work a little on the cosmetics.

_________________
51' Crosley Alarm Clock Radio–D-25MN
57' Heathkit EA-2 Amplifier
58' DuMont–Sound Stage 200


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 4:33 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5352
Location: Rochester NY USA
I measured the output transformer only, it's the one component that presents the biggest limits on a tube amp design. It had high frequency performance that was among the best I measured. (low frequency performance can be measured by the pound - the bigger, the better - and this one is big!).

I haven't measured the amplifier or listened to it, but would expect the power amplifier section to be as good as a Dynaco Mark III 60 watt (you DON'T want the mike preamp or control section though!) It would need a good matched pair of 8417 output tubes for optimum performance. They're there but are they good, and matched? They aren't made any more - a good pair would cost more than you would pay for the amp - and what about replacements in a few years?. If I had this amp and wanted to USE it, I would modify it to use EL34 tubes which are readily available. But I would probably sell it and use one that uses EL34s or 6L6s, (which I have in quantity). I have a couple of 30W amps (using 6L6s) which are more than adequate for my least efficient speakers.

_________________
My web page: https://bit.ly/2rxq4qx


Last edited by Tom Bavis on Nov Thu 29, 2018 4:48 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 4:44 am 
Member

Joined: Feb Wed 04, 2015 12:26 am
Posts: 948
T he Bogen will have a more "forward" sound to it, more "punch". They aren't bad sounding amps, but it really does depend on the model.

I have a Bogen stereo Hi Fi amp 14 + 14 watt (6V6,) and a Bogen challenger from late 40, also 6v6, the output xformer for both amps the same size physically, but with different preamp circuitry.

Grommes Precision was the outlier. They used high fidelity xformers in ALL their amps. PA and Hi Fi. These amplifiers have unbelievable sound quality. They are considered "sleeper" amps. Even with commercial PA speakers, the detail and clarity on the dance floor with GP tube amps was such that even MIDDLE SCHOOL kids at the dance were going WTH?


100 watt GP amp

https://www.ebay.com/itm/Grommes-Precis ... :rk:1:pf:0


6GT5 are available and the prices aren't too bad.


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 9:28 am 
Member
User avatar

Joined: Sep Mon 16, 2013 2:42 am
Posts: 3503
Location: Tucson, Arizona U.S.A.
That's another PA amplifier, a rather nice one but still PA.

When an amplifier has a frequency response spec, be sure that they give the power level. The response range gets considerably smaller as the power output goes up.

Another thing to consider is the cost of replacement tubes. You may want to think again if you find one that contains one of the super expensive types no matter how good the specs are.

_________________
Jim Mueller


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 9:50 am 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 4573
Location: Sunnyvale CA
Quote:
Quote:
If you really want a hi-fi amplifier from that era, you can certainly do better than this one. There are a lot of pretty good mono amps from the mid-late 50's like the Dynaco Mk III or MK IV, and decent performers from Heathkit, Eico, Scott. The less-good versions might fall into your price range as long as you are willing to work on refurbishing them. A quick survey of that auction site indicates several pretty good Heathkits that would serve your purposes and are under $200.

I would however note that there are many much better stereo amplifiers routinely available for about the same price or less. The Dynaco ST-120 can usually be found for under $100 and reworking it to be reliable is quite inexpensive, and the performance is far better than any 50's mono tube amp. I saw a couple of ST-150s, supposedly working, for under $200, and that is likely to be better than almost all tube amps of any age or cost.

Brett

I took at look at the specs of the Dynaco ST-120 (Freq. Resp. 5Hz to 100,000Hz, SNR 95dB, THD .5), and they are amazing. Though, I was really hoping to get a tube amp. I do like the Dynaco ST-70, but only if it is within my price range, and I've yet to see that.

A big buying factor for me is the look of the amp, as it will be going in my living room Yes, it's superficial, but this is something I want to have for the rest of my life, so I'll have to look at it for a long time. Might as well be something that I find attractive. So far, I really like the look of all the Dynacos, and I like the look of some of the Eico amps, especially the ones with the brass faceplates.

I'm not thinking of purchasing any time before the new year. I'm just gathering information so I can keep an eye out daily if anything comes up for a really good price. After talking to you guys, I have a much better idea of what I want.


You aren't likely to be finding an ST-70 in any sort of presentable shape for $200. Most of them are pretty crummy-looking, because the chrome plating has rusted through. If I ever build another one for myself, I will at least use a current-manufacture polished stainless chassis. The nice thing is you can get any required part up to an including an entire complete kit, all of much better quality than the original parts except for the transformers. Even really ugly examples go for $350 up.

Those gaudy specs for the ST-120 (particularly the 100 KHz part) is probably more of a defect than a feature. The nasty part is that it is fully capable of going unstable at frequencies far beyond the audible range, and at least the first version of the circuit did just that, frequently, which fried something in extremely short order - either your tweeter voice coil, or more often, the output transistors, which melt into little flaming puddles in a few seconds to tens of seconds. The flame is mostly blue, with some green in it. You have to either buy the second version with the modified driver circuit, or you need to modify it yourself using one of the proven-good altered circuits, to have reliable performance. You *do not want* your audio amplifier to run out to 100 KHz anyway, all that does is make it more susceptible to distortion, saturation, or whatever bad thing that interference can cause. I put filters on the input to knock down the response from about 15 to about 25KHz, and that cleaned up what I saw on the scope, and sounded better. They are also not too pretty, just a little black/chrome box, and tend to have the same problem with the peeling or rusted-through chrome. The internal parts are visible and always have about a million little dust dots where dust has drifted through the perforated cover.

Mine worked perfectly (after A LOT of work but no outright meltdowns, because someone warned me first) and was in perfect cosmetic shape. I would give it to you - if it hadn't gotten stolen from my storage unit!

As noted, there are always a bunch of acceptable-performance mono hi-fi tube preamps and amps from Eico, Heath, Scott, etc, and at least the Eico and Heaths are usually "giveaway" prices. I would assume that anything like that would require refurbishment to operate reliably, just like a radio, and for a mono system, it's about as easy as a radio, because there are no parts to match between left and right channels like a stereo amplifier. None of them will be really stellar performers, but the errors tend to be inoffensive and even "warm":

https://www.ebay.com/itm/Tested-Vintage ... :rk:2:pf:0
https://www.ebay.com/itm/Vintage-Heathk ... rk:11:pf:0

I have no stake in these listings, just an example.

A consideration is what speakers, er, speaker you want to use. These ancient tube amplifiers are all pretty weak by modern hi-fi standards, where you can easily get arbitrary power with transistor amplifiers, literally, as much as you want. Tube amplifiers tend to play "bigger" than equivalent transistor amplifiers, but you are talking about maybe 10-15 watts for the little ones at best. That will get acceptable loud with most modern speakers, but you will not have tremendous dynamics. Depending on what you listen to, that may not be a problem, but just be aware that most current speakers are in the 86-90 dB/watt range, and old speakers intended for these feeble amplifiers may have been more like 100 db/watt. You aren't going to want to take your little 8 watt EL-84 amp and hook it up to an OHM F, or AR-1, or B&W DM3000 - it will work, but you will hit the limits very easily.

Brett


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 12:30 pm 
Member

Joined: Feb Wed 04, 2015 12:26 am
Posts: 948
Jim Mueller wrote:
That's another PA amplifier, a rather nice one but still PA.

When an amplifier has a frequency response spec, be sure that they give the power level. The response range gets considerably smaller as the power output goes up.

Another thing to consider is the cost of replacement tubes. You may want to think again if you find one that contains one of the super expensive types no matter how good the specs are.


Jim,

It was actually Precision themselves that told me about those amps. I had to get the schematic for one of mine. The output transformers are as large as Dynaco or other high fi amps with the same amount of power.


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 12:46 pm 
Member

Joined: Feb Wed 04, 2015 12:26 am
Posts: 948
Brett_Buck wrote:
Quote:
Quote:
If you really want a hi-fi amplifier from that era, you can certainly do better than this one. There are a lot of pretty good mono amps from the mid-late 50's like the Dynaco Mk III or MK IV, and decent performers from Heathkit, Eico, Scott. The less-good versions might fall into your price range as long as you are willing to work on refurbishing them. A quick survey of that auction site indicates several pretty good Heathkits that would serve your purposes and are under $200.

I would however note that there are many much better stereo amplifiers routinely available for about the same price or less. The Dynaco ST-120 can usually be found for under $100 and reworking it to be reliable is quite inexpensive, and the performance is far better than any 50's mono tube amp. I saw a couple of ST-150s, supposedly working, for under $200, and that is likely to be better than almost all tube amps of any age or cost.

Brett

I took at look at the specs of the Dynaco ST-120 (Freq. Resp. 5Hz to 100,000Hz, SNR 95dB, THD .5), and they are amazing. Though, I was really hoping to get a tube amp. I do like the Dynaco ST-70, but only if it is within my price range, and I've yet to see that.

A big buying factor for me is the look of the amp, as it will be going in my living room Yes, it's superficial, but this is something I want to have for the rest of my life, so I'll have to look at it for a long time. Might as well be something that I find attractive. So far, I really like the look of all the Dynacos, and I like the look of some of the Eico amps, especially the ones with the brass faceplates.

I'm not thinking of purchasing any time before the new year. I'm just gathering information so I can keep an eye out daily if anything comes up for a really good price. After talking to you guys, I have a much better idea of what I want.


You aren't likely to be finding an ST-70 in any sort of presentable shape for $200. Most of them are pretty crummy-looking, because the chrome plating has rusted through. If I ever build another one for myself, I will at least use a current-manufacture polished stainless chassis. The nice thing is you can get any required part up to an including an entire complete kit, all of much better quality than the original parts except for the transformers. Even really ugly examples go for $350 up.

Those gaudy specs for the ST-120 (particularly the 100 KHz part) is probably more of a defect than a feature. The nasty part is that it is fully capable of going unstable at frequencies far beyond the audible range, and at least the first version of the circuit did just that, frequently, which fried something in extremely short order - either your tweeter voice coil, or more often, the output transistors, which melt into little flaming puddles in a few seconds to tens of seconds. The flame is mostly blue, with some green in it. You have to either buy the second version with the modified driver circuit, or you need to modify it yourself using one of the proven-good altered circuits, to have reliable performance. You *do not want* your audio amplifier to run out to 100 KHz anyway, all that does is make it more susceptible to distortion, saturation, or whatever bad thing that interference can cause. I put filters on the input to knock down the response from about 15 to about 25KHz, and that cleaned up what I saw on the scope, and sounded better. They are also not too pretty, just a little black/chrome box, and tend to have the same problem with the peeling or rusted-through chrome. The internal parts are visible and always have about a million little dust dots where dust has drifted through the perforated cover.

Mine worked perfectly (after A LOT of work but no outright meltdowns, because someone warned me first) and was in perfect cosmetic shape. I would give it to you - if it hadn't gotten stolen from my storage unit!

As noted, there are always a bunch of acceptable-performance mono hi-fi tube preamps and amps from Eico, Heath, Scott, etc, and at least the Eico and Heaths are usually "giveaway" prices. I would assume that anything like that would require refurbishment to operate reliably, just like a radio, and for a mono system, it's about as easy as a radio, because there are no parts to match between left and right channels like a stereo amplifier. None of them will be really stellar performers, but the errors tend to be inoffensive and even "warm":

https://www.ebay.com/itm/Tested-Vintage ... :rk:2:pf:0
https://www.ebay.com/itm/Vintage-Heathk ... rk:11:pf:0

I have no stake in these listings, just an example.

A consideration is what speakers, er, speaker you want to use. These ancient tube amplifiers are all pretty weak by modern hi-fi standards, where you can easily get arbitrary power with transistor amplifiers, literally, as much as you want. Tube amplifiers tend to play "bigger" than equivalent transistor amplifiers, but you are talking about maybe 10-15 watts for the little ones at best. That will get acceptable loud with most modern speakers, but you will not have tremendous dynamics. Depending on what you listen to, that may not be a problem, but just be aware that most current speakers are in the 86-90 dB/watt range, and old speakers intended for these feeble amplifiers may have been more like 100 db/watt. You aren't going to want to take your little 8 watt EL-84 amp and hook it up to an OHM F, or AR-1, or B&W DM3000 - it will work, but you will hit the limits very easily.

Brett



Brett,

You are correct, it does take the right speaker, but you easily fill a room and stay with the power limits of the amp. The living room HT system here uses Klipsch bookshelf speakers for the mains and a Packard Bell DP30 ( 6BQ5 x2 per channel, 18 watts per channel) and it easily gets too loud for the living room. My Packard Bell console stereo (correct amp and speakers, same amp, DP30) shakes the house. I've used that stereo for loud house parties.

With a pair of those tube Precision amps, (65 watt, 6GT5 x2) and a pair of Peavey SP2, I covered 700 screaming Elementary students at a Halloween dance in a gym. Those amps not were even breathing hard.

These new "thin" SS amplifiers, especially plate amplifiers used in powered PA speakers, are the equivalent of having a ice pick shoved into my ears in terms of sound quality. The same goes for most midrange Home Theater systems. I tried different speakers on a Sony HT reciever and it was like sandpaper.

Today's power ratings are severely overblown.


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 2:13 pm 
Member
User avatar

Joined: Sep Sat 29, 2018 8:42 pm
Posts: 480
Location: Hamilton, Ontario, Canada. L8R 3H4
Tom Bavis wrote:
I measured the output transformer only, it's the one component that presents the biggest limits on a tube amp design. It had high frequency performance that was among the best I measured. (low frequency performance can be measured by the pound - the bigger, the better - and this one is big!).

I haven't measured the amplifier or listened to it, but would expect the power amplifier section to be as good as a Dynaco Mark III 60 watt (you DON'T want the mike preamp or control section though!) It would need a good matched pair of 8417 output tubes for optimum performance. They're there but are they good, and matched? They aren't made any more - a good pair would cost more than you would pay for the amp - and what about replacements in a few years?. If I had this amp and wanted to USE it, I would modify it to use EL34 tubes which are readily available. But I would probably sell it and use one that uses EL34s or 6L6s, (which I have in quantity). I have a couple of 30W amps (using 6L6s) which are more than adequate for my least efficient speakers.

Great news about the transformer preforming so well; but the knowledge of the 8417 tubes being scarce and expensive makes me reconsider. How easy would it be to modify to EL34 tubes? Would have to be very easy for me to consider.

Quote:
T he Bogen will have a more "forward" sound to it, more "punch". They aren't bad sounding amps, but it really does depend on the model.

I have a Bogen stereo Hi Fi amp 14 + 14 watt (6V6,) and a Bogen challenger from late 40, also 6v6, the output xformer for both amps the same size physically, but with different preamp circuitry.

Grommes Precision was the outlier. They used high fidelity xformers in ALL their amps. PA and Hi Fi. These amplifiers have unbelievable sound quality. They are considered "sleeper" amps. Even with commercial PA speakers, the detail and clarity on the dance floor with GP tube amps was such that even MIDDLE SCHOOL kids at the dance were going WTH?


100 watt GP amp

https://www.ebay.com/itm/Grommes-Precis ... :rk:1:pf:0

The price of the amp is certainly right, but I question 'why' all these amps are going for such low prices on ebay. Also, I spent a good 30 minutes at least trying to find a manual with specs for these amps and ended up with nothing. I don't mean to put aside your suggestion, but I would have to see specs to consider.

Love the look of the amp, btw!

Quote:
That's another PA amplifier, a rather nice one but still PA.

When an amplifier has a frequency response spec, be sure that they give the power level. The response range gets considerably smaller as the power output goes up.

Another thing to consider is the cost of replacement tubes. You may want to think again if you find one that contains one of the super expensive types no matter how good the specs are.

I'd prefer it not be a PA, but if the PA is high quality then I will consider it. As to power, I really only need a few watts; I live in an apartment, and I respect my neighbours. But, the sound that I do hear, I want it to be clean and sharp and cover all of the frequencies. I'd like to listen to classical music on it. The previous comment on the 8417 tubes is right along what you say, too. I don't want to get into having to worry about replacing those expensive tubes.

Quote:
You aren't likely to be finding an ST-70 in any sort of presentable shape for $200. Most of them are pretty crummy-looking, because the chrome plating has rusted through. If I ever build another one for myself, I will at least use a current-manufacture polished stainless chassis. The nice thing is you can get any required part up to an including an entire complete kit, all of much better quality than the original parts except for the transformers. Even really ugly examples go for $350 up.

I'm slowly finding that out. Spent hours last night searching on Ebay with the price range at 0 - $200 CDN. Looked at what was available and what sold for. No much there. I'll have to up it to perhaps $300 CDN. (with an extra $100 for shipping... so $400 altogether) and save for a few months to get something nice. I want this amp for life, but at the same time, this amp is not my entire life, so there is a limit I would spend on it...

I'll search tonight under those prices and see what's available. As for ugly, I don't mind doing work to it (e.g., caps, sanding, painting, new knobs...).

Quote:
Those gaudy specs for the ST-120 (particularly the 100 KHz part) is probably more of a defect than a feature. The nasty part is that it is fully capable of going unstable at frequencies far beyond the audible range, and at least the first version of the circuit did just that, frequently, which fried something in extremely short order - either your tweeter voice coil, or more often, the output transistors, which melt into little flaming puddles in a few seconds to tens of seconds. The flame is mostly blue, with some green in it. You have to either buy the second version with the modified driver circuit, or you need to modify it yourself using one of the proven-good altered circuits, to have reliable performance. You *do not want* your audio amplifier to run out to 100 KHz anyway, all that does is make it more susceptible to distortion, saturation, or whatever bad thing that interference can cause. I put filters on the input to knock down the response from about 15 to about 25KHz, and that cleaned up what I saw on the scope, and sounded better. They are also not too pretty, just a little black/chrome box, and tend to have the same problem with the peeling or rusted-through chrome. The internal parts are visible and always have about a million little dust dots where dust has drifted through the perforated cover.

I had not considered this. Though I have heard a lot about these amps 'burning up' themselves. I don't plan on ever cranking the volume, but there is always the chance that accidentally the volume is cranked or a high input happens. The filter is a good idea. Also, I'm betting that ST-120 would require a pre-amp. I wouldn't mind doing all that. I'm thinking I could add a makeshift volume control to the input until then. So there are some options.

Quote:
Mine worked perfectly (after A LOT of work but no outright meltdowns, because someone warned me first) and was in perfect cosmetic shape. I would give it to you - if it hadn't gotten stolen from my storage unit!

You guys have been so kind to me. There is no happy crying smiley, but that would be appropriate in this case. :) Sad that people can sometimes be so low that they would steal it from you, when you might have even given it away had they asked.

Quote:
As noted, there are always a bunch of acceptable-performance mono hi-fi tube preamps and amps from Eico, Heath, Scott, etc, and at least the Eico and Heaths are usually "giveaway" prices. I would assume that anything like that would require refurbishment to operate reliably, just like a radio, and for a mono system, it's about as easy as a radio, because there are no parts to match between left and right channels like a stereo amplifier. None of them will be really stellar performers, but the errors tend to be inoffensive and even "warm":

https://www.ebay.com/itm/Tested-Vintage ... :rk:2:pf:0
https://www.ebay.com/itm/Vintage-Heathk ... rk:11:pf:0

I have no stake in these listings, just an example.

I'm really liking the specs on the Eico amps. They are cute little performers and great for what I'd use them for. Heathkit seemed a little under Eico in terms of specs during my comparison. Didn't see much of the Scott amps. Mono is okay, though stereo is better. As for the 'warm' sound, I prefer it, but I would like to get the highs in (e.g., +10kHz range). Currently, nothing in my home is capable of that.

That Heathkit EA-3 amp is a nice looker with it's brass (I love brass; I have several brass candlestick lamps and ornaments). Couldn't find the specs though, for either amp, only a one schematic for the EA-3.

Quote:
A consideration is what speakers, er, speaker you want to use. These ancient tube amplifiers are all pretty weak by modern hi-fi standards, where you can easily get arbitrary power with transistor amplifiers, literally, as much as you want. Tube amplifiers tend to play "bigger" than equivalent transistor amplifiers, but you are talking about maybe 10-15 watts for the little ones at best. That will get acceptable loud with most modern speakers, but you will not have tremendous dynamics. Depending on what you listen to, that may not be a problem, but just be aware that most current speakers are in the 86-90 dB/watt range, and old speakers intended for these feeble amplifiers may have been more like 100 db/watt. You aren't going to want to take your little 8 watt EL-84 amp and hook it up to an OHM F, or AR-1, or B&W DM3000 - it will work, but you will hit the limits very easily.

Currently, I have a Stromberg Carlson 863PM radio cabinet with its 12" speaker. I love the sound of it. :P Could only imagine what I would sound like on a decent amp (https://www.radiomuseum.org/r/stromberg ... nsole.html , has some speaker and chassis but not same cabinet). Even my 1.4 watt (max) radios run this quite loud. I am keeping my eye open for a wreak with a 15" speaker at a decent price. I have tweeters to go with it.

Quote:
It was actually Precision themselves that told me about those amps. I had to get the schematic for one of mine. The output transformers are as large as Dynaco or other high fi amps with the same amount of power.

If you could find the specs, would be awesome. Like the fact that the transformer is big. Might be worth the low price in itself!

Quote:
With a pair of those tube Precision amps, (65 watt, 6GT5 x2) and a pair of Peavey SP2, I covered 700 screaming Elementary students at a Halloween dance in a gym. Those amps not were even breathing hard.

Nice! :P

Thanks for all these informative replies. :)

I'll be searching ebay/kijiji tonight with these new considerations. Might post a WTB in the ARF classifieds... Gotta go. Time to teach the kinders! :P

_________________
51' Crosley Alarm Clock Radio–D-25MN
57' Heathkit EA-2 Amplifier
58' DuMont–Sound Stage 200


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 6:13 pm 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 4573
Location: Sunnyvale CA
Artcurus wrote:
You are correct, it does take the right speaker, but you easily fill a room and stay with the power limits of the amp. The living room HT system here uses Klipsch bookshelf speakers for the mains and a Packard Bell DP30 ( 6BQ5 x2 per channel, 18 watts per channel) and it easily gets too loud for the living room. My Packard Bell console stereo (correct amp and speakers, same amp, DP30) shakes the house. I've used that stereo for loud house parties.

With a pair of those tube Precision amps, (65 watt, 6GT5 x2) and a pair of Peavey SP2, I covered 700 screaming Elementary students at a Halloween dance in a gym. Those amps not were even breathing hard.

These new "thin" SS amplifiers, especially plate amplifiers used in powered PA speakers, are the equivalent of having a ice pick shoved into my ears in terms of sound quality. The same goes for most midrange Home Theater systems. I tried different speakers on a Sony HT reciever and it was like sandpaper.

Today's power ratings are severely overblown.


I am not sure why you mention these crude "plate" amplifiers (I had to look that up, since I had no idea what they are) in these terms. Those are just not in the discussion space I was in, if you want something like that, you could do better building one yourself from some 2n3055s and a salvaged transformer, or just jumping on eBay and buying a silver age Pioneer SA series for <$100. I thought you weren't looking at PA-style/quality amplifiers - the Stromberg-Carlson that started this thread or these Class D sound reinforcement-type systems.

But it's trivially easy to find 200+ watt transistor amplifiers that definitely give you everything claimed, and can drive low-impedance amps with ease, and I assure you that the ratings are not overblown. Even the first generation like the ST-120 gave nearly the full 60 watts/channel straight off out of the box, which put it ahead of it's older brother ST-70, which was "rated" at 35 watts/channel and gave about 22 or so.

I think we are starting to talk at cross purposes here, and this discussion is beginning to sound kind of familiar, so I think my previous suggestions are about the best I can do for your constraints.

Brett


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Thu 29, 2018 7:26 pm 
Member
User avatar

Joined: Sep Sat 29, 2018 8:42 pm
Posts: 480
Location: Hamilton, Ontario, Canada. L8R 3H4
Brett_Buck wrote:
Artcurus wrote:
I think we are starting to talk at cross purposes here, and this discussion is beginning to sound kind of familiar, so I think my previous suggestions are about the best I can do for your constraints.

Brett

Sorry about that. As I'm learning what is available, I'm sort of all over the place. :?

Found something I really like, and it was a recommendation that you guys made:

Heathkit EA-2

It's fully restored, in near perfect condition, and the seller is asking $150 USD (all shipping, taxes... included). This is the perfect little amp for me. It's all I need and nothing more. Even the bass and treble control frequencies are perfect for me. :)

Overall Frequency Response at 12 watts: ± 1 db 20 to 20 kc.
Harmonic Distortion at 12 watts: 1% or less @ 12 watts 20-20 kc.
Intermodulation Distortion at 12 watts: 1.5% (4:1 ratio 60 & 6,000 CPS).
Hum and Noise Level: 47 db below 12 watts, MAG phono. 60 db below 12 watts, AUX inputs. (This sounds a little high to me, but I'm sure it shouldn't be too noticeable)
Tone Controls: Bass (at 30 cps)—15 db boost, 17 db cut; Treble (at 15 kc)—15 db boost, 20 db cut. (Low bass boost, and high treble boost at 15 db!)
Tube complement: 1-12AX7, 1-6C4, 1-6AN8, 2-EL84, 1-EZ81. (Good, cheap tubes! :) )
Dimensions: 12½" W x 8 3/16" D x 4 3/8" H.
Power Requirements: 117V, 60 cycle AC, 120 watts. Shipping Weight: 15 lbs.

Courtesy of
http://www.heathkit-museum.com/hifi/hvmea-2.shtml

Sometimes when you find something you like it just 'clicks' and feels right. This is that amp. I'll be contacting the seller to arrange how we can go about this.

Thanks everyone! :D

*** EDIT ***

I called the seller and offered $110 and told him that it was what I could do (mentioned X-Mas coming...), which is the truth, as we know. He wanted at least $135 for it; he spent about $110 just for the servicing. It has been in the family. I told him that I don't flip and that this is a keeper for me. He said that he would like some time to think it over during the weekend. I also asked if he would be able to hold the radio if I gave him money to hold it, and that I could pay what he asked ($150), which I think was a very reasonable offer on my part. Obviously, if I chose not to buy, he'd end up with a free $20-$40 after a month, for nothing. He said, "I don't really wanna get into that."

I offered what I could and what he was asking. I got the vibe that even if I had offered more than he was asking to hold it a month, that he would not have done it. Seems he just wants to rid himself of it with without any hassle. This is a huge assumption, but i am thinking he is rich (by where he lives; his house is worth probably 1.5 to 2 million, easy) and that he doesn't want to condescend to a person like me, but he is too nice to say so.

Anyways, it's not his problem. But, ugh, that's what I get for getting my hopes up like this. :(


Attachments:
File comment: Same model but not selfsame amp.
ea-2.jpg
ea-2.jpg [ 180.78 KiB | Viewed 877 times ]

_________________
51' Crosley Alarm Clock Radio–D-25MN
57' Heathkit EA-2 Amplifier
58' DuMont–Sound Stage 200
Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Fri 30, 2018 1:16 am 
Member
User avatar

Joined: Sep Mon 16, 2013 2:42 am
Posts: 3503
Location: Tucson, Arizona U.S.A.
The mention of solid state Dynaco amplifiers burning up reminded me of something. On my job in the early '70s a couple of engineers got together to analyze the circuit of one of these (unfortunately I don't remember which model). We found that although the output had over current protection, it did not have second breakdown protection. So the output transistors could be destroyed by an improper load. Depending on the circuit, which I also don't remember, this might also destroy the speakers.

So if you go with one of these, be careful to have the correct load and not accidentally short the output.

_________________
Jim Mueller


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Nov Fri 30, 2018 2:36 am 
Member
User avatar

Joined: Sep Sat 29, 2018 8:42 pm
Posts: 480
Location: Hamilton, Ontario, Canada. L8R 3H4
Jim Mueller wrote:
The mention of solid state Dynaco amplifiers burning up reminded me of something. On my job in the early '70s a couple of engineers got together to analyze the circuit of one of these (unfortunately I don't remember which model). We found that although the output had over current protection, it did not have second breakdown protection. So the output transistors could be destroyed by an improper load. Depending on the circuit, which I also don't remember, this might also destroy the speakers.

So if you go with one of these, be careful to have the correct load and not accidentally short the output.

Generally I would be quite lax with speaker connections, but I will be extra careful now; I wouldn't have thought that the transformer would fry itself.

So many stories about these ST-120s blowing up, melting, smoking... Maybe it's a good thing that someone stole that amp from Brett's house? Perhaps, in a most ironic example of karma, that amp will end up burning that thief's house down; but, due to the amp's solid metal and quality parts, it is the only thing that sustains the fire, in turn, living on like a curse. :P

Just tryin' to think positive. :roll:

*** EDIT ***

Okay, final resolution: he accepted $180 CDN. ($135 USD.) for the Heathkit EA-2 amp. I'll be picking it up on Sunday. :)

_________________
51' Crosley Alarm Clock Radio–D-25MN
57' Heathkit EA-2 Amplifier
58' DuMont–Sound Stage 200


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Dec Tue 04, 2018 1:42 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 20672
Location: Utica, NY 13502 (USA)
bedtime wrote:
Okay, final resolution: he accepted $180 CDN. ($135 USD.) for the Heathkit EA-2 amp. I'll be picking it up on Sunday. :)

Great!

viewtopic.php?f=13&t=350454

Dave


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Dec Thu 06, 2018 5:59 pm 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 4573
Location: Sunnyvale CA
Jim Mueller wrote:
The mention of solid state Dynaco amplifiers burning up reminded me of something. On my job in the early '70s a couple of engineers got together to analyze the circuit of one of these (unfortunately I don't remember which model). We found that although the output had over current protection, it did not have second breakdown protection. So the output transistors could be destroyed by an improper load. Depending on the circuit, which I also don't remember, this might also destroy the speakers.


That's not the biggest issue with the ST-120. The biggest issue was the driver circuit going unstable, full-blown high frequency oscillation, which then blew the output transistors in very short order (seconds at most). There were many changes over the production to resolve this issue, and if you do not fix it, you will just blow the replacements, also almost immediately. The entire driver circuit has to be modified to the final production design to make it stable and remain that way. This is commonly known as the "TIP mod" but there are several competing variants on that, two of them appear to work, and the rest do not.

Unfortunately, even if you do this, you will then find acceptable replacement output transistors nearly impossible to find. The originals were specially-screened versions of the 2N3055 that were rated to operate at 90V instead of 60. Unless you know this, you will go down to the local NTE dealer and get some 2N3055 semi-rejects and they will blow in very short order, causing damage elsewhere. There are several better replacements that are also hard to find (2N5630 being the most likely candidate) that require other changes. This turns it into a Dynaco ST-400 Jr as far as this goes.

Note that once you blow one channel out, it frequently causes the Vcc to go high (only one channel instead of two), and then *blow the other channel due to overvoltage). The power supply regulator is a very slow series regulator, so the overshoot is non-trivial. If you are lucky, the power supply itself fails as the first channel goes down, keeping this from happening, but then it seems like *both* output channels are failed. Unfortunately, the power supply is also almost impossible to repair as well, again requiring specially-selected and matched parts, and if you don't have those (and you don't) you have to use subs and tweak it with select-in-test parts to trim it for proper operation. The solution to this issue is to completely replace the power supply with a different design, and to individually fuse the two channel power supply so that you don't get fratricide.

There are many different variants on these modifications, and many of them just repair the existing power supply, which, if you solve the other issues, is arguably OK. I would suggest the modifications from "Audio Basics" in August 1984, available from Frank Van Alstine's site. AT LEAST, put 3 amp fast-blow fuses In the Vcc line to each channel.

Do all this and it's dead reliable, performs very well, and sounds great. But that is A LOT of work when you can go buy a ST-150, that is like an ST-120 with all the horrible mistakes fixed, for $150.

Note also that the later Dyna transistor amplifiers are among the most bulletproof every made, sort of an overreaction to the early ST-120 problems. You could use the 416 as an arc welder if you wanted. Unfortunately these are frequently modified to greatly increase the power supply capacitance with one rather famous modification that increased it to either 470,000 mfd for the timid, and 940,000 for the die-hards, depending on *how many external capacitor chassis you felt like constructing*. This did not improve the performance, in fact, it reduced the performance and sometimes made it unstable and prone to shutting down via the self-protect circuits.

I had an ST-120 because that was all I could afford, it was the first electronic component I built, followed shortly by a PAT-4 preamp (also a very questionable design, particularly the tone control circuit, but also having some problems in the line amp section). I was quite dismayed when both went away and then probably wound up getting sold at the San Jose flea market for $10 for some hop-head to buy crystal meth,

Brett


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Dec Thu 06, 2018 6:07 pm 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 4573
Location: Sunnyvale CA
Jim Mueller wrote:
The mention of solid state Dynaco amplifiers burning up reminded me of something. On my job in the early '70s a couple of engineers got together to analyze the circuit of one of these (unfortunately I don't remember which model). We found that although the output had over current protection, it did not have second breakdown protection. So the output transistors could be destroyed by an improper load. Depending on the circuit, which I also don't remember, this might also destroy the speakers.


That's not the biggest issue with the ST-120 (which didn't have self-protect circuits and was AC-coupled) The biggest issue was the driver circuit going unstable, full-blown high frequency oscillation, which then blew the output transistors in very short order (seconds at most). There were many changes over the production to resolve this issue, and if you do not fix it, you will just blow the replacements, also almost immediately. The entire driver circuit has to be modified to the final production design to make it stable and remain that way. This is commonly known as the "TIP mod" but there are several competing variants on that, two of them appear to work, and the rest do not.

Unfortunately, even if you do this, you will then find acceptable replacement output transistors nearly impossible to find. The originals were specially-screened versions of the 2N3055 that were rated to operate at 90V instead of 60. Unless you know this, you will go down to the local NTE dealer and get some 2N3055 semi-rejects and they will blow in very short order, causing damage elsewhere. There are several better replacements that are also hard to find (2N5630 being the most likely candidate) that require other changes. This turns it into a Dynaco ST-400 Jr as far as this goes.

Note that once you blow one channel out, it frequently causes the Vcc to go high (only one channel instead of two), and then *blow the other channel due to overvoltage*. The power supply regulator is a very slow series regulator, so the overshoot is non-trivial. If you are lucky, the power supply itself fails as the first channel goes down, keeping this from happening, but then it seems like *both* output channels are failed. Unfortunately, the power supply is also almost impossible to repair as well, again requiring specially-selected and matched parts, and if you don't have those (and you don't) you have to use subs and tweak it with select-in-test parts to trim it for proper operation. The solution to this issue is to completely replace the power supply with a different design, and to individually fuse the two channel power supply connections so that you don't get fratricide.

There are many different variants on these modifications, and many of them just repair the existing power supply, which, if you solve the other issues, is arguably OK. I would suggest the modifications from "Audio Basics" in August 1984, available from Frank Van Alstine's site. AT LEAST, put 3 amp fast-blow fuses In the Vcc line to each channel.

Do all this and it's dead reliable, performs very well, and sounds great. But that is A LOT of work when you can go buy a ST-150, that is like an ST-120 with all the horrible mistakes fixed, for $150.

Note also that the later Dyna transistor amplifiers are among the most bulletproof ever made, sort of an overreaction to the early ST-120 problems. You could use the 416 as an arc welder if you wanted. Unfortunately these are frequently modified to greatly increase the power supply capacitance with one rather famous modification that increased it to either 470,000 mfd for the timid, and 940,000 for the die-hards, depending on *how many external capacitor chassis you felt like constructing*. This did not improve the performance, in fact, it reduced the performance and sometimes made it unstable and prone to shutting down via the self-protect circuits. It did, however, make for a bragging point at your hi-fi club meetings. Any more filtering than necessary to remove audible hum is probably pointless, but taking it to the extreme can be very detrimental.

I had an ST-120 because that was all I could afford, it was the first electronic component I built, followed shortly by a PAT-4 preamp (also a very questionable design, particularly the tone control circuit, but also having some problems in the line amp section). Mine had the Van Alstine modifications and never had an issue. I did, however, repair a large number of them for other people (at least a few dozen) that had already had repairs attempted, some multiple times, and which blew as fast as they could fix it. That's how I know the color of the flame the output transistor emit.

I was quite dismayed when both went away and then probably wound up getting sold at the San Jose flea market for $10 for some hop-head to buy crystal meth.

Brett


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Dec Thu 06, 2018 9:54 pm 
Member
User avatar

Joined: Apr Fri 06, 2012 3:36 pm
Posts: 1204
Location: Erie, PA
No one has mentioned the McIntosh mono block amps from the 50's. Very hard to beat their sonic excellence as well as construction. Downside is their price these days. If you are a hi-fi purist needing quality tube amplification go McIntosh. As for the comment of solid state amps sounding too harsh, many of the high-end mosfet amps sound very nice. Again you have to spend $$$ to get the quality sound.

_________________
If I had saved all the money I've spent on test equipment, I'd probably spend it on test equipment.


Top
 Profile  
 
 Post subject: Re: 50W Stromberg Carlson Amp. Is it worth it?
PostPosted: Dec Thu 06, 2018 10:24 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4273
Location: Boston, MA USA
I disagree with this 100%. Hi-fi equipment reached commodity status 40 years ago. Anything from the “silver age” or later will deliver quality sound, often for very little money. Now with Class D you can have quality and power with no heat, for very small $.

-David


Top
 Profile  
 
Post New Topic Post Reply  [ 47 posts ]  Go to page Previous  1, 2, 3  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 4 guests



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB