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A Very Compact Hybrid Amp - Page 91

post #1351 of 2213
wiatrob, running the 6N6P-i (900mA heater) that I "borrowed" from my Bijou. I'm not sure if it's the best operating point for it, but the 900mA mod is working well so far. I'm not sure if it matters, but using 470uF/35V C3H, and 470uF/16V C1H & C2H (wanted to try 12V tubes again). I'll have to do a comparison against my other 6N6P some day, but this seems to have a bit more kick. I say seems as I've been hoping between tubes and amps like crazy this weekend.
post #1352 of 2213
Quote:
Originally Posted by holland View Post
I say seems as I've been hoping between tubes and amps like crazy this weekend.
I know what you mean - I've collected so many tubes I have to limit myself to one per week to make any sense out of it. I'll be grabbing the 6N6 and 6N23's this week @ work...

I added a small stick on heat sink for ICH. Realized if it cam unstuck it would fall directly on D1-4H, so I put a small screw through it. Probably overkill.


Nothing but 'baby' inductors available at the store tis weekend, so no chance to try upping the value of L1/2H.
post #1353 of 2213
Quote:
Originally Posted by wiatrob View Post
Nothing but 'baby' inductors available at the store tis weekend, so no chance to try upping the value of L1/2H.
Guys, if you want to investigate heater > 4W support, consider downloading Switchers Made SimpleĀ® V4.3. It's a good ol' DOS app.

For inductors, it appears to report best/optimal values but be sure to review LM2595-ADJ chart on page 12... 220uH main coil seems best compromise value for std heater targets (6.3v / 12.6v loads <= 4W). But it seems the tool may report minimum values for caps & this would make sense because most designers are looking for lowest-cost solutions. We aren't

For what you are after, ripple filter comp values require you need to dig deeper. Optimal ripple filter cap value might be 180uf -> 220uf for what you are trying to do. But remember, it seemed heater circuit noise was NOT from tube heater element side of switcher, but from switcher's impact on common A/C. You will have to get cozy w/your scope I think, but don't forget your ears are the real judge
post #1354 of 2213
I was wondering where that app was located - thanks for the pointer. Your hunches about the ripple caps seem to be on the mark - I noticed no difference on the scope when I went from 100u ->200u
post #1355 of 2213
Thanks cfcubed. I did it the old fashioned way with the datasheet, which suggests a 220uF C2H, which is why I went with 220uF-470uF. I'm also using a 470uF C1H Panasonic FM, min should be about 330uF @ 1A. The larger value inductor (L1H) should be used for lower currents, i.e., 330uH for 150mA loads (12AU7, etc.).

Scope indeed, but no time for me till the weekend at the earliest.

I'll check out your link soon. It sounds like a nifty tool.
post #1356 of 2213
I'm slowly catching up and still see a few tweaks happening here and there. I;ve found a spare C3H 470u/35v but I think will let the dust settle and wait until Alex's site is updated with the official word (bom changes/tweaks/suggestions/etc.) thanks all for working so hard on this!
post #1357 of 2213
Just use it.
post #1358 of 2213
Quote:
Originally Posted by holland View Post
Just use it.
Agreed. Others are only messing around w/other components to support > std 4W tubes (for some heavy heaters).
post #1359 of 2213
I plan to holland

I'm just patiently waiting for tweaks others are also trying, observe for green light, then patch 'em all into the board in one sitting
post #1360 of 2213
Quote:
Originally Posted by cfcubed View Post
Agreed. Others are only messing around w/other components to support > std 4W tubes (for some heavy heaters).
And when it's all said and done, I'll probably migrate back to my trusty RCA 5963 BPs
post #1361 of 2213
I have been using the 6n6p for a while now on stock parts apart from the larger cap.... no issue so far.
post #1362 of 2213
So the noise problem was due to the use of particular tubes?
post #1363 of 2213
it was due to noise from the heater supply. Using a larger value cap seems to have cured it. Tubes drawing more filament current made the problem worse, hence the 12au7 often seeming very quiet, and the thirsty 6n1p humming on a lot of builds.
post #1364 of 2213
Cool, I get it now.
post #1365 of 2213
I like it when collective brain cells get to work on a problem, very cool.

I should have mine properly cased up soon too so that'll be fun, though not quite 'compact' any more
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