"I think there is no QSK because this amplifier is designed to be either
keyed, or off it is from a TX only system. I wanted to modify it for
TX/RX by adding a relay in the bypass line of R20 to put the amplifier in
standby during RX."
It looks like they're capable of supplying some well-constructed amps to the
ISC markets. Unless there's a specific requirement from a customer, they
wouldn't ordinarily supply QSK circuitry, especially at the power level for
their target market. The facilities look nice too. Would love to have
access to their production equipment.
http://www.ampsystems.com/asiprod-old.htm
Paul, W9AC
----- Original Message -----
From: "Paul Decker" <kg7hf@comcast.net>
To: "MU 4CX250B" <4cx250b@miamioh.edu>
Cc: <amps@contesting.com>
Sent: Sunday, May 04, 2014 10:30 PM
Subject: Re: [Amps] complicated Bias circuit
Hi Jim,
Thanks, that is what I needed to get me going. I couldn't see the exact
need for the T2 circuitry since D17 and D18 were still the traditional
high power 50W zeners. I would have thought since there was a secondary
bias supply that some sort of lower wattage bias circuit would have been
in place but it appears this is just a traditional bias.
After looking at the schematic for a while I just had to ask what the heck
T2 was doing since it didn't really make sense it was needed.
Thanks for the explanation!
Paul
kg7hf
----- Original Message ----- From: MU 4CX250B <4cx250b@miamioh.edu>
To: Paul Decker <kg7hf@comcast.net> Cc: amps@contesting.com Sent: Mon,
05 May 2014 02:22:36 -0000 (UTC) Subject: Re: [Amps] complicated Bias
circuit Paul, In standby, the 24V from T2 just biases the tube(s) to
cutoff. R20 by itself would almost do this, but without the 24V there
would still be some small cathode current in standby which could generate
noise. When the amp is operating, the 24V biases the Zener diode that
establishes the tube operating bias. R22 sets the bias current through
the Zener diode. Without the 24V, the tube cathode current would bias the
Zener diode, but the regulation would suffer (causing non-linearity) at
low currents. The 24V eliminates that possibility. It strikes me as a bit
odd that, since the designers went to the trouble of building a 24V power
supply, that they didn't just go ahead and implement electronic bias
switching, which facilitates QSK operation.
73, Jim W8ZR Sent from my iPhone > On May 4, 2014, at 7:49 PM, Paul
Decker wrote: > > > FYI, if it helps any, this goes to a 3cx800A7
amplifier of some sort. > > > > ----- Original Message ----- > From:
Paul Decker > To: amps@contesting.com > Sent: Mon, 05 May 2014
01:18:47 -0000 (UTC) > Subject: complicated Bias circuit > > > Hi
builders. > > Hopefully you all can view this schematic. > > I'm
trying to understand what T2 and associated circuitry do. D17 and D18
seem like a simple bias circuit as SW3 selects between "class C" and
"class AB1" It seems opening R20 puts tube in standby (RX). > > What is
the point of having 24VDC from T2? Is it to have a smaller wattage D17
and D18? > > >
https://scontent-a.xx.fbcdn.net/hphotos-frc1/t1.0-9/10289874_10202768703951918_1823401065078063020_n.jpg
> > > Thanks in advance, > Paul >
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