Traynor YVM-1 Conversion to Guitar Amp Suggestions

[Helmholtz]

Should there be V at V3 pins 2 and 7. I would think not and why does the Mitchell chart show V there?

For proper operation the grids need to sit at a voltage around 1V lower than the cathode.
Remember that the 1M grid leaks don't drop a voltage, so the voltage at both ends is the same.
The ~ 1V bias is produced by the voltage drop across the 470R cathode resistor.
Connecting a meter to one of the grids will lower both grid and cathode voltage - depending on meter resistance.

Who are Mitchell an Haus?

[g1]

Who are Mitchell an Haus?

Haus is a typo. It is Mark Huss (of the Hiwatt pages, Hiwatt.org). Mitchell I think is the author of a Marshall history book?

[misterc57]

Haus is a typo. It is Mark Huss (of the Hiwatt pages, Hiwatt.org). Mitchell I think is the author of a Marshall history book?

Yes Mark Huss and voltage charts from the Tom Mitchell service book.

[g1]

It can be difficult measuring grid voltage, like Helmholtz mentioned above. Generally, if the plate and cathode voltages are good, you can assume the grids are good.
Did adding the treble cap correct the 'anemic' issues?

[Helmholtz]

It seems that tube amp manufacturers no longer specify PI and power tube grid voltages on schematics.
I think for good reason.
To accurately (within 1%) measure the PI grid voltage you'd need a voltmeter having an input resistance of 100M or larger.
So something like a high impedance VTVM.

[misterc57]

Did adding the treble cap correct the 'anemic' issues?

No. I have no output at this point. I have signal out of the treble cap.

I have not had time but I need to revisit the V3 wiring. I did not do much at V3 (going with the YVM circuit). I think it needs a good review against the 2204 schematic.

[DrGonz78]

Perhaps the middle cap connected to the slope resistor. It probably is nothing but it looks like it was made on a Friday at 5pm. It might be weirding out or it’s fine. Anything from your treble cap down to the PI circuit could be causing the problem.

[misterc57]

Progress and issues

Updated the area around V3 PI tube using https://robrobinette.com/How_the_Mar...M800_Works.htm as a guide.

HI input has low output. This is the jack on the outer edge connected to the 68K grid stopper. Scratching my head on this one.
LO input cranks.
Presence produces a squeal when above 6. Pot, resistor and cap are original from Traynor and correct values for JCM800.
80 to 179 Hz hum present only when Vol pots are turned up. There are noises when taping and moving preamp wires at V1 and V2. I think I need to reflow all connections on the board and tube pins at V1, V2.

Reading 395 VDC on the EL34 plates.

Thank you

[mozz]

"HI input has low output. This is the jack on the outer edge connected to the 68K grid stopper. Scratching my head on this one.
LO input cranks."
Obviously a wiring error. Squeal could be out of phase output transformer wiring. Hum numbers don't make sense, it would most likely be 60hz or 120hz.

[g1]

You can't do the 4010 style switching arrangement with switchcraft jacks. You need cliff style jacks with 2 sets of switch contacts in use for the high jack.
Like in the diagram you showed in post #14.