[AMPS] UPDATE ON 3-1000Z OSCILLATION
Wed, 9 May 2001 05:17:25 -0400
> Many questions were asked about the construction and cicuitry in the
> amplifier (actually it's an oscillator at the moment). I will try to
> start at the input. There is 4 inches of RG-174 coax feeding a .01 cap
> going directly to the cathode/heater pin of the tube socket. There is
> another .01 across the filament of the tube and it is mounted directly
> to the pins of the Eimac socket. All of the grid pins are shorted
Is there an antenna relay? What type?
BTW, you get a lower impedance driving the filament if you split the
two .01 capacitors to a common point and feed it there, instead of
having one across the filament and one in series with the source. I
hope that coax is grounded at the socket, and you do need a tuned
input near the tube that is a low-pass or band-pass type with a low
VHF impedance at the cathode. That means a C-L-C pi or a
parallel tuned network.
> The tank circuit is entirely interconnected with 3/4" wide flat copper
> (sounds like the concensus was to go with something like stainless to
> help tame the parasites), the longest length being no more than 6
What is the TOTAL length of the path from the anode connector of
the tube to the tuning capacitor??? That is the most critical
LENGTH. How is the tuning cap grounded and how long is the
PATH from that point back to the tube socket including length
through mounting brackets?? Is that a wide path, or do you have
skinny wire or brackets?
That is all very important, much more important than very minor
things like making the connecting strap out of stainless steel.
What type of blocking cap?
> arrangements. My tune cap is a Jennings vaccum cap- 15KV, 2-35pf Its a
> tiny little thing but should be fine for 10 meters. My parasitic
> suppressor is a 50 ohm, 25 watt non-inductive resistor with 4 turns of
> nicrhome wire wound directly on it.
What type of "non-inductive" resistor? Is it a glo-bar type? Or is it a
non-inductive wire wound?
Is the wire wound over the resistor? What diameter and length are
e thing that someone mentioned was the size of the cabinet- It is
> large. The tank compartment is 22"w x 16"d x 14"h . It was a nice case
> I picked up at a hamfest. How critical is size? Could I have possibly
> constructed a big VHF cavity?
No, that's non-sense. The cabinet size is not critical but input to
output shielding is and so are ground path lengths.
There is quite a bit of unused space in
> there (room for a big ceramic someday). Should I put a panel in there
> to make it smaller? I have seen some amps that have the tank
> components totally seperated from the tube in a different compartment.
> Should I try this?
73, Tom W8JI
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