bad tubes question

[stratotone]

So, last night took the mighty VHT UL to the gig. Wheeled in the 1/2 stack, set it up, powered it on standby while I gathered other gear and set it up. Hit the standby switch, got a loud POP and the power tubes flashed briefly, stayed lit and the amp stayed on, but no sound.

SHIT!

Replaced the 1amp fast blo fuse, and the amp came to life, then popped again. Ran the amp on half power, and it stayed on... for three hours, then went out during a tune on the last set. Replaced fuse again, finished the gig.

One other thing I noticed was that my lead channel wasn't giving any more volume, it was like it was super compressing. It was weird.

So this morning, took the 6550s out of my 2/90/2 poweramp, put em in the UL, put it on high power and worked great. lead channel also gave a nice volume boost when I hit it.

Question to the tube gurus - if your power tubes are going out, can it affect a lead channel's volume? it was like anything past a certain volume just wasn't going to get louder... like the power tubes couldn't give any more. I didn't have the master cranked though, was at half power and maybe 1/4 up, with rhythm channel at 1/2 way up.

All seems to be ok, going to order new KT88s next week and taking my '92 VHT Classic for backup to tonight's gig just in case.

Pete

 

[Code001]

Yes, they can affect volume. One time, I remember when my GH100L was real low on volume. So what did I do? I cranked it, and cranked it, and cranked it. The volume never really got louder, but it started to hum like crazy. Then, I suddenly see this spark/arcing of the power tubes, and it took out a screen grid resistor.

 

[stratotone]

Yes, they can affect volume. One time, I remember when my GH100L was real low on volume. So what did I do? I cranked it, and cranked it, and cranked it. The volume never really got louder, but it started to hum like crazy. Then, I suddenly see this spark/arcing of the power tubes, and it took out a screen grid resistor.

I had a bad tube blow a screen resistor on one of my mesa boogies before (roadster) - I prefer the VHT way of popping a fuse.

What was weird was, I had plenty of gain with the clean and rhythm channels, but NOT the lead. I figured a bad power tube would have affected all three, not just one... maybe the lead channel was oversaturating it or something, who knows. Seems to be ok now.

Pete

 

[Loudness250]

The gain thing is weird but if you were blowing fuses it does sound like a power tube thing. It almost sounds like a preamp tube problem but the fact that you're blowing fuses points to power tubes. You might try replacing that preamp tube that is dedicated to the lead channel just to be sure.

 

[stratotone]

The gain thing is weird but if you were blowing fuses it does sound like a power tube thing. It almost sounds like a preamp tube problem but the fact that you're blowing fuses points to power tubes. You might try replacing that preamp tube that is dedicated to the lead channel just to be sure.

I replaced all the preamp tubes associated with the lead channel with no change. It pretty much has to be the power tubes, just seemed awfully strange!

Pete

 

[Bishop5150]

I just had the same sort of issue with my 5150 III. I kept blowing an internal fuse. My amp guy called Fender and they said that it was probably a bad tube somewhere causing the fuse to blow and suggested I change all the tubes. Switching out 4 6L6's and 8 12AX7's can be a little pricey. Well last night when I plugged in, my clean channel and rhythm channels were fine but the high gain channel had no gain or bottom end. I had two extra 12AX7's lying around so I switched out the 12AX7 in slot V4 which is the first tube out of 3 in the lead channel section and it did the trick. Hopefully this will solve my fuse problem too. Your issue could very well be a preamp tube also but could be a power tube issue as well. Good luck with it.