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Old 15th February 2012, 12:38 AM   #1
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Default ST-35 C-1 Capacitor on PC-13 board.

Greetings, gang,
I need some help in determining the proper capacitor for C-1 on a standard
Dynaco ST-35, PC-13. The Dynaco build manual calls for a .1 ufd 3V. I cannot find any, let alone any that looks like the one on the Dynakit parts PC-13 picture.

Can anyone help me with this? I am ready to order the other capacitors and resistors from Mouser, but seem to be stuck on this one.

Thank you,
Stevedel
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Old 15th February 2012, 12:56 AM   #2
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Hey Steve.....

Check out this spot:

diytube.com :: View topic - diytube ST35 docs & mods *3/22/11*

Great group, and Shannon's board rocks. Now as for your question...I assume C1 is the input cap...Any voltage rating would be OK there - but I'd suggest something high quality, so that most likely would be in the 400v range. In my updated board I used some russian PIO caps, and they sounded pretty nice.
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Old 15th February 2012, 01:09 AM   #3
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Thanks Steve,

I did look at those posts but I gather that they were talking about the modified Triode Electronics board. Looking through their parts list, I did not see anything I thought suitable. I am sure that I'm missing something, somewhere.

This is my first Diy project and decided on the basic ST-35 with mica and Orange Drops.
(Orange Drops look cool)

Stevedel
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Old 15th February 2012, 01:27 AM   #4
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Quote:
Originally Posted by Stevedel View Post
Greetings, gang,
I need some help in determining the proper capacitor for C-1 on a standard
Dynaco ST-35, PC-13. The Dynaco build manual calls for a .1 ufd 3V. I cannot find any, let alone any that looks like the one on the Dynakit parts PC-13 picture.
Yeah I see it too. Oddly, the ST-70 does not have an input cap. I went through my schematic collection and almost no companies other than McIntosh and Marantz routinely used input blocking caps. I mean, almost nobody. Even the current commercial modification houses don't use them.

Quote:
Originally Posted by Stevedel View Post
Can anyone help me with this? I am ready to order the other capacitors and resistors from Mouser, but seem to be stuck on this one.
You can probably just put a wire jumper there. If you REALLY WANT a cap there, just select a high quality film cap, .1uF or so, any voltage above 3VDC and start soldering. I'd make sure the lead spacing (the pitch) was the same just for the sake of looks.

Just be careful of the voltages than may still be present if you've turned on the amp in the past hour.
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Old 15th February 2012, 01:56 AM   #5
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Two things - Mouser stocks the wrong "Orange Drops" - 715P - with steel leads. You want 716P's - cooper leads.

Second - the Triode board is actually the diytube.com :: Index board - they have an online forum there that will be must helpful.
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Old 15th February 2012, 03:46 AM   #6
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Interesting stuff....I can say that 99.9999% of the time, you are usually safe going with caps rated OVER their specs call for. So if you find a .1uF 10v or higher, you will be OK.
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Old 15th February 2012, 04:19 AM   #7
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Quote:
Originally Posted by Steven-H View Post
Interesting stuff....I can say that 99.9999% of the time, you are usually safe going with caps rated OVER their specs call for. So if you find a .1uF 10v or higher, you will be OK.
Over their voltage, certainly. Over the cap value is a problem when it's in a frequency shaping circuit which doesn't seem to be the case here. I'd want to kinda stay close on the input cap voltage just because film caps are generally kinda big anyway, and I'm inclined to keep the lead spacing close to the original part. Some of those stacked-foil box jobs are pretty compact, though. A search on eBay for "capacitors .1uf" turned up quite a few candidates; metalized polypropylene, paper-in-oil (or whatever PIO means), etc. A moderately expensive cap at the input is money well spent, IMO.

Again, the input cap in this amp is unusual by its very presence.
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Old 15th February 2012, 04:45 AM   #8
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Remove it, as it will degrade performance how fine quality it might ever be! It was there to cut out the DC that are present on the old PAS-2(not PAS-3X) outputs.
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Old 15th February 2012, 12:00 PM   #9
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Revintage is correct - That cap is a DC blocking cap and is really not necessary since all modern preamps have a DC blocking cap on their output. Either bypass the cap or put in a jumper wire in place of the cap. For those that are interested there is more info on rebuilding the ST-35 is at the link below ...

Rebuilding the Dynaco ST-35

Bob Latino
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Old 15th February 2012, 01:22 PM   #10
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Thanks,folks

You guys are a wealth of information. When I order the caps and resistors for the ST-35,
I will also order parts for a ST-70. I can't go wrong, with you forum folks pointing me in the right direction.

Let's see, ST-35 for the 2420/HL-91's, ST-70 for the 130A's and a MK-III for the 2245H sub. 5.1? We don't need no stinkin' 5.1!

Thanks again,
Stevedel
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