[Hallicrafters] More on solid state rectifiers

[wb8jkr at juno.com]

 I'll probably get flamed, but from what I have seen 
here its a perceived problem. Cathode stripping
is an issue with high power transmitting tubes,
but with low power tubes and receiving tubes 
it is a non-issue. However, that's not to say
the delay hurts anything, its just not NEEDED.
 There is a WHOLE LOT of Heathkit HW/SB
rigs out there that are all tube except for the
power supply rectifiers, and they have been
turned on and off for 30 years.


Mark  WB8JKR


On Thu, 9 Dec 2004 16:58:20 -0500 "David C. Hallam"
<dhallam at rapidsys.com> writes:
> Is this a real problem or a perceived one?
> 
> I understand that in the case of a high voltage linear supply with 
> lots of
> filter capacity in rush currents can problems without some delay but 
> that
> delay only has to be for a few cycles of the AC line.
> 
> If there is a 1 1/2 to 2 second delay, what's the problem?
> 
> David C. Hallam
> KC2JD
> 
> -----Original Message-----
> From: hallicrafters-bounces at mailman.qth.net
> [mailto:hallicrafters-bounces at mailman.qth.net]On Behalf Of Craig 
> Roberts
> Sent: Thursday, December 09, 2004 2:43 PM
> To: hallicrafters
> Cc: ke7kk at earthlink.net
> Subject: [Hallicrafters] More on solid state rectifiers
> 
> Hi again,
> 
> On the topic of possibly damaging inrush currents being unleashed 
> when
> substituting solid state devices for tube rectifiers, here's when 
> Ted
> Weber himself -- maker of the luxurious Weber Copper Cap -- said a 
> few
> months ago. He's talking specifically about using them in Collins 
> 516F-2
> power supplies, but the same principle applies elsewhere.
> 
> 73,
> 
> Craig
> W3CRR
> 
> Ted says:
> 
> "The tube rectifier has around 8 seconds of warm up time. Since the
> internal
> resistance of the tube is high until the tube is warmed up, the B+ 
> rises
> slowly as it charges the HV filters. At that same time, the other 
> tubes are
> also warming up. When they get up to temperature, they provide a 
> load that
> drops the B+.
> So, the long delay of the rectifier warmup prevents a high voltage 
> B+
> condition on the other tubes in the rig until they warm up. Our 
> copper caps
> have an inrush themistor that has a negative temperature 
> coefficient,
> and as
> the B+ current increases, its internal resistance decreases. Hence, 
> it
> has a
> warmup time like the tube rectifier. However, the warm up time of 
> our
> Copper
> Cap is only about 1-1/2 to 2 seconds, depending on the current draw 
> as the
> filters charge. Bottom line is, with the C-Cap, the B+ might ramp up 
> higher
> than some may be comfortable with until the other tubes warm up and 
> pull
> the
> B+ back down to normal operating level."