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Buhl 28th November 2002 07:51 PM

EL84 BIAS problem - again....
Hi Forum!

Some weeks ago I asked a question about biasing my BEARD BB100 integrated tubeamp - using six el84 pr. channel, but only one bias pot for the six - witch fdegrove and gabevee pointed out, was a poor solution (thnx for the replys !). Reluctant to make the radical improvement of adding a bias-pot for each of the output tubes, I did as adwised, and turned up the bias little by little - alert of any tubes glowing cherry red. I did this little by little over the last few weeks - it was fine up til about 15mA, but when i reached 18-19 mA, I started to hear distortion - wery clearly - how come - any suggestions ?

The amp i defenetley hotter and better sounding than when operated at 8-9 mA - but before I had the tubes changed, i remember it to be driven at 22-23 mA (thats what the tech. who changed the tubes told me).



fdegrove 28th November 2002 09:40 PM


The only thing I can advise you to do for now is get them back at 15mA.

The only reason for the distortion when going deeper I can point at is a weak tube amongst the others.

If they sound O.K. like this keep them biased there till they are ready for replacement and get some really well matched ones.


Buhl 28th November 2002 10:16 PM

Hi fdegrove, and thnx for the quick answer - status right now is as you recommend - 15 mA and no distortion.

I think I will wait growing the beard longer until I can get a matched shaving knife - or simply replace the razor knife with the electric razor machine (Pass Zen 4) i have liying in my drawer, just waiting for some attention and a hot soldering iron.

(I need to try trans' amps again - although I am reluctant to say goodbye to the tube sound)



fdegrove 28th November 2002 10:21 PM

Hi Hans,


(I need to try trans' amps again - although I am reluctant to say goodbye to the tube sound)
I can well imagine you don't want to let it go easily.

Me,I wouldn't be able to live without at least one tube amp in the house.

Your problem can be solved though,only it is so hard to do when I don't have the amp in front of me.

Happy listening,;)

Buhl 28th November 2002 10:31 PM

Hi Frank

Yes, i have a fear that especially voices and acoustic instruments will be reproduced subjectively worse on the Trans-amp - this is what i think my tube amp does best of all - but still its hard to point out what makes this amp so much better than other expensive commercially available hifi amps that i have heard.

But, luckely - the Beard should stay in dha house a little longer - i will just have a new playmate / competitor in the Zen4.

When I have finished the zen i will proberbly head for a diy tube amp - when I open the beard, i see many components and solutions that I should be able to do better in a diy-amp. And then its nice to know in witch forum to ask the questions :)

Happy listening to you to, and dont forget to drink some of that wonderfull beer you guys brew down there !!!


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