Is there any reason why I can't try mixing up the output tubes on my ST70? Like a KT88 and an EL34 on each side. Of course each tube would be biased appropriately. I'm thinking it won't matter but I want to be sure.
Thanks.
Thanks.
3 posters
Mixing output tubes on VTA ST70
ruffian- Posts : 43
Join date : 2010-02-26
Bob Latino- Admin
- Posts : 3274
Join date : 2008-11-26
Location : Massachusetts
You won't get the best out of the amp by mixing an EL34 and a KT88 in the same channel (pushing and pulling together). These two tubes have different characteristics and don't "match up" well. In any push-pull amp, you always try to get the two tubes of a pair as closely matched as possible for best sound. This is comparable somewhat to two men on both ends of an old logging saw trying to cut (pushing and pulling) a large log. If both men have the same strength and endurance characteristics, then the log will be cut efficiently and smoothly. You don't want to pair up an experienced logger on one end with an 8 year old boy on the other end of the saw. They just won't cut the log in an efficient manner. The logger will wind up doing more work than the 8 year old boy.
Bob
Bob
ruffian- Posts : 43
Join date : 2010-02-26
Actually with a 2 man cross cut saw you only pull, otherwise the blade binds. 
This is one place where PRAT really matters. It is rather impossible to use one with an 8 yr old, I've tried.
But I get your point, thanks.
This is one place where PRAT really matters. It is rather impossible to use one with an 8 yr old, I've tried.But I get your point, thanks.
dunwichamps- Posts : 36
Join date : 2011-10-20
If you had a full quad of output tubes in a monoblock then you could mix 88s and 34s but thats going to generate some harmonic distortion given that the tube wont be matched that closely. It works well for guitar/bass tho! Another thing to consider is that both tubes bias up really differently so you would ne dedicated biasing for each tube in the quad. A better option would be a 6l6GC which is more closely rated to the 34 than a 88 would be.