This is all super helpful, and you guys are right. I need a new DMM.Bieworm wrote: ↑Tue 06/21/22 4:37 pmDon't worry.. 106% won't fry a healthy tube immediately in a cathode biased amp. That's not the problem if that would be the value. But did you take the voltages with the sale DMM? They wouldn't be correct either if the device is faulty.58T100 wrote: ↑Tue 06/21/22 3:36 pmMy point is just that if my meter is wrong and it is actually near 180ohms, and I measured the voltages with it in there, using 180 in the calculator and those voltages puts it at barely over the line. So I don't know if it is possible that just 106% dissipation would have caused what I saw - not sure what the explanation would be unless that resistor is significantly less than 180. I am assuming the meter is at least measuring voltage correctly though.
Trying to find some loose resistors to test.
I went and borrowed one and the resistor is 177ohm.
I am actually pretty confident that my voltage readings are okay or at least close - on a new AA I get 1.61, on a 9v I get 9.61, and wall was IIRC 117 and the heaters etc. were pretty much on IIRC.
Since I don't have anything else to go on until I restart it (will have to be with a higher resistor if using these tubes - see below), if we assume the voltage was correct (plate to cathode voltage - 343V; 14.2V drop) and use the corrected 177 value, what would be a best guess for what I should swap to to cool it off?
Also, as far as why these tubes aren't handling it if it was only 108%, I found mention in another thread of Amperex Holland tubes being problematic potentially due to not being rated for the voltage. Plus mine are Hammond pulls not NOS. One thing for sure, one is now dead and blew the fuse, and another started glowing pretty bright and humming within a couple of minutes at idle. Here's the thread -
viewtopic.php?t=7774
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Post by phsyconoodler » Sun 01/08/06 4:45 pm
I had the same problem with some NOS tubes.I had to up the cathode rsistor a lot and finally just went with some new EI tubes.The NOS tubes could not handle the voltage above 300v.That is not the case with all NOS EL-84's,just the ones I had.If I use a zener diode to drop the B+ they work fine,but the sound is not the same.Good,but not the same.I wanted to make it work with all EL-84's so i just ended up with new production tubes.They sound phenomenal!
The ones I had trouble with were Amperex."