What are the exact specifications of the power transformer?
Posted:
Fri Jun 19, 2009 1:22 amby Geek
For a hugely popular amp, there's diddly spit on the ST-70's power transformer specs. Imax of all secondaries, core VA rating, etc.
Anybody here know what they are?
Cheers!
Posted:
Fri Jun 19, 2009 10:23 amby EWBrown
You're right, I've not seen published technical specifications for the original Dynaco PA060 power trannie...
The new PA060s from Triode and Dynakitparts are rated thusly:
360-0-55-360 @ 300 mA (55 VAC bias tap)
2X 6.3VAC @ 5A
5VAC@ 4A
The original PA060s had somewhat smaller core stacks, and perhaps a somewhat lower I max (250 mA?) for the HV secondary. They tended to run quite hot.
The ST70 manual states that AC power consumption is 190 watts.
That agrees pretty much, if all the windings are "maxed out".
The main limiting B+ current factors are the GZ34 rectifier and the C354 choke, which is rated at 200 mA. In actual operation, with the EL34s properly biased (at 100 mA/channwel) and a few extra mA for teh 7199s, and the optional preamp connections, the actual DC current consumption could creep up ti around 220-230 mA.
The actrual 6.3VAC current consumption is 3.45 A for each channel, plus an additional Amp available at each of the front panel power take-ffs.
So that's 6.3VAC @ 4.45 A max per channel, so I'd believe the 5A rating for the 6.3V windings.
HTH
/ed B
Posted:
Fri Jun 19, 2009 2:27 pmby Geek
Thank you Ed!!!!
I obtained an ST-70 from a mate with the OK to "super" it (but keep the circuit mostly original) and was getting 405-0-405 unloaded from the PT.... seemed a wee high for the parts values to me.
Cheers!
Posted:
Mon Jun 22, 2009 1:34 pmby lynxx
Current would also be regulated by the GZ34 250ma Max
The triode electronics has the capability to run 2 of the GZ34 paralleled.
I have a Scott that runs 2 GZ34s
Bryan
Posted:
Mon Jun 22, 2009 1:48 pmby Geek
I've been considering a Mesa-esque "dual rectifier" with this... switchable.
Want sane listening, stay tube. Need to rock the neighbors out of their house... SS
Cheers!
Posted:
Mon Jun 29, 2009 9:31 amby EWBrown
An unloaded power trannie secondary will read between 5 to 10% higher than the rated (under current loading) specifications. Add to that the higher AC line voltages in current usage, back in the late 1950s, 1960s, it was generally around 115-117 VAC, now it is at least 120VAC, and can range up to 133 VAC, and sometimes as high as 128VAC.
You are more likely to see anything from 380 to 400VAC on the secondary even with a full B+ load, with an older PA060.
/ed B