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Re: [Amps] RF on audio using 374A

Subject: Re: [Amps] RF on audio using 374A
From: "Roger (sub1)" <>
Date: Wed, 14 Sep 2011 12:06:04 -0400
List-post: <">>
On 9/14/2011 11:25 AM, Jim Brown wrote:
> On 9/14/2011 6:19 AM, Carl wrote:
>> Glad to hear it wasnt a Pin 1 problem Roger (-;
> Ah, but it most likely WAS a Pin One Problem,

As am I.  It's just with the antenna imbalance every LED in the station 
was close to full brilliance when I'd reach 1KW output let alone 1.5KW.  
That made the pin one problem a losing proposition.

We talk about pin one problems but "I think" nearly *all* of today's 
rigs are wired that way. That means conditions have to be just right for 
them to work and "problems" are far more common than we realize.  I was 
listening to a couple of guys running SDRs the other night.  They were 
complementing each other on the quality of the signals and the ability 
to be "right on" frequency.  What happened to tuning so the other guy 
sounds right?  This is a family group so I can only say the one stations 
quality was... welllll... not good.  He had a real bad dose of RF 
getting into the audio, yet  instead of trying to ferret out the problem 
the other station was telling how great he sounded.

"In the old days" I remember operating FD with so much RF floating 
around you'd have to coordinate switching from transmit to receive 
between stations to keep from getting RF burns, yet the receivers never 
seemed to notice.

Now we have rigs that have capabilities and dynamic ranges we would have 
never dreamed about back in those days, but even with 120 db dynamic 
range they won't tolerate a little RF on the chassis just because ground 
is no longer ground. By floating it they can add a few functions and we 
have to sniff out the RF getting in.

My current rig, a Yaesu FTDX5000MP cost me more... More?  It was almost 
twice in actual dollars what my first new car cost, which was a Pontiac 
Bonneville convertible. OTOH that was back in late 1961. Still, the 
FTDX5000 which has a fantastic dynamic range, great digital noise 
reduction, will not tolerate RF on the chassis.

NOTE: today's dollar is only a fraction of a 1961 dollar.  To be a bit 
more precise it's worth only 16 cents compared to that 1961 dollar which 
makes that FTDX5000MP one of the cheaper rigs...Let me rephrase that... 
One of the least expensive rigs I've purchased over the years.  It's way 
less than my old Hallicrafters ran and that station would tolerate a LOT 
of rf on the chassis<:-)) Of course it also took a very strong back to 
move the individual pieces. It definitely was not a station to set up 
temporarily set up on a card table.  IIRC RX = 76#, TX=92#, and amp = 113#


Roger (K8RI)
>   and the choke to keep RF
> off the line was the easiest fix.  Think, Carl, about HOW the RF on the
> coax shield gets into the equipment!
> The way equipment is built makes Pin One Problems more likely, AND very
> difficult to fix without a complete rebuild. So the easiest solution is
> to kill the current that excites the Pin One Problem, which is what
> Roger did.
> 73, Jim K9YC
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