Oliver G400R no reverb

[52 Bill]

The number 031-0005-00 is probably a manufacturer's part number. I thought that it was a Kustom part number, they have a reverb tank part number 031-0049-00. I will look at the part lists that I have to see if it matches anything.

A few years ago I worked on an Oliver that would break into oscillation when you turned up the treble control. To fix it I had to cut a pc board trace and float a shielded wire away from the board to separate the signal paths.

[nickb]

When I said the output impedance of the 6DR7 stage is a few hundred ohms I forgot about the output being taken after the 1K resistor. That will raise it to over 1K.

I've just been looking at the plate curves for that tube. If you were to move the 270K grid leak resistor to the junction of the 1k & 2.2K as drawn it will bump up the current and therefore also the gm of that tube. That will lower the output impedance a little and give you more current drive. If you do try that then measure the cathode current (infer from the drop across the 1K) and plate to cathode voltage to calculate the plate dissipation before committing to it as it will be very high and the max is 7W. It could have been a deliberate change to tame the dissipation. Doing it graphically I'm coming up with about 6.5W.

[pontiacpete]

Remember that 270K resistor is not at the junction of the 1K/2.2K it goes to ground.
So I tried lifting one end and nothing.. Then I tried connecting it to the 1k/2.2K like the schematic and still nothing.
I also tried these two above adjustments with the 4FB and the 4EB tanks and nothing different in the reverb.

I feel it might be worth mentioning that under the base of the 6DR7 socket the pcb is darkened from heat. The whole socket itself is darker from heat.
Could some stray voltages interrupt the reverb signal because of this?
I had tried scrapping the brown colored area of the board between the traces but it is very deep.

[nickb]

Remember that 270K resistor is not at the junction of the 1K/2.2K it goes to ground.
So I tried lifting one end and nothing.. Then I tried connecting it to the 1k/2.2K like the schematic and still nothing.
I also tried these two above adjustments with the 4FB and the 4EB tanks and nothing different in the reverb.

I feel it might be worth mentioning that under the base of the 6DR7 socket the pcb is darkened from heat. The whole socket itself is darker from heat.

Moving it as shown in the sch only gives you about 50% more gain at the expense of a lot of heat. I suspect that is why it was modified. Don't ever float it.

Could some stray voltages interrupt the reverb signal because of this?
I had tried scrapping the brown colored area of the board between the traces but it is very deep.

At an earlier stage you measure a volt or so coming out of the reverb. That's quite a healthy level. So I don't htink you habe a problem there.