What to do now?

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fuzzyguitars

fuzzyguitars

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What do you guys do when you retube your diezels and you cant get the bias to the level you need.

ie ... either to cold or too hot. with the adjustment knob on max or min.

is there another adjustment knob inside the chassis?


i have a diezel herbert that i just got.

it came loaded with 6550s and it biased at 45 ma per pair! not per tube. too cold imo.

i tried and pulled out a crapload of new tubes that i had stashed away, and all the sets bias too cold per pair.

so i am thinking that the factory may have set the general bias way to low.

how can i fix this without having to take it to a diezel tech?

:cry: :cry: :cry: :confused:
 
check your other topic. I think you blew the f1 fuse or whatecer it's called.
 
Hey man... I never biased that amp, I got it straight from Inca Roads and never touched anything... are you using the tubes that are currently in it? Or are you trying new tubes? This is the exact issue that Peter is talking about with the SED 6550's, I actually bought some for my VH-4 and liked them at first, but they are getting way too hot and I'm having a difficult time as well get them to bias correctly... I would say it's the tubes, is everything else ok with the head?
 
Are you using a bias probe or a multi meter ?

If you are using a multi meter make sure the red probe is in the mA slot, not the V or + slot.
If it's in the + or V slot your readings will be wrong.
 
MARK2C":229zewsl said:
Are you using a bias probe or a multi meter ?

If you are using a multi meter make sure the red probe is in the mA slot, not the V or + slot.
If it's in the + or V slot your readings will be wrong.
Click to expand...


we have a winner.

i am such a tool.

this was exactly what i had done.

mark2c thanks a lot.
 
seriously? didn't you see your tubes glowing like a motherfucker? I'm surprised you didn't fry them.
 
The bias pots in Herberts and Einsteins (probably also in newer VH4s) have a super wide range, a plus if you go from EL34s to KT88 - no change of a resistor needed, but a minus to bias "fast" - it needs time and a calm hand b/c the pots are so "sensitive".
 
nbarts":2qaqyfy1 said:
seriously? didn't you see your tubes glowing like a motherfucker? I'm surprised you didn't fry them.
Click to expand...


they werent really glowing or super hot :confused:
 
lol, I had them hi like that once, I had fried chicken right away, it wasn't just glowing, it was smoking. Those 6550s must be badass.
 
Glad your problem is solved.


As for SED 6550's, i've seen them biased to 130mA a pair and they did not red plate at all.
 
Mizati20":1gi3nsy6 said:
Hey man... I never biased that amp, I got it straight from Inca Roads and never touched anything... are you using the tubes that are currently in it? Or are you trying new tubes? This is the exact issue that Peter is talking about with the SED 6550's, I actually bought some for my VH-4 and liked them at first, but they are getting way too hot and I'm having a difficult time as well get them to bias correctly... I would say it's the tubes, is everything else ok with the head?
Click to expand...

The 6550's technically run as hot as an EL34. Both have a 250 C operating temp according to the SED technical data sheets.

http://www.svetlana-tubes.com/pdf/sv6550c.pdf

http://www.svetlana-tubes.com/pdf/el34.pdf

Even with SED EL34's or EL34BHT's the VH4's power transformer get pretty hot after a while.
Just balance them between 60ma and 70ma per pair and enjoy them. Don't worry about the heat.
 
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