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,
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.
----- Original Message -----
From: "Carl" <firstname.lastname@example.org>
Sent: Wednesday, September 14, 2011 7:40 PM
Subject: Re: [Amps] RF on audio using 374A
> ----- Original Message -----
> From: "Jim Brown" <email@example.com>
> Cc: <firstname.lastname@example.org>
> 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
> for September 1847.
> Amps mailing list
Amps mailing list
Amps mailing list