by EWBrown » Thu Feb 21, 2008 9:09 am
The SS diodes will deliver a significantly higher B+, and the B+ voltage will surge to well over 500VDC until the tubes warm up and start drawing current. This is one case when the tube restifier is better / safer than SS rectification, ulness some mods or changes are worked in...
A somewhat different approach, is to use the SDS SS rectifiers, then wire in the 5AR4 / GZ34 with both plates connected, as a "series pass" element. this will return the B+ closer to normal voltage levels and the tube will allow the slow warm up of the B+ line, so that the rest of the circuitry doesn't get by the "high voltage hammer" while the EL34s and driver tubes fully warm up, and draw normal plate currents..
Combine that with the older trannies having a 115VAC primary in today's 120VAC + world, and this is definitely a case in which more "or bigger" is not better...
A normal tube rectified B+ at the OPT CT leads shoule be around 420-440VDC, (I get 446VDC with my 123VAC power lines and a Triode PA-060 power trannie, and JJ KT-77s biased at 50 mA each, SS diodes will deliver 10 to 20 V more, even under lfull current oad. Peak unloaded (SS rect) DC voltage can soar up to 550VDC, which is WAAAAAYYYY too much for a long and happy component lifetime.... :o
Does the can cap feel too warm (beyond what the nearby radiant heat from the EL34s would normally generate) ? Overvoltage will be evident with overly hot cap temperatures, and look for any swelling or deformation of teh cap body and check the rubber "burst seal" on the bottom, a little bit of "protrusion" is OK, but if it is poking way out or dribbling electrolyte then the cap is "toast"...
The SDS (and Cyrus Chong's) "bulk" caps are wired as pairs in series with equalizing resistors, and probably are good for well over 500VDC, with plenty of safety margin.
HTH
/ed B in NH
Real Radios Glow in the Dark