[Amps] Step Start on a 3KA Amp

[Bob Maser]

Thanks to all who responded to my search for info on the step start.  I 
realize now that it is the current that is being limited for a second and 
that's what saves the diodes and caps.  The guy I bought my recently 
acquired 3KA from was leaving it in the pre-op position for 5-10 minutes. 
He was a technician and didn't know any better and that's why I had to 
replace the cone heater.  It was fried.  The new cone heater I got from 
N5BIP corrected the problem.   Now, I am about to replace the humungous 3PDT 
relay with a RJ1A and an open frame NTE unit, which will quiet it down 
considerably.  I am also going to replace the original blower with a more 
quiet EBM blower.  After these mods are completed, the 3KA will be "good to 
go".  I am really impressed with it, and prefer it to my 4KU for ease of 
tuning.

73  Bob Maser
W6TR

----- Original Message ----- 
From: "Phil Clements" <philc at texascellnet.com>
To: "'Bob Maser'" <bmaser at tampabay.rr.com>
Sent: Monday, September 18, 2006 12:01 AM
Subject: RE: [Amps] Step Start on a 3KA Amp




> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Bob Maser
> Sent: Sunday, September 17, 2006 11:06 AM
> To: AMPS
> Subject: [Amps] Step Start on a 3KA Amp
>
> Can anyone tell me what good is it to have one of those cone heaters in
> series with the primary of the plate transformer?  When the cone heater is
> in the circuit, the secondary voltage is 2800VDC and when it is shorted
> out,
> it is 3000VDC.  Hardly seems worth the effort.  The cold resistance of the
> cone is ±30 ohms.
>
> Bob  W6TR

That's a step-start circuit, Bob...only three parts; switch, heater coil,
and your hand.
It is only intended to be in the circuit for a second or so. As you advance
the on/off switch from off to on, it step-starts the power supply, just like
a relay would, except the operator is the timing relay. They needed the coil
heater, as the normally used 50 watt resistors could over-heat if you left
the switch in mid-position too long.

(((73)))
Phil, K5PC