can I use EL-34 or 7591 tubes in a VTA ST-120? IF so what is a good bias range ? I now use KT-120's and run them at .585, and I have some 6550's I like to run at .535.thank you .I bet this could win stupidest question of the week if it wasn't for the fact that the stupidest question is: the one you don't ask.
4 posters
ST-120 / EL-34 and or 7591 ?
scottlowe- Posts : 38
Join date : 2014-04-05
Bob Latino- Admin
- Posts : 3276
Join date : 2008-11-26
Location : Massachusetts
I don't recommend the use of EL34 tubes in a VTA ST-120. Today's EL34's would probably have a short life in an ST-120 which runs B+ voltages in the range of 500 VDC. EL34's are better for ST-70 type amps which run a B+ of about 440 VDC. Another thing .. The bias system of the VTA ST-120 is set up for 6550, KT88 or KT120 output tubes. If you try to bias an EL34 in the ST-120, it will bias way over to one side of the bias pot's range OR you may not be able to bias an EL34 at the recommended bias setting of .400 VDC.
Bob
Bob
sKiZo- Posts : 1530
Join date : 2013-04-01
Location : Michigan USA
Wouldn't help tube life due to the excessive B+, but it's my understanding you could "swing" the bias range on the controls with an R39 resistor substitution? EL34's are cheap enough and have a unique flavor that it might make sense to give it a try ...
Roy Mottram- Admin
- Posts : 1838
Join date : 2008-11-30
7591 tubes have a totally different pinout and can't be sub'ed for a 6550, EL34, or KT88