Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => EZ Board postings => Topic started by: Geezer on June 18, 2005, 05:46:23 am
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Hoffman Amplifiers
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> Bias problems in a Deluxe Reverb
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brookgannon
Junior tube assistant
Posts: 56
(3/27/04 2:22 pm)
Bias problems in a Deluxe Reverb
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I thought I would have this down by now, but… . I just re-tubed my Hoffman board based deluxe reverb and I am having trouble getting it to bias correctly. Originally I had my EH6V6 power tubes biased at 23.5 mA with a 415V B+. Without adjusting and putting the new tubes (EH6V6 and new JJ GZ34 recto) in I have 2.93mA with 432V B+. So then I went on to increase the bias range resistor first to 1k and measured 4.5mA at 415V B+ then to 1.5k and measured 5.8mA at 405V B+. Now I felt as if something is wrong because at this rate the B+ will be pretty low when I get to the 70% dissipation that I aim for. Does anyone have an idea what is going on? Thanks for your time Brook
GroundhogKen
Forum Moderator
Posts: 2335
(3/27/04 3:02 pm)
Re: Bias problems in a Deluxe Reverb
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Put the old tubes back in.
Measure the pin voltage at the power tubes. ( pins 3,4,5,8 )
Make sure the 2 and 7 heater voltage is near 6.3vac.
Everything look OK?
Swap in the new recitfier. Everything still OK?
Swap in new power tubes. Everything still OK?
Ken
brookgannon
Junior tube assistant
Posts: 57
(3/27/04 6:56 pm)
Re: Bias problems in a Deluxe Reverb
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I found the problem using ken's method which is very logical. Somethings up with the new recto tube. Thanks Brook
brookgannon
Junior tube assistant
Posts: 58
(3/28/04 11:17 pm)
Re: Bias problems in a Deluxe Reverb
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The final numbers on this amp are 440V B+ at 22mA. My amp does not seem to break up as nicely. I have been daily playing the amp with the previous tube set for 2 years. I felt my amp was sounding tired so I decided to retube. Is this lack of breakup due to the "newness" of the tubes, the different bias setting (alhough I have used the same bias calculation method), or "no tubes alike" I should not expect the same sonic caracteristics, or what? Thanks Brook
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