[Amps] complicated Bias circuit

[Paul Christensen]

> "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 at comcast.net>
To: "MU 4CX250B" <4cx250b at miamioh.edu>
Cc: <amps at 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 at miamioh.edu> 
> To: Paul Decker <kg7hf at comcast.net>  Cc: amps at 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 at 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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