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Old 24th May 2011, 07:12 AM   #981
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Changing the subject slightly, I tried my 26 preamp with my 46 interstage 300b SET on stacked Quad 57 speakers last night at a friends. We compared this - my new system - with my older 10y transformer out preamp and my older 2a3 push pull amp (01A and 31 inputs), which he has. Both preamps are filament bias.

Results were heavily in favour of the new system, which was at times a religious experience - Schneiderhan playing the slow movement of Beethoven's Violin Concerto seemed to just float in the air. The 26 has a tonal beauty which I've never quite been able to capture with the 10Y much as I like that in other ways (plus it was cleaner in transformer out than with the capacitor coupling).

This 26 preamp is as my schematic posted a few pages back - two Hammond 156C plate chokes in series and Teflon FT-3 capacitor out. The only thing that took away from the listening experience - apart from the sound losing grip a little in congested passages which is the 300b SET - was, I think, the capacitor out. There was a slight but audible veil over the sound which was frustrating.

This listening experience leads me to believe that to get the best out of a 26 preamp it actually needs to be direct coupled to the first stage of the amp. You could do that with a stand-alone preamp, though it would only work with its partner amp, but the obvious thing to do is put the 26 stage in the amp. This would be a pain for most people with existing amps and preamps, though it's not difficult to construct. But having gone through this listening experience on very revealing speakers, that's the conclusion I came to. There are always many factors at work so it's hard to be conclusive with listening tests but I point the finger at the coupling cap. However good it is - and this was Teflon - the whole sound does go through this one capacitor and I'm sure it would be better if it didn't.

Andy
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Old 24th May 2011, 12:05 PM   #982
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Quote:
Originally Posted by Rod Coleman View Post
Hi Felipe,

1N4007 has large recovery-time, and makes big current-pulse noise (difficult to measure, easy to hear)

UF4007 Fairchild works really well, just add series-RC snubber across the secondary winding:

100-ohm 0,5W carbon composition and 22nF to 47nF 1500V FKP (LCR PC/HV/S best, or PAnasonic MKP 1000V).

No need for > 1A type!
As this schematic PSU part
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Old 24th May 2011, 12:14 PM   #983
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No Felipe, the suggested snubber components (R+C in series) are to be placed in parallel with the sec winding (Rod correctly stated "across the winding"), before the rectifier(s).
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Old 24th May 2011, 12:28 PM   #984
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Quote:
Originally Posted by massimo View Post
No Felipe, the suggested snubber components (R+C in series) are to be placed in parallel with the sec winding (Rod correctly stated "across the winding"), before the rectifier(s).
Thanks Massimo, You know what I meant!


.
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Old 24th May 2011, 12:31 PM   #985
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Old 24th May 2011, 01:04 PM   #986
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Quote:
Originally Posted by Rod Coleman View Post
Thanks Massimo, You know what I meant!


.
Thanks Rod, please remember me suggested Tx values in V & A for the filaments heaters that I bought you.
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Old 24th May 2011, 01:11 PM   #987
massimo is offline massimo  Italy
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Felipe, I replied about the Xfrm yesterday: 6V/5A (30VA), EI with split bobbins, not toroidal.
I got from Rod the same regs for #26 and I bought a pair of Hahn BV UI 396 0101 at Distrelec. They have a dual sec to be paralleled
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Old 24th May 2011, 01:13 PM   #988
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Thanks Massimo, it sounds perfect trasformer for the 26 filament regulator.

Are your filament regulators giving some good DHT sound?
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Old 24th May 2011, 01:19 PM   #989
massimo is offline massimo  Italy
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Not tried yet. I'm slower than a snail in my buildings..... but I've almost finished the double cabinet (1 for the tubes and two tango anode chokes, 1 for P.S.)
Stll waiting for some special rubber isolators from US...... (I must rely on a friend)
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Old 24th May 2011, 02:14 PM   #990
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Quote:
Originally Posted by massimo View Post
Felipe, I replied about the Xfrm yesterday: 6V/5A (30VA), EI with split bobbins, not toroidal.
I got from Rod the same regs for #26 and I bought a pair of Hahn BV UI 396 0101 at Distrelec. They have a dual sec to be paralleled
Grazie Massimo, so 2 Tx one for each tube Rod filament, right?
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