[AMRadio] Voltage check please


Gary Schafer garyschafer at comcast.net
Fri Mar 7 20:02:55 EST 2014


Hi Charlie,

With a capacitor input pi filter the voltage should be around 350 to 360
volts with full load. If it is dropping lower I would suspect that the input
filter capacitor is bad or the rectifier is weak.

250 volts is indicative of a choke input filter on a 300 volt transformer.

I usually use .9x rms with choke input and 1.25x rms for capacitor input
filter. That gets you in the ball park.

73
Gary  K4FMX

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of CL in NC
> Sent: Friday, March 07, 2014 3:57 PM
> To: amradio at mailman.qth.net
> Subject: [AMRadio] Voltage check please
> 
> I need another lucky Heath Apache owner to check a voltage for me when
> the opportunity arises.  The manual calls for 360V on the screens of the
> EL34's and throughout the TX for low B+.  In the process of repairing
> the modulator, I found mine to be about 250V.  If I unload the power
> supply, I get 350V, when I hook the load to it and it only draws about
> 15MA in STBY, it drops to 250V.  The TX operates fine, tunes up with no
> issues, full power out, no ripple on the carrier.  Is this  60 year old
> typo and it should show 250V?  The LV xfmr is 300-0-300, the rect is
> full wave and the filter is cap input with a choke, so theoretically,
> this PS under load should not give 360V out.
> 
> After finding this TX in  a drainage ditch in SC and repairing it's
> issues, it has given me good service for over 21 years.  Perhaps it is
> starting to get cantakerous in it's old age.
> 
> Charlie, W4MEC in NC
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