Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => EZ Board postings => Topic started by: Geezer on June 23, 2005, 05:20:10 am
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Hoffman Amplifiers
> Tube Amp Building - Tweaks - Repairs
> Radio Shack PCB Limits?
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TryingToDo613
Junior tube assistant
Posts: 72
(5/25/05 10:14 pm)
Reply Radio Shack PCB Limits?
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Hi guys. I have a bunch of snap in filter caps and I'd like to make cap farms on radio shack pc boards that I'll bolt don't into the amp. Is there something I should look for in the thickness of the trace or can they just handle it. I'm using them for filter caps in very high values, like a farm of 4 200uf 350v caps. (which I think comes out to 200uf/700v) on a 100w plexi. -613
Tiny Daddy
I only work on Fender's
Posts: 1228
(5/26/05 7:27 am)
Reply Re: Radio Shack PCB Limits?
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I made cap farm PCB's using the free software from PCB express:
www.pcbexpress.com/
Costs more but you can make exactly what you need using the mini-board service.
TryingToDo613
Junior tube assistant
Posts: 77
(5/26/05 8:27 am)
Reply cap farms
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Yes, that's for sure the ideal. But it's more for a production amp, not prototyping. Is there a way to measure the existing trace on a pcb, by resistance per inch or something? -613
Tiny Daddy
I only work on Fender's
Posts: 1230
(5/26/05 8:46 am)
Reply Re: cap farms
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Trace current density has a limit depending on trace thickness and width. You can figure the thickness by assuming used half-ounce copper. But for tube circuits the currents are low so the other consideration is trace spacing for high voltage. There were a couple of specs published on this but I forget what they are. Maybe the spec is on the web someplace. But you need wide spacing, like 1/4 inch between traces so you will need to peel off or etch off the copper in some places to prevent arcing.
TryingToDo613
Junior tube assistant
Posts: 80
(5/26/05 11:17 am)
Reply Hmmmmmmmm
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I see. That's interesting. The PCBs I have from radio shack have lines of connected holes, so I think that if I just jump over to the next one it should work at the 1/4". BTW I also found that snap in caps fit perfectly into Doug's terminal strips. That's a huge score alone because they are cheap and it's tough to find 1" ring clamps, and those are a buck each minimum. That is also the benefit of the PCB, but It's much more expensive. I'm going to radio shack today. -613
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