Axials for C1/C2 on SSE? - diyAudio
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Old 25th August 2010, 11:31 AM   #1
dr0ss is offline dr0ss  United States
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Default Axials for C1/C2 on SSE?

I'm getting ready on a Simple SE build, and have a couple of quick questions.

(1) Is there any reason why I can't use axial-lead caps instead of snap-ins for C1 and/or C2? Obviously I'd have to extend one of the leads to fit (I'd mount it Japanese-style). Reason: better cap selection, both locally and from the mail order vendors I'll be using, even up to 600v. (For that matter, one could wire a couple of 350v 80mfd caps in series, folded at the join, to replace C1 and get 700v capability...this must be a bad idea for some reason, or else it would have already been done by someone; what am I missing?)

(2) I'll be using the usual 6H choke, so following a suggestion on an earlier thread I was thinking of dropping C1 to 40mfd or even 33mfd. Is there any down side to this? I was planning to run EL34s, at least at first, and my power transformer is an Edcor XPWR002.

(3) I'll be running off a preamp, so will probably just leave off the pot and wire directly from the phono jacks to the board. The input is already being attenuated by R12/R22, so I don't need to add extra attenuating resistance, yes?

Sorry for the newbie questions; I do have some experience with tube amps, but it is from a very brief ham stint in the 60s, and my memory of that time is not as sharp as I would like...

Thanks much,
David
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Old 25th August 2010, 03:03 PM   #2
rknize is offline rknize  United States
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1) I don't think the pads are spread far enough to do a truly "japanese style" install, but there is no technical reason why you can't sub the cap with something else as long as they meet the minimum specs. Someone on here did an SSE with all film caps! If you are going to up B+, make sure you consider the CCS loads on the input tube. They may need some series resistance and/or addition heat sinkage to keep their dissipation in check.

2) Dropping C1 will make the choke do a bit more filtering work, but keeping it above 10-20uF should have very little impact on B+ voltages. You should end up with about 450V B+ or so.

3) R12/22 don't play any part in attenuation, since the tube grid is a trivial load to drive. They are called grid stoppers and are there for stability. But to answer your question, no you can just connect the RCA jack directly to the pads on the PCB.
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Old 25th August 2010, 08:11 PM   #3
bamph is offline bamph  United States
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Default C2 Cap - what to use?

I'm also just starting on a Simple SE build. I ordered the output transformers yesterday (hurray!), but am having some trouble figuring out what to use for C2. I have a snap-in cap that will work, but I am building a turret board amp. I've thought up some creative ways to mount the cap using eyelets and lugs (basically through-hole mounting), but it may not be worth the trouble if there is a readily available axial cap.

So, my question is, does anyone know of a good leaded cap to use for C2? Something in the neighborhood of 100uF.

My amp will use a NOS Stancor 325-0-325 power transformer with solid state rectification. I calculate out the max B+ voltage to be 325X1.4 = 455V, so if you subtract a few volts for drop across the rectifier, it looks like a 450V rated cap will work. However, someday I may replace the transformer with a higher voltage, so I think I want to use 500V caps.
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Old 26th August 2010, 07:37 AM   #4
dr0ss is offline dr0ss  United States
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Russ, thanks for the information. I don't intent to crank up the B+ to these levels, I just like the idea of a cap rated a little higher than necessary.

bamph: F&T, Jensen, and JJ all still make 500V 100MFD axials.

- David
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Old 27th August 2010, 09:26 PM   #5
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It seems that the worlds supply of reasonably priced snap in 500 volt electrolytics has dried up, so this might be a useful alternative. Electrically speaking it should not make any difference and as someone stated it is possible to use motor run caps for both of the power supply caps.
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Old 28th August 2010, 08:50 AM   #6
dr0ss is offline dr0ss  United States
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There are still a few around, but like everyone else I hate buying one part here, another there.

David
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