in article
, N2EY at
PAMNO wrote on 4/9/04 19:59:
In article , Uwe
writes:
Yes this is all very helpful. Indeed I was thinking that it would have taken
me a very long time to figure this out by myself, if at all.
I put another choke in there, a Hammond 1535B, the self resonant min. frequ.
is 1.3Mhz.
That should be a good one.
I guess it does take some deeper inside what parameters to look for since
this one improves things slightly but not yet altogether (slightly more
pronounced dip).
Who carries the sort of chokes you were refering to?
"Play Things of The Past" (www.oldradioparts.com) is one. Antique Electric
Supply (www.tubesandmore.com) is another. JWMiller still makes pie-wound 2.5
millihenry chokes with phenolic (no iron) cores. Check Digi-Key and Mouser.
Also google "AC1 ameco" - several websites with more info. One site I visited
(whose url I didn't save!) listed the plate voltage as approximately 325
volts.
This site also cautioned that the original grid resistor (47 K?) is way too
high, and that better results are obtained with a grid resistor of 4.7 K to 15
K. The author says the smaller value grid resistor gives less chirp.
The traditional amateur way to measure grid current is with a small lamp in
series with the xtal. "Small" means a #48 or #49 bulb - 2 volts at 60 ma. The
common #47 lamp needs 6.3 volts at 150 ma. and is way too insensitive. Small
flashlight lamps such as used in single-cell penlights may also be useful.
But the lamp should only be used for testing. Its resistance may cause chirp.
and before I forget:
CONGRATS ON YOUR GENERAL, Uwe!
73 de Jim, N2EY
Thanks for the good wishes. Yes I got the ticket and I am out there with my
5 wpm but sometimes I really feel I don't belong there, 5 wpm in the
"laboratory conditons" of the test is one thing, out there with all that
noise and distraction is an altogether different thing and "stagefright"
takes over sometimes.
(www.oldradioparts.com) seems like a good source, I might buy from them
sometimes, I still need a transformer for the little transmitter. By the way
about specifying these transformers, to get those 320Volt with a tube
rectifier do you need a centertapped transformer with roughly 160V in each
winding, what they call a 160-0-160??
I did see these other AC-1 sites and yes I do use the smaller resistor
parallel to the crystal.
I read a little more about chokes in old radio amateur handbooks and it
seems that even their placement in the chassis can be tricky.
I would love to know a way, because even with the 'new' choke the rig is not
'there' yet, to possibly make a test setup for this entire pi section and
'bench test it. Is there such a thing?
If I terminate it with a 50 load and feed my HF generator signal on the
input (plate) side this would not be appropriate because the tx and the test
generator have a different output impedance??
And what do you want the pi section to do, resonate at the transmitter
frequency?
Ways to go...
73 Uwe