EH 6v6's in a JTM45?
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Ledvedder5150
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EH 6v6's in a JTM45?
I'm building a JTM45. Well technically a Dirty Shirley, but the power section is a JTM45. I'm ready to power it up, but the 5881 tubes that I ordered won't arrive until late this week. I've gone through all the initial testing with the GZ34 rectifier tube and 3 preamp tubes installed. It's reading around 457v on the plate pins. Can I run a pair of EH 6v6's in it temporarily until the 5881's arrive?
Last edited by Ledvedder5150 on Mon Dec 18, 2023 2:03 pm, edited 1 time in total.
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Stevem
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Re: EH 6v6's in a JTM45?
Yes you can just to fire it up and play a bit on, but that plate voltage seen on pin 3 of the output tubes seems low to me at least in regards to a true jtm45, and especially with no output tubes drawing current.
If the amp has a bias adjustment then before you slap in the 6V6s be sure to set the negative voltage on pin 5 to the highest you can get.
You should not have to idle the outputs at more then .022 Amp to get a fat tone out of the amp.
If the amp has a bias adjustment then before you slap in the 6V6s be sure to set the negative voltage on pin 5 to the highest you can get.
You should not have to idle the outputs at more then .022 Amp to get a fat tone out of the amp.
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Ledvedder5150
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Re: EH 6v6's in a JTM45?
Sorry, I meant 457v.
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martin manning
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Re: EH 6v6's in a JTM45?
You should be ok. The B+ will drop with the current draw. Just bias them conservatively. What primary impedance do you have?
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Ledvedder5150
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Re: EH 6v6's in a JTM45?
Primary impedance is 6k6. What about EL34's?martin manning wrote: ↑Mon Dec 18, 2023 2:46 pm You should be ok. The B+ will drop with the current draw. Just bias them conservatively. What primary impedance do you have?
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Stevem
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Re: EH 6v6's in a JTM45?
Well not likely since your power transformer will need to supply 1.200 more amps of heater current since a 5881 pulls .900 amps and a 34 needs 1.500 amps.
Also pin 1 needs to be jumped to to pin 8 and a 34 will need about 8 volts less bias voltage which may be out of range of your bias pot without changing a resistor or 2 to sink more voltage.
Also pin 1 needs to be jumped to to pin 8 and a 34 will need about 8 volts less bias voltage which may be out of range of your bias pot without changing a resistor or 2 to sink more voltage.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Ledvedder5150
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Re: EH 6v6's in a JTM45?
Yeah, I figured that. I'm just anxious to get it up and running. But I'll have to wait for the 5881's to arrive.Stevem wrote: ↑Mon Dec 18, 2023 5:02 pm Well not likely since your power transformer will need to supply 1.200 more amps of heater current since a 5881 pulls .900 amps and a 34 needs 1.500 amps.
Also pin 1 needs to be jumped to to pin 8 and a 34 will need about 8 volts less bias voltage which may be out of range of your bias pot without changing a resistor or 2 to sink more voltage.
What do you mean by "jumper pin 1 to pin 8"? I have a 1r resistor across those pins to ground.
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Re: EH 6v6's in a JTM45?
Pin 1 in an EL34 is internally connected to the suppressor grid and must be grounded. Pin 1 on a 5881 or any other 6L6-type tube usually has no connection, so if your 1 and 8 socket pins are jumped, then an EL34 would be fine except for current draw limitations on your PT.Ledvedder5150 wrote: ↑Mon Dec 18, 2023 5:07 pmYeah, I figured that. I'm just anxious to get it up and running. But I'll have to wait for the 5881's to arrive.Stevem wrote: ↑Mon Dec 18, 2023 5:02 pm Well not likely since your power transformer will need to supply 1.200 more amps of heater current since a 5881 pulls .900 amps and a 34 needs 1.500 amps.
Also pin 1 needs to be jumped to to pin 8 and a 34 will need about 8 volts less bias voltage which may be out of range of your bias pot without changing a resistor or 2 to sink more voltage.
What do you mean by "jumper pin 1 to pin 8"? I have a 1r resistor across those pins to ground.
Just plug it in, man.
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sluckey
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Re: EH 6v6's in a JTM45?
That's fine if pin 1 is connected to ground.Ledvedder5150 wrote: ↑Mon Dec 18, 2023 5:07 pm What do you mean by "jumper pin 1 to pin 8"? I have a 1r resistor across those pins to ground.