[ARC5] Army/Navy transmitters from a NON COLLECTOR viewpoint, the ham version...

[Kenneth G. Gordon]

On 11 Feb 2020 at 15:35, Brian Clarke wrote:

> The ARC-5 transmitter stall power plug, in terms of pin spacing and
> arrangement, is the same as the receiver IFT plug, except you need to
> drill a hole in the centre to fit a mini-banana plug.
> 
> Voltage doublers have several problems:

...and advantages...

> 1. if half-wave, DC is fed back into
> the mains; yes, I know it's done in computer SMPSUs, but sending DC into the
> mains is against the law in Australia and New Zealand, and if enough
> hornswogglers do it, the distribution transformer (pole pig in USA) gets
> unhappy 

I suspect you are talking about transformer-less voltage-doubler supplies, Brian. I don't 
know too many technically competent hams who would dare use such a supply. DC can't get 
back to the mains through a transformer.

> 2. at start-up, increasing the capacitance of the filter increases the load on
> the diodes, the power transformer and the mains fuse. 

The peak load, yes. I don't think the average load is changed much. At least Duncan Amps 
Power Supply Designer tells me so. But in the case of my SB-200s and other rigs I have 
used this technique with, the diodes I use are over-rated for this service and the 
fuses/circuit breakers have never been changed for higher-rated ones. IMHO, that would be 
kinda dumb.

> 3. increasing the size of the mains fuse increases the risk of taking out the
> power transformer, and no longer protects the power supply from excess load. 

Yes, but I most certainly have never done that, and won't. As I said, all my fuses and circuit 
breakers are exactly as they were originally. Furthermore, I have never had any problem 
with any of them.

Properly designed and implemented voltage-doubler supplies are quite useful and work 
well. They also have several advantages, amongst others, the HV transformer doesn't have 
to be rated for the full DC output voltage.

Also, FYI, according to Rich Measures (SK) the power transformers in the Heathkit SB-200 
and SB-220 (and possibly others) are specifically designed to ramp up their output voltage 
"slowly" so that a "soft-start" isn't needed with them. I have found this to be true. 

Even with my much larger filter caps, the lights don't dim, even momentarily, when I turn the 
SB-200 amps on, and watching the HV (2250VDC) come up on the meter it rises fairly 
slowly. It doesn't "jump up" to the full voltage.

I have never tripped a breaker or blown a fuse on start-up with any of the voltage-doubler 
supplies I use.

Ken W7EKB
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