Tweet
Re: JJ or Groove Tubes
According to Roger Crimm with Peavey, EL34L's aren't true EL34's (don't conform to the spec) and Peavey is getting a lot of XXX's in for service because of them. Here is a direct quote from one of Roger's public posts at the Peavey Amp forum:
"I can't speak to what complaints Bob has received, but we have certainly seen more than one customer who has had a problem with that particular tube [the JJ EL34L]. Here is notice once again, just so there is no confusion. Note that this information comes from the company and engineering staff which designed the amp, and not from a tube vendor:
The GT-E34-LS may not operate correctly when using 100 Ohm screen resistors, even though that is the recommended value in the Telefunken manuals. Since the Triple XXX amplifier conforms to this recommendation, this tube is judged unsafe to use in this amp unless the amp is modified.
NOTE: Telefunken is only being mentioned here because they instigated the original and accepted EL34 spec.
These particular Tesla/GT "E34L" parts are only really safe in amps with screen resistors which are larger than what Telefunken recommends for an EL34 design. They are not, in our view, true EL34 parts. They are a newer design made to draw more current and produce more power. The "E34L" name was used universally on these to set them apart from EL34s.
The manufacturer probably assumed that all EL34 guitar amps had large chokes and/or screen resistors to provide screen regulation like many older designs have. It is recommended that any amplifier with 100 Ohm screen resistors using this tube be modified with a larger value resistor (700 to 1K Ohms)."
Having said that, and to get back on your question about biasing the XXX, Peavey couldn't have made it any easier: stick a good meter's leads into the bias jacks on the back of the amp, and turn the knob until your meter reads -55vdc. Again, that is per Roger. If you're going to use EL34s, flip the switch next to the bias knob to "EL34" and the vdc reading should be something like -41vdc (I think, I don't remember, and I don't have EL34s in mine).
My two cents...
Keith
According to Roger Crimm with Peavey, EL34L's aren't true EL34's (don't conform to the spec) and Peavey is getting a lot of XXX's in for service because of them. Here is a direct quote from one of Roger's public posts at the Peavey Amp forum:
"I can't speak to what complaints Bob has received, but we have certainly seen more than one customer who has had a problem with that particular tube [the JJ EL34L]. Here is notice once again, just so there is no confusion. Note that this information comes from the company and engineering staff which designed the amp, and not from a tube vendor:
The GT-E34-LS may not operate correctly when using 100 Ohm screen resistors, even though that is the recommended value in the Telefunken manuals. Since the Triple XXX amplifier conforms to this recommendation, this tube is judged unsafe to use in this amp unless the amp is modified.
NOTE: Telefunken is only being mentioned here because they instigated the original and accepted EL34 spec.
These particular Tesla/GT "E34L" parts are only really safe in amps with screen resistors which are larger than what Telefunken recommends for an EL34 design. They are not, in our view, true EL34 parts. They are a newer design made to draw more current and produce more power. The "E34L" name was used universally on these to set them apart from EL34s.
The manufacturer probably assumed that all EL34 guitar amps had large chokes and/or screen resistors to provide screen regulation like many older designs have. It is recommended that any amplifier with 100 Ohm screen resistors using this tube be modified with a larger value resistor (700 to 1K Ohms)."
Having said that, and to get back on your question about biasing the XXX, Peavey couldn't have made it any easier: stick a good meter's leads into the bias jacks on the back of the amp, and turn the knob until your meter reads -55vdc. Again, that is per Roger. If you're going to use EL34s, flip the switch next to the bias knob to "EL34" and the vdc reading should be something like -41vdc (I think, I don't remember, and I don't have EL34s in mine).
My two cents...
Keith
Comment