sKiZo wrote:Somebody refresh my memory ... will the 5U4 family work in an ST120? Electronically similar, but the 5U4's are direct heated instead of the indirect heat of a 5AR4 or GZ34 (or GZ37) ... best I can tell, that's internal, and the pin outs are identical?
Major concern I understand would be "cathode stripping" on the power tubes, as they'll be getting full DC way before they're ready ... indirect heating avoids that by ramping current up slowly. You can get 5U4's on the cheap, but I suppose not a good trade off if you're saving money on a rectifier only to shorten PT life.
Then again, that could be compensated for by adding a slow start board?
PS ... I notice the TAD KT88STR's I just got heat up a LOT faster than the KT120's using the Mullard GZ37. I still give them a good five minutes warm up before jamming ... no big rush here.
Hi Skizo, my ST-120 is running on 5U4GB (NOS Sylvania), TAD 12BH7 and TAD 6550 STR's...... it does have the TDR board.
Sound is terrific ! No problemo whatsoever.