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Old 30th June 2010, 05:01 PM   #1
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Default Looking for a 866a powersupply schematic

Id like to add a MV rectifier circuit, to a current project involving "large" tubes, I have not found a good MV rectifier circuit yet, that breaks down the proper usage of 2 or more pairs of the 866's!



Thanks in advanced.
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Old 30th June 2010, 05:24 PM   #2
kevinkr is offline kevinkr  United States
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Given these contain mercury, and may emit significant levels of UV depending on the envelope glass (hint: avoid quartz glass) it might be wise to avoid these.

There is plenty of information on the web about the 866A and its application.

They need at least a 1 minute warm up before the application of voltage to the plates.

When first placed in operation should be preheated for 15 - 30 minutes or so to assure that there is no liquid mercury anywhere that could result in a short or arcing damage to the filament.

When moved should be preheated for the same time and for the same reasons as mentioned above.

Should always be operated in a vertical orientation to prevent shorts...

Generate lots of RF hash if not filtered and shielded correctly.

Typically have forward drops of 15V or so in operation, and can deliver relatively high currents.

Do not like large input capacitors and are often used with choke input supplies.

Not sure about the advisability of using pairs in parallel.. I would use the higher current rated 872 instead..

I have never seen them used anywhere in parallel, there could be a reason for this, but I suspect that adding small series resistor would assure that they share current properly. A single pair of 866 in the right circuit can provide 0.5 amp of dc current at any voltage under 2500V so I can't imagine what you are powering that needs more current than this..

Are a potential eco disaster if the mercury gets out due to breakage.

Emit UV that may not be fully filtered out depending on the glass envelope. In close proximity this can cause burns and retinal damage.

I've decided not to use these for them in my latest GM70 amp design where technically they make sense for all of the above listed reasons.

http://www.mif.pg.gda.pl/homepages/f...049/8/866A.pdf

http://www.mif.pg.gda.pl/homepages/f...081/8/866A.pdf (Note typo in 872A portion of data sheet: piv is actually ~10KV, not 1000V as stated)

http://www.uli.de/tubes/83.htm

.
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Last edited by kevinkr; 30th June 2010 at 05:38 PM.
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Old 26th July 2010, 11:20 PM   #3
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Thanks again, I got the 2 tube version up and running, kinda....



I'm torn between a decent filtering cap, and a 5h 150ma choke More testing will insure proper application.


Plus plenty of feedback from this forum cant help
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Old 27th July 2010, 02:26 AM   #4
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The 3B28 is a drop in replacement for the 866A without the mercury. Far less RF noise too. It uses Xenon gas instead of mercury. The voltage drop is slightly higher, and the glow is a very pale purple instead of bright blue.
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Old 27th July 2010, 03:13 AM   #5
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How are the 3B28's for availability?


<3 the 833 amp you did.
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Old 27th July 2010, 01:57 PM   #6
jlsem is offline jlsem  United States
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They seem more readily available than 866As. The 836 is a high vacuum replacement.

John
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Old 27th July 2010, 05:09 PM   #7
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Quote:
How are the 3B28's for availability?
I have found several at hamfests. I don't buy them unless they are $5 or less. I have 5 or 6 but haven't built anything permanent with them yet.

The 833A amp used a power supply from an old radio transmitter. The rectifier was silicon.

The 845 amp used 5AR4's, 3 of them.
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Old 27th July 2010, 11:36 PM   #8
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by tubelab.com View Post
I have found several at hamfests. I don't buy them unless they are $5 or less. I have 5 or 6 but haven't built anything permanent with them yet.

The 833A amp used a power supply from an old radio transmitter. The rectifier was silicon.

The 845 amp used 5AR4's, 3 of them.
Last MIT hamfest I attended a fellow offered me 7 NOS 3B28 for $5 total.. Guess I should have grabbed them being that I am building a GM70 amp..

I'm not clear on their propensity to emit UV which is why I have not bought any. Have not researched the issue either, lazy me..
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Old 28th July 2010, 04:04 PM   #9
Pyre is offline Pyre  Canada
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Quote:
Originally Posted by 807tubenut View Post
Id like to add a MV rectifier circuit, to a current project involving "large" tubes, I have not found a good MV rectifier circuit yet, that breaks down the proper usage of 2 or more pairs of the 866's!



Thanks in advanced.
Hello,

I took my schematic pretty much from the 866A data sheet and use two per channel on my GM-70 amp. Please heed all of Kevin's advice when using these tubes.

I apologize for my rough drawing I am at work so just quickly drew it out from memory.

Click the image to open in full size.
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Old 28th July 2010, 04:30 PM   #10
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That's just about how Mine is right now, minus the part about your tranny's being labeled wrong, the 2.5vct tranny does not feed the anodes, it feeds the heaters


something tells me 1200vct on the heaters wont work to well.
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