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Old 29th August 2012, 07:26 AM   #1971
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Alberti - what are those resistors you have for the filament bias? Did you do some experimenting to find the best sounding ones?

Andy
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Old 29th August 2012, 02:07 PM   #1972
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Quote:
Originally Posted by andyjevans View Post
Alberti - what are those resistors you have for the filament bias? Did you do some experimenting to find the best sounding ones?

Andy
They're all Vishay from your supplier. I've the 95w one and I like this combination better.
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Old 29th August 2012, 02:56 PM   #1973
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Ah right - I've been using Dale wirewounds. Obviously you like these Vishay - they are wirewound, right?

andy
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Old 29th August 2012, 03:14 PM   #1974
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Dale=Vishay no?

Vishay - Vishay Dale - Vishay Brands
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Old 29th August 2012, 05:51 PM   #1975
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Ah right - I've been using Dale wirewounds. Obviously you like these Vishay - they are wirewound, right?

andy
Yes, they're wirewound 5w. What I did is to paralle 10pcs 100R 5w to make a 10R 50w. It runs a bit hotter than one 95w which was around 75c as I could remember, but the paralle one are varied from 85c to 95c. The temperature is higher, but sounds better to my ears.
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Old 29th August 2012, 05:55 PM   #1976
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Yes, they are the same. they actually are with the name - Dale - stamped on.
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Old 4th September 2012, 01:26 AM   #1977
tcqanh is offline tcqanh  Viet Nam
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I have only 1 AC winding for heater and 2 DC board, eg Rod Coleman board/ simple Regular circuit with LM317 for 2 tube 26. I have never tried this manner before. Has it got problem ?

Last edited by tcqanh; 4th September 2012 at 01:46 AM.
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Old 4th September 2012, 04:43 AM   #1978
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Stereo 26 linestage works correctly with 2 Filament transformers. Please remember, the filament of 26 is the cathode! We don't want any coupling between L-channel's cathode and the R-channel.

With 1 transformer, having 2 secondary windings - the amplifier will work - but 2 completely separate transformers is best (lowest coupling of rectifier current-pulses and noise from winding-to-winding).

LM317 is too noisy for 26 linestage - you will even hear residual noise through the speaker!
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Old 4th September 2012, 06:00 AM   #1979
dhtrob is offline dhtrob  Netherlands
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There is one possibility: At ground potential you can get away with one filament supply (transformer and Coleman). Put both filaments in series, adjust for 3 Volts. Ground the filament between the two filaments, so you have one 26 at 1.5Volts and one 26 at -1.5Volts. Bias the 26 with a battery (9Volt).
I have tried this succesfully, however not exactly cathode-bias, sound is excellent..

Rob
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Old 4th September 2012, 06:15 AM   #1980
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Rob, nice idea!

you can do this with the "Coleman" regulators, because they do not couple the + and - outputs.

But, any other heating method that has a capacitor at its output will directly mix L and R channels, (large crosstalk) so please take care.
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