6v6 plexi-ish build questions

[donzoid]

Oh, I bet the line of least resistance is following the new R's and basically bypassing the 6K (and cap) that were feeding it before.

Correct?

If so maybe I should parallel the 2nd and 3rd filter cap instead of having that 8.2k dropper in-between them. Of course that would raise everything in the string thereafter.

[Littlewyan]

That should definitely not be the case. Have you put the 1K Resistors in series with the 6K Resistor? Sounds like they are connected to the wrong side of the 6K.

[donzoid]

No I grafted them right onto the sockets. The 6k feed line was one step further down the B+ rail, that's why I'm looking at MHuss's schematic now, perhaps I just need to re-plumb the whole string to match...

Edit: I say one step further, because the choke is between the old screen feed hookup and that. I am thinking it's unnecessary now, since the feed is coming from the plate / OT primary and I should just raise the resistor value directly on each of the sockets.

[Littlewyan]

So the 1K resistors are just bypassing the 6K resistor? If so then thats why the voltages have gone back up.

[donzoid]

OK I see what I did. I soldered them on between the plate and the screen and they should go from the original feed to pins 4 of each tube. For some reason I thought they went direct from pins 3 to 4 on each socket.

[martin manning]

A schematic is worth a thousand words...

[donzoid]

Yes Martin, I see that now.

I've downloaded and installed Express Sch and will try that going forward.

I installed a small term. strip by my output tubes and placed the screen R's there. Right now I have the 6k in series to the term., and an 820R to each pin4. 356v at the plate, 346v at the screen.

So all my voltages are "safe" but oddly, I don't care much for what I'm hearing. So tomorrow I'll play on it when it's daylight and I can open it up a bit, and I'll try going with a higher value pair if I can find one.

[donzoid]

OK Martin, ya can't say I didn't at least try.... I am "pretty sure" I have everything right from the power supply/output tubes but have not finished the preamp section quite yet (I need to add the separate normal channel and a mid control) but at least it's something to look at.

[Littlewyan]

If you're still getting a bit of hum you could try increasing the 2.7K Resistor on the HT to 8.2K or 10K. That will provide a bit more filtering so might help.

Are you happy with the sound?

[donzoid]

Thanks Wyan I may try that tonight...

So far I can't say I'm particularly thrilled with the sound of it, for the following reasons:

1. It sure isn't very loud (but I haven't recalculated the output) Compared to my Express with 6v6 or a Deluxe, it's nowhere even close. I would guess I'm yielding about 8 watts maybe ten. I helped a friend with a SE champ (one of those with the 6L6) a couple months ago, and it was louder...heheh!
2. It needs serious tone tweeks even with a .1 cap in place of the 1uF on the TMB side cathode bypass it is starting to sound brighter, but still not there. So it's now just beyond the "blanket over it phase" but not bright enough, and I may want to look at the 6V6 cathode values too.

I still plan on elevating the heaters also to get rid of more hum.

Any suggestions are always appreciated! It has the potential to be real good, but this one is going to need some serious dialing in.

[Littlewyan]

What sound are you looking for? What amp do you want it similar to?

[Colossal]

Don,

Just looking at a few things on your schematic.

Things to consider to be closer to a Plexi and get more out of your 6V6s

1. PI plate loads to 82k/100k
2. PI cathode and tail resistors to 470R/15k
3. increase PI null input cap to 0.1uF from 0.02uF
4. Change output coupling caps from 0.01uF to 0.022uF
5. Decrease output grid leak resistors from 470k to 220-270k
6. Bass pot to 1MA from 500kA
7. Bypass V2a 820R with 0.68uF for nice midrange bump.
8. Reduce power tube cathode cap from 470uF to 47uF or bump up 1000-2200uF (stiffer feel)

[Littlewyan]

He might benefit from actually decreasing that 6K Resistor on the screens. That could be the cause of the blanket over the speaker sound. You've got a load of things to try here, do one at a time and see what you like .

[Colossal]

He might benefit from actually decreasing that 6K Resistor on the screens. That could be the cause of the blanket over the speaker sound. You've got a load of things to try here, do one at a time and see what you like .

I agree. His plate voltage is already low enough. Dump that resistor entirely or make it 1k and up the screens to 1k each.

On the original 6V6 Plexi for which I thought he was going for (but Plexi-ish suggests a looser interpretation) a 5k 5W was used in series with the choke because the plate voltage was 440VDC. That 5k -> choke dropped the screen voltage 40V. Not really needed here.

[statorvane]

I don't see the mixing resistors and cap where V1A and V1B output join. Usually each has a 400K resistor with the bight channel's resistor bypassed with a 470pF cap. Don't know if that would introduce hum though or reduce the blanket over the speaker sound.