Author Topic: 6l6-el34 bias in a 6505+...how?  (Read 4835 times)

jonathan perez

6l6-el34 bias in a 6505+...how?
« on: October 22, 2007, 05:51:43 PM »
how can it be done in my peavey 6505+ so that i can use either 6l6gc tubes or el34 tubes? there is a bias adjustment control, but does that only cater to 6l6 tubes? if i put in a quad of el34s, could the bias control get me close to home? anyone know what im talkin about?  :D
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The Tone God

Re: 6l6-el34 bias in a 6505+...how?
« Reply #1 on: October 22, 2007, 06:08:05 PM »
I think the bigger issue at the moment is if pin 1 connected.

Andrew

jonathan perez

Re: 6l6-el34 bias in a 6505+...how?
« Reply #2 on: October 22, 2007, 06:08:52 PM »
and if it isnt, conversion cannot be completed?
no longer the battle of midway...(i left that band)...

i hate signatures with gear lists/crap for sale....

i am a wah pervert...ask away...

jonathan perez

Re: 6l6-el34 bias in a 6505+...how?
« Reply #3 on: October 22, 2007, 06:10:34 PM »
**edit**
from what i can tell, the first pin on the first tube is not connected, but on the other tube sockets, pin1 appears to be going to ground. is this correct?
« Last Edit: October 22, 2007, 06:13:58 PM by thebattleofmidway »
no longer the battle of midway...(i left that band)...

i hate signatures with gear lists/crap for sale....

i am a wah pervert...ask away...

MetalGod

Re: 6l6-el34 bias in a 6505+...how?
« Reply #4 on: October 22, 2007, 06:44:59 PM »
For EL34s you want both pin1 and pin8 connected to ground.

I'd be concerned about the PT taking EL34s since you're drawing much more heater current than with 6L6s.

One way to tell if the PT is able to take the extra load is to put the EL34s in and measure the heater voltage at idle.  If it's being pulled down under 6v I'd say the PT ain't gonna like the extra load. 

If you really must run EL34s and want to play safe, get a small filament transformer to run the heaters.  That way you could go one better and use 6550s and KT88s in there for some SERIOUS grunt  :icon_twisted:

 8)

jonathan perez

Re: 6l6-el34 bias in a 6505+...how?
« Reply #5 on: October 22, 2007, 06:50:07 PM »
kt88s would be pristine...ok, ill do the check on it right now.

also, is it okay that the first power tubes pin1 and 8 are not connected to ground?

come to think of it, ive seen someone (voodoo mods, think) do a mod that adds a switch/bias control to the old 5150 amps so that you can swap between el34 and 6l6..
no longer the battle of midway...(i left that band)...

i hate signatures with gear lists/crap for sale....

i am a wah pervert...ask away...

brett

Re: 6l6-el34 bias in a 6505+...how?
« Reply #6 on: October 22, 2007, 10:51:24 PM »
Hi
my JTM60 came with 6L6s in it as a direct sub for EL34s.  It was running hot when I got it.  So much so, that the screen resistors were blistering and smelling bad (that's why it was cheap).
EL34s went in and biased with some adjustment.  Most amps seem to have a wide range of bias voltage available.  If possible, work out which end of the pot gives low bias, so that you can adjust upwards from there (instead of adjusting downwards from glowing plates). 
EL34s often run well at around 35 mA, but if the B+ is more than 500 V, you might want to decrease that a bit.

Lastly, and most importantly, don't touch anything unless you know what you are doing.  For valve amps, trial and error can involve funerals.
cheers
Brett Robinson
Let a hundred flowers bloom, let a hundred schools of thought contend. (Mao Zedong)

ethanw

Re: 6l6-el34 bias in a 6505+...how?
« Reply #7 on: October 22, 2007, 11:02:21 PM »
For EL34s you want both pin1 and pin8 connected to ground.

I'd be concerned about the PT taking EL34s since you're drawing much more heater current than with 6L6s.

One way to tell if the PT is able to take the extra load is to put the EL34s in and measure the heater voltage at idle.  If it's being pulled down under 6v I'd say the PT ain't gonna like the extra load. 

If you really must run EL34s and want to play safe, get a small filament transformer to run the heaters.  That way you could go one better and use 6550s and KT88s in there for some SERIOUS grunt  :icon_twisted:

 8)


+1 on the comments above. Bias voltage would probably have to be adjusted by a resistor swap. I did this same thing to a 5150 a few years ago and was disappointed in the sound, I think the tone on those amps is so preampy that the power amp makes little difference.