Burning question about two VAC amps and dead tubes

Try Grant Fidelity

anyone know where to get kt88 treasure tubes for the vac phi200,the sellers from china are not listed on ebay anymore and the canadian stores only have pairs to sell

You can continue on with this brain damage or you can just call VAC, explain what happened and ask for a bit of advice. I know that sounds too easy for some of you, but it really is the simplest solution.

I invested in a Variac just for this type of problem. If you bring up the line voltage slowly, you have a chance to measure the voltages on the tubes, assuming you have the schematics and a digital voltmeter. If no schematic, then compare the voltages of the working side with the one not working.

I also have a tube tester to check all the tubes before powering on the amp. Tube testers are relatively cheap and if you have tube equipment, well worth the investment. Make sure you get one that measures transconductance not just good-bad indicator. I use the tube tester to make my own matched set of output tubes rather than pay a high premium for them.

Plates glowing cherry red indicates there's a huge current draw of that tube only. This could be caused by a defective coupling capacitor which allows plate voltage from previous pre-amp stage to be on the grid of the power amp tube, thus forcing it to conduct max current.

The loud hum also indicates the most common problem: bad electrolytic caps in the power supply. I also invested in a ESR (effective series resistance) capacitor tester. This will measure caps "in circuit" if the cap is bad (leaking, shorted, etc.) and gives you the actual value. Unfortunately it gives false reading if a filter cap is attached to a choke or power transformer, so I have to clip one lead before I measure it.

Thats why i love my Rowland 8T.Had many tube amps CJ ,ARC etc too much trouble!!

Sounds weird. I have a PA 100 with RCA cleartops and Valve Art KT88. Whenever a KT88 dies it blows the fuse. The first time that happened I freaked not knowing what was happening. Now I know it's just time to buy a new quad and a fuse. I'm suprised your fuse didn't blow. Good luck.

If the bias lights remained green, I would figure a bad tube or maybe there is a fitment issue between the tube pin sockets and the pin diameter on your replacement tubes, ie. too loose.

VAC is nice to 2nd owners so you can call them and ask.

Possibly your speaker cables are shorting out. Odds of two amps doing the same are very remote. It has tobe the cables or the speakers causing a short or oscillation
Alan

Demonic possession is often NOT covered under warranty (or divorce decrees seemingly)...I think tube amps should last for about 72 years with only minor maintenance and tubes should die a long protracted death, not flame out. Wall voltage is rarely the issue but possible of course, so maybe it's speaker impedance matching, a crappy amp channel needing caps or resistors or something, or your horrible karma from another life spent as a bad, bad person.

Yes very red!

How do you notice a tube overheating? Are you referring to the plate structure glowing cherry red (a bad thing)?

Oh the joys of tube power amps... Seriously,before you do anything, I would check the voltage at the outlet you are using.