HW-101 IF receive oscillation problem after long transmission

[Dick KF4NS]

Darn thing bounced due to length, here goes again:

> Ok Charles, I found it. The problem is secondary emission from the screens 
> of the finals.
>
> I tried several things over the years before finding the one that worked. 
> What you need to do is place a silicon diode in the screen circuit for the 
> finals. I used a 1N4004 just ahead of R920 100ohm at the connection of the 
> wht-org-org wire. (see the schematic area just below V8). Give it a try.
>
> Credit must be given to the archives for one of the Collins lists, cannot 
> remember which one.
> Good luck and 73, Dick KF4NS
> St Petersburg, FL 33714 USA
> Keep The Glow!
>
> ----- Original Message ----- 
> From: "Dick KF4NS" <kf4nsradio at verizon.net>
> To: <HEATH at LISTSERV.TEMPE.GOV>; <charlesmorris at hughes.net>
> Sent: Tuesday, January 23, 2007 6:55 PM
> Subject: Re: HW-101 IF receive oscillation problem after long transmission
>> Charles,
>> I had the same trouble back when I built my HW100 back in 1970. Got the 
>> fix from Heath tech. Will look back through the files and send the fix if 
>> I can find it. By the way, I am still using the rig to this day. Many 
>> technical upgrades and mods later, I still enjoy using it.
>> 73, Dick KF4NS
>> St Petersburg, FL 33714 USA
>> Keep The Glow!
>> ------------------------------Original 
>> Message-------------------------------
>>
>> Date:    Mon, 22 Jan 2007 14:30:57 +0000
>> From:    "charlesmorris at hughes.net" <charlesmorris at HUGHES.NET>
>> Subject: HW-101 IF receive oscillation problem after long transmission
>>
>> I'm new to this list, but have had Heathkits for a long time (and loved
>> to build them, probably like most of you :)
>>
>> Anyway I've had an HW-101 for a long time as my primary rig...I
>> acquired it in the mid-90's and it was built by another ham back in
>> 1977. There was a gradually increasing "shot noise" problem over the
>> last couple of months which turned out to be a noisy 6AU6 at V4 (2nd
>> receive IF). I replaced it with another new surplus JAN-6AU6-WC.
>>
>> But now it has another IF problem, an intermittent oscillation after
>> long periods of transmitting, which I discovered this weekend. I
>> usually keep my transmissions short but on Saturday morning I had the
>> chance to be a bit long-winded. When I let go of the mike button, the
>> receiver was completely cut off and the S-meter was nearly pinned. It
>> very slowly returned to normal over about 15 seconds. On subsequent
>> short transmissions, operation was normal, but on any extended key-down
>> it recurred.
>>
>> I got out the schematic, took the cover off, and quickly discovered
>> that something was driving the AVC line several volts negative as soon
>> as I released the PTT after long transmissions. Just holding the PTT
>> closed with no modulation did not cause the problem.
>> thanks for any help.
>> -Charles

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