Mercury Vapor 866A Power Supply Schematic Analysis

[Zarrir]

I have found this neat 866A Power supply schematic to start building my own. It seems so simple, clean and straightforward that i need to ask the specialists: Does it look about right?  I could not find any errors. 866A datasheet attached.

[Paul1453]

If needing a HAZMAT team to clean up the mess if one of your rectifier tube breaks is not enough of a deterrent to using these tubes.

Really, some teenagers got a hold of some mercury and were playing around with little blobs of it in the street by their house.
Apparently, the Authorities questioned them about what they were playing with.
When identified as Mercury, the HAZMAT team in their bunny suits were called out.
They cordoned off about 1/2 the block as they went through their clean up procedures.
The TV news also came out to report on the use of the HAZMAT team.
I'd guess the kids parents were not too happy if they got stuck footing the bill for the clean up.  LOL   

Maybe the cost of a PT capable of running them might be?

You need 10A's of 2.5VAC just to heat these monsters.
Then a 45 second delay relay on top of that.

A couple of SS diodes can do the job without carrying around blobs of mercury, and cost about $0.10  I'm just saying.

[PRR]

Seems like sticking 50 Ohms right in series with the rectifier makes it as lossy as a vacumm rectifier. Confirmed by the numbers: 375VAC should make toward 530V DC, 510V DC counting Mercury arc drop, but it is noted as 440V DC output (unspecified current).

Go ahead. (Not in my watershed though: 20th century Mercury pollution closed a lot of shellfish beds, and folks here would be upset.)

[Paul1453]

I purchased a Bench PS cheap and it needed a minor repair.

While troubleshooting and implementing the repair,
I became enchanted by the pretty neon purple glow of it's 2 OD3 tubes.
I then wanted to incorporate that pretty purple glow in some of my guitar amps.

The extremely knowledgeable PRR informed me that the OD3 also contains some non-human friendly gasses inside.
I too was not immediately deterred from using that pretty purple tube.
But as time went by, I eventually realized that even though I could possibly make a PS with a pretty purple glow,
it would cost a lot more, be more difficult to build, and be potentially hazardous to unsuspecting guitar players.

I have yet to put that pretty purple tube in any of my guitar amps.   

I still sometimes feel the urge to pull the cover off my bench PS and gaze at that pretty purple glow.  LOL   

[Willabe]

I still sometimes feel the urge to pull the cover off my bench PS and gaze at that pretty purple glow.  LOL   

   

[trobbins]

Zarrir, 


PSUD2 will allow you to estimate what continuous peak diode current occurs in your power supply.   Below is an example screen - that simulation model needs to be adjusted with the actual tube model (or something close), and the transformer  effective winding resistance, and the max loading, and the capacitors you would use.


It can also identify the turn-on surge peak current - that spec is not in your datasheet but possibly could be the fault current rating (not sure - more background reading is needed).


The rms current levels in the diodes, or resistor, can be used to select a fuse for HT winding protection.


A safer circuit could possibly be to use the 2.5V heater to power the delay relay, but the relay coil voltage would then be non-standard and the insulation rating may not allow that.


A MOV across the HT primary may be a better way to alleviate relay contact arcing.


All the transformers and fuse ratings would need to be cross-checked with the final build, as no current levels or load levels or part numbers are indicated on the schematic.


The mains AC caps are a worry - as you may not have the correct parts.


You may want to test the HT secondary windings for a good damped snubber using a bell-ringer test.


You may want to initially test using ss diodes, to confirm all the circuitry works before finally powering up with the mercury diodes.


These are just a few issues to consider.

[Zarrir]

trobbins and PRR, Pretty useful info, thank you!! PRR, how would you go about dropping that voltage if you actually needed 440VDC at B+?  Would you simply choose a different power transformer?

[silverfox]

http://www.tubebooks.org/technical_books_online.htm#Vacuum%20Tube%20theory%20&%20circuit%20design

This morning while attempting to find: Mullard, Tube Circuits for Audio Amplifiers, I ran across the tubebooks site and noticed several texts written on Mercury Arc Rectifiers. For those of you unfamiliar with the site- Tons of great stuff there.

silverfox.