124 low volume in clean channel (solved)

[dariez75]

Hi guys,
I've recently finishend a #124 ODS using files you shared here, the amp sounds fantastic, as I ever desired. Unfortunaly I hear a big difference in volume between clean and OD channel. Could this be normal with low-plate design or maybe I did some mistake? Fort instance, when I play the clean channel I've got to set master volume at 2 but if I want to swich to od without lot of db in difference I have to set Drive/Level on 7-8 and Ratio on 3...
ps in order to acheave a suitable od I've set my 250KL internal OD trimmer on the max.

[pompeiisneaks]

I don't know the direct answer, but my first question is to clarify. Your subject seems to imply the clean channel volume is low, but then your message says that it's perfect at a volume of 2. Then you say that the drive channel seems to not have enough drive. Is it the drive that has low output or the volume? If you turn the master volume up, it should get a lot louder.

I think if you were to include some photos of the insides of the amp it would help us see if we can see anything wrong. Ultimately, though, low output from any part of an amp usually means that one of the components in that part of the triode is sending too much signal to earth. Check solder connections to ensure none are looking dull and grey. Do continuity tests between all points on the signal path to make sure you've got good connections etc. Chopstick the amp with a wooden chopstick to see if touching something specific causes the sound to suddenly change and either that component needs better soldering, or it may be bad.

~Phil

[67plexi]

Set your OD trim pot at 24k for starters on the tube side. I have used a 24k resistor then a 250k audio pot on the back of the amp for fine tuning.

In the photo trim pot set at 24k with a 250k pot on the back of the amp.

001 (2).JPG

[dariez75]

Sorry for bad explanation, what I want to say is that my amp sounds good but when this one is on clean channel the master seems too low despite when od is engaged.

[67plexi]

A photo may help make sure the outside lugs on your 1 meg master volume pot reads 1 meg and check your coax to make sure you don't have a piece or a strand of outer coax
shorting out. And check your ground to the master volume pot. if that's all OK voltage chart your amp

Voltage Chart.JPG

[martin manning]

Sorry for bad explanation, what I want to say is that my amp sounds good but when this one is on clean channel the master seems too low despite when od is engaged.

I think your OD entrance trimmer is set much too high.

[dariez75]

Thank guys, when I'm home I fill the tab.

[dariez75]

Sorry for bad explanation, what I want to say is that my amp sounds good but when this one is on clean channel the master seems too low despite when od is engaged.

I think your OD entrance trimmer is set much too high.

But if I set the 250K OD trim halfway, I have too low drive sound

[martin manning]

What does your OD entrance look like? I recommend going with something like 220k into a 100k trimmer, and setting about 25k to ground at the wiper.

[dariez75]

Now 220K on 250 trim
previously (attachment) 220K on 100K

[dariez75]

Here the voltage chart.
Trannies are classic tone twin set
PT secondary wired for delivery 345-0-345

[martin manning]

Those voltages don’t look out of line. V1 plates could be 20-30V lower, but that is not the reason for the low clean volume.

[dariez75]

This eveninig I try to change v1 tubes

[martin manning]

I was suggesting that you might want to adjust the first dropping resistor to bring the preamp voltages down.

It might be that you have some feedback and parasitic oscillation going on with your rear panel OD trim. Maybe take that out of the circuit and see what happens.

[dariez75]

I haven't an OD trim installed on rear panel but only 250K trim installed on board after 220k entrance resistor. I can try to remove 250k trim from the board