[AMRadio] AMRadio Digest, Vol 69, Issue 4


sbjohnston at aol.com sbjohnston at aol.com
Mon Oct 5 21:32:02 EDT 2009


Don wrote:

>That would be true only if the original rectifiers were high vacuum 
tube
>types.  With mercury vapour or xenon gas rectifiers, the voltage drop 
across
>each tube is about 15 volts, regardless of the current.  When you are
>talking about 2500 or 3000 volts total on the plate, the voltage drop 
across
>the rectifiers is insignificant.

My experience has been that solid-state stacks cause the B+ to rise 
more when replacing vacuum rectifiers, but it also does it to a lesser 
extent with mercury vapor rectifiers.  I don't think I've ever done it 
with a xenon-filled tube.

Could also be something else at play in those cases, or faulty memory, 
I admit.  I might have upgraded filter caps at the same time, for 
example.  In any case, your observation indicates it is even easier to 
do the replacement for vapor/gas tubes.

Mercury vapor tubes put on a very pretty light show, so they should be 
used if possible.  -grin-  How do xenon tubes look in action?

Steve WD8DAS

sbjohnston at aol.com
http://www.wd8das.net/
---------------------------------------------------------
Radio is your best entertainment value.
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-----Original Message-----
From: D. Chester <k4kyv at charter.net>
To: amradio at mailman.qth.net
Sent: Sun, Oct 4, 2009 4:36 pm
Subject: Re: [AMRadio] AMRadio Digest, Vol 69, Issue 4










> You can expect somewhat higher voltage from the new stack than the
> original tube rectifier - if that is a problem for the rig, then add a
> series power resistor to simulate the internal voltage drop of the
> earlier tube.  So far I've only needed to do that once when the new
> higher B+ exceeded the rating of the by-pass caps in the other 
sections
> of the rig.  Otherwise the rigs seemed to thrive on the higher 
voltage.
>
> Steve WD8DAS

That would be true only if the original rectifiers were high vacuum 
tube
types.  With mercury vapour or xenon gas rectifiers, the voltage drop 
across
each tube is about 15 volts, regardless of the current.  When you are
talking about 2500 or 3000 volts total on the plate, the voltage drop 
across
the rectifiers is insignificant.

With solid state, the voltage drop across each diode is about 0.7 
volts.  So
if you have 20 1kv diodes series strung to give 20kv p.i.v., you will 
have
approximately the same rectifier voltage drop that you would have with 
a set
of MV tubes.

Don k4kyv


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