I am just now finishing a complete update of a SCA-35 using new xformers and Dave's circuit boards so I am on the prowl for my next project. Many thanks in advance.
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tubes4hifi wrote:a fair price for that item, but realize you can get a completely new ST70 with our better performing VTA driver and all new tubes for around $300 more than that.
You'll likely spend that much on that amp upgrading it over the next year or two.
evoroadster wrote:Shipping costs to Hawaii can be brutal.
daveshel wrote:When I first came to this site, I was looking for comparisons of my Van Alstine U-70 with the VTA sound and nobody seemed to have had experience with both. As I heard more amps, particularly my ST-35 rebuild, I became convinced that my U-70 was boomy in the mid-bass and lacking in the high end. I sold mine. I later picked up a nice clean stock ST-70 with a view toward doing the VTA upgrades, but I have yet to pull the trigger for financial reasons - and I may have to abandon the project and sell the ST-70 if things don't look up soon. So I've never actually heard a VTA ST-70.
Bob Latino wrote:I totally agree with Roy here ... The original Dynaco ST-70 driver circuit with the single 7199 driver tube per channel was designed not for good sound but to allow Dynaco to "save a tube". That circuit was designed as a cost cutting measure. Those 7199 driver tubes back in the early '60's were $1.25 to $1.50 each. Since Dynaco sold about 350,000 ST-70's, they saved ($1.25 X 350,000) = $437,500 in 1959 dollars by using that circuit. $437,500 in dollar value in 1959 (the year that the ST-70 was introduced) would equal $3,552,500 in today's value.
The 7199 driver circuit with the AVA two resistor and two capacitor mod IMHO is a band-aid to limit bandwidth to something that this driver circuit can handle. Its like have an automobile whose front end shakes at any speed above 70 mph and then creating a solution to the problem that equates to placing a governor on the auto so that it can never reach 70 mph. To use the AVA mod and then having an amp with a power bandwidth of 50 to 5500 Hz is not a good thing.
The present VTA CCS circuit is (IMHO) head and shoulders above the original Dynaco 7199 driver circuit or the AVA bandwidth limiting version of this circuit.
In 1974 the Federal Trade Commission came out with standards for amplifiers with respect to power, distortion, bandwidth etc. Below is the page from the Dynaco 1974 brochure where Dynaco now had to rate the power, distortion and bandwidth according to standards set by the FTC. No more 35 WPC - now 20 WPC, bandwidth 50 to 10,000 Hz .. a more realistic rating for the ST-70 amp.