[AMPS] more about the input swamp circuit

[skipp isaham]

more alpha input circuit talk
-
>>The Alpha type circuit provides low swr to the exciter, 
: Not low enough for transistor radios unless 
: a tuner is used.  
-
Based on all the examples I've seen, the swr is low 
enough for most radios.  
- 
>is also relatively broadband, is low in cost and physical - 
>mechanical part requirements and easy to install. 
- 
: The tradeoff of having no flywheel is not small. - 
-
True but it was a relative trade off Alpha felt would 
work, and it does to a point. 
- 
: Two 8874s in parallel have a driving Z of roughly half 
: of 26-ohms at the negative V peak.  This requires 
: matching with a Pi-network/flywheel.
-
Since this thread started, I tried to locate the magic 
drive Z value with mixed bag and varied results.  An 
amps member reported ~95 ohms for a single tube, 
a W6SAI Radio Handbook says ~160 ohms and now 
your 2 tube value.   Someone has to have the real value, 
it's not listed anywhere in plain sight on the Eimac data 
sheet I just looked up on the web. 
- 
The single tube ~95 ohm Z value works with the other 
circuit values in the Alpha circuit diagram. 
- 
>The alternate half cycle is (for the example) pretty much 
>just the resistor network and some C. So the toroidal rf 
>xmfr secondary "load" halves. 
- 
: What is the swamper resistance?
- 
The Alpha 274 (two hole version) has a total parallel 
swamp R value of 47 ohms as reported on the diagram. 
The R network value in parallel with the 47.5 ohm dynamic 
tube Z works out the 23.6 ohms.  The toroid secondary 
value is reported to be 22.2 ohms.
 -
: With solid-state radios, sans-tuner, the SWR usually 
: needs to be 1.2:1 or better to avoid power foldback.  A 
: swamper/transformer is not capable of that.  
-
Without getting into an argument, I will say that many if 
not most of my common transceivers will drive into swr 
levels higher than 1.2:1 without a problem. 
- 
>It would not provide flywheel, just "better" exciter 
>matching in the alternate half cycle.  
- 
: Exactamente
- 
Better matching and the broad band response were 
the desired results, above a flywheel effect.  I would 
say the engineering goal was reached with the expected 
results. 
-
skipp 

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