The Amp Garage

Hi. I have a Bandmaster build that has this constant hum, the only thing that affects is the bias pot, it gets louder as the the value is towards -37. I have have basically tested everything, changed parts etc. The funny thing is that when I put in just one power tube, the hum goes away, with two it...

erwin_ve wrote: ↑Mon Mar 20, 2023 8:30 pm Oddvar, what about this one: https://www.tube-town.net/ttstore/netzt ... -watt.html
Its a good PT, has the right voltages, relay power winding.

Erwin

Good point, thanks...

Thanks Guy.

Hi. Any advice on transformer for the dumble 50w (022814715PP7D). I have use transformers from Weber, but they have gone twice. Could I use this?: https://www.tube-town.net/info/datenbla ... o50-pw.pdf

I have many amps with Hammond, so I would like to try something else?

Roe wrote: ↑Thu Jun 09, 2022 4:21 pm

martin manning wrote: ↑Thu Jun 09, 2022 2:36 pm

Roe wrote: ↑Thu Jun 09, 2022 1:25 pmafter rebuilding two, the noise decreased significantly

Rebuilt how? What changes were made wrt the original?

I rebuilt the grounding and power supply, using merlin as a guide. One filter cap per preamp tube

Could you be a bit more specific?

Yes, please?

Great build, good looking. Is the grounding scheme compatible with the BAndmaster AB763 I wonder?

You’ll definitely get hum with only one power tube installed. Have you tried a different pair of output tubes (hopefully closely matched) or do you have a bias probe to check the bias on each tube? Sounds a bit like mismatched output tubes to me but could be something else. I have tried all tube co...

I still have hum in the Bandmaster. I have changed all the capacitors, the filter caps, tried all different grounding locations, changed all the tubes, but still has hum, even with only one power tube installed. What could possibly be the cause of this? The only time I get a reaction in lowereing th...

Yes it does.

I also tried to cennect a master volume as drawn in the layout underneath, that lowered the noise to almost zero, but that might be cause by the lower volume I guess?

Thanks. Just want to try and connect 1 wire to a Bandmaster configuration.

Just wondered if I need to connect all the three, 4-8-16, ohms wires to outputs, or if I could just choose one and isolate the the others?

So now, for some reason, the amp is dead silent whern I remove the 12at7, (I have tried different tubes here, so I guess it isn't the tube?) I also tested, as suggested by Martin Manning, the AC voltage as in the picture and got 1.2v on the upper and 0.160v aprx on the lower. It also seems to be a b...

Would be nice to hear if this has a solution. I have the same problem with my Bandmaster, allthough this is a clone build. Whatever I do, no change in the hum.

Some people say things like "there is always a little hum".... But I do believe it is possible to get these amps too quiet for your ear to notice without holding it up against the speaker. It is the sum of all the little things... Your bias, each and every tube, your components, your lead dress, so...