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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 12:24 am 
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My 6sj7 tubes arrived today and I put it in the amp , but the audio is all about the same ... so it seems to be good with any of the tubes listed. I noticed the Plate and SG voltage are different depending on which tube is in.

Image

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Last edited by Pbpix on Oct Tue 24, 2017 10:22 pm, edited 4 times in total.

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 1:09 am 
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john8750 wrote:
Yes, I think I will. Id rather build my own HV supply. I will look for some ideas. I have a 6sn7 here. Would that work? The 6.3volt transformer is no problem. Couldn't I just build a voltage doubler for the B+ right off the 120vac.
That's a good way to get yourself killed. Never EVER connect directly to the AC line unless the circuit is totally enclosed with no external connections whatsoever. That automatically excludes any kind of audio amp, especially, in spades, one you're working on.

The difficulty in making a bench supply is in making it variable. If it's series pass regulated the more it's 'dialed down' the more heat the pass element has to dissipate. Say you have a 400 V 100 mA capable supply. When it's dialed down to 250 V the series pass element has to dissipate at least 15 Watt (at the 100 mA). In fact it'll be more than that because of the 'drop out' voltage which, at 400 V, will likely be 50 V, or more (the filtered supply has to be 450 V to get 400 V out), depending on the tube used. That ups the power dissipation to 20 Watt at 250 V (and 100 mA). So, no, a 6SN7 would be totally inadequate, even if there weren't other disqualifying issues.


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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 1:37 am 
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Flipperhome wrote:
john8750 wrote:
Yes, I think I will. Id rather build my own HV supply. I will look for some ideas. I have a 6sn7 here. Would that work? The 6.3volt transformer is no problem. Couldn't I just build a voltage doubler for the B+ right off the 120vac.
That's a good way to get yourself killed. Never EVER connect directly to the AC line unless the circuit is totally enclosed with no external connections whatsoever. That automatically excludes any kind of audio amp, especially, in spades, one you're working on.

The difficulty in making a bench supply is in making it variable. If it's series pass regulated the more it's 'dialed down' the more heat the pass element has to dissipate. Say you have a 400 V 100 mA capable supply. When it's dialed down to 250 V the series pass element has to dissipate at least 15 Watt (at the 100 mA). In fact it'll be more than that because of the 'drop out' voltage which, at 400 V, will likely be 50 V, or more (the filtered supply has to be 450 V to get 400 V out), depending on the tube used. That ups the power dissipation to 20 Watt at 250 V (and 100 mA). So, no, a 6SN7 would be totally inadequate, even if there weren't other disqualifying issues.



Excuse me Flip. I am a retired high voltage motor control electrician. 12,600vac is the normal water pump voltage we worked with. I know very well what I am doing. So what about a simple voltage doubler on the bench? The VFD to control that high voltage, but very low amperage is very
interesting. Thanks for the thought.
But, I found a 200 volt PT with 6.3volts, not very high current.
What was the current requirement for the one channel? Couldn't be much.

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 1:59 am 
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john8750 wrote:
Flipperhome wrote:
john8750 wrote:
Yes, I think I will. Id rather build my own HV supply. I will look for some ideas. I have a 6sn7 here. Would that work? The 6.3volt transformer is no problem. Couldn't I just build a voltage doubler for the B+ right off the 120vac.
That's a good way to get yourself killed. Never EVER connect directly to the AC line unless the circuit is totally enclosed with no external connections whatsoever. That automatically excludes any kind of audio amp, especially, in spades, one you're working on.

The difficulty in making a bench supply is in making it variable. If it's series pass regulated the more it's 'dialed down' the more heat the pass element has to dissipate. Say you have a 400 V 100 mA capable supply. When it's dialed down to 250 V the series pass element has to dissipate at least 15 Watt (at the 100 mA). In fact it'll be more than that because of the 'drop out' voltage which, at 400 V, will likely be 50 V, or more (the filtered supply has to be 450 V to get 400 V out), depending on the tube used. That ups the power dissipation to 20 Watt at 250 V (and 100 mA). So, no, a 6SN7 would be totally inadequate, even if there weren't other disqualifying issues.
Excuse me Flip. I am a retired high voltage motor control electrician. 12,600vac is the normal water pump voltage we worked with. I know very well what I am doing. So what about a simple voltage doubler on the bench? The VFD to control that high voltage, but very low amperage is very
interesting. Thanks for the thought.
But, I found a 200 volt PT with 6.3volts, not very high current.
What was the current requirement for the one channel? Couldn't be much.
And I'll wager that you didn't leave live HV wires on the ground or live circuits open to touch my just any one who passed by either. But that's exactly what you'd be doing powering an audio amp direct off AC. Sorry, but I'm not eager to help anyone build something that's inherently unsafe.

The current draw of a single channel 6V6 SE amp at 250 V is around 55 mA.


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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 3:38 am 
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Hi John:
The reason I suggested the High Voltage Bench supply is that it comes in handy while experimenting now or in the future and not very expensive and it is an adjustable power source and also supplies the filaments and negative supplies as well.
https://www.ebay.com/itm/Jackson-607D-R ... SwE2hZ5VH1

But sure you can just build a fixed output voltage doubler the same as we built on the 6V6 amp.
...easy peasy.
But certainly...for safety put a 120v transformer in front of it.
Attachment:
doubler supply.png
doubler supply.png [ 47.83 KiB | Viewed 419 times ]


Adjust the value of R2 for the 220v desired output to get B+ for this amp.
(for R-2 maybe try a 2k 10W)
While you test the voltage doubler..attach a dummy load resistor for dissipating 220v@ 45 -50 ma or so.
Try a 4.3k or 4.7k 20 watts as the dummy load.

Any of these tubes will work: 6sj7, 6sh7, 6sg7, 6sd7 .... in that order of preference.
They are all dirt cheap ( except the 6sj7 )

But I just bought four 6SJ7 tubes here on ARF through the classified from Tom Bavis for only $2 each.
So I bought 4 = $8 + $5 shipping.
$13 is nothing.

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 5:10 am 
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Wait a minute guys. I didn't mean I want to build a variable HV supply. Just a 220volt with a voltage doubler.
Your right Flip. Safety was preached every day at work. Although we never worked live, always had arch jacket
and gloves on.
Good idea to build the 6V6 power supply. I do have an isolation transformer. And I ordered the three 6SG7's
from ebay.
I absolutely know how to be safe.
Funny thing Flip, about the Prince John. I am looking at the amp, planning a little touchup of the wiring.
I noticed that on one of the 6HB6 output tubes the 470uf cathode bypass cap was connected to pin3.
It should be on pin1/9 with the 330ohm cathode resistor. Don't ask me how that happened.

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If I did something right, I made a mistake.


Last edited by john8750 on Oct Sun 22, 2017 5:31 am, edited 1 time in total.

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 5:26 am 
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Pbpix wrote:
Hi John:
The reason I suggested the High Voltage Bench supply is that it comes in handy while experimenting now or in the future and not very expensive and it is an adjustable power source and also supplies the filaments and negative supplies as well.
https://www.ebay.com/itm/Jackson-607D-R ... SwE2hZ5VH1

But sure you can just build a fixed output voltage doubler the same as we built on the 6V6 amp.
...easy peasy.
But certainly...for safety put a 120v transformer in front of it.
Attachment:
doubler supply.png


Adjust the value of R2 for the 220v desired output to get B+ for this amp.
(for R-2 maybe try a 2k 10W)
While you test the voltage doubler..attach a dummy load resistor for dissipating 220v@ 45 -50 ma or so.
Try a 4.3k or 4.7k 20 watts as the dummy load.

Any of these tubes will work: 6sj7, 6sh7, 6sg7, 6sd7 .... in that order of preference.
They are all dirt cheap ( except the 6sj7 )

But I just bought four 6SJ7 tubes here on ARF through the classified from Tom Bavis for only $2 each.
So I bought 4 = $8 + $5 shipping.
$13 is nothing.



Will do Peter. And I ordered two octal screw sockets for testing. What can I use for an output transformer?
All I have is an 8K PP, 16ohm.

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 5:34 am 
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john8750 wrote:
Wait a minute guys. I didn't mean I want to build a variable HV supply. Just a 220volt with a voltage doubler.
Your right Flip. Safety was preached every day at work. Although we never worked live, always had arch jacket
and gloves on.
Good idea to build the 6V6 power supply. I do have an isolation transformer. And I ordered the three 6SJ7's
from ebay.
I absolutely know how to be safe.
Funny thing Flip, about the Prince John. I am looking at the amp, planning a little touchup of the wiring.
I noticed that on one of the 6HB6 output tubes the 470uf cathode bypass cap was connected to pin3.
It should be on pin1/9 with the 330ohm cathode resistor. Don't ask me how that happened.
It's not a bad idea to mount components so it's obvious as to what does what but pin 3 is internally connected to pin 9, which should be connected to pin 1, so it shouldn't matter. That said, it does make me a teensy bit nervous (for no particular reason) having cathode (bypass) current traversing the internal guts of the tube so I concur with moving it to pin 9/1 as part of the 'cleanup'.


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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 6:03 am 
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Flipperhome wrote:
john8750 wrote:
Wait a minute guys. I didn't mean I want to build a variable HV supply. Just a 220volt with a voltage doubler.
Your right Flip. Safety was preached every day at work. Although we never worked live, always had arch jacket
and gloves on.
Good idea to build the 6V6 power supply. I do have an isolation transformer. And I ordered the three 6SJ7's
from ebay.
I absolutely know how to be safe.
Funny thing Flip, about the Prince John. I am looking at the amp, planning a little touchup of the wiring.
I noticed that on one of the 6HB6 output tubes the 470uf cathode bypass cap was connected to pin3.
It should be on pin1/9 with the 330ohm cathode resistor. Don't ask me how that happened.
It's not a bad idea to mount components so it's obvious as to what does what but pin 3 is internally connected to pin 9, which should be connected to pin 1, so it shouldn't matter. That said, it does make me a teensy bit nervous (for no particular reason) having cathode (bypass) current traversing the internal guts of the tube so I concur with moving it to pin 9/1 as part of the 'cleanup'.



Thanks Flip. I will do that.
What do you think about these OT' for experimenting? Cheap enough.
https://www.ebay.com/itm/NOS-pair-of-ou ... Sw2xRYhQS7

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 6:42 am 
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john8750 wrote:
Thanks Flip. I will do that.
What do you think about these OT' for experimenting? Cheap enough.
https://www.ebay.com/itm/NOS-pair-of-ou ... Sw2xRYhQS7
Well, knock me over with a feather. :lol: Yes and no. Probably no for your purposes.

Those are the original SPECO line transformers I used to use. Like in my Stealth AX amp.

Attachment:
Tube Glow 640.jpg
Tube Glow 640.jpg [ 236.7 KiB | Viewed 407 times ]


They used to go for something like 4 bucks. They have limit bass response and can't tolerate DC because they're not OPTs. I have since switched to 'real' OPTs in Stealth.

Attachment:
Stealth HK OPTs 640.jpg
Stealth HK OPTs 640.jpg [ 71.59 KiB | Viewed 407 times ]


My last use was in Top Cat, a "twin coupled" design that uses TWO SPECOs per channel which, in addition to extremely low distortion, extends the bass response (doubles it).

Attachment:
Top Cat 17 Watt sm.jpg
Top Cat 17 Watt sm.jpg [ 67.75 KiB | Viewed 407 times ]


The second transformer for each channel is on the underside using the same bolts as the ones on top. It was during the Top Cat build that I discovered they had radically changed the transformer design even though keeping the same part number. I had to steal the two off Stealth to finish it (and put 'real' OPTs in Stealth).

The SPECO was the absolute best of the line transformers and my 'specialty', at the time, was making ultra low cost designs for what I called "near Hi-Fi" or "almost Hi-Fi" amps, something that Peter has never been able to grasp no matter how many times I explain it. I think you'd be surprised at how good they sound, especially in Top Cat, but as a run of the mill 'OPT' they aren't very good. I had to play some tricks and put in a lot of design effort to get them to work as well as they eventually did.

BottleHead's 6DN7 & 6EA7/6EM7 Single Ended Experimenter S.E.X. amps used them parafeed, no DC through them, and the triode outputs are to get low driving impedance to partially make up for the limited low end. I used a different approach but the effect was similar and, in the case of Top Cat, better.


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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 7:20 am 
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john8750 wrote:
What can I use for an output transformer?
All I have is an 8K PP, 16ohm.


I think it will be ok ... close enough to use that 8k-16 ohm OT

all we need to do is calculate the turns ratio and see how it compares to a normal 5k-8ohm

Basically if it is an 8k -16ohms ... that means 16 ohms reflects back 8k
so then it stands to reason then that 8 ohms would reflect back half the 8k ... or only 4k


Here's why.
The 6v6 SE is normally looking for 5k reflected impedance.... and in this case I think 4k is close enough.

Here's the math.
that OT you now have is 8k to 16 ohms.... right?
So we divide 8k by 16
8000 / 16 = 500
so if you use 8 ohms on the secondary, then you'll get 500 x 8 ohm = 4k reflected.
(the sq root of 500 =22 .... so it has a 22:1 turns ratio)

By comparison:
The more correct OT would be 5k - 8 ohm... right?
5000/8 =625
sq root of 625= 25 that's a 25:1 turns ratio

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Last edited by Pbpix on Oct Sun 22, 2017 7:29 am, edited 1 time in total.

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 7:25 am 
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I went to your thread and read all about it. They are cheap enough. And could be used for testing.
I believe I do have a set of ot's you use for the Top Cat. Will dig back in the storage unit and see.
Remember, I do want to build that amp sometime.

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 7:28 am 
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Pbpix wrote:
john8750 wrote:
What can I use for an output transformer?
All I have is an 8K PP, 16ohm.


I think it will be ok ... close enough to use that 8k-16 ohm OT

all we need to do is calculate the turns ratio and see how it compares to a normal 5k-8ohm

Here's why.
The 6v6 SE is normally looking for 5k reflected impedance.... and in this case I think 4k is close enough.

Here's the math.
that OT you now have is 8k to 16 ohms.... right?
So we divide 8k by 16
8000 / 16 = 500
so if you use 8 ohms on the secondary, then you'll get 500 x 8 ohm = 4k reflected.
(the sq root of 500 =22 .... so it has a 22:1 turns ratio)

By comparison:
The more correct OT would be 5k - 8 ohm... right?
5000/8 =625
sq root of 625= 25 that's a 25:1 turns ratio




That's great Peter. But they are for PP use. Is that still ok?

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 7:35 am 
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john8750 wrote:
That's great Peter. But they are for PP use. Is that still ok?


Just use half the primary winding from CT to one end.
That's exactly what I'm doing here now with this PT-291 OT

Image

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 7:49 am 
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john8750 wrote:
I went to your thread and read all about it. They are cheap enough. And could be used for testing.
I believe I do have a set of ot's you use for the Top Cat. Will dig back in the storage unit and see.
Remember, I do want to build that amp sometime.
Well, when you get around to building it we might want to revisit the OPT matter because, in your case, I'm not sure but what you'd be happier with 'real' OPTs.


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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 7:50 am 
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John:
I'm sure, ... knowing you, you're gonna be pleasantly surprised at how nice this simple amp sounds.... watch. (with or w/o the nfb)
I've been listening w/the NFB connected tonight using the 6SJ7 for a while and now again the 6SG7.... and it's so nice either way.
(Remember that the 6v6 is 450ma and 6sg7 is only 300ma... so the filaments need to be in parallel.)
Also pin one on these metal tubes is the shield and you should connect it to ground.

I was fiddling around tonight and tried the cathode follower idea and strapping the 6V6 as a triode.
I had it working... seems alright ... but since my B+ is only at 220v instead of the 335 suggested on that print I posted in the beginning of this thread;
... so I think...as a result I just didn't get enough volume to suit me. So I'll just put that cathode follower OT idea on the back burner for another day.
I like the way this amp sounds just as it is... so much that, I'm now anxious to build it as stereo and do both channels now.

So I'll think on it a bit as to how I want to lay it all out and what kind of chassis... etc.
But I do really like it.

BTW... this is very sensitive.. so it you un-plug the Mp3 cable while the amp is on you'll get loud hum.
Even if you turn off the Mp3 player it makes hum.

There should be a way to keep the input grounded when the Mp3 is powered off or disconnected.
When my input cable is out floating making hum I can jumper across the tip and ring and it's silent.
So.. it's just picking up extraneous noise without it grounded.
Image

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Last edited by Pbpix on Oct Tue 24, 2017 10:23 pm, edited 2 times in total.

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 8:20 am 
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john8750 wrote:
I went to your thread and read all about it. They are cheap enough. And could be used for testing.
I believe I do have a set of ot's you use for the Top Cat. Will dig back in the storage unit and see.
Remember, I do want to build that amp sometime.
I forgot to deal with the "testing" thing. What are you going to 'test' with them? They can't handle DC so they're completely unsuitable for SE and there's nothing you can do about it (unlike PP where you can balance the DC so it cancels).


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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 8:24 am 
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Flipperhome wrote:
john8750 wrote:
I went to your thread and read all about it. They are cheap enough. And could be used for testing.
I believe I do have a set of ot's you use for the Top Cat. Will dig back in the storage unit and see.
Remember, I do want to build that amp sometime.
Well, when you get around to building it we might want to revisit the OPT matter because, in your case, I'm not sure but what you'd be happier with 'real' OPTs.




Of course Flip. My main thought is on the 300b right now. All these amps and other tube sets I have will be on display
in my hobby shop. Will send some photos. I do realize that I have no need for all of them. There is something about
the great feeling of an accomplishment with each project. Like the Little Prince, you showed me the very best caps to buy.
And the better resistors. The layout in the inner sanctum. The shielded tubes. Designed the DC heater circuit, and right
down to the exact components for the RIAA. Worked out the schematic for me. That is one fine amp, and that makes me proud.
I think it was the Paraphraser amp we were thinking about, not Top Cat.

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 8:24 am 
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Flipperhome wrote:
john8750 wrote:
I went to your thread and read all about it. They are cheap enough. And could be used for testing.
I believe I do have a set of ot's you use for the Top Cat. Will dig back in the storage unit and see.
Remember, I do want to build that amp sometime.
I forgot to deal with the "testing" thing. What are you going to 'test' with them? They can't handle DC so they're completely unsuitable for SE and there's nothing you can do about it (unlike PP where you can balance the DC so it cancels).

If they can't handle DC... how'd you use them as output transformers?

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 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 22, 2017 8:33 am 
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Flipperhome wrote:
john8750 wrote:
I went to your thread and read all about it. They are cheap enough. And could be used for testing.
I believe I do have a set of ot's you use for the Top Cat. Will dig back in the storage unit and see.
Remember, I do want to build that amp sometime.
I forgot to deal with the "testing" thing. What are you going to 'test' with them? They can't handle DC so they're completely unsuitable for SE and there's nothing you can do about it (unlike PP where you can balance the DC so it cancels).



How about peters idea to use half the 8K primary on a PP transformer
for testing.
I need to build a cheap but good sounding amp for my cousin.
This one will be fun to set up for testing. Or it will be another PP 6V6.

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