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Re: [Amps] RF on audio using 374A

Subject: Re: [Amps] RF on audio using 374A
Date: Thu, 15 Sep 2011 04:56:27 -0400 (EDT)
List-post: <">>
Have you considered the dynamic bias circuit on the Alpha?
I have an old Alpha 77 with dynamic bias that had a choppy sounding audio  
problem. I think the Alpha 374A may employ the same circuit as the Alpha  
77.  My original dynamic bias board didn't have an dynamic bias  adjustment, 
carbon comp resistors were old and the board was probably out of  
specification.  I noticed that newer boards had a pot in place of a  critical 
 I replaced mine with a pot and adjusted it until the  transition from 
cut-off bias to operating bias was smoother and the choppy  sounding audio went 
In a message dated 9/14/2011 9:02:20 P.M. Eastern Daylight Time, writes:

I am now  convinced the problem is within the Alpha I sent this earlier but 
it never  made it to everyone. A question was asked about which mic 
I am  using with the Flex and it is the front connecter.

Okay I did the choke  thing last night spent about 4 hours testing here is
how it went. Ferrite  on the Mic line right at the socket same for the
speakers the power cord  has ferrite on them as well cable from computer to
flex has them on both  ends no luck still having issues. So into the dummy
load with the Alpha I  have distortion that sounds like RF on the audio I
do not feel it is an RF  problem I have had several operators describe what
they are hearing and I  guess it got me chasing RF in the shack. I swapped
amps again with my MLA  2500 and it works perfect just like the SB220 I
even wheeled over my  2X4-1000 and good clean audio. I guess I have been
chasing my tail I was  convinced it was RF getting back down the feedline
or in the shack - Now  what could be wrong with the amp? Very frustrating
> more to  follow.

Bob, kc0hfl

----- Original Message ----- 
From:  "Carl" <>
To:  <>
Cc: <>
Sent:  Wednesday, September 14, 2011 7:40 PM
Subject: Re: [Amps] RF on audio using  374A

> ----- Original Message ----- 
> From: "Jim  Brown" <>
> Cc:  <>
> Sent: Wednesday, September 14, 2011 4:34  PM
> Subject: Re: [Amps] RF on audio using  374A
>> On 9/14/2011 11:00 AM, Carl  wrote:
>>> IMO Pin 1 is overblown (as are parasitics by another  individual) and I
>>> would expect any of the radio manufacturers  to already be aware of it.
>> You would likely change  your mind (assuming it is still open for change)
>> if you took the  time to read the extensive documentation of it, some of
>> which is  on my website. It is a very clear concept, easily grasped by
>> those  with even the most minimal engineering education. EMC authority
>>  Henry Ott has included a discussion of it in the latest edition of  his
>> classic text on EMC.
>> > 73, Jim  K9YC
> Ive read enough to be almost permanently bored regarding  your rather
> constant promomotion of that web site.
> However I  always keep an open mind, something I learned decades ago when
> taking  law courses.
> I'll suggest you read Pierce v. Delamater, a case  in the NY Court of 
> Appeals
> for September  1847.
> Carl
> KM1H
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