help with older sds cap board

natoe: Posts: 34
Join date: 2010-03-06
Location: Pittsburgh, PA

Post n°1

help with older sds cap board

by natoe on Sat Mar 06, 2010 7:27 pm

The question that i have for the cap board is about the choke wires and there placemant? The instructions are as clear as mud and thought that someone here would have done this upgrade. Yes i'am using the 5ar4. Instructions say to put one wire of the choke to the board and the other to pin 8 of the 5ar4 socket that just confused me so I bring the question to the experts.

thank you for your time, pete

Bob Latino

Bob Latino: Admin; Posts: 1524
Join date: 2008-11-26
Location: Massachusetts

Post n°2

Re: help with older sds cap board

by Bob Latino on Sun Mar 07, 2010 4:13 pm

natoe wrote:The question that i have for the cap board is about the choke wires and there placemant? The instructions are as clear as mud and thought that someone here would have done this upgrade. Yes i'am using the 5ar4. Instructions say to put one wire of the choke to the board and the other to pin 8 of the 5ar4 socket that just confused me so I bring the question to the experts.

thank you for your time, pete

Hi Pete,

Check the photo below. The two choke leads go to the two eyelets on the SDS board that I have shown in RED.

Bob

natoe

natoe: Posts: 34
Join date: 2010-03-06
Location: Pittsburgh, PA

Post n°3

sds board

by natoe on Sun Mar 07, 2010 4:42 pm

Thanks BOB, I really appreciate the help but that is not the board i have. I think mine is the older version.

Bob Latino

Bob Latino: Admin; Posts: 1524
Join date: 2008-11-26
Location: Massachusetts

Post n°4

Re: help with older sds cap board

by Bob Latino on Sun Mar 07, 2010 4:49 pm

Hi Pete,

If you have the instruction diagram of the older version of this board like the one above see if you can scan it OR take a digital photo of it. Then send the diagram as an attached file to an Email to me at Bob01605@aol.com and I should be able to figure it out for you ..

Bob

natoe

natoe: Posts: 34
Join date: 2010-03-06
Location: Pittsburgh, PA

Post n°5

Re: help with older sds cap board

by natoe on Sun Mar 07, 2010 5:13 pm

will do bob. thank you for your time.

Bob Latino

Bob Latino: Admin; Posts: 1524
Join date: 2008-11-26
Location: Massachusetts

Post n°6

Re: help with older sds cap board

by Bob Latino on Sun Mar 07, 2010 5:20 pm

You know sometimes people will replace the stock quad cap on a Dynaco ST-70 amp with an underchassis cap board such as the one seen above and think (somehow) that the underchassis cap board is somehow highly "superior" to a quad cap. Well - any NEW high voltage capacitor will probably be better than the old original Dynaco quad cap because the original one is 40 to 50 years old AND had limited B+ power storage (90 uF).

What are the advantages and disadvantages of the SDS cap board?

Advantage > It has more capacitance than the stock Dynaco quad cap > 505 uF
Disadvantage 1 > It is expensive > $75
Disadvantage 2 > It is only rated at 500 volts
Disadvantage 3 > Unless you just leave the old quad cap sticking up there and disconnected if you remove the old quad cap you have a big hole in your chassis and now your amp doesn't look original anymore.

In comparison with the Dynakitparts 80, 40, 30, 20 cap ..
1. The Dynakitparts cap is less costly than the SDS cap board at only > $52.95
2. The Dynakitparts cap board is rated at 550 volts with a 600 volt surge rating.
3. OK - The Dynakitparts quad cap has less capacitance (170 uF) but in the ST-70 anything over 150 uF or so is really more capacitance than you need to run that amp. Adding more capacitance does not really help the sound or let the amp play any louder. I have added capacitance to the second section of the quad cap just after the choke. When I have done this on an ST-70 the amp sounds (IMHO) exactly the same.

Not to hijack Pete's thread here, but this is something I have been asked about (underchassis quad cap replacement boards) a few times and this is the answer I have always given.

IMHO you are better off with the Dynakitparts 80, 40, 30, 20 quad cap than a quad cap replacement board.

Dynakitparts 550 volt quad cap

Bob

Bob Latino

Bob Latino: Admin; Posts: 1524
Join date: 2008-11-26
Location: Massachusetts

Post n°7

Re: help with older sds cap board

by Bob Latino on Sun Mar 07, 2010 5:42 pm

Hi Pete,

Just connect the two choke leads on your ST-70 to the two eyelets on the board marked in RED.

Bob

natoe

natoe: Posts: 34
Join date: 2010-03-06
Location: Pittsburgh, PA

Post n°8

Re: help with older sds cap board

by natoe on Sun Mar 07, 2010 5:47 pm

thanks again for your time. No problem with the thread I hope this helps out some other people.

thanks,pete

natoe

natoe: Posts: 34
Join date: 2010-03-06
Location: Pittsburgh, PA

Post n°9

Re: help with older sds cap board

by natoe on Sun Mar 07, 2010 6:05 pm

And this will still let me use the 5ar4?

natoe

natoe: Posts: 34
Join date: 2010-03-06
Location: Pittsburgh, PA

Post n°10

Re: help with older sds cap board

by natoe on Sun Mar 07, 2010 6:07 pm

And also the wire that was original from the quad cap to the 5ar4 socket i would assume it gets elimented.

thank pete

Bob Latino

Bob Latino: Admin; Posts: 1524
Join date: 2008-11-26
Location: Massachusetts

Post n°11

Re: help with older sds cap board

by Bob Latino on Sun Mar 07, 2010 6:11 pm

Yes - You will also have to run a wire from pin 8 of the rectifier tube socket to one of the eyelets that I marked in RED. Connect the wire from pin #8 of the rectifier tube socket to the eyelet marked in RED that is furthest to the RIGHT on the diagram above of the older version of the SDS board.

Re: "And also the wire that was original from the quad cap to the 5ar4 socket i would assume it gets elimented"

Yes - The wire is is not really "eliminated". That wire now goes from pin 8 of the rectifier tube socket to the quad cap will now go from pin #8 of the rectifier tube to the eyelet marked in RED that is furthest to the RIGHT on the SDS cap board instead.

Bob

natoe

natoe: Posts: 34
Join date: 2010-03-06
Location: Pittsburgh, PA

Post n°12

Re: help with older sds cap board

by natoe on Sun Mar 07, 2010 6:41 pm

great, thanks for the answers to these complicated directions that went with this board.I agree with you on the quad cap but this is how it came and luckily there is no hole for the quad cap.But the next one I do I already talked to Kevin about that cap,and by the way what a great guy to deal with for parts.He is just on the ball.

pete