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Re: Few suggestions

Posted by glc (A) on February 2, 2004 at 12:44:18

In Reply to: Few suggestions posted by Gordon Rankin on February 2, 2004 at 06:32:31:

Thanks to Gordon, Paul and Triodekingdon for the big help.

Starting from Gordon quotes:
First on the B+ side the 2 450V/100uF caps. Put a 330K/2W resistor across each one to make sure they both have equal voltage. Many times one will take over the other and cause excessive hum.

---Gordon, here I have changed the two electrolitics in series with a Solen 47uf/630V as first C and last C in the 630V supply.
Only on 440V supply for E83CC where in the CLC there was 100uf/550V I changed each 100uf with two 220uf/350V in series, with resistor 100kohm 2 watt across each capacitor. Is it better to use higher value resistors (330kohm)??

Also is the HUM 60 or 120Hz. If you have a meter that says you can more easily get the hum down.

---Gordon, from the oscilloscope I see it is noise modulated at 100hz (here in Europe supply is 230V-50hz).
I have hum noise 14 mV rms at the output transformer 8ohm output and I have about 270mV rms on the VT52 (now really a 6A3 Sovtek for tests) tubes plate pin (both seen on oscilloscope as noise modulated 100hz).

I would suggest investing in a 10 turn 100 ohm pot. There are several types to try. You get better resolution.
----Gordon, I am using Spectrol 3W 10 turns 100ohm with 100ohm Kiwame 2w from pot ends to the wiper as you suggested in an your old e-mail.

If it is 60Hz you may try reversing the polarity of the filaments of the output tubes. Remember hum is cumulative and sometimes swapping filaments can make a change of 2-3mv of hum.
----I repeat it seem 100hz.

I am also not a fan of parallel caps of different types. Best bet buy a good Black Gate N or NX to bypass cathodes.
----Gordon, I have used on E83CC (now for test purpose ECC83 Siemens) Solen 47uf/250V with parallel Orange Drop 716P 0,47uf/400V, and on VT52 (now 6A3) Sprague Atom 100uf/350V with parallel Orange Drop 0,47uf/400V and Solen 0,56uf/630V.

On the filament side using seperate filament transformers for the outputs (instead of integrated with the HV) will work best.
---Gordon, I used a big Bartolucci transformer as on schematic, with 6,3V outputs on the same transformer (the two HV and the three filaments outputs). I have understood that it is not the better solution but I had it and used it.

I would like very much your amplifiers noise (hi). Also after building my amp I understand better the high price of your "jewels": sure they receive a lot of your work to perform so well.
I am not an electronic engineer but a bank director with some electronic know how in RF becouse I am also from 20 years an amateur radio (IK4EWX). But this is really my first audio project and I am not very experienced as you understand.
So many many thanks for your help

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