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 Post subject: Re: On the 12th Day of Christmas An Amplifier Came to Me
PostPosted: Jun Wed 05, 2019 1:36 pm 
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Steve, the capacitors in the link to Mouser are the ones that I am referring to. Note that they are 600 VDC as opposed to the usual 630 VDC. That is how all of mine are marked. I did throw away some a few years back that had split open, unused. But they were likely from the 70s or earlier. Maybe the epoxy (or whatever it is ) shrunk. But I have had great success with them.

Here is my first HH Scott restoration, done I guess about 16 years ago. This amplifier had "Brown Drops" going from the phase inverter to the output tubes already. They originally came with Pyramid paper capacitors. As you can see, those .1 µFD Orange Drops do take up some real estate. I also did my brown faceplate LK-72 with the same capacitors. I know that others get into the "sonic" properties of coupling capacitors. I am not in that camp nor do I debate it. Everyone is entitled to their own likes and dislikes. It's all very subjective when it comes to "sound". Changing the Pyramid capacitors on the tone and volume controls was tedious. But the selector switch was a real challenge. Patience and it worked out, no damaged terminals and ALL of the old capacitors leads were removed carefully.

BTW, this was done in my early days here on ARF. I peeled open the filter capacitors and "Stuffed" them with new electrolytic capacitors. I thought I was on to something. Little did I know, you guys were already doing it! It took the wind right out of my sails... :cry: .

I never did get around to changing those disc capacitors in the preamplifier. Some do say that the value can change slightly with frequency, due to Piezeo effect?


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 Post subject: Re: On the 12th Day of Christmas An Amplifier Came to Me
PostPosted: Jun Wed 05, 2019 9:03 pm 
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hi don,

they do take some space. what were your values on those big ones in the center/low part of the pic ?

i have space, but i don't want to over do it and crowd a nice underneath chassis.

yea, as for tone...i won't go there either and start an all out war. i'm sure there *can* be sonic differences between a no-name 29 cent capacitor and a 40 dollar auracap/janzden, but i would *bet* the difference is so minimal that only the best refined ears...if even then...would notice a difference.

it is no difference if i were to put one of my top line realistic receivers from the early 80s on a great pair of speakers, say it was a pioneer/sansui/marantz/etc., put a sheet over it, have everyone be amazed how good it sounds, and then pull the cover off the system to reveal a "realistic".

what do you think about these cornells ?

https://www.mouser.com/Passive-Componen ... ipZ1ywtgm3

they may be of a smaller envelope and be easier to mount with true axial leads.

...i just want a better than average capacitor for this. i'm ok putting in the 49-69 cent yellow caps into radios and general amplifiers, which i've never had any problems with, but i just want to "one up or two up" for a 'better than' in this amplifier.

it will be my last project for quite a while if ever. after this is all done, i want to do other things. i'm losing interest after all this time and i am trudging myself to get these done. it has become the same ole same ole routine since i was a kid and i don't seek much pleasure out of it anymore.

it is like yep, here's an old set, let's trouble shoot it to the defective component, make it work a little bit to see what we have, then do a full restore, shine it up, sit it on a shelf, and there you go, it's done, next (le't predict what will happen).... :roll: .

i don't say that to be negative about the hobby, the interest will always be there, but the restoration process has become so mundane and ho-hum for me--again, i'm not saying that as a bad thing.

i have only one empty shelf left in the new radio room, have a few radios that i've just restored plus this amp to place on it. there will be no clutter or radios stacked on radios. after these last 5-6 sets, i'm officially out of room for a nice and uncluttered display room.

steve

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 Post subject: Re: On the 12th Day of Christmas An Amplifier Came to Me
PostPosted: Jun Thu 06, 2019 10:05 pm 
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Dutch Rabbit wrote:
hi don,

they do take some space. what were your values on those big ones in the center/low part of the pic ?

...
steve


Steve,

The big fat ones are .1 µFD @ 600 VDC.

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 Post subject: Re: On the 12th Day of Christmas An Amplifier Came to Me
PostPosted: Jun Fri 07, 2019 3:17 am 
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that's big

what do you think of these cornells ?

they are yellow caps, but seem to be about double of the general yellow caps that i get from AES.

i just want to go one up or two up on capacitors in this amp over the genereal yellow caps i've used in radios.

https://www.mouser.com/Cornell-Dubilier ... ipZ1z0zlgf

.1 orange drops where there are .1 capacitors in this amplifier might not fit well and i won't change lead dress or component location.

steve

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 Post subject: Re: On the 12th Day of Christmas An Amplifier Came to Me
PostPosted: Jun Fri 07, 2019 5:31 am 
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Steve, those caps might be too pricey for this amp.
Think most are made overseas anyway these days except perhaps some Illinois brands (yellow ones?).
I've had good success in sound amps over the years using the ones made in Japan or Taiwan from Mouser as opposed to China, Malaysia, etc.
You may have to look on the spec sheets or ask them to find out for sure, but they seem to sound better (& are certainly more durable) to me
when manufactured there.
-Kent


Last edited by ampstamp88 on Jun Sat 08, 2019 3:11 pm, edited 1 time in total.

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 Post subject: Re: On the 12th Day of Christmas An Amplifier Came to Me
PostPosted: Jun Fri 07, 2019 5:59 pm 
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Steve, any of the IC yellow jobs would work for me. I don't buy expensive capacitors and I would submit that in the double blind (taste) :wink: test, it would be difficult to hear any difference.

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 Post subject: Re: On the 12th Day of Christmas An Amplifier Came to Me
PostPosted: Jun Sat 08, 2019 4:39 am 
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ok guys, thanks.

will advise this summer as i am finishing up my last few radios for the new room. the chassis are done, but three little wooden sets need a refinish.

i am very good at the refinishing, but HATE to do it. it is the worst part of the restoration for me..

steve

any help here at the link below ?

viewtopic.php?f=15&t=360022

steve

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 Post subject: Re: On the 12th Day of Christmas An Amplifier Came to Me
PostPosted: Jun Sat 08, 2019 6:13 am 
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If you do not need all of those inputs, you could add another 6SN7 stage to increase gain.

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 Post subject: Re: On the 12th Day of Christmas An Amplifier Came to Me
PostPosted: Jun Sat 08, 2019 2:53 pm 
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what ?

:D

steve

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 Post subject: Re: On the 12th Day of Christmas An Amplifier Came to Me
PostPosted: Jul Wed 10, 2019 2:41 am 
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restoration has begun.

tonight I hooked it all up stock to a variac, iso, and an ammeter. I attached my meter to the B+ on the 5U4 and slowly fired it up.

nobody panic--all was closely monitored and the set did just fine for the whole minute it was on.

it works well for being stock, but certainly needs help.

here is what I observed.

1. the coupling capacitors are definitely leaky. on each grid of the 6L6g tubes, one has 8 volts on it, the other has 5 volts on it.

2. the B+ is a whopping 400-410 volts on the cathode of the 5U4.

3. the plates of the 6L6g tubes have 375 volts on them.

I have a few observances/questions.

they are hitting the 6L6g plates just a few volts under the max. I will bet this amp will be happy with a set of used/good RCA 6L6gc tubes in it when it is done.

:arrow: the original 5U4g had a busted keyway pin. I replaced it with a 5U4gb. is it *possible* that the GB version of the 5U4 is allowing a tad more B+ than if I were to use a 5U4g as called out for the amplifier ?

I believe I read on here that someone somewhere sometime experienced the same thing--using a 5U4gb I place of a 5U4g increased the B+ by 20-30 volts. the late bigbandsman told that story.

https://www.antiqueradios.com/forums/vi ... p?t=130406

so, I wonder if I need to go the G route ?

all I know is that for an amp that uses 6L6g and compared to many other amplifiers that I serviced of this typical type, I've rarely seen a B+ of 400-410 volts on the cathode of the rectifier.

this amp will get a full restoration and since the tubes are not exposed, I will go for the 6L6gc for the outputs. as for the called out 5U4g versus the 5U4gb that I have installed, are there any thoughts about definitely using only a 5U4g instead of the GB version based on voltage drop ?

the G version drops 44 volts at 225 mA as per specs. the GB version drops 50 volts at 275 mA.

parts will be ordered this week as many resistors have varied and some of the 2 watt carbon comps have a black spot in the center. they have run pretty hot in this amp's life.


steve

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 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 11, 2019 2:28 am 
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since there was no insight on the above question, i dropped about 10 5U4 GB and G tubes into the amplifier. they yielded anywhere between 400 and 425 volts, and there was no rhyme or reason between the voltage drop on a G or a GB.

the 5U4 tubes that i installed did not drop any more or any less voltage based on whether it was a G or a GB.

steve

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 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 11, 2019 7:03 pm 
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Did you measure your line voltage?

Perhaps you could use a 5AR4 rectifier.

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 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Fri 12, 2019 1:58 am 
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sams folder calls for 117 vac in. that is what it received from the variac.

the voltages are dead-on with 117 vac into the set based on the sams folder.

the 5AR4 is indrectly heated ; the B+ might even be a few volts higher using one of those.

this is an EXTREMELY well built amplifier. i would believe that it was top-line back in the day for the models that were out there.

i am very impressed with it and i will kick my OCD into overdrive during the restore.

i won't get to it until next weekend of the 20th. parts will be in next week.

steve

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 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Fri 12, 2019 8:38 pm 
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I wouldn't worry to be too exact when measuring B+ or such other voltages...
1.) A little variation is not important
2) The meter used at the time of manufacture may not have the same highimpedance as tjhe DVM you use.

If you find the the cathode bias resistor is correct then the cathode voltage (bias) can be used to calculate the idle current.

If both output tubes measure correct idle current at noted bias... and if they sound ok too.. then you probably won't need to replace them.

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 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Sat 13, 2019 2:55 am 
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yes on knowing all that.

i have not calculated anything yet until the restoration begins next weekend. i've never become excited about B+ in the set versus the schematic--as long as they are close.

i have not run it more than a minute since the input grids of the 6L6 have 5 and 8 volts on them due to those wonderful Tiny Chief resistors..errr, i mean capacitors..LOL.

the electrolytics have been replaced and i am waiting on some good illinois yellow capacitors and resistors that will come next week for the rest of the set.

when it is done, i will take the final measurments in the amp, and test the tubes for emission and mutual conductance. i will also make sure that each cathode current is within 5 mA or less of each other.

this amp might be a nice candidate for a CL-90... :idea:

the build of this amp is impressive. it is so neat, tidy, and well built that it most likely was top-line back in its day.

i can't wait to hear how the 6N7 sounds with the outputs. i am hoping it is as smooth, deep, and rich as the 6P5-6AC7 lineup that i have in some of my most wonderful sounding sets.

steve

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 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Sun 14, 2019 1:57 am 
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this amp has 3 can caps in it. all are 10 mfd at 450v. two of the cans (can common negative) have both 10 mfd legs tied together for 20 mfd.

why ? ....

because they got a good deal on 10x2 cans and paralleling the10x2 for 20 ?

or was there a real advantage or a good reason to parallel two 10 mfds to make 20 ??

i replaced them with a single 22 at 500v.

was there a reason that i should not have installed a single 22 mfd based on original design ? ( and should have paralleled two 10 mfd capacitors ??)

this is one of the best designed and well built PA amplifiers that i have *EVER* seen and i want to keep it that way.

this all might be a stupid question and an OCD calming technique (OCD has really kicked in on this restore 8) ) , but i am wondering...and need to know.

based on since forever doing this, i see no issue or problem.

steve

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 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Sun 14, 2019 1:21 pm 
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Dutch Rabbit wrote:
this amp has 3 can caps in it. all are 10 mfd at 450v. two of the cans (can common negative) have both 10 mfd legs tied together for 20 mfd.

why ? ...

steve


Steve, HH Scott often did that in their amplifiers. I am wondering if they decided that the original design didn't have enough B+ or maybe had too much hum. But I have seen it too. Could it be that they had the hole already punched for the chassis?

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 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Sun 14, 2019 3:19 pm 
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nope, things look to be a "normal" build.

other than the fact that they got a great deal on or had a vast amount of 10 x 2 @ 450 can capacitors...

from what i have known all my life is that 20 mfd is 20 mfd, whether it be 5+5+5+5 paralleled , 10+10 paralleled, or a big straight-up 20 mfd capacitor.

steve

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 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Sun 14, 2019 4:32 pm 
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Dutch Rabbit wrote:
.

from what i have known all my life is that 20 mfd is 20 mfd, whether it be 5+5+5+5 paralleled , 10+10 paralleled, or a big straight-up 20 mfd capacitor.

steve


Certainly that is true.

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 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Sun 14, 2019 8:07 pm 
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Dutch Rabbit wrote:
this amp has 3 can caps in it. all are 10 mfd at 450v. two of the cans (can common negative) have both 10 mfd legs tied together for 20 mfd.

why ? ....

because they got a good deal on 10x2 cans and paralleling the10x2 for 20 ?

or was there a real advantage or a good reason to parallel two 10 mfds to make 20 ??

i replaced them with a single 22 at 500v.

was there a reason that i should not have installed a single 22 mfd based on original design ? ( and should have paralleled two 10 mfd capacitors ??)

this is one of the best designed and well built PA amplifiers that i have *EVER* seen and i want to keep it that way.

this all might be a stupid question and an OCD calming technique (OCD has really kicked in on this restore 8) ) , but i am wondering...and need to know.

based on since forever doing this, i see no issue or problem.

steve

Essentially... you are "basically" correct that two 10 = 20.
However you can study conservative engineering concepts and learn a few methods of parallel and series-parallel arrangements for various safety or other design reasons.

Go to the link here to the Cornell Dublier Application data sheet on Aluminium E-Caps; on page 11 and see what arrangement ideas they show. ( Read the whole document to learn more than you'll ever need to know)
BTW Page 9 covers how to make a non-polar cap by connecting two polar caps in "anti-series" ( back to back)
http://www.cde.com/resources/catalogs/AEappGUIDE.pdf

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