well, unfortunately, if you are going to use 5ar4 the new production are not the equal of the vintage units. You might have to do a hybrid SS/tube mod to make the rectifier reliable.Need to buy a pair of rectifier tubes for a pair of Dynaco MK IV amps never had to pick them up before anyhow any thoughts on what ones to get, like I said never paid much attention to those tubes just seemed to last forever any help apprecitated.
Canton
Then again, if you can score a couple of the old Mullard GZ37's ...
The GZ37 should be ok to use in the VTA ST-70's, no?I suppose it is worth repeating the rectifier tube has a specific voltage and current rating for the heater. The Dynaco specifies a 5AR4 with a 5V 2A rating for the heater secondary of the power transformer. Personally, I use the 5V3A/5AU4 ($15) rectifier whenever possible since it is a more robust replacement for the 5U4GB with extra current and voltage capabilities. However, this tube uses 3.75 A of current so could overload the Dynaco power transformer which are notoriously under spec already. The GZ37 draws 2.8A of current while the transformer secondary is rated at 2A; so not as egregious as the 5V3A/5AU4, it still will overload an already stressed transformer. At the very least if you use a GZ37 measure the heater voltage to ensure it is a full 5V and not loaded down by the GZ37. The GZ37 is a good robust rectifier: I bought 8 at $12 each back in the 1980s from Ned Carlson for my Quicksilver monoblocks. They are still in their original boxes because I find the internal impedance drops too much B+.
The GZ37 should be ok to use in the VTA ST-70
5ar4 is what is recommended with the kit.Check the power transformer secondary. Is it rated at 2A for a 5AR4 or 3A for a 5U4GB?
That's why i was wondering if the beefier ST-70 power trany could handle the GZ37.The Mark IV used the exact same A470 power transformer as the ST70 ...
Hadn't really thought of that though - my Latino kit has much stronger iron than the OEM Dynacos did. Tube complement includes the GZ37, a quad of KT120's, and three drivers, including a 6SN7 center. I also lose some B+ dropping the line voltage to around 117vac and that takes a slight hit from an inline thermistor as well. Several years now since the build with no issues ...
(I also drive the amp to relatively insane levels ... ) ;-}