[AMPS] Ameritron AL-80A

[Jon Ogden]

on 11/5/99 8:14 PM, Tsachy Lindenbaum at ernie@netvision.net.il wrote:

> My AL80A was upgraded to 10 meters operation by previous owner (I guess).
> The amplifier manual suggests caps on input-pi , but the 27pf cap at the
> tube side (c5) is missing for some reason.
> The amp works OK on 10 meters, but the input pi has only 1 cap on antenna
> side,  and the other "cap" available is the leftover of the short green wire
> from the input coil which was cut to allow for 10 meters operation (this
> wire grounded the tube side on "ten" prior to modification and the
> manufacturer's way to enable 10 meters is by cutting it).
> What's the idea - can this wire provide 27 Pf (5 cm #20) ? Luck ?
> Ur comments will be apreciated.

Hi Isaac.

Here is what could be happening and it's a guess since I am not all that
familiar with the AL80A.

The tube itself has some capacitance from the cathode to ground.  When
designing a g-g amplifier's pi-network from scratch, you always have to take
this into account.  Ameritron should have taken into account on their
upgrade instructions, but perhaps they didn't.

My bet is the previous owner tried it out and liked the performance of the
circuit better with the 27 pF cap out of the circuit.  I don't know, it's
just a guess.

Bottom line is that if you have good SWR on 10M and get the Pout you expect,
I wouldn't worry about the cap.  If you want you could put a cap in there
and see for yourself the new results.  Either way, you won't hurt anything.

And no, the green wire doesn't provide 27 pF capacitance by itself.  :-)

73,

Jon
KE9NA

-- 
-------------------------------------
Jon Ogden
KE9NA

http://www.qsl.net/ke9na


"A life lived in fear is a life half lived."


--
FAQ on WWW:               http://www.contesting.com/ampsfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm