Dammit, another preamp tube smoked --help?

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tweed

tweed

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So after my last adventure with preamp tubes and my bogen vplexi, i replaced them all with shiney new ones. EH12ax7 in v1, c9 in v2, eh in v3 and life was good. Played the amp for maybe 30 mins, switched it off. Unplugged it from the wall and left it on the bench.

Four or five days later...

I go in my shop last night to do some work and glance over at the amp on my bench. I notice that the shiney new EH in v1 is probably toast due to the silver portion at the top of the tube being ghost white. WTF!!! It was silver when I turned the amp off and fine.

Do preamp tubes just turn like that when the amp is just sitting on a shelf and no power is running thru it? :confused: :doh:
 
FWIW -
Krank stopped using EH 12AX7s and switched to Ruby because of a high failure rate. It seems as if these things go in cycles, perhaps right now the EH tubes have some flaws that appear after they are heated and cooled a few times?
I would try a different manufacturer to see if there is some pattern to what is happening that could be related to the amp, or just a lower quality run of tubes.
 
Yea this seems to be a trend, Jeff (Egnater) and Steve (VHT) were telling me that ALOT of tubes are bad right now, been hard trying to find good quality tubes.....

Had one pretube go in my Sig:X, replaced it with an older but still new GT and all is good in VHT land again :D
 
Crap I gotta find something else. I tried putting a C9 in the slot in question, no dice it doesn't work for some reason. What other higher gain tubes would you guys suggest? This is a plexi style amp, 50watt with PPIMV so it's somewhat bright to begin with. A little bit darker preamp tube would be good but not super dark if that makes sense.
 
JJ are the only "dark" sounding tubes I can think of. but my experience is somewhat limited, I have a few certain tubes I like in certain amps, and now I'm relearning with this VHT. :D


Good luck, hope you find what your needing. :thumbsup:
 
I'd stay away from JJ for a bit as well. Everyone in my band (myself, our other guitarist and out bassist) used JJ tubes untill recently. We got several quartets with imperfections in the glass, a definite manufacturer defect. I myself have had a few of their preamp tubes burn out recently. I just moved over to Penta power and Penta/Tung Sol/Mullard pre's.
 
tweed":hn27jfqo said:
Crap I gotta find something else.
Click to expand...
Have you tested for normal voltage and resistance in the V1 circuit?

Sad to hear that several new tube brands are seemingly having bad runs.
Glad I have good stock on old and older runs:
SD053.jpg

:)
 
MOAAH":30f75zeu said:
tweed":30f75zeu said:
Crap I gotta find something else.
Click to expand...
Have you tested for normal voltage and resistance in the V1 circuit?

Sad to hear that several new tube brands are seemingly having bad runs.
Glad I have good stock on old and older runs:
SD053.jpg

:)
Click to expand...

Oh you bastard! :rock:

Talking with Doug at Doug's Tubes, he's been having alot of trouble with JJ Tesla as well. Wnder what's going on over there.
 
Get some NOS of the type you want. Most of the tubes in my amp are from the 50s and 60s and last forever and sound good.
 
DMM to 20 AC volts, read on a preamp tube's sockets between 4 or 5 and 9.

Also if the second tubes blows often, check the plate and cathode voltage (plate: pin 1/6, cathode 3/8). DMM to 1000V DC then.
 
duesentrieb":3gbw5jlg said:
DMM to 20 AC volts, read on a preamp tube's sockets between 4 or 5 and 9.

Also if the second tubes blows often, check the plate and cathode voltage (plate: pin 1/6, cathode 3/8). DMM to 1000V DC then.
Click to expand...

with the amp on or with the amp on standby?
 
The heaters voltage can be read with the amp in standby.
Plate and cathode with the amp in run mode, Randy.
 
tweed":117ovnpy said:
So after my last adventure with preamp tubes and my bogen vplexi, i replaced them all with shiney new ones. EH12ax7 in v1, c9 in v2, eh in v3 and life was good. Played the amp for maybe 30 mins, switched it off. Unplugged it from the wall and left it on the bench.

Four or five days later...

I go in my shop last night to do some work and glance over at the amp on my bench. I notice that the shiney new EH in v1 is probably toast due to the silver portion at the top of the tube being ghost white. WTF!!! It was silver when I turned the amp off and fine.

Do preamp tubes just turn like that when the amp is just sitting on a shelf and no power is running thru it? :confused: :doh:
Click to expand...

What happened to your tube is it lost it's vacuum. If the sliver stuff (getter flashing in tube nerd speak) turns milky white it means the glass cracked somewhere. It happens man, in my experience it usually happens with preamp tubes from tension at the pins. I've had killer nos stuff go ghastly white just sitting in the box for no apparent reason, painful when it's old stuff that's getting irreplaceable these days. It could be a factory flaw in the tube, could be that your amp has sockets that are too tight, could even be that the tube in question needed it's pins straightened before it got to you. I've straightened tube pins when they were crooked only to have them fail months later after many heat cycles. I'd put my money on a duff tube though, new production tubes suck but we're stuck with em, if anything we're all lucky anybody's still making them at all. See if your tube dealer will exchange it for you.
 
duesentrieb":14nw8zvk said:
The heaters voltage can be read with the amp in standby.
Plate and cathode with the amp in run mode, Randy.
Click to expand...

I pulled the tube in question, cracked across the bottom by pins...
replace with new tube
here are the readings, have no idea if they are where they should be.

4/9 on V1 = 1.30
1/6 on v1 = 2.52
3/8 on v1 = all over the place
 
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