Bob Latino wrote:fedoragent wrote:Bob Latino wrote:In the VTA ST-70 KT88 output tubes do have more output at the frequency extremes - the very bottom and the very top of the frequency range. This may be a benefit IF you have speakers or other associated equipment that are "soft" on the top end. It may, however, be a liability if your speakers are a little "bright" to begin with. KT88's also have the liability of costing twice as much as an EL34. They will, however, last longer than an EL34 in the VTA ST-70 which offsets somewhat their increased cost.
EL34's are the traditional output tube used in ST-70 type amps. They are cost effective and are really good sounding tubes especially in the mid bass and vocal range.
In the VTA ST-70 you can use EL34, 6L6, KT66, KT77, KT88 or 6550 output tubes. NOTE - do not use the last two output tubes mentioned in a STOCK ST-70 unless you have an upgraded power transformer. They draw more current and can put an already overworked ST-70's original PA-060 power transformer "over the edge".
Bob
Bob,
Is this still your assessment for those that have the original PA060? Can one decrease the bias down to .400 or .350 to lessen the change of.....PA060 Chernobyl?
Thanks,
FG.
FG,
The original Dynaco ST-70 came out in 1959. Some of these 350,000 original Dynaco ST-70 amps are now 60+ years old and have an undersized original power transformer that is hanging on by a thread ! Just my opinion but > KT88 and 6550 output tubes draw more current than EL34 output tubes. Personally, I wouldn't risk using an original Dynaco ST-70 (with the original Dynaco power transformer) with KT88 output tubes.
Bob
Bob,
HAPPY NEW YEAR!
I recently emailed with Dan...and I think I'm going to upgrade the PA060. Do I have to do the OTs as well? And yes, my unit is from 1961...got it from the original owner. I'm thinking those suckers are getting worn.
Thanks,
FG (Jon)
