Uwe wrote in message ...
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.

You do belong there, Uwe. You just need to develop skills, that's all.
And the only way to get them is on-the-air.

(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??

No! That will get you far less than what you need.

With theoretically "perfect" rectifiers and transformers, the output
voltage depends entirely on the type of filter and the transformer
voltage. With a full-wave center-tap rectifier and a choke-input
filter, the maximum voltage obtainable is 0.9 times the transformer
voltage, and with a capacitor input filter, the maximum voltage
obtainable is 1.414 times the transformer voltage. With the full-wave
center-tap rectifier, "transformer voltage" means "each side of center
tap".

The above numbers assume perfect components whose ratings are big
enough to do the job.

With real world components, it's a little more complicated, but the
results are always that you get less voltage.

The AC-1 uses a capacitor-input filter and a 6X5GT rectifier. Also,
the transformer is not "perfect" - just good enough to do the job. End
result is that the transformer is about 320-0-320 and the resulting DC
is about 325 volts.

Easiest way to work with tube rectifiers is to look them up in the
tube manuals (there are several tube manuals on-line) and look at the
design curves.

I did see these other AC-1 sites and yes I do use the smaller resistor
parallel to the crystal.

Excellent. May take some experimentation.

btw, check out AF4K's website for crystal suppliers.

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?

Yes, but it's not necessary. You know the capacitors are the right
ones, so it's merely a matter of the chokes and coil.

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??

That's exactly right.

And what do you want the pi section to do, resonate at the transmitter
frequency?

Yes. But more than just resonate, it transforms the load impedance
from 50 ohms to whatever the tube needs.

Ways to go...

Good luck & congrats again!

73 de Jim, N2EY