[Central-Electronics] Solid State Power Supply for 100V

[K6JEK]

Jim,

  I missed the beginning of this thread.  But if you're talking about 
replacing the tube rectifiers in a 100V you do realize that Central 
Electronics  replaced them in the 200V with plain old ordinary diodes, 
no funny business.  Someone more familiar with 200V can answer if they 
did anything to lower the voltages.

Perhaps an even more interesting case is my 100V.  The last person to 
work on it before it went into a closet and years later found its way 
to me was none other than Wesley Shum, founder and president of Central 
Electronics.  Apparently he did a small business working on these 
transmitters after Zenith bought CE and he left.  What do you suppose 
he did with the tube rectifiers?  He replaced them with solid state 
plug-ins.

I will admit, though, that I run this executively solid-stated 100V off 
a Variac, keeping the voltage down to 117.  I don't know that I need to 
do this but I do.

Jon, K6JEK


On Feb 24, 2005, at 11:47 AM, Jim candela wrote:

>
> Lyman,
>
>     The manufacturer states the following, "It is a combination of 
> diodes,
> power resistors, and other circuitry that emulate the warm-up and 
> operating
> curve of the tube type rectifier it replaces. Each model emulates the
> forward conduction resistance curve of the tube type it replaces and 
> also
> has linear in-rush current limiting to simulate the warm-up of a tube
> rectifier, however, it is in the 1 to 2 second range, rather than the 
> 7 to 9
> seconds of a typical rectifier tube."
>
>     To me this implies he uses suitable diode(s), a series power 
> resistor,
> and a negative temperature coefficient thermistor in parallel with the 
> power
> resistor. My guess is that he uses the copper top as a heatsink for the
> power resistor. Maybe my guess is incorrect. If someone knows the 
> details,
> please jump in and clarify the situation. This is a clever marketing
> strategy, and it will probably work just fine in many applications.
>
>      One thing concerns me here. The stated 1-2 second warm-up is 
> faster
> than the original rectifier if it were indirectly heated. It might be
> comparable to say a 5U4 which is directly heated, and will supply B+ 
> very
> quickly after turn on. I worry about the power supply electrolytics 
> where
> the surge voltage may be higher than with a vacuum tube rectifier. This
> surge may damage the filter capacitors if too high.
>
>      I have observed poor power supply performance in rigs like the EF
> Johnson Viking I where the B+ may sag a 100 volts or more with 
> modulation
> (AM). Converting the P/S to solid state really wakes this rig up with 
> higher
> B+, and much stiffer regulation. As for the 100V / 200V I believe the 
> stock
> design is "higher-end" than what Mr. EF Johnson used in the Vikings. I 
> am
> not sure what advantage if any this proposed power supply change would 
> do
> for a 100V. If the surge, or B+ is higher, the filters might be at 
> risk, and
> the 6550 pin 3 (plate) may flash over to ground.
>
>      If you go ahead to try this copper rectifier, please take some 
> time to
> evaluate stock versus modified performance, and report back to the 
> group.
>
> Thanks for getting a topic going again,
> Regards,
> Jim Candela
> WD5JKO