[AMRadio] Too much HV

Tue Oct 18 23:01:40 EDT 2011

I have found the discussion in this thread interesting. What's silly about
it?

Brad K4RT

------ Original Message ------
Received: Tue, 18 Oct 2011 09:27:26 PM EDT
From: "Bernie Doran" <qedconsultants at embarqmail.com>
To: "Discussion of AM Radio in the Amateur Service" <amradio at mailman.qth.net>
Subject: Re: [AMRadio] Too much HV

look up the voltage drop for Vacuum tube rectifiers, mercury vapor, and 
diodes. VTs drop around 50 to 60 volts, MV tubes 15 volts, almost identical 
to a string of diodes. each diode is about 1/2 volt or so.    This is 
getting silly, just what is on the currant amateur radio tests?    If the 
voltage changes a measurable amount, something else has happened. not the 
diodes
original Message ----- 
From: "CL in NC" <mjcal77 at yahoo.com>
To: <amradio at mailman.qth.net>
Sent: Tuesday, October 18, 2011 1:52 PM
Subject: [AMRadio] Too much HV

> Well, anytime I ever replaced a tube rect. with a diode, I always ended up 
> with a higher B+.  The HA 10 I am working on does not have the choke in 
> it.  It arrived with a 1900VCT xfmr, a bridge rect. and  a cap string 
> totaling 16uf.  Unloaded, the plate volts rests at 2300, to much for 
> idling 811's.  I removed the bridge rect. used only half the diodes in 
> full wave configuration and get 1700 no load, which is OK.  I picked up an 
> original Heath 3kv CT to put in it.  But in conjunction with Bill, who has 
> the an original HA10 with correct PS plate xfmr, swinging choke, and oil 
> caps, gets 2500 with a W2AU diode block.  I expect to end up with the same 
> problem if I switch out the xfmr,  So I'm looking to solve Bill's HV 
> problem and avoid creating a similar one.  I am putting inrush protection 
> in it since the original HA10 plate xfmr was a known weak point, along 
> with an internal  ant/amp bypass relay.  Guess the choke will not make a 
> return since it is
> obscenely expensive when newly manf., so upping the filter to a string of 
> 6  450uf at 450vdc.  While the amp is not needed for use with the Heath 
> Apache, it does come in handy with the C Line when running it on AM.  One 
> fellow questioned the xfmr, both xfmrs have the proper 3kv AC out of the 
> secondary, with 1500 each side of CT, no imbalance, so does not appear to 
> be a xfmr issue.
>
> Charlie in NC
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