by EWBrown » Tue Mar 27, 2007 6:22 am
One trick, if you are undecided whether solid state or tube rescifiers are better, is to take an old dead octal tube, and carefully remove the base (it should at least have pins2, 4, 6 and 8 on it, some may not have all 8 pins). solder in two SS rectifiers, anodes to pins 4 and 6, cathodes joined together and connected to pin 8. Pin 2 isn't used with SS, it's the other side of the 5V filament winding. uF4007s are pushing their maximum safe performance envelope here, look for devices with at least 1200V PIV and 2 to 3 A current capability. If you settle with SS rectifiers, it's a good idea to install an inrush current limiter into the primary circuit, just to soften the initial power-up "impact".
Now it's a simple matter of being able to painlessly swap between rectifier types.
Note: with the SS rectifiers, the B+ voltage will be higher, so biasing will have to be checked and reset as required.
I've used both tube and SS rect, each has its merits and de-merits.
One long listening session, over at a friend's house, we were pushing my ST70 to its maximim, with every kind of music including some hard rock/heavy metal (Nickleback at just below clipping levels) and the JJ 5AR4 stood up just fine, no fireworks... Since then, I changed from Svetlana EL34s to JJ KT-77s, and I like the difference. That particular ST70 has the C CHong PSU cap board, Roy Mottram's VTA-70 driver board (got it before the Red Board was born) , the Triode PA-060 power trannie, new C354, and the OPTs were NOS Dynaco "house numbered" for Hammond Organ (?) equivalents to the normal A470s. I replaced the stock speaker terminal strips with heavy duty dual binding posts, they fit nicely into the slots, and once tightened down, they don't slide around.
/ed B in NH
Real Radios Glow in the Dark