Did I damage my amp by a speaker disconnect?

[meblaw1]

Major blunder today. I was swapping out speakers on my epiphone valve junior and after disconnecting the speaker I didn't realize that the amp was still on. After 10 minutes, I discovered my mistake. A mic with a cm element was plugged in. I immediately turned it off. I reconnected the speaker and turned it on to test the amp. I plugged in a guitar. When the volume knob was past 2 o'clock, the sound was intermittent, in and out like waves. When there was nothing plugged in and I turned the volume knob past 2 o' clock, I heard intermittent white noise. I assume that this is not normal. I believe (although I am not sure) that intermittent (on/off) sound is probably realted to the output transformer. Is this correct or what did I just damage?

And if it is the output transformer, can anyone recommend a comprable replacement that costs less than $100. I heard people have used heyboer or hammond. is the following a direct replacement for the version 3 output transformer: http://www.hammondmfg.com/jpeg/125CSE_B.jpg .Also, would it be a good time for a slight upgrade, such as this http://www.hammondmfg.com/jpeg/125DSE_B.jpg .For instance, a transformer that allows for a 6V6 or would that change the character of the amp?. I don't want to use Mercury as they are too expensive (beyond the cost of a new epi!).

[Mark B]

First, replace the power tube...you will have definitely blown something, eliminate the cheap parts first.

IF the OT is shot - Any OT that has a primary impedance of 5K to 8K will work, 40-50mA rating...going much bigger isn't really beneficial for harp. I'd be driven by finding an OT that fits reasonably without to much redrilling. Your B+ voltage is on the low side for a 6V6 amp.

first, I'd measure the dc resistance between B+ and power tube plate wires, I'd expect to see 200-300ohms (a bit more isn't a problem), not the acid test, but I wouldn't scrap the OT until it is proven to have failed.

[meblaw1]

After further troubleshooting, we have discovered the following: When you use low volume, the amplifier works fine, when you increase the volume the amplifier begins to oscillate, the voltage coming from the power transformer before the diodes oscillates about to 12% to 15%. It appears that something might be wrong with the power transformer. My question is does anyone think that there might be another issue. The voltage coming from the power transformer should be fixed regardless of volume. Why is it oscillating? Thanks. Mike

[Mark B]

I'd be surprised if the PT was at fault. If you have oscillation, the fluctuating load on the power supply may be causing the PT voltage to oscillate, rather than the other way around.

Have you changed anything on the amp since it worked OK without oscillating (lead dress etc)?

How did the OT check out?

[meblaw1]

Did I damage my amp by a speaker disconnect? The answer is NO. This turned out to be a misdiagnosis. AT the time of the speaker disconnect, I had made two mods pursuant to Randy's epivalve mods. I had switched out the C1 and C2 coupling caps to .47. I also increased the value of C9 as recommended by the mods page. I stopped there. Since the oscillation issue, which I thought was caused by a speaker disconnect, I changed the R13 resistor to 180K as recommended by the mod page. This did the trick. THe oscillation disappeared. For the record, the output transformer, power transformer and tubes were not damaged. This issue might be a good lesson, however, to take the mods as a whole and not as independent pieces. Regards, Mike