Hi,
I´m about to rebuild an old PC86/6AV5GA SE amp to use more commonly available tubes like EF86 and 6L6GB/C/whatever. The raw B+ is around 400V during startup and I want to replace the messy Mosfet capacitance multiplier in the PSU with a simple choke. Adding an IDH tube rectifier to get delayed B+ is unfortunately not an option.
I'm sure the output tubes can handle 400V without any stress but I'm a little nervous about EF86 in triode connection.
I'm planning to sell the amp so I want it to be quite reliable.
Best regards,
Daniel
I´m about to rebuild an old PC86/6AV5GA SE amp to use more commonly available tubes like EF86 and 6L6GB/C/whatever. The raw B+ is around 400V during startup and I want to replace the messy Mosfet capacitance multiplier in the PSU with a simple choke. Adding an IDH tube rectifier to get delayed B+ is unfortunately not an option.
I'm sure the output tubes can handle 400V without any stress but I'm a little nervous about EF86 in triode connection.
I'm planning to sell the amp so I want it to be quite reliable.
Best regards,
Daniel
Surely they do not see the full 400V? More likely 200V on the tube and 200V on a plate resistor? (It is hard to talk about an invisible circuit.)
As for "startup":
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They will see the full voltage when cold, but as you show in the datasheet, Vao and Vg2o is 550V. Pretty safe.
Fuling,
Drawing a schematic and posting it takes work.
But a schematic is worth 1,000 words of description and writing questions and answers.
There may be a very simple solution to your problem, but we may never know without a schematic.
"Blindfolded Archer tries to hit the target"
Having your own amplifier fail in your possession is one thing;
Selling an amplifier and having it fail elsewhere is another thing.
Drawing a schematic and posting it takes work.
But a schematic is worth 1,000 words of description and writing questions and answers.
There may be a very simple solution to your problem, but we may never know without a schematic.
"Blindfolded Archer tries to hit the target"
Having your own amplifier fail in your possession is one thing;
Selling an amplifier and having it fail elsewhere is another thing.
Ah, please let me elaborate a bit, I posted the question just before bedtime after a long day and it seems it came out a bit confused and laconic:
This project started some fifteen years ago when my brother asked me to build a tube amp for him. That resulted in a fairly nice E-linear amp with E280F input tubes, 807 power tubes, Edcor 5k/8R OPTs and an AnTek 300VAC mains transformer.
After my brother had kids the amp was returned to me (kids and tubes with top caps, not the best combo).
For some reason I decided to gut the whole thing and rebuild it with PC86 inputs and Sylvania 6AV5GA output tubes. I think the Mosfet cap multiplier was added at this point. The amp never saw much use, probably because of a slight hum that I never bothered to fix.
Recently, someone at a local forum wanted to buy a small tube amp to drive some fullrange speakers with. I came to think about this amp and contacted the guy. Last night I put the amp on the bench to see if I could locate the source of the hum and it struck me: the whole inside is a bloody mess.
I quit drinking a couple of years ago but this rebuild was done before that, probably with the soldering iron in one hand and a beer in the other...🤐
The chassis, transformers, tube sockets and contacts are all fine though, and after taking a good look I decided the best thing I can do is probably to tear everything out and rebuild the whole circuit once again. Since the amp is up for sale I want to get rid of the oddball tubes at the same time (Good luck finding 6AV5GA in Europe) and replace them with a tube lineup that is still available.
Re. schematics, I don't have one for the amp as it is. As for the upcoming version, just visualise a basic SE topology with a triode wired EF86 RC coupled to a cathode biased 6L6 (probably Ultra-Linear with cathode feedback) and a simple 300VAC - bridge rectifier- CLC filter PSU.
In short, the question was if EF86 will be able to handle 400V on plate and G2 during startup. That question was kindly answered by PRR above if Vao and Vg2o means what I think it means?
Best regards,
Daniel
This project started some fifteen years ago when my brother asked me to build a tube amp for him. That resulted in a fairly nice E-linear amp with E280F input tubes, 807 power tubes, Edcor 5k/8R OPTs and an AnTek 300VAC mains transformer.
After my brother had kids the amp was returned to me (kids and tubes with top caps, not the best combo).
For some reason I decided to gut the whole thing and rebuild it with PC86 inputs and Sylvania 6AV5GA output tubes. I think the Mosfet cap multiplier was added at this point. The amp never saw much use, probably because of a slight hum that I never bothered to fix.
Recently, someone at a local forum wanted to buy a small tube amp to drive some fullrange speakers with. I came to think about this amp and contacted the guy. Last night I put the amp on the bench to see if I could locate the source of the hum and it struck me: the whole inside is a bloody mess.
I quit drinking a couple of years ago but this rebuild was done before that, probably with the soldering iron in one hand and a beer in the other...🤐
The chassis, transformers, tube sockets and contacts are all fine though, and after taking a good look I decided the best thing I can do is probably to tear everything out and rebuild the whole circuit once again. Since the amp is up for sale I want to get rid of the oddball tubes at the same time (Good luck finding 6AV5GA in Europe) and replace them with a tube lineup that is still available.
Re. schematics, I don't have one for the amp as it is. As for the upcoming version, just visualise a basic SE topology with a triode wired EF86 RC coupled to a cathode biased 6L6 (probably Ultra-Linear with cathode feedback) and a simple 300VAC - bridge rectifier- CLC filter PSU.
In short, the question was if EF86 will be able to handle 400V on plate and G2 during startup. That question was kindly answered by PRR above if Vao and Vg2o means what I think it means?
Best regards,
Daniel
Excellent, that was the answer I needed.
Thanks for your input guys, I'll post a picture later on!
Thanks for your input guys, I'll post a picture later on!
