Hi guys,
I'm wondering about a very simple hi-fi amp.
It's a direct coupled concertina feeding a pair of cathode biased EL34.
The concertina plus self balancing PA idea comes from a compressor repair I did time ago, where balancing the circuit greatly improved dynamics, breath and bandwidth of the equipment.
Next step will be the OT.
Anyway, to balance both sides of the PA I need to use cathode biasing, and to optimise the dynamics of the PI I need around 420 V on it (plus elevated heaters, for the 12ax7 and the EL34s too). I would like to go around 450 V on screens and 650 V on plates.
Anyone has ever used cathode biasing with such high voltages?
Any reccomandation?
Thank you all in advance,
Roberto
How far can I go with B+ in cathode biasing?
Moderators: pompeiisneaks, Colossal
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Stevem
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Re: How far can I go with B+ in cathode biasing?
The tube spec's call for a OT of 3400, a plate voltage of 355 with a 375 supply, a common cathode resistor of 130 ohms and a signal drive voltage of 21 volts rms.
This will provide 35 watts.
This will provide 35 watts.
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: How far can I go with B+ in cathode biasing?
Yes, that's what datasheets say.
I'm looking for people who experienced a bit around this topic with cathode biasing and high voltages.
I'm looking for people who experienced a bit around this topic with cathode biasing and high voltages.
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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: How far can I go with B+ in cathode biasing?
Why are you hung up on it being cathode biased, just for a simpler build?
Also I do not understand why you want to push the build, 35 watts is not enough for what you have in mind?
It may interest you to do one of the free downloads for the RCA rc-30 tube manual, as near the back of it they have 3 really nice power amp builds to check out!
Also I do not understand why you want to push the build, 35 watts is not enough for what you have in mind?
It may interest you to do one of the free downloads for the RCA rc-30 tube manual, as near the back of it they have 3 really nice power amp builds to check out!
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: How far can I go with B+ in cathode biasing?
Not exactly.
I would like to go with the Blumlein configuration with some slight modifications to it.
[img:374:436]http://www.tubecad.com/2005/May/21/Blum ... ircuit.png[/img]
I would like to go with the Blumlein configuration with some slight modifications to it.
[img:374:436]http://www.tubecad.com/2005/May/21/Blum ... ircuit.png[/img]
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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: How far can I go with B+ in cathode biasing?
Well once again according to the tube chart 34's in Triode form will be happy at 400 volts with a 5K OT, so that's not pushing it?
If you are going thru the trouble of biasing each tube seperate then I would make 100 ohms of each 200 ohm resistor adjustable !
If you are going thru the trouble of biasing each tube seperate then I would make 100 ohms of each 200 ohm resistor adjustable !
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: How far can I go with B+ in cathode biasing?
In fact this is 370V as far as the tube knows.
I want to have direct information from someone who did experiments just because I don't use 12ax7s at 100k 1k5 and 250V.
I want to have direct information from someone who did experiments just because I don't use 12ax7s at 100k 1k5 and 250V.