Question about tube amp power supply caps

gjo · 1st March 2006, 04:05 PM

Folks

I have a Dynaco ST 70 clone from Welborne Labs, the model V.35, and would like to replace the electrolytic capacitors in the power supply board.

The original unit came with Panasonic 330mfd, 450V caps, and these appear to be quite expensive. I have located affordable snap in electrolytic caps at apexjr, of similar rating and welcome any advice from any of you knowledgeable people out there

Link:http://www.apexjr.com/capacitorsR.html

Thanks

George
Bangalore, India

anatech · 1st March 2006, 05:54 PM

Hi George,
Make sure you are not buying NOS. You want brand new stock, fresh. Given how long you will own this amp, good caps are not that expensive.

-Chris

Tom Bavis · 1st March 2006, 05:59 PM

$6.17 (5.22 qty 10) is expensive? That's the price at DigiKey.com.

What's wrong with the caps that are in there? Surplus caps may not be any newer.... If you want some, I have 330@400V pulls - you can have'em for postage.

gjo · 2nd March 2006, 12:21 AM

Thanks Chris, I'll check.

Tom:

I saw the price on the Welborne Labs site at $14 a pop, and figured that $84 for six caps was a bit higher than I could afford. The Digiikey option opens up possibilities..

I am looking at replacing them is because when I power off the amp, one channel doesnt retain the audio for more than a second or so, whereas the other channel continues for about 8-10 seconds, leading me to think that there is a problem. Could there be any way for me to check whether the caps need to be replaced, or if the problem lies elsewhere?

Thanks

George

anatech · 2nd March 2006, 02:04 AM

Hi George,
This could be caused by low bias current, or turn off transients. I normally look at the waveforms across the caps with a 'scope. If I see big "pips" on the leading edge, the cap may be defective. I measure them to be sure in an unfamiliar amp.

-Chris

Geek · 2nd March 2006, 05:52 AM

Illinois Capacitor, Nichon and Xicon are about the lowest priced and I have had no problem with them in PSU.

Xicon's make great cathode bypass too for their price, though Panasonics do sound better there.

jmartins · 3rd March 2006, 01:21 PM

Geek

Do you use electrolytic to bypass? try Silver Mica or MKP

[]s
João

lndm · 5th March 2006, 12:34 PM

Old computer switchmode power supplies are a good source of HV electro's. Some are sonically good brands. Most (check for expansion) are undamaged and useable within their marked tolerances.

Geek · 5th March 2006, 05:07 PM

Hi,

Quote:

Originally posted by jmartins
Geek

Do you use electrolytic to bypass? try Silver Mica or MKP

I bypass with electrolytic and couple with MKP.

I have tried all sorts of caps in cathodes for bypass. Tantalums are interesting, but not so interesting to warrant $4 over $0.40

Nordic · 5th March 2006, 06:36 PM

Most of the cheap stuff I can get is Jamicon and Hitano, are those any good?

1st March 2006, 04:05 PM	#1
gjo diyAudio Member Join Date: May 2003 Location: Bangalore, India	Question about tube amp power supply caps Folks I have a Dynaco ST 70 clone from Welborne Labs, the model V.35, and would like to replace the electrolytic capacitors in the power supply board. The original unit came with Panasonic 330mfd, 450V caps, and these appear to be quite expensive. I have located affordable snap in electrolytic caps at apexjr, of similar rating and welcome any advice from any of you knowledgeable people out there Link:http://www.apexjr.com/capacitorsR.html Thanks George Bangalore, India

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1st March 2006, 05:54 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi George, Make sure you are not buying NOS. You want brand new stock, fresh. Given how long you will own this amp, good caps are not that expensive. -Chris

1st March 2006, 05:59 PM	#3
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	$6.17 (5.22 qty 10) is expensive? That's the price at DigiKey.com. What's wrong with the caps that are in there? Surplus caps may not be any newer.... If you want some, I have 330@400V pulls - you can have'em for postage.

2nd March 2006, 12:21 AM	#4
gjo diyAudio Member Join Date: May 2003 Location: Bangalore, India	Thanks Chris, I'll check. Tom: I saw the price on the Welborne Labs site at $14 a pop, and figured that $84 for six caps was a bit higher than I could afford. The Digiikey option opens up possibilities.. I am looking at replacing them is because when I power off the amp, one channel doesnt retain the audio for more than a second or so, whereas the other channel continues for about 8-10 seconds, leading me to think that there is a problem. Could there be any way for me to check whether the caps need to be replaced, or if the problem lies elsewhere? Thanks George

2nd March 2006, 02:04 AM	#5
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi George, This could be caused by low bias current, or turn off transients. I normally look at the waveforms across the caps with a 'scope. If I see big "pips" on the leading edge, the cap may be defective. I measure them to be sure in an unfamiliar amp. -Chris

2nd March 2006, 05:52 AM	#6
Geek diyAudio Member Join Date: Sep 2004	Illinois Capacitor, Nichon and Xicon are about the lowest priced and I have had no problem with them in PSU. Xicon's make great cathode bypass too for their price, though Panasonics do sound better there.

3rd March 2006, 01:21 PM	#7
jmartins diyAudio Member Join Date: Apr 2005 Location: São Paulo	Geek Do you use electrolytic to bypass? try Silver Mica or MKP []s João

5th March 2006, 12:34 PM	#8
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	Old computer switchmode power supplies are a good source of HV electro's. Some are sonically good brands. Most (check for expansion) are undamaged and useable within their marked tolerances.

5th March 2006, 06:36 PM	#10
Nordic diyAudio Member Join Date: Sep 2005	Most of the cheap stuff I can get is Jamicon and Hitano, are those any good?

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