When I tap my tube it heats up

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donniecrump

Member
So I have an odd issue. A few days ago I re-tubed my Rockerverb MKIII. I had originally bought a quad of Groove Tubes KT77. One was broken so I used the other pair and 2 matched pair of JJ branded ones I had.

So they are like this away from the input. GT - JJ - GT - JJ

I got everything biased and started testing everything out. When I fired up the amp I noticed that the second GT was not glowing. I was still getting sound out of my amp with all settings turned on full power.

So ... I gently tapped the tube with my fingernail and it started warming. I am pretty sure that with a gentle tap that it is not my amp. I was curious if anyone else had seen this type of issue with a tube.

tube.jpg
 
I swapped them and the possible bad tube heats up when turned on but a few seconds slower than the others to turn red. I have a new set from Eurotubes on the way. I think the Groove Tubes got bounced around and possibly damaged. One of the 4 actually had a cracked/chipped base. The box was sealed and not damaged so I am kinda confused on how they got damaged with the box in tact. Oh well .. live and learn.

I have a new set of Ruby EL34B I may try. That is actually what came in the head.
 
Cool. I will switch them out this evening. My thought process was from the manual it says tube 1 and 3 will be on for 1/2 power mode.
 
With 4 trim pots you can definitely bias it more accurately. If one tube is way off of the other ones you might not be able to get it in range, but as long as it's not too far off then yeah, 4 trim pots is awesome!
 
So now I have a new problem. I put my new JJ tubes in my amp and now my multimeter reads -.002 mA when I switch out of standby. It is doing it on all tubes. I took one of the JJ's I had in it before the new tubes and it is doing the same. The first end tube I biased everything worked as it should. Once I moved my multimeter to the opposite end is when things went bad. I moved the multimeter back to the end that I just biased and got the -.002 reading on that one also.

I checked all of the fuses and they "look" good. No blackening or popped wires inside.

Any ideas on what I have done to cause this or how to fix it?
 
Did you turn all the trimpots down first. I usually do that and then after the new tubes are in and the amp is turned on, I bring the bias back up. try turning up the bias on one of the tubes?. That's sounds weird.
 
Donnie, whats your thought of the Rockerverb MKIII as a metal amp? I was thinking of picking one up soon and throwing a boost infront of it ( i never use OD's ) or does it not need one?
 
Just because I have to ask, how are you measuring the current? Are you measuring voltage across a 1ohm resistor? Using an octal probe? Placing the meter in series wrt ground?

Regardless, I believe you've blown a fuse. 2uA is biased hard into cutoff region, meaning no B+ on the tubes and the bias circuit pulling the tubes into cutoff. I'd suggest taking the amp to a tech.
 
I was measuring mA using a bias probe. Although ... late last night I found the test points on the PCB. There is one for each power tube. So I turned my multimeter to mV and everything read as it should. I think I have blown the amp fuse in my fluke. 87. I have some on order so I will know for sure when they come in this week.

The good news is my RV has been re-tubed.
Preamp.
Ruby 12AX7AC5 HG+
Ruby 12AX7AC5 HG
Ruby 12AX7AC5 HG
TAD 12AX7A-C
Ruby 12AT7C
Ruby 12AT7C

Power tubes: JJ KT77

This is a similar setup I have in my Diezel Hagen. It sounds heavy but clear. Don't think I would recommend this tube layout for standard rock though.
 
Surprised nobody took the subject line into the gutter. So without further ado:

When I tap my tube...it gets swole.
 
Donnie, how would you say the orange rockerverb would work for metal? does it require a OD to get a tight enough tone or is it fine by itself?
 
Just a heads up, those JJ tubes are known to have very thin pins and sometimes they don't make good connections with the tube base. I've had to solder each pin on a quad of 6L6's to make them work properly.
 
I think that was the issue. I put in a set of EL34B's and it worked as it should. Kinda bites. I really like the KT77 tubes.
 
JJ Tubes have smaller diameter tube pins which sounds like what you are describing, they don't make good contact and cause issues as you described, in some case the input grid doesn't make good contact and then you don't get bias voltage to the tube and presto firecracker time.

That is why Eurotubes is really big on contact cleaner and tube socket tightening, because they know the pns are smaller.
 
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