5C3 Paraphase Inverter: How to Balance?

[Cygnus X1]

Actually-two questions.

I'm having trouble understanding the concept of adjusting the balance on the paraphase inverter on V2 (the second 6SC7).
Do I measure for voltage at the #5 pins of the 6V6's?
Which resistors/caps would I change off pins 2 or 3 of the pi?
Should I sub a pot or two in there to get a ballpark value?

Layout:
http://www.turretboards.com/layouts_...5c3_layout.gif

Looking for more efficient operation and a tad more headroom. I already read about the only source that discusses this-Gerald Weber's article on harp amps, and his info on the 5C3 circuit. He mentions that it may need to be adjusted for balance, but doesn't say how.
There is also mention of reversing the primaries on the OT and altering the NFB.

Also-the grid leak bias on V1.
I am getting -.5VDC on pins 3 and 4, with 90 volts on the plates (pins 2 and 5). Schem calls for -.8VDC...with 85 Volts on the plates. Should I mess with this, or is it "close enough"?

So that is four options to explore.
I will never build this circuit again, at least not in this configuration,
It has been the biggest PITA I have ever dealt with.
Any help is appreciated!

[steve25]

Dont screw with all that as part of the greatness of that amp is the way that PI make the amp distort when cranked.
What I would do for more punch and clean head room would be to pop in a 5AR4 rectifier for a tad more B+ voltage, you just ahve to make sure that the higher voltage output does not exceed that first power supply caps rating.
The other good thing about the 5AR4 is that it is a slow warm up recto and will extend the life of all your tubes.

[Cygnus X1]

I have a severe shortage of 5AR4's.
I don't think I have much to worry about on the cap voltage
ratings, as I had to double up 10uf500V caps to achieve 20uf total. So I guess that arrangement gave me a 1000V max.

What about a 5U4GB?
I have a literal boatload of those.

[Cygnus X1]

I hate to admit this one.
D'oh.

After staring at the inside of this amp for a better part of a week, something just occured to me.

The NFB wire isn't hooked up.
It isn't really even "there".

[cdw2000]

I don't think the NFB will fix the loudness and headroom problem you've been describing. NFB wll actually reduce the gain of the power amp a little.

But you may want to try it just the same.

[fran]

NFB will give you a bit more headroom and "tightness".
5U4 will drop the B+ voltage a bit less than 5Y3, yes, but the heater draws 3 amperes, versus 2 amperes with 5Y3, so check your power transformer.
By the way, yo can play with the value of 25k resistor going from the "bottom" PI grid (in the schematic) to ground, as it's the voltage divider of 1M and that 25k resistors that define the drive to the "bottom" triode. Put a pot instead of the resistor and find your sweet spot. It will depend on the characteristics of the tube, so it's not a bad idea to put a trimpot there, as you will probably have to change it when you change the tube

[Cygnus X1]

NFB will give you a bit more headroom and "tightness".
5U4 will drop the B+ voltage a bit less than 5Y3, yes, but the heater draws 3 amperes, versus 2 amperes with 5Y3, so check your power transformer.
By the way, yo can play with the value of 25k resistor going from the "bottom" PI grid (in the schematic) to ground, as it's the voltage divider of 1M and that 25k resistors that define the drive to the "bottom" triode. Put a pot instead of the resistor and find your sweet spot. It will depend on the characteristics of the tube, so it's not a bad idea to put a trimpot there, as you will probably have to change it when you change the tube

Shazam (with all due respect)!
Where did you come from?

I am getting two schools of thought for responses from my favorite amp building sites:
Either A: It's all good, that is the way it is supposed to sound
Or B: Tweak it.

I am going with option B.
This circuit is teaching me more than I have ever learned, and it is very touchy. I have a trim pot handy for just this occasion. Thank you, fran...and all.

[Gris]

I am a huge opponent of trying to change a classic amp into something else,

... unless I'm doing it, LOL

[Cygnus X1]

I'm with you, Gris.
Let me make sure I haven't gotten this one too screwed up before I jump ship on it.

It has potential-I hear it.
I just want a tad more. Not much.
It is a journey fo' sho'.

[Cygnus X1]

Well, now I have two problems.

The only set of 6V6's it "likes" are an old set of Sylvania 6V6GT's. But they are red plating, and I can't see where all the current is coming from. 385 on the plates, 21V on the grid. I suppose I have to play with the 250 ohm power resistor to get the current down. But, it sounds best this way. (for now-it might last a week if I'm lucky).

Other-very odd opportunity (problem):

The tone control shows bad distortion on anything but full up, or full off. Within the sweep, the distortion is worst at midpoint on the pot. I thought it could be bad pot, bad caps.
So I changed everything, both caps and the pot. No change. What should I look for? The 50uf caps?
Bad karma in V1? (Yes, I tried several different 6SC7's-I now have a set of Tung Sol JAN glass 6SC7's in there).

This amp is far too much fun for my abilities.
(Note sarcasm).
Any help with that tone control distortion would be greatly appreciated.

[Cygnus X1]

Good grief.

Next time remind me to post a detailed
pic of my build before I start shooting off
questions.

Part of the Grommes build was to have the #5
pins of the 6V6's tied together.

Guess who forgot to remove that wire!
Works fine now-all problems solved.
Sounds awesome!