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


It is currently Aug Fri 23, 2019 9:07 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 127 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6, 7  Next
Author Message
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Mon 15, 2019 3:18 am 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 12357
Location: Central PA 16801
thanks much for that information.

steve

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Tue 16, 2019 3:41 am 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 12357
Location: Central PA 16801
after reading all that information about capacitors and thinking on this for a few days, I decided to go for original design.

here is why:

1. the design engineers at bell knew more than I do about designing the filtering circuit.

2. there was a reason to parallel two 10 mfd capacitors instead of using one 20 mfd capacitor.

3. I don't believe that bell used a can with two 10s in it "just because they got a great deal" on that type of can.

4. I take a very conservative view on nearly everything in my life and this amp will be no exception as I too will restore as it was originally designed: 10 x 2 paralleled for 20 mfd.

here is a view of the filtering circuitry.

steve


Attachments:
Untitled.jpg
Untitled.jpg [ 122.2 KiB | Viewed 275 times ]

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.
Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Tue 16, 2019 3:54 am 
Member
User avatar

Joined: Mar Sun 11, 2007 6:55 am
Posts: 10875
Location: Mission Viejo, southern California
If that makes you happy, no need to worry, as the amplifier will not care. If you look at the Mallory books, you will see that at they suggest two conected on parallel only because they think people are more likely to have the dual units in stock.

_________________
many of my radios http://s269.photobucket.com/user/FSteph ... t=3&page=1


Last edited by FStephenMasek on Jul Wed 17, 2019 4:55 am, edited 2 times in total.

Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Tue 16, 2019 4:26 am 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 12357
Location: Central PA 16801
no matter what, it is per original design and i can rest assured that it is.

i paid two bens for this amp and being in the condition that it is in, it will be very perfect under the hood.

steve

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Tue 16, 2019 5:25 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 23799
Location: Haledon, NJ, usa
I'm puzzled.. sorry.
That schematic shows 4 caps not 2 .... right?

Image

It shows that a 10uf cap (C1A) is in parallel with another 10uf cap (C2A) = 20uf A

It also shows that a 10uf cap (C1B) is in parallel with another 10uf cap (C2B) = 20uf B

But then ( possibly to raise the voltage rating) it shows that the two caps in group "A" ...are in series with the two caps in group "B" using balancing resistors.... right?

So if that is accurate ... 20uf in series with 20uf = 10uf total

I didn't know what those three symbols "X" were supposed to be indicating in that part of the schematic however.... So wasn't sure if it meant "no connection"?
[ EDIT - I see a note that says "dotted in" parts are not used in all units and if shown as dotted-in then the "X" marks indicate "no connection".]

It doesn't look to me as though C2A and C2B are "dotted in"
If correct...In that case then .. the total series/parallel cap arrangements are = 10f @ 900v

But if it does mean "no connection" then both of those two C2 caps are not part of anything.

If the "X"s means "no connection"... then only the two, 10uf C1A & C1B caps are in series with each other using 100k balancing resistors = for a total of 5uf.

If 5uf is correct, it may seem small... however L1 and the next two 20uf caps are probably doing most of the filtering in this amp.

According to the print, all e-caps have a 450vDC rating.
Therefore the two 450v 10uf caps (C1A & C1B) in series as the input filter cap = 5uf @ 900v now.

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Wed 17, 2019 3:20 am 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 12357
Location: Central PA 16801
yes, i have thought the same thing(s).

one thing is for sure, C1 and C2 are two can capacitors. each can has two 10 mfd capacitors in it and the two 10 mfd tabs are soldered together and then taken to the cathode of the rectifier and the other one goes to the other capacitor.

i have it *exactly* the way it was designed...two 10s in parallel for each can.

mfd in each one was verified with a capacitor meter to make sure there really was 10x2 paralleled for 20 mfd.

steve

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Wed 17, 2019 4:06 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 23799
Location: Haledon, NJ, usa
Dutch Rabbit wrote:
yes, i have thought the same thing(s).

one thing is for sure, C1 and C2 are two can capacitors. each can has two 10 mfd capacitors in it and the two 10 mfd tabs are soldered together and then taken to the cathode of the rectifier and the other one goes to the other capacitor.

i have it *exactly* the way it was designed...two 10s in parallel for each can.

mfd in each one was verified with a capacitor meter to make sure there really was 10x2 paralleled for 20 mfd.

steve

Not according to the print...
C1A and C1B would have separate negative tabs and C1A has the +10uf tab tied to the tube cathode .. but C1A neg goes to C1B's +10uf tab, and C1B's neg goes to ground.

C2A and C2B would also have separate negative tabs and C2A has the +10uf tab tied to the tube cathode .. but C2A neg goes to C2B's +10uf tab, and C2B's neg goes to ground.

So... I can't see how you'd have two +10s in parallel for each can = 20uf @450v per can.
Doesn't agree w/the print.

But ... regardles... if you somehow have two 20uf cans
They need to be placed in SERIES with the other one... for a total of 10uf @ 900v... Right?

two cans, each 20uf @450v ...in SERIES= 10uf @900v

You should be able to measure the cap total there ... after the rectifier ...but you may need to lift the choke lead. You should measure 10uf total

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 18, 2019 1:26 am 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 12357
Location: Central PA 16801
typing here in altoona on a rain delay...

looking at each electrolytic can..each can has "can common negative". each leg of the can measures 10 mfd to can shell and each leg is tied together..10 x 2 paralleled for 20 mfd.

i have two 10s in parallel for each can. both parallel banks are in series with each other, with a series resistor across each paralleled bank.

it goes: 5u4 cathode to positive cap bank one... neg cap bank one to positive cap bank two..cap bank two neg to ground. i know the print has an X on the common negs..but that is not possible since each can is " can common negative with two 10 sections..all verified with a meter.

i will verify it all again when i get home.

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 18, 2019 2:15 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 23799
Location: Haledon, NJ, usa
Dutch Rabbit wrote:
typing here in altoona on a rain delay...

looking at each electrolytic can..each can has "can common negative". each leg of the can measures 10 mfd to can shell and each leg is tied together..10 x 2 paralleled for 20 mfd.

i have two 10s in parallel for each can. both parallel banks are in series with each other, with a series resistor across each paralleled bank.

it goes: 5u4 cathode to positive cap bank one... neg cap bank one to positive cap bank two..cap bank two neg to ground. i know the print has an X on the common negs..but that is not possible since each can is " can common negative with two 10 sections..all verified with a meter.

i will verify it all again when i get home.

Sounds good
That's really the only way that two dual 10uf-450v cans could be properly connected to achieve the (10uf@ 900volt) goal of the schematic.

The way that that print is actually drawn would work only if there were four separate 10uf caps because when two 10uf caps are in the same can... the negatives cannot connect exactly the way that that print draws it.
But that's fine.... it doesn't matter now.
..because ...What you have ( as you just described it) will achieve the exact same goal of 10uf@900v

Each of your dual-10uf @450v cans ...are now connected as 20uf @450v

So if those two (now 20uf @450v) cans are connected in SERIES with 100k balancing resistors then it will work properly to provide a total of 10uf @900v

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 18, 2019 2:40 am 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 12357
Location: Central PA 16801
ok. game on..type between innings.

yes on all that. the schematic is right but not right compared to what is in the amp. both are correct..but look "different" aalthough they are the "same".

i believe they seriesed due to the caps seeing 520 volts at turn on current inrush. it stabilizes at 410-420 B+ on 5u4 cathode.

bottom of 7th inning. gotta go..

steve

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 18, 2019 5:57 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 23799
Location: Haledon, NJ, usa
Hooray... glad we got all that cleared up... :-) .. (no thanks to the guy who drew the print and his friend who purchased the particular can-cap parts.. and kudos to whomever the poor soul was who had to build it)

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 18, 2019 6:02 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4256
Location: Boston, MA USA
Be very careful that the can connected to the B+ line (5U4 cathode) is mounted on a fiber washer and has a cardboard insulator over the can. This can is not grounded, but is at over 250 volts.

-David


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 18, 2019 8:25 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 23799
Location: Haledon, NJ, usa
dberman51 wrote:
Be very careful that the can connected to the B+ line (5U4 cathode) is mounted on a fiber washer and has a cardboard insulator over the can. This can is not grounded, but is at over 250 volts.

-David

Very good info!
I had not been actively thinking about that aspect.
.. (probably ... mostly because, I personally, never need or use any kind of those top-mounted, exposed, old-style, can-E-caps anymore)
.. So for me, I would have used 4 "regular" newer-style radial-E-caps which are already wrapped in plastic and everything mounded below the chassis on terminal strips.

So thanks a lot for mentioning (reminding) that very important safety element/warning.

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 18, 2019 9:19 pm 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 12357
Location: Central PA 16801
yes, the cardboard tube is/was present.

the can is completely disconnected from all circuitry since the new capacitors were installed.

steve

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 18, 2019 9:31 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 23799
Location: Haledon, NJ, usa
Dutch Rabbit wrote:
yes, the cardboard tube is/was present.

the can is completely disconnected from all circuitry since the new capacitors were installed.

steve

So what type/size dual e-cap did you replace it with?
Are they regular type big metal cans?
Where/how did you mount them?

The reason I ask is because if you did not mount them in the same location as the old ones.. why bother getting dual-can caps at all? Why not use 4 individual 450v-10uf caps of the smaller size underneath?

Do they look like this one?
Image

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 18, 2019 9:40 pm 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 12357
Location: Central PA 16801
https://www.tubesandmore.com/products/c ... ectrolytic

10 @ 500v

steve

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Thu 18, 2019 11:18 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4256
Location: Boston, MA USA
Pbpix wrote:
dberman51 wrote:
Be very careful that the can connected to the B+ line (5U4 cathode) is mounted on a fiber washer and has a cardboard insulator over the can. This can is not grounded, but is at over 250 volts.

-David

Very good info!
I had not been actively thinking about that aspect.
.. (probably ... mostly because, I personally, never need or use any kind of those top-mounted, exposed, old-style, can-E-caps anymore)
.. So for me, I would have used 4 "regular" newer-style radial-E-caps which are already wrapped in plastic and everything mounded below the chassis on terminal strips.

So thanks a lot for mentioning (reminding) that very important safety element/warning.

It's very common to see a capacitor configuration like this on a set with a voltage-doubler power supply, since one of the capacitors in that circuit will be at a high voltage potential. So it will either be an insulated type, or be under the chassis.

-David


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Fri 19, 2019 2:33 am 
Member
User avatar

Joined: Mar Sun 11, 2007 6:55 am
Posts: 10875
Location: Mission Viejo, southern California
That amplifier is a good example of a device which could also be restored with film capacitors. Mouser and others carry units with AC and ripple ratings, not just DC ratings.

_________________
many of my radios http://s269.photobucket.com/user/FSteph ... t=3&page=1


Top
 Profile  
 
 Post subject: Re: My Xmas Present Bell Amplifier Restoration Begins - Page
PostPosted: Jul Fri 19, 2019 2:53 am 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 12357
Location: Central PA 16801
funny you should mention the film cap situation, Stephen...

the amplifier section, phono in preamp section, everything around the rectifier, outputs, phase inverter, and phono preamp (5u4, 6L6s, 6SF5, 6N7) and the power supply section is all done.

the 6SF5 and the 6N7 were noisy and I believe one of them had a cathode to heater problem b/c a noticeable hum was eliminated when I replaced these noisy to tap tubes.

the only part of this amp that is not done are the 4 mic inputs and their preamps. there is big capacitor trouble there b/c when i move the volume controls on the mics, the audio from the phono IN is hindered and is noisy. there are two tiny chief capacitors that are leaky in each 6AU6 mic/preamp section. i pulled the mic tubes so these sections are not active.

restoration of the mic sections is saturday's project as the A/C will be pumping to avoid 103 degrees outside.

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.

here is my situation, question, and plea for help:

every capacitor is happy EXCEPT for C3.

this capacitor 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 ?

i am running blind and have absolutely NO experience on using a film capacitor in place of an electrolytic in a power supply.

i need help with my questions and the "go-ahead" to proceed.

thanks much.

steve


Attachments:
Untitled.jpg
Untitled.jpg [ 171.28 KiB | Viewed 181 times ]

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.
Top
 Profile  
 
 Post subject: Re: Bell Amplifier Restoration Begins - Page 3 with Question
PostPosted: Jul Fri 19, 2019 6:36 am 
Member
User avatar

Joined: Apr Sat 04, 2015 6:15 am
Posts: 1193
Location: Dos Rios, CA. region
You may want to roll a bunch of 6N7G and 6SF5GT's in the mic preamp/mixer sections for microphonics (tapping)
for best results after rebuilding those sections...Quite a few of the metal tubes in tube PA'a after all these years have microphonics (ringing),
though a select few have no microphonics at all...


Top
 Profile  
 
Post New Topic Post Reply  [ 127 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6, 7  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 7 guests



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB