[Top] [All Lists]

[AMPS] Power Supply Question

To: <>
Subject: [AMPS] Power Supply Question
From: (Tom Rauch)
Date: Thu, 13 Jul 2000 08:20:43 -0400
<italic><color><param>0000,0000,0000</param>> Don't overlook the other supplies 
that bias the tube{s}.  Thoroughly check

> them out also.  Problem might be more minor. Aloha & 73, Ed Pagaduan

</italic></color>I'll vote for that!

<italic><color><param>0000,0000,0000</param>> > A high voltage probe on the 
plate voltage (3800V) revealed that

> > with only 100 ma of current, I had 170VAC riding on top of the

> > DC. 

</italic></color>So was that peak-to-peak? 

If that was under light load, you have something else going on. 

<italic><color><param>0000,0000,0000</param>The next day, I brought home a 
Sencore L/C analyser and

> > verified that the three oil caps had not changed their value

> > significantly. At the same time, I checked the rectifiers for

> > uniformity of avalanche voltage and they were okay also.

"</italic>Avalanche voltage" is a non-issue. <italic>

> > I had everything disconnected, I put the Sencore on the AC

> > filter choke. I was surprised to note that instead of 8 Henrys

> > inductance (per schematic)it was 6. The surprise was because

> > there were no signs of windings shorting out, like charring,

> > stink, seepage, etc.

</italic></color>Are you sure the Sencore is right? Are you sure the schematic 
right? What is the tolerance of the choke?

<italic><color><param>0000,0000,0000</param>> > One has only to do the math to 
understand the function of that

> > choke and two .1uf filter caps in parallel. They are in series

> > with the rectified AC as a trap for 120 Hz, prior to the 16 uf

</italic></color>> > filter cap.

<italic><color><param>0000,0000,0000</param>> > By design, .2uf x 8H = 125 Hz. 
Close enough for 120 Hz.

> > Currently  .2uf x 6H = 145 Hz. Too far off?

</italic></color>No, not too far off.

First remember, you NEVER want to have the choke resonant. I 
was almost killed by Bill Orr's book when I followed his instructions 
to resonate the choke!

IMO, any tuned choke needs a spark gap for protection in case it 
hits resonance!

You always want the system to be on the high side of resonance.

The choke will drop inductance as the load increases, swinging 
choke or not. You NEVER want to design a supply so that the 
resonance is a key factor in ripple suppression in a variable load 
supply, because ripple will increase at a much accelerated rate as 
load current increases.

<italic><color><param>0000,0000,0000</param>> > I have contemplated adding a 
third .1uf 7.5Kv cap in parallel with

> > the existing two, or replacing them all with a .3uf 7.5Kv cap.

> > .3uf x 6 Henrys = 119 Hz

> > Any input would be appreciated before I jump in.

</italic></color>Input?  If you hit exact resonance, especially at higher surge 
currents, be prepared to run like hell! 

73, Tom W8JI

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>