Installing some Mixed tubes on my VH4: BURN SMELL (wtf)

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Joeytpg

Joeytpg

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I'm running 4 6L6 and one of them is not good, so I want to use two of them and two KT77 I have laying around...... I wanna knwo how to bias them....I should leave the 6L6 bias switch but how can I bias it? what's the proper way?

EDIT:

I biased one of the KT77 tubes, everything was fine, then I used my bias probe to biased the other one and when I turned on the amp there was a burning smell coming out of the tube socket and there was smoke....I turned it off immediately........... any ideas?
 
oh another question.....are the two inside tubes the same and the outer ones the same?
 
The VH4 doesn't support mixing tubes in the power section.
 
well, still there was only a KT77 tube in it when I tried biasing the other one

btw, the fuses are ok...... but still there was burn and smell
 
Sometimes tubes smell like that when they get hot and the printing one the glass starts to evaporate. Nothing to worry about usually.

And you cannot bias individual tubes in the VH4 but only a quartet of tubes.
 
I have a biasing probe that allows me to bias each tube.....
 
But you only have one bias trimmer. The bias probe only measures the individual tubes.

You need a matched quartet of power tubes for the VH4.
 
MourningEngine":2zeodfad said:
But you only have one bias trimmer. The bias probe only measures the individual tubes.

You need a matched quartet of power tubes for the VH4.
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^^^^^^^^^^^^^
Your going to get a load mismatch on the transformer with the two different sets of tubes in there. The burning smell could be the print on the tubes burning off or you could be doing something like this pic. Either way its your 4grand amp. Do what you want with it. But you need a matched quad in it for it to perform at it's peak.
 

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oh, I'm not trying to use the unmatched set, I didn't know so I stopped right away.
 
so Peter? Olaf?

what do you recommend I do? I don't know if I should start the amp back on.
 
You should probably check under the hood and see if you burnt any components. It's usually pretty obvious if you see smoke. If you don't see anything wrong put a matched quad in there and start it up. Hope everything works out for you!

-Alex
 
always bias with a matched quartet plugged, one with the bias socket. bias current can still vary by +-5mA from tube to tube, so don't max it unless you know which tube draws the most.
 
Joeytpg":1mnqfs03 said:
so Peter? Olaf?

what do you recommend I do? I don't know if I should start the amp back on.
Click to expand...
I've replied yesterday in the normal forum, Joey.

You cannot use KT77 and 6L6 in the same amp with just one bias pot. The reason is that the current draw for these types is too different.

Send pics of the power tube sockets please.
 
Ok, thank you Doc, here are the pics......

http://gallery.me.com/jtpg#100215

This is what I did, step by step:

NOTE: master volume down to 0, as well as each channel vol. cab plugged in and instrument cable plugged in too.

1) took amp off headshell
2) pulled out all 4 power tubes (6L6)
3) hooked the tubetown probe to the 2nd tube socket
4) pulled in one KT77 into the probe and rebiased to 35, then turned off amp and unplugged tube and probe.
5) Hooked probe into tube 3rd tube socket and pulled in another KT77 into the probe.
6) turned on amp and flip on the stand by switch
7) a little smoke came out of the 3rd tube socket (the one where I had the probe and tube hooked in.
8) stand by switch off and turned off amp immediately.
9) unplugged amp.

MISTAKES I MADE:

I had the 6L6/EL34 switch on the 6L6 side (I though the KT's tubes were on the 6L6 family :doh: :doh: :doh:
 
I'd get a quartet of either tube and rebias, Joey.
Those screen grid resistors don't look that bad . . . could be that the 1 Ohm R inside the adaptor caused the smell too.

Just wait what Peter says when I has seen the resistors.

Olaf
 
thank you Doc.

btw I checked the tube fuses and they're all fine.
 
it's been so long since I last rebiased the VH4 that I forgot.

So basically if I'm using a matched quartet I only have to bias ONE tube using the probe, and then just hook all the other 3 tubes and I'm set to go? :)
 
Joeytpg":hpg797f1 said:
it's been so long since I last rebiased the VH4 that I forgot.

So basically if I'm using a matched quartet I only have to bias ONE tube using the probe, and then just hook all the other 3 tubes and I'm set to go? :)
Click to expand...

Yes :) Put all the tubes in and put your probe on one tube and bias the amp.
 
cool, now I remember why it was so freaking easy :D (the hardest part is taking the amp out of the headshell and putting it back in :D
 
Put all tubes into the amp, one of them sitting in the adaptor. Otherwise you get a faulty reading.
 
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