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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Fri 19, 2019 7:26 am 
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You said:
"the amp is purring nicely and each capacitor sees 200-250 volts stable and will surge around 400 at turn on. the voltage doubler circuit with the balancing resistors, both capacitor paralleled banks see exactly 210 volts--excellent and well done."

That section is NOT a "voltage doubler" circuit per se.
No. It is only a series cap arrangement to allow for double the voltage RATING or tolerance of the series-combined caps.


You also said:
"also, from what i understand, these capacitors have NO polarity and do not care what direction they are placed in the circuit. the amp won't care either. right and right ?
i am running blind and have absolutely NO experience on using a film capacitor in place of an electrolytic in a power supply."


Do not think of your power supply in terms of DC Caps or AC caps.
Because generally speaking ... a cap is a cap... they both work the same way.
(like ANY cap ...They charge and they discharge.. that's it.)
The ONLY reason E-caps exist is because they are a lower-cost way to make a large value cap in a reasonable size package.
The dielectric material used to achieve this ...is an electrolyte ...which when polarized properly acts as a good insulator. That's All.
.. otherwise... generally speaking any non-electrolytic cap will work the same for ripple filtering in the same place for any power-supply.

So E-caps are only ever used when it is easier and cheaper. That's all.
If you can get a cost effective NON polar (film cap) in the required values .. use it.

E-caps must only be used in DC circuits because the electrolyte must not see any reversal in polarity or it explodes. But that's what makes them GOOD in DC power supply filter circuits. Because the RECTIFIER only ever allows +DC voltage through. Even if it has ripple ... that ripple is simply more positive or less positive DC because the voltage never goes below zero and never reverses as A/C does.
Remember A.C. Means alternating current.
So in A/C the current flow reverses on every 1/2 cycle.
... BUT ..In DC, the current flow is only ever in one direction.


Otherwise ...Functionally ...A cap is a cap is a cap.

So then.. if you CHOOSE to use E-caps you simply must observe the polarity to keep the electrolyte functioning... therefore that's the only reason you cannot use an e-cap for A/C if the polarity of the electrolyte will ever reverse.

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Fri 19, 2019 12:30 pm 
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I got your message Steve, and yes I would recommend a 10 uf 600V capacitor. Either one from Solen such as found at AES.

https://www.tubesandmore.com/products/c ... ylene-fast which the 10uf is $7.50 a piece.

OR from Mouser such as this one which is $4.12 a piece

https://www.mouser.com/ProductDetail/Vi ... b4cZzdYBla

I recently bought a bunch of the Vishay capacitors from Mouser as they fit nicely into the can of a Zenith 1933 radio I was working on.

The Illinois Capacitor one would also be an excellent choice. I chose the Vishay's onlt because of room constrtaints.

Hope this helps
-Steve

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Fri 19, 2019 3:14 pm 
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great info guys on the capacitors

i ordered some illinois capaitors from mouser for the said capacitor and to have on hand.

fortunately, the new old stock 6n7 and 6sf5 tubes are quiet.

not a doubler circuit..i don't know what i was thinking on that.

thanks guys.

steve

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 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Fri 19, 2019 7:50 pm 
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Dutch Rabbit wrote:
C3 is separated from the B+ by a 470 ohm resistor. C3 idles at 400 volts as the cathode of the 5U4 idles at 410-415.

when i turn on the amp at cold start, C3 sees a 495-500 vdc surge before it settles down to 400 volts. this is a 500 volt capacitor as per my link from AES a few posts above..

i DO NOT like C3 or any capacitor to see 5 volts less than it is rated for at turn-on surge-AND-i don't want it to see 400 working voltage either. i do not want to replace it with a series bank of two 22mfds with balancing resistors to make a 900v 10uf capacitor.

i must and will take a very conservative approach and want to use ONE capacitor such as this 600 volt FILM CAP from Mouser ???

https://www.mouser.com/ProductDetail/Il ... pzGRHE0%3D

also, from what i understand, these capacitors have NO polarity and do not care what direction they are placed in the circuit. the amp won't care either. right and right ?
Hi Steve,

The schematic shows 440 volts on C3, but the AC line voltage is not shown in this image. It may be given elsewhere on the schematic so you can compare it with yours. In any case, I agree that it's best to run an electrolytic at no more than 80% of the rated DC voltage.

One critical factor for any filter capacitor is the maximum ripple current. But C3A is a filter only in the general sense. It follows the entire filter network, so it sees very low AC ripple.

Illinois Capacitor is one of my preferred manufacturers. Your proposed cap should work fine.

Film capacitors do not have polarity, so it matters not how you connect the part.

- Leigh

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Fri 19, 2019 10:20 pm 
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thanks guys. i understand everything that was said.

i have to restore the mic channels. they are the only circuits left to do. when i turn them up now, they shunt the audio wwhen the phono is playing my computer.

that will be tomorrow's easy project. the film capacitor comes tuesday and when that is in, i will match some 6L6g tubes between 7 straight evenings of altoona (pirates A farm) baseball with some doubleheaders.

life will be really good.

then it is post some pictures time on arf.

steve

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Sat 20, 2019 3:45 am 
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question time to ease my mind:

C17 is a tubular 0.0005 mfd capacitor on the 6N7. i have always replaced "like style for like style" meaning that i never used a ceramic disc in place of a film capacitor, etc.

since i did not have a tubular paper or film capacitor that is 0.0005 mfd, i replaced this capacitor with a silver mica 500 pf capacitor.

:arrow: i see absolutely NO reason why i cannot do this :idea: .

reason i am very particular about this amp is that it is mint, beautiful, and works perfectly. it is a piece of history and is a classic for the era and style. when it is done, i want it to be perfect as i am even more particular for those reasons.

i did go ahead and restore all the mic inputs this evening. when i turn up the volume on the mic inputs whilst playing the phono input, it does not shunt and cut out the phono input's audio. the audio is clean and each mic input does not hinder the audio anywhere in the amp. the coupling capacitors on the 6AU6 tubes only passed 10 volts, luckily, not 175.

each and every one of the "tiny chief" capacitors in this amp leaked anywhere between 5 and 10 volts.

thanks.

steve


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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Sat 20, 2019 5:34 am 
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I don't think you really meant "tubular" like those hollow, ceramic tubular-caps found in RF circuits. These types.. NEVER fail.
Image


I think you probably just meant cylindrical.shaped wax-paper?
Image

So ...
Well 500pf is 500pf.... so why not?
And there is no DC voltage there either... so again... why not?
Image

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Sat 20, 2019 12:17 pm 
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A dipped Silver Mica would be perfectly fine. Even a ceramic should be fine because there isn't any DC bias across it and being 500 pf I doubt it would have any microphonic effects, but a ceramic NP0/C0G would be just as good as the mica.

-Steve

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Sat 20, 2019 3:56 pm 
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tubular capacitor...voltage doubler...how else am i going to show my arse in this thread ? i might as well bend over and let the kicking begin.

i know all of this and it is not like me, but i'm too consumed with getting this amplifier done perfectly, beyond OCD style.

yes, the capacitor in question is paper/cylindrical...a pink Tiny Chief with yellow letters.

perhaps it is Prozac time, but by the time the SSRI kicks in in 2-3 weeks, the amplifier will be done.

"bear" with me...

(yes, i know, "BARE" :D )

steve

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Sat 20, 2019 4:06 pm 
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If you wanted to be a stickler electrically, you could series two .001 mylars which would be .0005, but then it wouldn't be as perfect visually.

I'm not sure which you would OCD on more. (I say that with 100% respect, as I understand fully)

-Steve

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Sun 21, 2019 3:25 am 
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^^^^
azenithnut wrote:

I'm not sure which you would OCD on more. (I say that with 100% respect, as I understand fully)

-Steve



respect taken. you understand. sometimes it is a blessing ; sometimes it is a curse.

here is another interesting restoration detail i forgot to mention.

the last section that i did before the mics was the volume control/bass/treble section.

before i restored this part, i noticed that when i turned up the bass, it was "flubbery", "boomy", and kind of had an "emphasis/de-emphasis" on bass notes. i could not turn the bass up past half way without things sounding unnatural and unclean.

ALL the coupling and bypass "tiny chief" capacitors were so bad that even this capacitor, the one in the bass control circuit that saw only a couple of volts, was LEAKY.

i measured it on my capacitor meter and the 0.003 measured 0.011 indicating a great deal of leakage on a 9 volt capacitor meter...

once i replaced it, the bass is so clean and defined.

the amp is all done except for installing the 10 mfd film cap that was discussed on page 4. i am running the amplifier at 105 volts as the schematic calls for 117.

i must say, this is a PRIZE, an absolutel perfect prize. i can't wait to post pictures especially of the glowing huge dial with all the red pointers.

this truly was an amazing find and it is a very high quality amplifier. it sounds wonderful and i am surprised that it would not be considered HiFi.

it sounds so much better than some of the "HiFi" amplifiers that i had/have. it kicks the pants off my Heathkit A9-C which sounded flat and awful compared to this one. it sounds as good as some of the good RCA, Motorola, and Fisher true "HiFi" amplifiers that i have as well.

also, it has power and "kick". i love the warm robust sound that it has which could be contributed to the 6N7.

i installed a matched pair (within 1 mA of each other) of 6L6ga shoulder tubes and they look as good as they sound.

i am extremely happy to the point of being goo-goo over it :shock: .

the *only* thing that could make it better is that for the mic section to use the octal 6SL7, 6SN7, or the 6SJ7 instead of those frumpish miniature 6AU6 tubes.

:arrow: real radios and amplifiers don't use miniature tubes 8) .

steve


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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3
PostPosted: Jul Sun 21, 2019 3:53 am 
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this amp has the screw on mic connectors.

anyone have some 332 to 1/4 phone jack adapters ?

steve


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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Sun 21, 2019 4:32 am 
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Dutch Rabbit wrote:
tubular capacitor...voltage doubler...how else am i going to show my arse in this thread ? i might as well bend over and let the kicking begin.

i know all of this and it is not like me, but i'm too consumed with getting this amplifier done perfectly, beyond OCD style.

yes, the capacitor in question is paper/cylindrical...a pink Tiny Chief with yellow letters.

perhaps it is Prozac time, but by the time the SSRI kicks in in 2-3 weeks, the amplifier will be done.

"bear" with me...

(yes, i know, "BARE" :D )

steve

Ahhh ... but can you bear the sight of a bare bear on your camp site?
"Fuzzy Wuzzy" was a bear
Fuzzy Wuzzy had no hair
Fuzzy Wuzzy wasn't fuzzy... was he?

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3
PostPosted: Jul Wed 24, 2019 4:20 am 
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holy smokes !

the capacitor has a diameter as large as a quarter dollar.

the size will be quite disproportionate to the rest of the components under the chassis.

NOT AT ALL to my liking physically and i DO NOT approve of the look it will give in the chassis, but I have not a safer choice.

a well rated voltage capacitor versus "the looks"

--as much as it will drive me nuts, I have to go with the "well rated capacitor" (600v) which is in the best interest for the safest operation of the amplifier.

one more time for OCD's sake: this capacitor does not care (and neither does the amplifier care) what direction of which the capacitor is installed...and I'm not going to kill my amplifier... :?:

https://www.mouser.com/datasheet/2/88/P ... 553004.pdf

https://www.mouser.com/ProductDetail/co ... cycode=USD

thanks,

steve

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3
PostPosted: Jul Wed 24, 2019 7:48 am 
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YES the non-polar film cap can be installed either way... "no polarity" means exactly that.


Remember ONLY electrolytic caps care about polarity ...and so they are marked with polarity because the electrolye substance inside only works as an insulating dielectric when the proper polarity voltage is applied.

No other caps care about polarity.

... the amp itself, or ( its design) doesn't know or care which type of cap you choose... a cap is a cap. Remember... all it does is charge and discharge.
Yep .. It charges up then it discharges that charge into the load.

It's only the type of cap you choose that determines if you should care about polarity.
... It's the cap that cares about polarity... NOT the amp.

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Last edited by Pbpix on Jul Wed 24, 2019 7:46 pm, edited 2 times in total.

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3
PostPosted: Jul Wed 24, 2019 4:52 pm 
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Those mic adaptors to ¼" are hard to find, (I may have one or 2 I could dig out here I use for testing amps I may not want to modify with modern inputs)
my suggestion is to remove (gasp!) the bayonet mic jacks on the channels you'll use most often and replace with ¼" jacks, preferably US made if you have some kicking around, the new ¼" jacks from overseas sometimes contain so little conductive metal you need a solder gun to wire 'em!

You may need to use a couple large hole washers (Hardware store?) to be able to tighten the ¼" jacks down in the larger bayonet openings, sometimes the washers included with the bayonet jacks will work for this purpose.
Kent


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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3
PostPosted: Jul Wed 24, 2019 5:06 pm 
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I think the Amphenol connectors are still around, you could make up some short adapter cables.

-David


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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3
PostPosted: Jul Wed 24, 2019 6:53 pm 
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the capacitor will go in this evening. i hope to find some adapters. i just can't bring myself to remove the original connectors. on top of that, i most likely will never use the mic inputs anyway.
thanks for the info.

steve

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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3
PostPosted: Jul Wed 24, 2019 7:21 pm 
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You may need to use a mic input if you want to play an iPod or a phone through the amplifier. The phono input may require a fairly high output voltage. You could buy this:

ebay item #223560720931

-David


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 Post subject: Re: Bell Amplifier Restoration Begins - Page 3
PostPosted: Jul Wed 24, 2019 10:23 pm 
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Unfortunately, the non-electrolytic caps like these are rather large compared to their electrolytic counterpart.

When used in radios from the late 20s and early 30s, they are about the same as or even smaller than equivalent electrolytics, but by the late 30s, electrolytics had shrunk enough that getting the Mylar or polypropylene caps stuffed inside of the original cans is a real challenge.
I had a fun time stuffing them into the cans of my 1936 GE A125, but I managed to get it done by paralleling two smaller values.

I looked at the Solen caps and a 10uf 630VDC cap is 29 mm or 1.14 inches in diameter.
I bought a group of 15 uf 630V Solens some years ago for my Zenith 1000Z and they all fit into the original cans, but one or two BARELY fit in. This makes getting the wires past the cap difficult.

I think the newer ones are a little smaller than the older stock, so I may order a few more in hopes of a better fit :D

-Steve

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