It is currently Mon Mar 16, 2020 10:52 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 8 posts ] 
Author Message
Post subject: Bias cap and diode question. These look like the wrong size.
Posted: Sat Mar 26, 2016 10:33 pm
Offline
Hobbyist
Hobbyist

Joined: Fri Feb 19, 2016 9:56 am
Posts: 28
AB763 Showman rebuild in progress.
I had to completely rebuild the bias/rectifier board but the caps I ordered from Antique Electronics seem like the wrong size. The bias cap is supposed to be a 25uF/50v but the one they sent me is tiny. The one I'm pulling out is 5x as big.
This cant be right can it?
What is it I need to order?

Secondary question.
I also ordered this cap "set" which is supposed to be the filter caps and bypass caps. The bypass caps look small too. Granted I know you double them up but just making sure this is right also...

Heck, while I'm at I should also double check these diodes I got are proper replacements too.
1N5408 for the rectifier and 1N4007 for the bias.

here's a photo of the caps I ordered and the rectifier board partially populated before I realized the cap is the wrong size.
The main cap in question is the little one next to the dime.

Image


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Bias cap and diode question. These look like the wrong s
Posted: Sun Mar 27, 2016 12:29 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
That is proper OEM values. New cap technology allows for much smaller dimensions, for same mfd/VDC caps. However, as a side note, I like to run slightly higher mfd/VDC rated caps in the bias circuit. Bit better filtering and life. Something like 50-100mfd/100VDC.

If you are going to run two 25/50 caps, think you'll be ok.


Top
Profile
Post subject: Re: Bias cap and diode question. These look like the wrong s
Posted: Sun Mar 27, 2016 2:51 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14047
Location: Province de Québec, Canada
BMW2002Ti wrote:
That is proper OEM values. New cap technology allows for much smaller dimensions, for same mfd/VDC caps. However, as a side note, I like to run slightly higher mfd/VDC rated caps in the bias circuit. Bit better filtering and life. Something like 50-100mfd/100VDC.

If you are going to run two 25/50 caps, think you'll be ok.


+1

oKoors,

Wy did you buy cheap bypass caps, your amp need good quality parts if you want to have the better tone and keep value. :(
Good parts is not very expensive and it is same labour time.

You ask about that on another post and we give you good answer, why don't you listen us ? Why another post same amp ?
viewtopic.php?f=12&t=100819


Sprague , Mallory or F & T caps only.


Top
Profile
Post subject: Re: Bias cap and diode question. These look like the wrong s
Posted: Sun Mar 27, 2016 5:58 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
One last thing...

Image

The bias circuit supplies negative DC to the tube grids. The filter caps should be solder in, with (+) end to the chassis.

:mrgreen:


Top
Profile
Post subject: Re: Bias cap and diode question. These look like the wrong s
Posted: Mon Mar 28, 2016 12:42 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14047
Location: Province de Québec, Canada
BMW2002Ti wrote:
One last thing...



The bias circuit supplies negative DC to the tube grids. The filter caps should be solder in, with (+) end to the chassis.

:mrgreen:


+1000


Top
Profile
Post subject: Re: Bias cap and diode question. These look like the wrong s
Posted: Mon Mar 28, 2016 9:58 am
Offline
Hobbyist
Hobbyist

Joined: Fri Feb 19, 2016 9:56 am
Posts: 28
stratele52 wrote:

+1

oKoors,

Wy did you buy cheap bypass caps, your amp need good quality parts if you want to have the better tone and keep value. :(
Good parts is not very expensive and it is same labour time.

You ask about that on another post and we give you good answer, why don't you listen us ? Why another post same amp ?
viewtopic.php?f=12&t=100819


Sprague , Mallory or F & T caps only.



I though I was buying good parts. In that other post I originally asked about the Sprague Atoms but the consensus was that F&T was just as good and cheaper. Those caps I pictured came in the "cap set for Showman AB763" which I linked in the first message. They are F&T filter caps and the rest are whatever they gave me.
I'm a bit bummed, because I agree, I'll spend the money to get the best components for this amp. But also I don't have the experience to know what the good components are or what to order specifically.

Not trying to frustrate anybody. Had I not posted this question I would not have known, so thank you :(

I guess the better question to ask is, if I were to reorder caps (which I'll do now) are these the recommended values and quality:
Image

These are Sprague Atoms, 100uF/100V bias cap (x1) and 25uF/25V bypass caps (x5)
Filter caps are F&T and already purchased.

PS, sorry for clogging the forum w/ redundant questions. I appreciate the help.

BMW2002Ti wrote:
One last thing...

Image

The bias circuit supplies negative DC to the tube grids. The filter caps should be solder in, with (+) end to the chassis.

:mrgreen:


Understood.
The cap in the photo was laying there so the values could be read, not how I was going to solder it in :mrgreen:

New/better/higher value caps in the shopping basket anyway.


Top
Profile
Post subject: Re: Bias cap and diode question. These look like the wrong s
Posted: Mon Mar 28, 2016 4:12 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
oKoors, those 25/50 caps appear to be IC caps (Illinois Caps). Despite the name, most consumer level IC caps are made in China, these days. They are mid-level caps. Personally, I wouldn't use them in any critical stage of the amp. And yes, the bias supply is considered critical.

If I were you --- get a pair of F&T 33mfd/160VDC caps. The extra voltage rating will help with resistance to breakdown due to heat. Last a lot longer than those IC caps. IMHO.

https://www.tubesandmore.com/products/C-ET33-160-FT

Or you can use one F&T 100mfd/100VDC, in place of the two OEM 25/50 caps.

https://www.tubesandmore.com/products/C-ET100-100-FT


Top
Profile
Post subject: Re: Bias cap and diode question. These look like the wrong s
Posted: Mon Mar 28, 2016 4:19 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Here's a photo of a AB165 Bassman rectifier board I redid. I replaced the two OEM 25/50 cap with one 100/100.

Image


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 8 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: