[Amps] amp with push-pull output and magnetic coupling to the antenna

[Carl]

----- Original Message ----- 
From: "Ron Youvan" <ka4inm at tampabay.rr.com>
To: "amps" <amps at contesting.com>
Sent: Friday, January 28, 2011 3:03 PM
Subject: Re: [Amps] amp with push-pull output and magnetic coupling to the 
antenna


> Gene May wrote:
>
>> 1.  Does anyone know of a source for components or parts that could be 
>> used to make such a system?  I am willing to consider taking it/them out 
>> of existing assemblies (e.g., military surplus) but would prefer assemble 
>> it from "basic" parts.  I won't go so far as to say I'm desperate, but 
>> after considerable looking, I am very flexible and open-minded.
>
>   B&W made "plug in" P-P coil assemblies in 100 Watt and 1,000* Watt 
> sizes, I am looking for a set

There were several manufacturers of coils in the 25-1000W range in 5 power 
steps. Considering that the 1000W version was more than able to handle 
roughly 700W out on CW and 2800W PEP on AM they are quite adequate today.


> of each each myself.  The coil sets can all be plugged in and relay 
> switched, my plan.
> 100 Watts is the input coils, I plan on grid driven and input swamped.
>
>> 2.  It is necessary for the Q's of the tube circuit (probably to be 
>> around 10 to 15) and antenna circuit (probably to be around 1) to be 
>> compatible with the range over which the coupling coefficient between the 
>> two coils could vary.  As I understand, it is difficult to impossible to 
>> get coupling coefficients higher than about .3 using coils that would be 
>> compatible with the voltages and currents associated with an output of 
>> 1.5 KW.  Comments, please?

This was always a problem and is a big reason why the Class C efficiency of 
70-80% wasnt attained in amateur construction.


>
>   The swinging link (or in the case of B&W a rotating link) adequately 
> loads the resonant circuit.
> These coils did not have the third harmonic suppression (the second 
> harmonic distortion is canceled
> out by the P-P circuit) that we need now so it should be followed by a low 
> pass filter for each band
> and the swinging link should be made from coaxial cable, the ridged mw 
> kind the size of # 6 wire to
> minimize the capacitive coupling.  (Cross neutralization is required!  And 
> Easy!)
>
>   I plan (5 or 6 projects down the road) on using a pair of 4-1000s or 
> Russian tubes class "B."
> Another advantage of P-P is the absence for the need for a "plate choke."


And at the same time increases the plate tuning cap spacing requirements.

I built a few PP, plug in coil, 600-1000W amps in the 50-60's and can say 
without a doubt that I will never go back. Once I discovered the pi network 
and a bandswitch I was hooked. My 4 current AM amps use the old tubes 
(250TH, 813, HK-354, 304TL and a 6C21 version in the works) but are all in 
parallel to a pi network, its so much easier to control, stabilize and 
operate.


>   The 100 Watt coils plug into a 5 pin tube socket (like the 807)
> The 1,000 Watt size (frequently used with a pair of 813's) connector was a 
> row of (5 I think) male
> banana plugs.


>
> * not 1.5 kW OUT size, 1kW INPUT size!

See above! The wire size is similar to 1500W+ amps today.

Carl
KM1H


> -- 
>    Ron  KA4INM - If you have any criticism for me constructive or 
> otherwise
>                  keep it to yourself, at my age I just don't care anymore.
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