Biasing the Renegade el34 side wierdness

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Festus

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I sent this email to info@egnateramps.com, and to hans@egnateramps.com. No reply yet, so thought I'd try here.

I'm running into a couple of issues when setting the bias on my Renegades on the el34 side. I have a new Renegade head (purchased September of this year), and one that I bought used.

On the new Renegade head, I'm having a hard time finding el34 tubes that will bias up to 70mV. I've tried several pairs of el34 tubes so far, and with most of them, with the bias adjustment maxed, they get to about 63mV.

On the used Renegade head, no el34 tubes that I've tried in the el34 side will bias higher than about 60mV. I swapped the tubes around (6L6's in the el34 sockets, el34's in the 6L6 sockets), and they seem to bias up just fine.

Are there internal bias trim pots that work in conjunction with the external bias controls?
 
Festus":2rw4h7uf said:
I sent this email to info@egnateramps.com, and to hans@egnateramps.com. No reply yet, so thought I'd try here.

I'm running into a couple of issues when setting the bias on my Renegades on the el34 side. I have a new Renegade head (purchased September of this year), and one that I bought used.

On the new Renegade head, I'm having a hard time finding el34 tubes that will bias up to 70mV. I've tried several pairs of el34 tubes so far, and with most of them, with the bias adjustment maxed, they get to about 63mV.

On the used Renegade head, no el34 tubes that I've tried in the el34 side will bias higher than about 60mV. I swapped the tubes around (6L6's in the el34 sockets, el34's in the 6L6 sockets), and they seem to bias up just fine.

Are there internal bias trim pots that work in conjunction with the external bias controls?
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I don't know what kind of meter you're using but,always remember that 65mV is for the pair of EL34's..(some people are using devices made to measure a single tube).I wouldn't worry if i had a 63mV bias for the EL34's..Btw,i'm not aware if there are internal trim pots in this case. Good luck !
 
Do you have the same problem if you take the pair out of the "good" amp, where they will bias correctly, and put them in the newer one that is giving you trouble?
 
Sorry, I just reread your original post and see that you already did this. Are you saying the original tubes that came in the new amp will not adjust properly but work fine in the older one? If you put the same pair of tubes in each amp and turn the bias control full up, do you get the same reading on both amps? Of course, it is perfectly safe to use the amp at 60 - 63mV but clearly there is something exactly right.
Please give me serial numbers for both amps and indicate which is which. You can email this info bruce@egnater.com
 
bruce egnater":2l3byyed said:
Sorry, I just reread your original post and see that you already did this. Are you saying the original tubes that came in the new amp will not adjust properly but work fine in the older one? If you put the same pair of tubes in each amp and turn the bias control full up, do you get the same reading on both amps? Of course, it is perfectly safe to use the amp at 60 - 63mV but clearly there is something exactly right.
Please give me serial numbers for both amps and indicate which is which. You can email this info bruce@egnater.com
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Bruce, thanks for the reply, appreciate it!

Bluesplayer, s'ok, I've done that too.

Viking, I'm using a good digital meter set to mV, into the respective test points on the back of the amp. My other el34 amps bias to 36 or so, actually. 65-70 seems high comparatively, but there's 4 tubes basically running on a 65 watt output transformer, so I imagine that would result in very different bias specs.

I'll send the info to your email, Bruce. NEW Renegade: The new amp with the stock tubes would not bias up to 70mV - maybe 63 or so(Renegade manual says 65 to 75mV for el34). I had to sort through my stash of el34 tubes to find a few pairs that would bias to 70. Currently it's biased to spec. I realize it's safe to run the amp at 60mV on the el34 side, but it would be running a bit cold.

USED Renegade: The stock tubes would bias to about 55mV with the bias pot maxed. I tried a variety of new and ANOS el34 tubes, highest I could set the bias with those tubes was about 60mV. So...I put the el34 tubes in the "6L6" sockets, and any el34 tubes I try in the 6L6 "side" will now bias to spec no problem. Kinda wierd.
 
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