Ceriatone ots, hrm.

[Frankie]

I changed all those bypass caps today, ( 5mdf to 4.7)
Problem is still there, so it was not the bypass caps.
Arrrrrrrg!

[BobW]

Frankie, since the issue is still there using the loop, it is in the pre section. However it still could be a power problem at B+4 or B+5. If you don't see any voltage changes and you have swapped out preamp tubes, then Re-check and resolder your joints. If you are using solid hook-up wire, maybe you have an intermittent or full break under the insulation. hth

[LPSGME]

As someone asked about earlier - are you always using the same speakers, and have you tried any others since?

[Frankie]

As someone asked about earlier - are you always using the same speakers, and have you tried any others since?

I have tried the speaker in my Bruno cowtipper. The same problem.
I use the speaker cabinet for my Bruno underground 30 also, but the cab never fail on that amp ;) so it`s not the speakers.

[Frankie]

Frankie, since the issue is still there using the loop, it is in the pre section. However it still could be a power problem at B+4 or B+5. If you don't see any voltage changes and you have swapped out preamp tubes, then Re-check and resolder your joints. If you are using solid hook-up wire, maybe you have an intermittent or full break under the insulation. hth

Did resolder the main board with the b+ 1,2,3,4, Still got the odd problem.
Checked all wires, nothing wrong?
This is given me a headache!!!!!!
Did also swap out the signal resistors on v1a input with new ones. :(
It must be somthing that is loading down, cause the amp plays huge , and full when I turn it on, but while playing the volum, is getting weaker and the tone gets harder and more narrow. If I stop playing for 5 minutes the amp sounds louder and fuller again. the od varies also, it looses gain after playing a while. That made me think of the first part of the preamp.
If the first stage is loosing volum, then it will not send as much gain into the od part, so then the od will not gain as much. It`s like turning down the input volum, and the overall gain goes down. But I somehow can`t find out what`s causing this f... problem. :( :(

[Structo]

Yes but if it is losing gain and volume, it should be something you can measure.

[bcook]

Ok, when it acts up measure the grid voltages of the preamp tubes. If they don't read 0v dc, you have too much resistance to ground. Measure the heaters too.

[nickm57]

Lead dress? small amount of shield or solder clipping.
It could be something as simple a a small wiring bug on the input jacks.

Have you tried running a signal back from the phase inverter then OD then input stages. Just an old CD Walkman(run it on batteries) with a set of alligator clips will do. Follow the layout and don't connect it to voltage......

Another approach is a tone generator and a Scope.

Nick

[LPSGME]

ignore

[LPSGME]

Another approach is a tone generator and a Scope.

Nick

I'd say so... especially as it fails consistently and remains bad for as long as you need, so as to easily compare readings.

[llemtt]

Ok, when it acts up measure the grid voltages of the preamp tubes. If they don't read 0v dc, you have too much resistance to ground. Measure the heaters too.

+1

already suggested...

using a scope would also be a plus!

[Frankie]

Ok, when it acts up measure the grid voltages of the preamp tubes. If they don't read 0v dc, you have too much resistance to ground. Measure the heaters too.

+1

already suggested...

using a scope would also be a plus!

Did measure the grid on V1, V2, they read 0 volt dc. Heaters 6,3V ac, so they are fine. V3 reads 33 volt on grid? Is that normal?
I have a scope, but I don`t know how to use it yet, just got it! :(

[Structo]

Yes I have 37v and 35v on the grids of V3.

[llemtt]

good! I think you have to start using your scope

do you have a signal generator that puts out a sine wave? (you can also use a PC sound out and some sw, I use SignalSuite on mac...)

send a 250-300hz 100mV sine wave to the input of the amp, then connect the scope to the preamp output

you should see your sine wave on the scope

let it run for the amount of time usually required to build up your problem while looking at the scope, how the wave changes?

[llemtt]

Heaters 6,3V ac, so they are fine.

I presume you mean before/after and that they are correctly ground referenced and not floating... anyway can you check also that each leg measure 3.15v relative to preamp ground?