JTM45 rectifier question

[Reeltarded]

it should go to other side of the board between NFB and bias. There is an 8k2 or 10k dropper there.

The yellow wire terminates control side of the board at that next node dropper.

It continues on a separate wire from the junction of the termination to the sockets.

It's appropriate to connect that dropped either at the control side junction but better on the socket in the case that the layout is correct for a stock setup as described above.

[martin manning]

I followed the instructions when setting bias. With my plate voltage I got 38-39, I set it to 39.

The change in pin 5 voltage is very large though. Is that a transcription error?

I think you re correct. I followed the Metro instructions. The yellow wires go from 32uf cap to V5 then to the V4 then they used to go direct to the circuit board. Now there es a 1k resistor there instead of the wire. I don't think it does anything...

So if you replaced the jumper going from V4 pin 6 to the tube-end of the 8k2 with a 1k (that's the left side of the yellow loop in the schematic I marked up), what you have now is a 9k2 dropping resistor, which will make little difference except to lower preamp voltages a bit, which is what you're showing.

[Reeltarded]

This

Marked E terminates at the 10k then a wire from that same termination to screen. The resistor locks on the socket with the other end of the screen resistor on V4

[SPeter]

The Metro instructions say that the yellow wire from the 8.2k (10k on your drawing) resistor's tube side turret (the one between the NFB and the Bias) should be connected to pin 6 of V4 and this is how I did it, then when installing the flying resistor I simply replaced this yellow wire with the resistor. Your drawing shows a yellow wire from the 10k (my 8.2k) resistor to the V4's pin 6 bypassing the 10k resistor. Mine is not wired like that.

[Reeltarded]

The layout pictured is the way it's supposed to be.

See how the shared resistor would come in that string from the junction of the screen supply and the next node? I don't have a way to draw it in on ipad.

[martin manning]

The easiest way to get SPeter’s amp to the desired result is to remove the wire going from the screen filter to V5, pin 6, and run a new wire from the screen filter direct to the 8k2 dropping resistor, where the 1k flying resistor is now connected.

[Reeltarded]

Yes

[SPeter]

...
The change in pin 5 voltage is very large though. Is that a transcription error?

I think you re correct. I followed the Metro instructions. The yellow wires go from 32uf cap to V5 then to the V4 then they used to go direct to the circuit board. Now there es a 1k resistor there instead of the wire. I don't think it does anything...

...

Yes, typo sorry, it is 39.5 not 49.5.

[SPeter]

The easiest way to get SPeter’s amp to the desired result is to remove the wire going from the screen filter to V5, pin 6, and run a new wire from the screen filter direct to the 8k2 dropping resistor, where the 1k flying resistor is now connected.

Which side of the 8k resistor that wire should go? Control side or tube side? Sounds like I have to lift the circuit board LOL

[martin manning]

Tube side, like this. You could run the yellow wire from the screen filter next to the V5 pin 6 to V4 pin 6 jumper, then solder to the 8k2’s turret on the top side of the board.

[SPeter]

Thanks for the clarification, I still have the old wire which used to be between the turret and V4 pin 6 tucked away under the board, I will just connect it with the one from the filter cap. Easy peasy. If it worked out I can lift the board and put in a new wire and clean things up a little at a later time...

[martin manning]

Sounds like a plan. Splice them together and shrink wrap. That will be good to go.

[SPeter]

I did the modification and measured the pins. Pin 5 voltage is 43Volts on both V4 and V5. The pin 4 and 6 voltages dropped about 6-8 volts from previous measurement.

Fired up the amp and I could not dial in the tone like I was able to last night. The break up was early and harsh. I have to dial back the guitars volume knobs all the way to 3 and plug into the low input jacks to get any kind of clean tones.
I rolled some tubes to see if I can tame it down... I ended up with tung sol in v1 sovtek in v2 and mullard in v3. The good news is that I tested my second sovtek lps in v1 and this one was not microphonic at all but that was the harshest sounding so I moved it to v2.

I dialed back the bias values from 38 to 34mV to get more headroom. I think it helped a little.
I have the values recorded will post them tomorrow night.

In the process i had to resolder some v1 and v2 pins. I'm not sure that has anything to do with the harshness. I checked for cold solders but I don't see any.

[Reeltarded]

Defeat the PPIMV. Amp should be generally clean until 4 on the dial when you bang it pretty hard. PPIMV defeats NFB once it's about half down, That is unrefined and hairy.. anything below 7 sounds like an aircraft fire to me.

[SPeter]

You are probably right, there are too many knobs to turn on this thing I should start make notes of where everything is when I like what I hear...