Hi, thanks for your help, So just to be sure, remove all circled in yellow (not physically) install a resistor as shown. The area marked with ? will be ok just disconnected I take it? The signal just goes to the grid. Also for the audio coupling capacitor the one marked 0.02uf what size range is acceptable here approx if I was to replace it? I presume even an 0.1uf would be ok?
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Might as well 86 the whole stage. Disconnect everything between where the rumble switch gets signal from the rotary switch to the top of the volume control. Then tie those points together.
All good fortune,
Chris
All good fortune,
Chris
Yes, and yes. V3 is a Baxandall anode follower, unity gain, so no gain is lost.
All good fortune,
Chris
All good fortune,
Chris
That's a unity gain feedback stage. If you retain the tube, but delete the tone control parts,
there will be way, way too much gain and noise.
Just connect a wire from the rumble switch input terminal, to the top of the volume control,
and delete all the rest of the parts in between.
there will be way, way too much gain and noise.
Just connect a wire from the rumble switch input terminal, to the top of the volume control,
and delete all the rest of the parts in between.
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Would I still need a 2M ohm resistor marked in Blue ? Or also remove this? I know the volume pot will do the same but am wondering if it will be enough. I have located the Center input from the rumble switch,(left and right) so will disconnect this, install a coupling cap 0.02uf and connect to bottom pins on volume control, (the top pins actually goes to ground) I have removed all the resistors going to V3, removed the tube, but will leave the heater pins connected, presume this is no harm ?
No resistor or coupling capacitor is needed, just a wire as in post #8.
That capacitor is just part of the rumble filter, which you are removing.
You should check to see if you actually can remove the tube filament from the circuit.
Sometimes the tube filaments are in series, or otherwise can form part of a required load.
That capacitor is just part of the rumble filter, which you are removing.
You should check to see if you actually can remove the tube filament from the circuit.
Sometimes the tube filaments are in series, or otherwise can form part of a required load.
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Great it is working perfect and sounds much better, the main reason I wanted to bypass the tone control, there was some random noise, like a faulty carbon resistor, which was already present at the volume control, I tried freezing resistors, heating them but could not find which one was causing it. Also already replaced the resistors, valve and film caps, but reackon it was one of the 100pf caps maybe. But bypassing all that stuff is better anyway, I found the amp sounds good with tone controls in center anyway, I left the components encase someone in the future wants to reverse it, the next generation maybe, because I won't be hehe
Thanks so much for all your help everyone.
Thanks so much for all your help everyone.
Also dismantled the volume pot while I was at it, and gave it a proper clean, spraying switch cleaner in is just not the same, looked like it was the first time the clamps were removed.
Sometimes a neon pilot lamp can cause noise in the audio.
You could try disconnecting it and see if there is less noise.
It appears that all the tube filaments are in parallel, so the
unused tone tube V3 can be removed entirely.
Also clean and readjust the two hum balancing pots.
This can make a significant improvement in noise.
You could try disconnecting it and see if there is less noise.
It appears that all the tube filaments are in parallel, so the
unused tone tube V3 can be removed entirely.
Also clean and readjust the two hum balancing pots.
This can make a significant improvement in noise.
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No the noise is gone since I done the bypass, the only thing left that I did not swap out of the tone control network was the 100pf caps in parallel with the resistors and the bass / treble pot. It has not recreated since, I had already tried a few different tubes in V3 position also. But it was well worth the mod for the sound improvement alone, thought the hum control was for phono only ? The procedure says to put the selector switch to phono, crank the volume and adjust to lowest setting, maybe that is why 🙂 I have already cleaned them. The noise I was getting was random, to me it sounded like a failing carbon resistor. There is no hum at present, or noise, the HV capacitors are all replaced already, along with all electrolytic's. Never would have thought about the Neon pilot lamp, I presume this would case noise on both channels, unless it is pulling power from one side. So happy with the mod, I found the amp sounded the best with neutral bass / treble anyway. I am running infinity QB with it at low volume, also tried some old philips 22rh426 / and 427's with upgraded cross overs. I though it would not drive the infinity, keeping an eye on heat of the output transformers. One getting slightly hotter than the other, the output decoupling caps have been replaced with film caps to protect the output transformers. The plan in the future is to upgrade the power transformer, it was 110V so was converted to 220V, but in Ireland we have 240Volts so using some power resistors to reduce it down to 220V.