TCS transmitter power supply

[stevef]

I need to build a P/S for a TCS transmitter.

I could just copy the original version, but it takes 4 filter chokes (2 in the HV supply, 2 in the LV supply).  The correct inductance/current combinations are not easy to find.

Can I get away with a single choke in each supply?
Or perhaps I should be looking at a more modern regulated supply design?

Tnx,

Steve
KK7UV

[WQ9E]

Steve,

You should be fine with a single choke plus plenty of output capacitance.  I would suggest using SS rectifiers.  My TCS setup came with a nicely built homebrew AC supply in addition to the original dynamotor supply and I am sure a single choke modern supply is going to provide better dynamic regulation than the original dynamotor supply.

[WU2D]

Steve,

I use a simple choke input with a cap and a good bleeder and it works fine. My supply is quite modest and was based on a transformer and choke from an old FAA receiver.

Mike WU2D.

[stevef]

Thanks Mike.

One clarification.....are those 10-20H swinging chokes, or do you mean a fixed choke that is between 10 and 20H?

Your supply is certainly much simpler.

My design conundrum last night was dealing with the 225v supply.  The TX uses 26mA from the 225v supply.  The handbook suggests a bleeder value for 10% of the load current, or 2.6mA.  I calculated an 86.5k bleeder.

Then the handbook suggests a critical inductance for the choke wherein it is the bleeder resistance divided by 1000.  In this case 86H!!!  What did I miss there?

Steve, KK7UV

[KE6DF]

Thanks Mike.


My design conundrum last night was dealing with the 225v supply.  The TX uses 26mA from the 225v supply.  The handbook suggests a bleeder value for 10% of the load current, or 2.6mA.  I calculated an 86.5k bleeder.

Then the handbook suggests a critical inductance for the choke wherein it is the bleeder resistance divided by 1000.  In this case 86H!!!  What did I miss there?

Steve, KK7UV

Designing the bleeder for 10% of the load makes sense with higher power, higher voltage transmitter supplies where a higher bleeder current would waste too much power.

With only 26ma needed, you don't have to worry about wasting too much power in the bleeder.

So shoot for something like 15hy and a 15K bleeder and you would have a nice stiff supply.

15Hy low current chokes are pretty easy to come by.

[stevef]

Okay, thanks.

I have some needed parts on the way.

[WD5JKO]

An alternative idea....

The low current draw from the LV 225v (26ma) invites another solution that might be worth looking at. Instead of a separate LV supply coming off the transformer C.T. use a series pass tube like a 6L6 off the 500V B+. So omit the choke, add a tube, then on the grid (G1) of tube use three 75v 1 watt zeners in series to get 225v (to gnd), and add a dropping resistor from 500v to the zener string cathode (about 150K), and bypass the zener string with a cap to gnd, maybe 4.7uf. Then triode connect the tube (G2 to plate through 10 ohms). The cathode goes to the 100uf and bleeder.

I'm sure your saying why? Well this approach is pretty simple (just adds a few more parts, and omits the 2nd choke). Here are a few pros and cons;

pro's:

~ 3 second turn on ramp of the LV as the 150K-4.7uf time constant ramps up

The extra load on the HV supply will allow the HV bleed resistor to pass less current (higher ohms and lower wattage) for the same % regulation

The 150K - 4.7 uf R-C will eliminate nearly 100% of the ripple in the LV output

The LV supply no-load to full load regulation will be good since the Rs will be the Rp of a triode connected 6L6

The voltage will be close to 225v as determined by the zener diodes.

 Cons:

A short circuit will likely kill the 6L6

The HV supply has to provide 26ma more

The zeners will drift up ~ 5 volts as they warm up

The pass tube will dissipate power that was not dissipated before. (500-225) * .026 = 7.2 watts

Need to add an extra filament transformer for the 6L6.

I know, I just violated the KISS principle....

Jim
WD5JKO

[KA3EKH]

GE Master base station power supplies provide 400 and 250 volts along with a regulated 12 volt DC power supply. I have bought several at hamfest for around $5 to $10 and found them real useful. The original design has a 250 volt supply with a 400 volt supply stacked on top in series for providing +650 but the two power supplies are easily separated. I have one I am currently using on an ARC-38 but had one that powered a TCS 12 receiver and transmitter with no issues for years. With a little work all the junk on the front of the power supply can be striped, the transistors can be hung on the back and the original T/R relay can be used and it  fits on a standard nineteen inch rack. If you need any schematics or additional information contact me.
Ray Fantini KA3EKH