I wouldn't use a 5U4 in a ST-70 either. Also, Dynaco didn't recommend it back it the day. Nowadays, the voltage from the utilities is higher in a lot of areas than it was back then too. That means the 5U4 could be harder on the amp's power transformer than it was in the '50s to '60, when the AC line voltage was typically lower.
5U4G suitable for Dyanco ST-70?
There have been several threads at various times on the suitability of subbing a 5U4G rectifier tube for either a 5V4G or a 5AR4 in a ST-70. I asked Will Vincent, a respected re-builder of ST-70s (among others) for his opinion and received the following email:
Harry: Never use a 5U4 in a Dynaco 70.....The power transformer is rated for 2 amps on the 5 volt winding....The 5U4 is rated at 3 amps......Not good......Will
So, I thought I should pass this along...
Harry: Never use a 5U4 in a Dynaco 70.....The power transformer is rated for 2 amps on the 5 volt winding....The 5U4 is rated at 3 amps......Not good......Will
So, I thought I should pass this along...
Showing 2 responses by hifitime
When I worked for an electronics store back then, I don't ever remember Dynaco saying it was okay to use them. Here is a copy of the owners manual where on page 9 it states, "A 5U4 type of tube can be used for testing purposes." I have never seen the 5 volt filament ratings that I can remember. A 5U4 draws about 50% more filament current than a 5AR4. They run warm enough with a 5AR4 in them in my opinion. I don't think it's worth the risk, especially if you have a '59 to '62 built unit, with the better transformers a lot of people like. |