audio-talk

Ali Tait wrote: ↑

Wed Jul 17, 2019 3:26 pm

I remember liking that EL34 PP Nick made for one Owston.

I had to think, do you mean the one I made using Collins output transformers and the sowter interstage phase splitter?

Still have most of that somewhere.

Nothing is a simple resistance. Certainly not a heated wire. But remember the part that matters is not the hefty heater power, its the tiny fragile audio signal that has to coexist in the same circuit.

Nuts! You'd convinced me with the space charge scenario! :) I can't think why a different part of the DC supply might sound different though? Well, if its regulated, one end will be the emitter of a transistor, the other the ground or a sense resistor for the supply. Remember Mark found that he cou...

1000v, 80ma, -100v on the grid is not a bad operating point.

Had another one of those "Are we looking in the wrong direction" moments. While most DC supplies may be floating, I don’t thing they are balanced. At least not from the perspective of the audio signal path. So the fact that causing the signal to exit from one or the other end may well make a differe...

I don’t know, I could imagine one end of the filament may sound different to the other, not because of the filament voltage, but physically, they may be different. I don’t; know, so can't say. The cause of the effect may not be the one that’s expected, or it may be, reality can be tricky.

I've always thought, perhaps erroneously, that hum pots were used with AC filaments to find the "balance" point across the filament potential difference where the hum was minimum. Yes, thats what they do, but what I never found was a explanation of how they do it. I'm not sure why a hum pot or pair...

Its based on a mathematical analysis of how the centre tap works I did some years ago (there is a copy of the maths somewhere on here). As to if there is any noise , don't know. the odd thing is, its hard to find a explanation how a hum pot works, so I worked out my own answer to that and its applic...

I have argued that a centre tap with DC will help reduce any residual noise. But I think it practice its not worth doing and may be worst as you are adding extra resistors in the circuit.

Yep maybe also check for a short somewhere. Trace back from the gate if that meet and see if the pulse appears.

Yep, though TBH, I would just get a replacement and replace it.

Yes, its the sample and hold that implements the phase lock. the pulse samples the ramp at the position it is at the time, and that held value is then used to provide the phase lock signal to the turntable.

THat would point to a short somewhere or a fault somewhere around the sample and hold area and R186. Maybe a failed TR151.

The correct setting is in the service manual. Show us what you are getting.

Was about to congratulate you till I realised it was Neal showing what the trace should look like.

I wondered if you had a different scope