Tube Amp Archive

Hi Gang, Need some advice please. I have most of my preamp together but am struggling with noise from the SMPS. I can use a modified V Pump converter from Tubetown at 300v and it is silent. However it cannot take a 24v input and I need 24v to drive the sidechain on the compressor circuit. My goal is...

Making some progress with this now although its turning out to be quite a lot more complex than I initially thought.

Thanks Martin, I hooked up the scope to the grids on the power tubes and another probe on the output. I've got a Siglent 1202xe and with all the measures switched on I couldn't see anything moving toward zero as I increased the power. which means I probably need a different setting somewhere to see ...

Thanks Martin, Had another good go at this today. I had swapped over the preamp tubes for some good Nos ones I have and I redid the voltage chart and all the sinewave reading as attached. the sine readings are a lot better now. Most of the assymetric clipping has resolved so I think there might have...

Thanks Martin, I've had some comms with this particular clones designer in Germany and he says he thinks 40w is in the right ball park. I was also considering whether its possible that the limiting factor is the phase inverter tube and not the power tubes as its got a pre PI master Vol. I wonder whe...

Thanks Martin, I have implemented dual bias pots so they are exactly balanced. Both sets of power tubes I have tried were matched sets. I have tried several PI tubes with similar results. The originally supplied tube was marked as "balanced" The amp actually sounds very good and I experimented with ...

So I had another good look at this today. I checked the PI trim pot and it made no difference on when the wave starts to clip. It was also similar at any of the impedance setting. The bottom of the wave starts to clip at 7.4vrms and the top at 13vrms when on 4ohm load/ so power about 13 clean watts ...

Hi again, thanks for all your help. I'm not sure if there is still something wrong here. i have tried to measure the power output to see if I'm getting 50w and although the amp sounds pretty loud now I am unable to get a clean 50w power output when using the scope. I'm now getting maybe 35w. The bot...

Well Chaps, I owe you a massive thank you, you were exactly right about the phase inverter grid resistors. I probably saw 0.998 show up on my meter when measuring them and forgot to note that this was K not M! Once again thanks for taking the time to look at this it was driving me crazy. I did waste...

Just to let you guys know that I'm partially color blind and I can't read resistor codes, I measure every single resistor just before fitting. It is very possible i made a mistake and I can't wait to get home and check this out, I'll be over the moon if this is it. i can't remember whether I recheck...

Many Thanks for looking at this. My new signal generator arrived which is much better and I have taken a comprehensive fresh set of readings. I have established that Vin = Vout at the master Vol with the reverb circuit removed, but not when it is in place. I have taken a lot or readings with it in p...

Oh I didn't realise that.

thanks

Many Thanks Martin et al, Sorry I have been wasting some of your time due to a stupid mistake. I realised that I have been using the sine generator I have wrong. It has a DC offset button that is default on and I got 12v dc on the signal as well as the ac. Its not the best and I have a better one on...

Ok with the equipment I have I had to use 500mv to get a steady signal (I have a better signal gen on order). There is a very small drop at V1 pin 1 about 16mv. if I connect the other side of the 30k resistor that is connected directly to the same pin I get 500mv so no change in the cable. best Steve

Thanks Steve

I’ll try that tomorrow, can’t do anymore this evening

Best

Steve