Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mehfuzhoss on August 16, 2021, 11:22:52 pm
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Hello Sir,
I put new 6v6GT in the amp. The bias current is 50ma per tube and the bias pot is at minimum position.
What should I do?
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turn the pot clockwise to add resistance in order to drop the bias current.
let us know the minimum current value (mA) that you can achieve with your current circuit configuration.
50ma is too high for 6V6s.
what is your plate voltage?
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Bias milliamps reding is only usefull if you know plate voltage.
With 50 ma your plate voltage must not be over 200 volts, I guess is much over that, close to 400 ?
And close to 400 volts bias must be 20ma
At 50 ma at 200 volts it is 70 % power dissipation. I like bias close to 60% not 70%
Your power tubes may have a short inside to have so much current. Try know good tube.
https://www.tedweber.com/bias-calc/
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Hello Sir,
I put new 6v6GT in the amp. The bias current is 50ma per tube and the bias pot is at minimum position.
What should I do?
What happened when you read the install instructions for that board?
https://el34world.com/schematics.htm#Hoffman_Plexi_6V6
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Hello Sir,
I put new 6v6GT in the amp. The bias current is 50ma per tube and the bias pot is at minimum position.
What should I do?
Is this the first time you turn the amp on?
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Plate voltage 400
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Is this the same amp you asked about in May?
https://el34world.com/Forum/index.php?topic=27537.msg302492#msg302492
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yes sluckey. I liked the amp a lot and had a duet mesa boogie 6v6 in it and i was able to set the bias current to 27mv. I recently built a dlite 22 and took out the power tubes to test it. now the mesa 6v6 duets are in the d'lite.
i bought brand new Groove Tube 6v6GT from local music store and put it in. the bias reading was showing 250mv and I turned the bias pot all way to minimum and currently the reading is 50mv. I left the amp aside for now.
I read that these 6v6GT can handle upto 70mv maximum, but I would like to keep it under 30mv.
please advise.
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yes sluckey. I liked the amp a lot and had a duet mesa boogie 6v6 in it and i was able to set the bias current to 27mv. I recently built a dlite 22 and took out the power tubes to test it. now the mesa 6v6 duets are in the d'lite.
i bought brand new Groove Tube 6v6GT from local music store and put it in. the bias reading was showing 250mv and I turned the bias pot all way to minimum and currently the reading is 50mv. I left the amp aside for now.
I read that these 6v6GT can handle upto 70mv maximum, but I would like to keep it under 30mv.
please advise.
I posted the link to the install instructions
Did you read the section on how to bias the amp?
All the info is there on how to adjust or modify the bias section
Did you read the instructions?
https://el34world.com/Hoffman/instructions.htm (https://el34world.com/Hoffman/instructions.htm)
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I read that these 6v6GT can handle upto 70mv maximum, but I would like to keep it under 30mv.
please advise.
Wrong, you don't understand what are bias.
6V6 GT can handle 12 watts, that is only you need to know first
Reading plate voltage are a must . Let say for 300 volts plate voltage and for a tube dissipation at 60% ( don't go over 70% in Class AB amp )
If you read 70 mv ( ma )
Power = 70 mv (ma ) X 300 volts =21 watts !!!!!! for a 12 watts tube :BangHead:
You will blow you tube
12 watts X 70% = 8,4 watts. at 300 volts you must read close to 27 mv ( ma
At 400 volts Plate voltage, don't go over 21 mv (ma)
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yes sluckey. I liked the amp a lot and had a duet mesa boogie 6v6 in it and i was able to set the bias current to 27mv. I recently built a dlite 22 and took out the power tubes to test it. now the mesa 6v6 duets are in the d'lite.
i bought brand new Groove Tube 6v6GT from local music store and put it in. the bias reading was showing 250mv and I turned the bias pot all way to minimum and currently the reading is 50mv. I left the amp aside for now.
I read that these 6v6GT can handle upto 70mv maximum, but I would like to keep it under 30mv.
please advise.
Put the mesa 6v6s back in the plexi amp and re-bias. Return the Groove Tube 6V6s to the local music store. Buy another set of 6V6s for your d'lite from an online electronics store.
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Plate voltage 400
(14/400) * .7 = 25mA. set bias around 22-25mA and you should be good to go.
PD for 6V6 = 14w.
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After setting bias first time ,check plate voltage it may change and re adjust bias with this new plate voltage.