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Mercury rectifier tube selection

post #1 of 15
2/17/10 at 10:40pm
Thread Starter 
I am trying to get a sense for what tubes are the ones to look out for sound- and quality- wise. I am interested in building a linestage PSU with mercury vapor rectifiers. It looks like 81/82/83 - series tubes, and 866A are available. I am not sure what else people have been using and like. It seems most will be more voltage than I need, and I will end up throwing some away.

Any input appreciated. Perhaps Frank and Al/pabbi1 and any others can share some experience?

thanks
serge

Also I am aware of the inherent dangers of Mercury - it is a toxic substance that is a calamity to clean up due to its physical form. I would like to keep this discussion focused on build experiences though, thanks for your understanding.
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post #2 of 15
2/17/10 at 10:47pm
I *considered* using some (which I'm now selling, with sockets, etc) because it is beyond me. Pete used them here, and I know Frank is fond of them as well.
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post #3 of 15
2/18/10 at 12:58am
Al is right, I am a big fan of mercury rectifiers. It's a big part of the sound of my amps. Subjectively, they impart a big, bold, dynamic sound to an amp. Sort of like a shot of nitrous oxide to a "big block" V-8. Most engineering types would probably ascribe this to the regulatory effect achieved by their low fixed voltage drop regardless of current demand. Probably true, but whatever the case, once you try them you won't want to build without them. Implementation is a pain in the ass. You have to pre-heat them and then you usually need some sort of soft start mechanism because they turn on hard. It's also difficult to find pairs that behave in exactly the same manner. You'll need 6 or 8 to get a decent matched pair. Still, well worth it. My wife, who's normally ambivalent about such things, can immediately tell if an amp has mercury rectifiers.

Common types are the 83, 816 (miniature 866 with a plate cap), 866jr ( my favorite-no plate cap and a killer blue glow) the 866, which was the standard industrial rectifier of the '30's and '40's. And if you really want to go totally nuts, check out the 872.

Please remember, there are considerable, and to many people insurmountable, safety issues involved in the use of these tubes. Definitely not for the beginner or even the average diy type.
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post #4 of 15
2/18/10 at 1:18am
Quote:
Originally Posted by FrankCooter View Post
Please remember, there are considerable, and to many people insurmountable, safety issues involved in the use of these tubes. Definitely not for the beginner or even the average diy type.
I was smart enough to realize this, and think a solution has been found...
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post #5 of 15
2/18/10 at 4:50am
Thread Starter 
Thanks Frank. So the 866 is a decent starting point? One thing that was attractive about the 83 is that it is a full wave rectifier (in contrast with the 866 which is a half wave I believe), so I assume it doesn't require as close matching, just channel matching.

I had in mind either a relay, or a simple dual start switch with a timer/safety light for the startup delay.
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post #6 of 15
2/18/10 at 10:58am
Certainly a CL6(0) is in there somewhere?
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post #7 of 15
2/18/10 at 1:33pm
Quote:
Originally Posted by sergery View Post
So the 866 is a decent starting point?
As a side note, Morgan Jones writes that if you use the 866, you need a bleeder resistor across the output of the rectifier that'll draw 10% of the full load current.
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post #8 of 15
2/18/10 at 2:11pm
The 83 would probably be the most practical merc. for a preamp. It's the physically smallest, is full wave, and has a reasonable filament current. Only downside is you won't get much of a "light show". In a preamp, you could simply manually sequence a pair of start switches and then turn on your power amp later. A timing relay would be a better idea and would add a safety factor against accidental premature power up. As far as I can tell,sonics are the same in all of them. Choke input filters are a must.

The amp I'm bringing to the NorCal meet has uses 4 866jr's in the power supply. You're welcome to come check it out.

Timjo's mention of a hefty bleeder resistor is a good idea. These things need a bit of current draw to kick on.
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post #9 of 15
2/18/10 at 2:23pm
Quote:
Originally Posted by sergery View Post
It looks like 81/82/83 - series tubes, and 866A are available.
Also I am aware of the inherent dangers of Mercury - it is a toxic substance that is a calamity to clean up due to its physical form. I would like to keep this discussion focused on build experiences though, thanks for your understanding.
Correction - 81 (half wave) is not a MV tube - Gorgeous tube though - looks like a 50 - huge voltage drop unlike MV's.
I always used a separate filament supply for them and gave it 30s or so warm up before PT power up. Longer if not used in long durations.
I have heard issues of high frequency harshness but have not experienced myself. If an issue, it is fixed with high current and very low DCR chokes in series with the filaments.
All this is explained in the RCA Radiotron Manuals.
I have never heard of a MV breaking during operation - the biggest concern. If it broke on carpet, replace carpet and do not vacuum. On hardwood, it would clean right up.
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post #10 of 15
2/18/10 at 2:24pm
Quote:
Originally Posted by FrankCooter View Post
The 83 would probably be the most practical merc. for a preamp. It's the physically smallest, is full wave, and has a reasonable filament current.
You mean 82.
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post #11 of 15
2/18/10 at 3:39pm
Quote:
Originally Posted by macm75 View Post
You mean 82.
Actually I did mean the 83. The 82 and the 83 are the same tube. 82 has a 2.5v filament, 83 has a 5v filament.

Your right about the 81 however. I've used these too. The 81 is a half wave version of the 80, which is basically a 4 pin 5y3. Too much voltage drop for my tastes, but those old huge globes are definitely "eye candy".
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post #12 of 15
2/18/10 at 4:58pm
Quote:
Originally Posted by FrankCooter View Post
Actually I did mean the 83. The 82 and the 83 are the same tube. 82 has a 2.5v filament, 83 has a 5v filament.

Your right about the 81 however. I've used these too. The 81 is a half wave version of the 80, which is basically a 4 pin 5y3. Too much voltage drop for my tastes, but those old huge globes are definitely "eye candy".
Voltage wise correct but not current capability. The 83 can handle double an 82. That is why I thought you meant 82 (for preamp as opposed to power amp) - sorry for specifying "you mean".
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post #13 of 15
2/18/10 at 6:27pm
Thread Starter 
Quote:
Originally Posted by TimJo View Post
As a side note, Morgan Jones writes that if you use the 866, you need a bleeder resistor across the output of the rectifier that'll draw 10% of the full load current.
Good suggestion. I will plan to use some sort of constant current dissipation power resistor to keep the MV rectifiers loaded.

Quote:
Originally Posted by FrankCooter View Post
The 83 would probably be the most practical merc. for a preamp. It's the physically smallest, is full wave, and has a reasonable filament current. Only downside is you won't get much of a "light show". In a preamp, you could simply manually sequence a pair of start switches and then turn on your power amp later. A timing relay would be a better idea and would add a safety factor against accidental premature power up.
Perhaps a combo for maximum safety, I think that might be the way to go, with a display light and an turn-key 'ignition'.
Quote:
Originally Posted by FrankCooter
As far as I can tell,sonics are the same in all of them. Choke input filters are a must.
Good to know about sonics, I know tubes can vary a lot in in sound quality, so nice to feel confident in my choice. Ok, sounds like the 83 is a safe bet - bummer about the light show, but I suppose a large enough 'bleeder' resistor would take care of this.

Quote:
Originally Posted by FrankCooter
The amp I'm bringing to the NorCal meet has uses 4 866jr's in the power supply. You're welcome to come check it out.

Timjo's mention of a hefty bleeder resistor is a good idea. These things need a bit of current draw to kick on.
Love to, much obliged

Quote:
Originally Posted by macm75 View Post
Correction - 81 (half wave) is not a MV tube - Gorgeous tube though - looks like a 50 - huge voltage drop unlike MV's.
I always used a separate filament supply for them and gave it 30s or so warm up before PT power up. Longer if not used in long durations.
I have heard issues of high frequency harshness but have not experienced myself. If an issue, it is fixed with high current and very low DCR chokes in series with the filaments.
All this is explained in the RCA Radiotron Manuals.
I have never heard of a MV breaking during operation - the biggest concern. If it broke on carpet, replace carpet and do not vacuum. On hardwood, it would clean right up.
So even the filament supply should be LCR filtered? I have started choke shopping for the mains supply, I intend something normal around 5-20H (depends what I can get a deal on). Do I need to go crazy here too or can I use a uH impedence choke? I will look up the manual you mention later tonight.

Also I was considering building a faraday cage around the MV rec out of a cylinder of screen - I know they need ventilation. It will kill the aesthetics, but I imagine it should provide a really clean EM environment. Then again if you guys all use them naked and feel they are pretty clean, maybe it isn't needed.

Thanks for all the info!

serge
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post #14 of 15
2/18/10 at 7:01pm
I'd consider an 82 or 83 a great light show :-) But maybe not this (from the MV king)...
hifi heroin blog.: Field Coil Supply...
On the rare side but you can get 82's in globe too - just a little more interesting than the ST's.
Filament supply MIGHT need a RF inductor to reduce RF hash - ~100uH, 5A - little buggers - Mouser - JW Miller. See what it sounds like w/o. I've tried them with and without and heard no difference - maybe inaudible with my single drivers. I've only read cases that required it - mentioned as a just in case.
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post #15 of 15
2/19/10 at 12:17am
Quote:
Originally Posted by macm75 View Post
Filament supply MIGHT need a RF inductor to reduce RF hash - ~100uH, 5A - l
I've never had any "hash" problems either and I run them bare-ass naked. Any stray RF is going to be WAY outside the audio band. Perhaps if the guy in the next apartment is watching analog tv with a pair of rabbit ears it might be an issue, otherwise I wouldn't worry about it. Only filament supply you need is a center tapped transformer of the appropriate voltage/current ratings.
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