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In Reply to: RE: It is not just the cap, the load matters as well, and the ST70 is very "loadie" posted by xaudiomanx on July 11, 2014 at 15:09:20
When the ST70 was designed and introduced, 1959 or thereabouts, selenium rectifiers with the nec current and voltage ratings were large and had high voltage drop. Silicon rectifiers new and really expensive and usually required 2 in series to get the nec voltage rating. So, considering the budget nature of the amp, the 5AR4 was a logical choice even if run pretty much at absolute max rating. Too bad Hafler didn't opt for dual 5AR4s and more filtering beef like some other stereo amps of the time did. That would have been a giant killer.
Follow Ups:
So you are saying that two parallel 5AR4's would do wonders to that amp? I have pulled out the choke on many occasions and it woke the amp up much more than I thought.
Think solid state in an ST70
"Wonders" might be a little bit of hyperbole but dual rectifiers and beefed up PS would be a big improvement. Or, if you're not committed to 100% tubes, go silicon for the rectifier with due precautions for higher B+. Dave Gillespie covered the SS route in some detail @ Audio Karma a while back. Worth checking out!P.S. Don't mean to imply a stock ST70 can handle 2x5AR4...PT isn't up to addl filament load. Just that ideally, dual rectifiers would have been the way to go at the time. SS can be done with the stock PT.
Edits: 07/11/14
Hi,
Dave Gillespie is a very frequent poster on AudioKarma. Can
you please provide a link to the specific SS discussion you
mention????
Thanks and regards to all,
John
...a long thread but worth a read. Interesting conclusions about the stock circuit of the amp.
Edits: 07/12/14
Thanks, Steve. I appreciate you.
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