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/frank/sheets/049/8/866A.pdf
http://www.mif.pg.gda.pl/homepages/frank/sheets/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
.
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/frank/sheets/049/8/866A.pdf
http://www.mif.pg.gda.pl/homepages/frank/sheets/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 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..
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.
An externally hosted image should be here but it was not working when we last tested it.
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.
HA-HA, you are so right. I will fix that and change the doc on my server so someone does not nuke some tubes.
we have to preserve these 866's, no one else likes them
Just scored a NOS set in the box, RCA 866a's $25 shipped
What kinda amp are you building?
I fixed that schematic, thanks for catching that, doing too many things at once here.
Right now, a ebay 12ax7 preamp (head phone amp for the wife) It's the china PCB they keep calling a "marantz 7c clone" but if you ask me, if it's not the full circuit, it's not a clone... Just a simple 12ax7 pre!
Ill post some pics in a bit.
The 866's are for a quad of 807's, as soon as I figure out where my other box of NOS 807's went to.
Ill post some pics in a bit.
The 866's are for a quad of 807's, as soon as I figure out where my other box of NOS 807's went to.
Here are some pictures of the beast in its latest form with dual B+ supplies. I had to break the amp into two parts I can barley move instead of one that would take a gang to get from my workshop in the basement to my second floor. One 866A is not glowing as I was testing pairs of 866A's and that one was going all lightning strike on me then died.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
They are Eastern Audio 10K 150VA's, Chinese iron but sound not too bad. I bought them to get me though until I can afford some real nice ones. I wanted to get something up and running and then upgrade along the way.
A word of caution about NOS 866 rectifiers from the 60s & 70s. When first heated up, the coating on the plate very often crinkles up and peels off. The flakes get between the plate and cathode and POW!!! Filament power alone can be enough for cause flaking. So watch them very closely and make sure any flakes get to the very bottom of the inside where they are out of the way. Newer production 866s with the smaller envelope do not seem to suffer from this flaking.we have to preserve these 866's, no one else likes them
Just scored a NOS set in the box, RCA 866a's $25 shipped
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