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What I plan on doing though is building with a matched pair of black-plate 807's, adding then additional 6GW6's (which is what I'm using instead of the 6LF6 called for) and an additional dual triode.
Unfortunately, this schematic/ project does not have a power supply schematic. I've built a dual 6L6 transmitter on BCB AM, but that only used ~265V B+. From what I understand the voltage must be high in this build because it's all in series with the 807. Fine, I have a 1160VCT transformer sitting on my bench. It also has the 6.3v windings, which is nice.
I also am planning on using two 866a mercury vapor rectifiers, but I have a few questions. (FYI I have a separate ~2.5vct @ 20A filament transformer as specified by the full wave 866a circuit on the data sheet.)
1. How the hell do I filter these things? I understand it must be an LC circuit for optimal performance, but I have no idea as far as what kind of choke to use.
2. Capacitors for filtering- any suggestions? Would like to keep these things cheap as possible while still maintaining smooth current.
3. If I DO decide to double up on the audio circuit & add an 807, what kind of games will that play with my current requirements as well as my power supply filtering?
4. I have disputed info about the radiation given off by these 866's- is it x-ray, UV, RF, or all or none? If there is some issues, what is the best method of shielding?
It's too bad really that power supplies just aren't my strong suit. Definitely appreciate any help you guys provide. When I finally start building I'll post in the Projects to keep everyone informed. (Assuming anyone cares, lol :p)
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
As always, the PSU must be designed to suit the needs of the application.
Once you have decided what voltage, current, and maximum ripple is required of the PSU, you will be in a position to calculate your circuit values.
I would use a pi filter in this kind of application, because I can - electrolytics in series to withstand the working voltage with a good safety margin, and a laminated iron LF choke, but you may find an inductor of suitable size and rating difficult to come by if you are hoping for something inexpensive. You might precede the pi filter with a swinging choke if you want that extra bit of regulation.
You'll need a reinforced steel chassis to take the weight of it all.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
steve516 wrote ...
Proud Mary wrote ...
You'll need a reinforced steel chassis to take the weight of it all.
I had begun to notice this as I picked up my power transformer for the first time. :p That thing is already like 30 pounds.
Do you think dual chassis would work better for this? PSU and RF&Audio separate? If only for space and weight concerns.
I'd put them on separate racks with the PSU at the bottom to keep the centre of gravity of the cabinet as low as possible.
steve516 wrote ...
When calculating current requirements, what is the preferred method of doing this with tube circuits? Would something like SPICE do this?
The manufacturer's data sheets and characteristic curves are always the first point of departure in thermionic valve circuit design. I wouldn't want to go to all the complication of fiddling around with a circuit simulator when the characteristic curves of 807 were handed down to us personally by Moses on tablets of stone, but I don't suppose any great harm will come of it if it will make you happy.
Registered Member #3832
Joined: Thu Apr 14 2011, 11:57PM
Location: Downtown Chicago, IL
Posts: 37
Probably a better idea.
I looked again at the values and curves for the 866a and they don't have L and C values for voltages under 2000. (may even have been higher, it was a few days ago I looked. Have to double check.)
Should I assume the linear relationship continues?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
steve516 wrote ...
Probably a better idea.
I looked again at the values and curves for the 866a and they don't have L and C values for voltages under 2000. (may even have been higher, it was a few days ago I looked. Have to double check.)
Should I assume the linear relationship continues?
Take up thy choke and walk.
Wouldn't it be a good idea to get in a bit of practice with circuits having just one or two thermionic valves, and a good deal less high voltage, until you get the hang of it all, and can do your own calculations?
Registered Member #3832
Joined: Thu Apr 14 2011, 11:57PM
Location: Downtown Chicago, IL
Posts: 37
Sorry DP, but on that image you provided and on other data sheets, is the capacitor value in Microfarads or milifarads? I don't understand why most caps which use mfd or MFD are actually uF???
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Microfarad was once abbreviated MFD, back before the Greek letter mu came into use for it. This is often written as a lower case u due to the similar appearance and easier to type.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
James wrote ...
Microfarad was once abbreviated MFD, back before the Greek letter mu came into use for it. This is often written as a lower case u due to the similar appearance and easier to type.
A glance at data sheets of the 1930s will show both μF and μμF (i.e. pF) to have been in general use.
Type face and alphabet die sets not having Greek symbol options left type setters little choice but to represent μF as MFD.
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Transmitter DC Filtering, 866a full wave
