dynaco mark IV

I have Dynaco Mark 4, the power transformer is vibrating, it can be? Hello and thanks

Is this a restored Mark IV? The only reason why I mention this is the possibility of the transformer pulling to much current with a bad quad capacitor, I have seen this in a ST-70 where the power transformer was vibrating until I replaced the quad capacitor. Putting neoprene washers under the transformer as Bob says is a good idea as sometimes these transformers just vibrate, but make sure you don't have an "overload" problem too.

You can remove the 5AR4 tube so there is no B+ (high voltage) going to the quad capacitor to see if the vibration goes away as a quick test.

Sal

Sal,
I recently completed a vintage ST70 rebuild using a new 80-40-30-20 quad cap (HV version) from Dynakit Parts and a vintage Mullard 5AR4. I also wired two UF4007 in series between the secondaries of PA-060 and pins 4 and 6 of 5AR4 to protect 5AR4 from transformer flashback.
With that configuration my amp's PA-060 also vibrated and became quite hot. In addition, I thought the bass was very full and deep, but a little flabby. Because of the heat and vibration I swapped in another 5AR4 (Vintage HH Scott made in USA) which reduced the heat and vibration but also thinned the bass up a bit. Same result using a new Sovtek 5AR4.
Pulling the 5AR4 does eliminate the vibration but how can I tell if I have a problem with the new cap? Before installation all 4 sections tested fine. And I applied power slowly with a variac for the initial power on. Is the first section of the capacitor (40uf) that PA-060 sees too big? A DIY friend suggested I add another 22uf to the 80uf section to improve bass but I'm concerned that 5AR4 is becoming overtaxed.
Any thoughts?
Rich

Rich,
If you have a DC milliamp meter, remove all the tubes including the 7199 tubes but leave the 5AR4 tube in place. Disconnect the wire on pin 8 of the 5AR4 tube and connect your milliamp meter from pin 8 to the wire you disconnected to measure the current. Your meter must be connected in series. Be very very careful as there will be over 500 volts on pin 8 of the 5AR4 tube. You should measure a few milliamps at most after the capacitor charges up. It might be a good idea to use your variac so the voltage does not exceed 525 volts going to the quad cap.

Sal

PS: You are right about a 5AR4 tube causing a vibration in the transformer, I forgot I had another ST-70 with a bad Sovtek 5AR4 tube causing the transformer to vibrate.

Sal,
How many mA is too much? Is there a range it should be within?
Also-inserting the mAmeter at pin 8 measures current draw between the 5AR4 and the capacitor. How about the current drawn from PA-060 from 5AR4? Any range it should be in? What current can PA-060 safely supply without overheating?

with no tubes in the amp, the current draw should be less than 1ma, that would all be capacitor leakage