I had a customer send me one of his new Ike monoblocks after it was consistantly blowing fuses on power up. I sent him several suggestions, which he patiently implemented to no avail, so it seemed like a good amp to debug on my bench.
It ends up being related directly to the HV center-tap implemented standby switch. After placing caps across it and using IRCLs to tame things, I figured the current was under control, so I needed to look at the secondary taps more closely. Then I about blew up my DMM a few times trying to take measurements, getting 2kV DC in the secondary from either leg to ground (with no tubes and center tap lifted, ie standby off).
At the least, this can cause a eventually blown diode which then causes a blown fuse. While having some load in there, like tube filaments, may help tame the high voltage peak, I'm not willing to risk my DMM or anyone's health on it. I'm going to discourage the use of standby switches here on out.
Those with standby switches, leave them 'on' all the time. Better yet, disconnect the center tap from the switch and connect it directly to the PCB. With the center tap grounded, I have seen no problems whatsoever. The delayed turn on benefit is small, in my opinion, to the damage that can be done otherwise.
I've researched this problem and can't find anything. Using diodes in series (two UF4007's for 2kV rating) and a high voltage cap strapped across the primary/secondary or to ground might alleviate some of this problem. But I'll see if anyone has some experience in this area and wants to share. My personal opinion has probably been made, choosing to err with caution. I tested a PA774 and saw the same thing, so this is not Hammond or diytube specific.
If you have blown fuses, be sure to check your diodes first thing. With the amp off and bled, check with your DMM on the diode setting. Touch the black probe to the band (cathode) and the red to the anode. You should see a voltage drop of about 500mV. If you swap the black and red probes, the diode should appear as an open. Otherwise, you've got a blown diode. Swap them both out and disconnect your standby switch while you are at it.
Tube gurus, opinions welcome. Let's keep this a fun, safe hobby with gear that lasts a lifetime.
Shannon