SET Asylum

Posted by Neff on May 11, 2008 at 05:46:08

In Reply to: RE: Thinking of converting PP KT88 monos to SET... posted by ABliss on May 10, 2008 at 18:14:35

I bought a pair of W5Ms to find out one had a bad audio transformer- errrr. Stripped the chassis and converted to SE. I used original power transformer, choke and chassis. Not violating rest of parts rules for minimal quality, they are:

Vishey resistors and NOS Allen Bradley resistors for grid stoppers
Genelex KT88
MA meter for adjustable bias installed on each chassis
Sylvania 5R4GB
Hammond 3.5K primary Classic audio transformer
TungSol 6P5GT preamp
1/2 a very rare Tung Sol flat plate 5687 driver (1951 era)
FT-3 coupling capacitors
2x 47uF Panasonic capacitors in series on 5R4GB plate
100 uF motor run caps on output of CLC B+ supply
160uF Solen for KT88 cathode capacitor
20HY choke and Solen 40uF LC section to the 5687 plate
0A2 regulator to RC section for 6P5GT plate with 10uF Solen
DC filaments on the 6P5GT and 5687

I just fired up & tweaking, but using 470 volts plate with about -62 vdc cathode bias and the amp sounds good. Normally I would not go with Hammond audio outputs, but this Classic series is good quality. My 'ace in hole' was to convert to a 300B, but I think that is unnecessary.

Only other amp I owned that compared was a junker stereo SE EL84 I found with about 3-watts output. That 'no name' junker used GE EL84s, Mullard EZ81 and an old Mullard 12AX7 long plate. I grabbed it for the tubes, but powered it up for fun with new capacitors. My jaw dropped- go figure.

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