[Hallicrafters] Rectifier replacement

[Jim Liles]

Heads up, the BZT03C220 zener is a 220v 3 watt diode --- not correct for a 100 watt receiver.  Determine the power requirement and select an appropriate 200 or 220 volt diode to handle the load for a radio that has 185 volt B+.

Kindest regards Jim K9AXN



-----Original Message----- 
From: Jim Liles 
Sent: Monday, November 17, 2014 10:15 AM 
To: Chris Farley ; Hallicrafters 
Subject: Re: [Hallicrafters] Rectifier replacement 

I believe switching to solid state rectifiers in these old radios is not a good idea.  The radio is protected from incredibly high B+ by the rectifier tube.  The B+ is not supplied to the radio until the tubes are warm enough to present a load for the high voltage.  Without that load the B+ will be approximately 30% higher than with load.  If you have solid state rectifiers, measure the B+ at turn on and watch it drop as the tubes warm up.

Most boat anchors were not designed for that kind of B+.  The later tubed radios were designed to use solid state rectifiers i.e. (SR-150, SR-400, and SR-2000).

When an SR-2000 is first powered on the B+ will measure at approximately 380 volts and drop to 285 as the tubes warm up but it’s designed for that kind of abuse.   

If your going to use solid state diodes, do something to quench the over B+ while the tubes are warming.  Use a Zener diode sufficiently higher than the design voltage with a load resistor in series to ground for a load that is sufficient to prevent the B+ voltage from exceeding safe design limits.  A good Zener clamp for a 185 volt radio is a BZT03C220 by Vishay.  Select an appropriate bleeder resistor to mimic the load.  The Zener will conduct at 220 volts and the bleeder resistor will limit the current to normal load conditions until the tubes warm up, dropping the voltage below Zener conduction. 

Kindest regards Jim K9AXN











---Original Message----- 
From: Chris Farley via Hallicrafters 
Sent: Sunday, November 16, 2014 11:17 PM 
To: Hallicrafters 
Subject: Re: [Hallicrafters] Rectifier replacement 

There was a thread on those "Coppercap" rectifiers some time ago in a different group, I'll be darned if I can find it now.  From what I remember, PIV of the diodes they use can't hold up to the HV found in most boatanchor transmitters.  Someone dissected one which had let the smoke out, and confirmed this.  For guitar amps or receivers with B+ of say 500v or less they're fine, but for (example) a HT-32/37 running more like 800-1000v, they're no bueno.  I would build my own in a tube base.  

The higher voltage realized by switching to solid state rectifier is valid, make sure you're not exceeding the voltage rating of filter caps, etc as others have suggested.
Regards, 
Chris



     From: Waldo Magnuson <magnuson at mac.com>
To: hallicrafters at mailman.qth.net 
Sent: Saturday, November 15, 2014 9:35 AM
Subject: [Hallicrafters] Rectifier replacement
   
Hi,  I've used several Weber CopperCap SS replacements for 5Z3 (SX-28) and other Hallicrafters boat anchors to reduce the heat and strain on the power transformer.  Recently I had a CopperCap short and blow fuses.  Weber is graciously replacing it but the tech expressed concern over the "high voltages" in the vacuum tube outfits.
  My question is; have any of used anything else, constructed your own, have used Webers, or what?  Thanks.
Skip Magnuson. W7WGM
Spokane, WA


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