[Amps] Henry 3K-A choke failure...workaround?

[David Gow]

Thee years ago I was given a 3K-A with the same problem.  I did put the
choke on a piece of thick Bakelite and it worked great.  I talked to
several other hams that had done the same thing.  However, I worried about
safety if it went to another ham and I had the original choke rewound by
the fellow in Maine who does such things,  It cost about $300, worked
perfectly and I loved it until I did a real stupid thing and when replacing
the PA cover after tuning   I failed to noticed that the brass  safety
shorting strip had came loose from its singe screw mounting and shorted the
3000 volt HV to ground.  When I hit the power button there was a huge bang
and flash.  It took out the HV rectifiers,the entire B+ protection circuit
(melted the relay) , and melted much oft he HV wiring. The brass shorting
strip was completely vaporized.  I sold it to for the cost of the choke
rewind. I t was pretty dramatic,  I can look up the contact info for the
rewinder if you like, he is well known but the company name escapes me at
the moment.
Dave W7VM

On Thu, Sep 26, 2019 at 8:17 PM David Harmon <k6xyz at sbcglobal.net> wrote:

> I bought a new 3K-A in 77' from the Henry Los Angeles store and picked it
> up
> at the factory.
> Two years later the choke went to ground just like Jeff's unit....but his
> lasted a lot longer than mine did!
> I ordered a new Dahl choke and put it in the center tap and had no more
> problems.
>
> You cannot put the original choke with the winding that is already grounded
> in the CT of the transformer.
> But....like others have said...insulate the choke from ground and it might
> last awhile longer.
> The Dahl choke I bought is not insulated from ground....because the winding
> does not already have a ground on it....kaff...kaff
>
> I mention all this because it is a fairly well known fact that all the
> Henry
> amp transformers and chokes from that era were prone to failure.
> I remember asking a guy at the factory why there were so many failures and
> he said the quality was poor because they were cheaply made by some guy in
> his garage!
> So far....my 3K-A has given very good service and the original xfmr is
> hanging in there.
> While I had it all torn down to replace the choke I bought a vacuum relay
> from RF Parts and replaced that horrible ear shattering antenna changeover
> relay with the dime sized contacts.
> That was 1979 and haven't had it open since.
>
>
> 73
>
> David Harmon
> K6XYZ
> Sperry, OK
>
> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Ron
> Sent: Thursday, September 26, 2019 10:00 PM
> To: amps <amps at contesting.com>
> Subject: Re: [Amps] Henry 3K-A choke failure...workaround?
>
>    Jeff wa1hco millar wrote:
>
> > Hello wise ones...
>
> > Bought a nice 3K-A at a flea market and made one SSB contact.  On the
> > second contact it tripped off on HV overcurrent.  After some
> > debugging, the Plate choke is leaky to ground at HV but open with an Ohm
> meter.
> > Can I just put the choke up on insulated standoffs?
>
> > Any other suggestions?
>
>    It is a pleasure to be helpful.
>
>    The CURE is to put it in the ground side of the circuit, typically where
> the rectifier or the grounded side of the transformer goes to ground.
>
> --
>    Ron  KA4INM - Understanding is much better than
>                                        knowing how.
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