[AMRadio] Shorting stick


W5OMR/Geoff w5omr at satx.rr.com
Sat Jun 3 11:38:09 EDT 2006


Donald Chester wrote:

> As I recall the 610 doesn't have a plate voltage  meter.  


No sir, it does not.

> That's one reason why all my HV supplies shut down on standby.  I 
> don't like the idea of HV silently lurking in the rig when it's not in 
> use.  If I ever did slip up, I think I would have a better chance of 
> survival discharging a capacitor through my body, than serving as a 
> load resistor on an active power supply.
>
> Besides, keeping the HV on all the time often generates noise and hash 
> in the receiver. 


About a year or so after I got my General Class ticket (KA5THB) when I 
was still a 'Johnny Novice' in the AM world, and got my 250TH 
transmitter (with the help of W5MEU, W5BU and WA5BXO), John/BXO said 
'let's do it this way' and instead of a bias supply for the final, a 
relay was installed from the grid circuit to ground.  When RF drive is 
applied, the relay closes, and primary voltage is applied to the final 
and modulator plate transformers.  As an added step of extra protection, 
there's a switch installed, in series with the primary that allows me to 
effectivly kill the B+ so I can tune the grid circuit if I ever change 
bands on the transmitter and exciter (Johnson Viking II).

The rectifiers filaments are always hot, but the relay only closes when 
sufficient RF drive is applied.  When the plate switch is closed, it's 
only -then- when the primary voltage is applied to the transformers and 
B+ comes up.

I still think I'd like to install a huge ceramic HV switch to kick in a 
-110vdc bias supply, and by-pass the modulator secondary, to run the big 
rig on CW.  I havn't done it yet, because I can't see operating 
high-powered CW, when 100w does just fine, and I don't 'do' contests. 

But that's just my opinion.
Your mileage may vary.
Void where prohibited by law.
All other normal disclaimers apply.

-- 
Driving your AM Rig without a scope, 
is like driving your car at night, without headlights. (K4KYV)

--
73 = Best Regards,
-Geoff/W5OMR





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