Valve Itch phono

[Salas]

There will be many capacitor types to test. One very good interstage will be K72 0.047u 500V Teflon also. And other types for the Riaa as well as small value changes from 0.015-0.0155u to evaluate. Always >250VDC all signal caps don't forget.

P.S. Any under the hood pictures will help people visualise what we talked about bus bar GND and fixing.

[woodturner-fran]

OK,

It was easier to sketch it than photograph. That would have meant turning it off.....


So bear in mind that the layout used here is most likely not ideal. I used it because it suited a case I already had (holes drilled etc). So I'm sure having the 4 valves nearer one another or laid out in a different way would be better.

So, the basic premise is that 1 long bar runs along the lenght of the 4 valves. Low current grounds (inputs and input valve cathodes) are connected right at one end. Next up along are all the RIAA grounds (close to the input grounds) and then right at the far end of the bar I have connected the PSU ground, output grounds, heater ground, connection to chassis and the output cathode grounds. The shields on the 2 x 6N2 are along the bar.

As I said, I'm sure there are better ways, but I now have very low hum.
http://www.diyaudio.com/forums/attac...1&d=1304973716


Fran

[Salas]

Thanks Fran, that will help the other guys next. Kraftwerk Man Machine LP?

[woodturner-fran]

Yup - moving on to transeurope express next, with coltrane ballads after that. Heatsinks are pretty toasty... up at 60 id guess.

I've learned a lot on this build so far, I feel like going back and rewiring a few other amps now!

[Salas]

I have seen them on their Mix comeback tour in Liverpool 20yrs ago. TEE was hypnotic with the wheels revolution video in the classic theatre decor.

After making a 60dB gain valve circuit quiet, what you learn is a boon for working on HV & vacuum. What is your ICCS? Maybe you can shave off some? High heater regs sink temp too?

[woodturner-fran]

They were here some years back but I missed it. They played a small concert which was meant to have been great..

coltrane ditched for sketches of Spain + glass of rioja (bad for Monday night!)


Fran

[Salas]

No! You make Merlin want to make one too.

[woodturner-fran]

sounds even better after a glass!

R1 is 47r...... so maybe I could shave a bit off. Heater regs have puny sinks anyway so I'm probably going to change those anyway. I have some bigger ones I could use. It's just that when it's boxed up there will probably be 10 degree more heat easily.


Fran

[Salas]

See your voltage drop across the 47R, then divide by 47R. That is the CCS current. Two itch channels are draining ~10mA. See to have 30-35mA CCS total. 20-25mA are OK for the reg to consume internally for proper Zo. Each 10mA extra spare is 3W dissipation @ 300V on the IRF840...

[taniknight]

Just to clear something up, from Salas' advise on bar grounding, I thought that the bar should only see chassis ground at the input end and power ground at the output end.

Originally Posted by Salas

On a bar we ground at the input side to chassis only, and we go from lighter to heavier currents in a row on it ending at PSU. Something must be mixing there most likely.

However, Fran's sketch shows chassis ground at the PSU grounded end. Naturally, Fran, if it sounds good, it is good. I just thought I'd make sure I hadn't missed something.



Regards,
Tani.