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Old 20th October 2002, 04:26 AM   #1
SHiFTY is offline SHiFTY  New Zealand
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Exclamation Using 866A Mercury Vapour Rectifiers?

I am considering using a couple of 866A rectifiers in my next project (probably a transmitting tube amp.). These monsters use mercury vapour, and are rated up to 5000V. I will probably run them at ~800V and 200mA, not too huge. The main reason I want to use them is because I have access to a large store of dirt cheap NOS ones, and I like the blue glow! (check this pic: 866A in operation )

Has anyone had any experience using them? From what I understand, in normal use they need to be preheated for about 1 minute before B+ is applied, and if they have not been used for a while, they should be heated for several hours.

I am not too worried about mercury getting loose, or the small amount of UV that might be generated. I live in New Zealand, so the Springtime ozone hole that covers us means lots of UV anyway!!

What I would like to know is: do they generate a lot of heat, do they create a lot of switching noise, and has anyone successfully used them with a CLC filter? I was thinking around 2uF for the first cap. I could use LCLC if necessary, but it lowers the B+.

Thanx
~ShiFtY~
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Old 20th October 2002, 06:32 AM   #2
Colt45 is offline Colt45  Serbia
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theyre rated for 10kV actually!

they look much cooler in real life :-)

but there are problems:
overkill, suck up alot of heater current.

CLC isnt much of an option.. they like choke input. ( i think if you do do it CLC, the first cap has to be <1F ).

I'm not sure how much of the UV the glass filters out, but it can't be too good for your eyes.

ill attatch a pic if i can find it..

OK! heres a picture of a british 866AX on my hickok... (pardon the crappy digicam)
Click the image to open in full size.
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Old 20th October 2002, 07:23 AM   #3
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Don't know much about them. Have a couple dead ones. The mercury scares me. Josh Stippich uses them in his amp and they do look cool.

Some pictures

Click the image to open in full size.

dave
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Old 21st October 2002, 12:46 AM   #4
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Default Freddy Mercury Valves

Hello,

IMHO this series of rectifiers are very noisy devices.
They were designed for industrial usage and I wouldn't use them in any audio application.
Moreover,and this goes for any rectifier valve when used way below their intended design use, they tend to be even more noisy and unpredictable in behaviour in such apps.
I hear a lot of people using TV damper tubes as common HT rectifiers in cicuits using 300 to 500 B+ and noticing funny noises and tubes turning belly up.
This is to be expected.
So unless you use these at their intended voltages and adhere to their ratings I would advise against them.
If you must use these go for a LC filter,not CLC and use a big choke to isolate the rectifiers from the rest of the circuit.

Just my 2 Eurocents worth,
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Old 21st October 2002, 01:55 AM   #5
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Default Re: Freddy Mercury Valves

Quote:
Originally posted by fdegrove
Hello,

IMHO this series of rectifiers are very noisy devices.
They were designed for industrial usage and I wouldn't use them in any audio application.
I agree, but my information is anecdotal. I have a few but haven't used them yet (no need). Reports are that they can be noisy, and are a PITA to use, even though they look very cool. They are very low impedance though.
Quote:
Moreover,and this goes for any rectifier valve when used way below their intended design use, they tend to be even more noisy and unpredictable in behaviour in such apps.
I hear a lot of people using TV damper tubes as common HT rectifiers in cicuits using 300 to 500 B+ and noticing funny noises and tubes turning belly up.
This is to be expected..
Huh? The damper diodes I've used are <i>very,very</i> quiet and have given no greif so far. They're a heck of a lot tougher than things like 5AR4 etc, cheap too. However, I never load them less than 100mA or so.
Quote:
So unless you use these at their intended voltages and adhere to their ratings I would advise against them.
If you must use these go for a LC filter,not CLC and use a big choke to isolate the rectifiers from the rest of the circuit.
Yep. But PSU's always sound better with a LC supply rather than a CLC.

TTFN

PS: Try a 5C8S for rectifier with transmitting triode amps. Easier.
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Old 21st October 2002, 02:25 AM   #6
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Default TV dampers

Hi,

Ok Brett ,if you know what you're doing,then fine.

The info I shared is from sleeping whith the RCA secretaries.
You can call that anecdotal for sure.

The Freddy M. tubes' low internal impedance is something of little importance to me.Not necessarily a blessing.
I always try to depend on very good PSU regulation where called for so that I do not depend on the capabilties of transformer and rectifiers to respond immediately to current demands.

Seriously,I see a lot of people toying with tubes having read page one of the books and then complaining afterwards that things don't seem to turn out what they expected.

As a general rule of thumb a tube is designed for a certain job and logic has it that when it can do more it can do less,right?
Well,with tubes this just doesn't hold up:there are working points that need to be respected or results can be unpredictable.
Sometimes you can get away with it,other times you face Mr.Murphy.
Pretty soon you'll have someone using thyratrons to fire up their B+....

It was meant as a cautionary note.

See you,

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Old 21st October 2002, 02:37 AM   #7
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Default Re: Using 866A Mercury Vapour Rectifiers?

Quote:
Originally posted by ShiFtY
What I would like to know is: do they generate a lot of heat? <snip> Thanx
~ShiFtY~
I think they have a constant voltage drop of about 15 volts so not as much anode dissipation as a vacuum rectifier for a given current. I've heard they are very noisy too. Big ones were installed in metal cages probably for RF shielding as well as safety.

GP.
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Old 21st October 2002, 02:42 AM   #8
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Default FM

GP,

10/10

Absolutely correct on all counts.

Regards,
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Old 21st October 2002, 02:59 AM   #9
richt is offline richt  Puerto Rico
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salute guys

an opinion that can help !



recently in my audio preamp, i tried a lot of different rects.

normal/fast recovery/hexfreds & then i decided to use a tube
rectifier.
i pulled out an old 5u4 & wired up to my preamp and the improvment was so huge i could not believe.

i learned that solid states rects are very noisy specially hexfreds.

so guys i consider that tube rect is the best option for diy
(at least on preamps)

i have a question.

on this design i have a pi type ( cap+resistor+cap)

on one of the posts says that eliminating the first cap
sonds better or performs better, why??/

thanks
richt
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Old 21st October 2002, 03:00 AM   #10
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Default Re: Re: Using 866A Mercury Vapour Rectifiers?

Quote:
Originally posted by Circlotron
Big ones were installed in metal cages probably for RF shielding as well as safety.
Great,

I have some huge trannys that are specifically for the 866A, so I've thought about powering up the dozen 866As I have in front of a rotisserie, and cookin' me some audiophile grade chickens.
Hmmmm, so sweet in the middle.
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