261 is DC resistance. Impedance should be ~8k ohms for a 6V6. Have a look at single-ended output stage load lines here: https://www.valvewizard.co.uk/se.html
Bias pot instead of cathode fixed bias
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martin manning
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Re: Bias pot instead of cathode fixed bias
Re: Bias pot instead of cathode fixed bias
The article that Phil_S posted got me thinking,
When one of the EH 6V6s in my Benson Monarch failed I replaced them with some JJs which were notably quieter for a given clean volume setting.
I've since put some NOS 6V6's in and the volume is restored.
If the JJs were passing more current then the cathode voltage would be higher, would that explain the difference?
I know it would be simple to go back and test, the EH's dropped 20V across the 250 Ohm shared cathode resistor.
Craig
When one of the EH 6V6s in my Benson Monarch failed I replaced them with some JJs which were notably quieter for a given clean volume setting.
I've since put some NOS 6V6's in and the volume is restored.
If the JJs were passing more current then the cathode voltage would be higher, would that explain the difference?
I know it would be simple to go back and test, the EH's dropped 20V across the 250 Ohm shared cathode resistor.
Craig
Thinking about my second build.
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Stevem
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Re: Bias pot instead of cathode fixed bias
The second 1.5k on the 12ax7 is the one to mess with.
This stage controls how much of the audio signal level is recovered after the loss of passing thru the tone controls.
This stage controls how much of the audio signal level is recovered after the loss of passing thru the tone controls.
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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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Bias pot instead of cathode fixed bias
In terms of the bias voltage on pin 8 of the output tubes, the higher the voltage seen, then in terms of volume the more balls the amp will have.
The JJs are a bit of a cross between a 6V6 and a 6l6 and tend to sound more reserved in a class A SE amp like a champ.
You can bias it a little hotter, but you risk burning up the small OT in these amps.
The JJs are a bit of a cross between a 6V6 and a 6l6 and tend to sound more reserved in a class A SE amp like a champ.
You can bias it a little hotter, but you risk burning up the small OT in these amps.
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!
Re: Bias pot instead of cathode fixed bias
Wow that is a lot to read and hopefully learn, thank you very much.martin manning wrote: ↑Sat Jan 07, 2023 11:14 am261 is DC resistance. Impedance should be ~8k ohms for a 6V6. Have a look at single-ended output stage load lines here: https://www.valvewizard.co.uk/se.html