123.30.165.182
In Reply to: RE: Interstage Monoblocks posted by gillougillou on November 13, 2012 at 08:06:41
Hi,
I highly recommend that you get a pair of filament chokes and do a passive CLC or LC supply for each 300b filament, using the existing 8V AC supply.
Or even better like what I have in my mono block now: a separate filament transformer -> Schottky bridge -> LCL filter which is 200mH 40,000uf 200mH. No hum at all. The 6sh7 is fine to be run on AC.
The stock voltage regulator sounds quite inferior to both of the above passive filament supplies. I mean quite a big margin: I did not know the piano sounded so wrong until I get the filament supplies right for my amps.
Search in the Tube DIY and/or diyaudio. There are many technical posts by the regular technical people there.
And also try the 6sh7 capacitor coupled to 300b like in Brian's Legend Mono Block. You could like it better! this is not a complicated mod. The sound is very typical of the famous WE91 (300b driven by a pentode).
Follow Ups:
How to do the monoblocs more silent ?
A little noisy with hight efficiency speakers...
Use of Tenlab heater modules for the 300B ?
Need advice, regards, Gilles.
Gilles, when I wrote my reply above I did not realize you owned the monos. What is your experience with how they sound?
I see you are having a hum issue. While I have not measured the hum in mine, I run through both ANE HE (98db) and Altec Valencia (100db) and the hum is neglible. For comparison, my kit1 has audible hum from the listening seat but only with the Altec. So, have you followed the grounding scheme from the plans? What changes have you made to wiring routing?
Before adding a filter stage (cap or choke) I'd recommend the above. If you do add another stage, let us know what you find!
Best,
Doug
Hi Doug !
I found the hum problem, it was a bad connexion in the heaters board, the same main transformer winding for the two boards !
I now use séparate transformer windings for each heater board.
One problem remain, sound is a little harhs and I suppose some ringing with the interstage.
When I tried the monoblocks whith pentode mode and cap instead the interstage trans, the sound was more easy on ear.
I will investigate with a scope soon and let you now.
Need advices.
Gilles.
I did scope investigation and found nothing bad.
No ringing.
I have to look around the amplifier and not in the amplifier ! ;-)
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