# El34 bias



## guitar69freak (Jul 29, 2019)

Just replaced the tubes In my Peavey XXX II as I come to find the tubes in this amp weren’t matching. Replaced the 6L6s with Ruby EL34BHT’s I had in my XXX. (first edition)

ii don’t remember what thetubes bias rating was set for. (Of course I didn’t check on the previous amp before I’d taken them out. 

anyone have any leads, what would you bias this amplifier at?


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## guitar69freak (Jul 29, 2019)

I found these at ruby tubes web site.

EL34BHT
We have had a great response to our new RUBY EL34BHT tube. Many engineers have asked about what kind of power can be expected from the EL34BHT. In our tests, we used 600 V on the plates, 540 V on G2 and a bias setting of –54V. The tubes idled at 25ma each. The power output from a pair of EL34BHT tubes using these voltages was 70 watts at clipping.

The Ruby EL34BHT's were developed for very high plate voltage applications. They have the same gold plated grid and extra thick glass as the BSTR's, but with the addition of welded wings on the plates these are a perfect option for Bogner amps and others. The tone is sweet on top with a perfectly balanced mid-range emphasis, not too compressed, and a firm focused low end that has become a favorite choice for hifi applications.


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## guitar69freak (Jul 29, 2019)

Pics


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## jb welder (Sep 14, 2010)

Peavey biases their amps quite cold. That 25mA number Ruby used sounds good to me, ballpark of what Peavey probably uses.
Peavey only gives a voltage spec. for these, -42.5VDC at the test jack for EL34 (-55VDC for 6L6)


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## guitar69freak (Jul 29, 2019)

How do I measure mA using this multimeter? Right now it it hovering at 86.1 and 86.2 V. How do I measure mA?


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## Frenchy99 (Oct 15, 2016)

guitar69freak said:


> How do I measure mA using this multimeter? Right now it it hovering at 86.1 and 86.2 V. How do I measure mA?



First off, this is very dangerous since your dealing with high voltages. Its not recommended for people who don't know how. I bought a bias meter to avoid doing this following procedure. 
if you don't have a bias meter:

Red multimeter wire on OT center tap and black multimeter on pin 3 of each tube socket. 

I bias mine between 35-40 mA with EL34`s 
30-35 mA with 6L6`s


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## dtsaudio (Apr 15, 2009)

Frenchy99 said:


> First off, this is very dangerous since your dealing with high voltages. Its not recommended for people who don't know how. I bought a bias meter to avoid doing this following procedure.
> if you don't have a bias meter:


Agree with Frenchy. Your are dealing with +450VDC (possibly more) biasing this way. Lethal to say the least. If you decide to proceed, learn about safety precautions and how to properly use your meter.


Frenchy99 said:


> Red multimeter wire on OT center tap and black multimeter on pin 3 of each tube socket.


You will be measuring the voltage drop across the output transformer primary leads. So right on the high voltage. You also need to know the DC resistance of the primary in order to do this. Then you would need to calculate the current from ohms law, and divide by two (two tubes in parallel) to get the current through each tube.

If this is sounding confusing or above your head, find someone to bias it for you.


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