[Amps] SB-220

Ron W4BIN Youvan ka4inm at gmail.com
Wed Mar 24 14:10:44 EDT 2021

On 3/24/2021 10:46 AM, Joe wrote:
> Need advice,
> I am assuming some of you here are also on the Heathkit HF Amps E -Mail 
> list.
> So I won't go into the long drawn out story here unless asked to do so 
> if needed.
> I re-built this old SB-220 practically from scratch. And changed a lot 
> of stuff to make it better.
> But one change it has been determined, has made it in the Need of 
> needing more "L" in the output network.
> That of course if even possible would be some major surgery to say the 
> least. Trying to think of how I can add some more "L".

> At 2 AM last night I had a thought. How about like an old Drake VFO!? 
> Drakes varied the "L" in their VFO's not the "C" as most others did.
> And they varied it by inserting a ferrite bar into the coil.

   As did Collins.

> > Research says that inserting Ferrite into a coil will increase the 
> amount of "L" the coil has.

> I wonder if I could cheat and do the same on the L7 coil of this amp?
> Get some ferrites like on a plastic threaded rod and insert them into 
> the coil.

> What Mix of Ferrite would be best for such an application?

> And anyone thoughts of possibility of success?

   This has been a common practice, sometimes, in years before.

   I was talking to a Chief engineer at out local 250 Watt station
and he told me that he was part of a team that moved an old
transmitter from one company station to another and they
needed a "more L" plate inductor at the new frequency and
no one thought of it before hand.  So they wrapped a pair of
house hold pliers in paper towel and stuffed that into the tank
coil and then it easily tuned to the output frequency.
It resided there for several months until the proper coil could
be constructed.
   I would try a ferrite or powered iron bar, (antenna coil or
filament isolation style) and I would avoid plastics and use
aluminum or brass to suspended it from one end only.
A piece of a old flyback transformer core (remember?)
would be worth a try.
   Ron  W4BIN - Understanding is much better than
                                     knowing how.

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