In article , Uwe
writes:

12V, holy cow!
If I go low voltage I keep it at around 5. I am building a controller board
with basic stamps and recently fried an A/D chip by letting it have 12V, it
was lethal.

Heh heh heh...you low-voltage kids are all alike. Us vacuum veterans
would not think twice about the +120 VDC (the "B+") in the old
"All-American Five" cheap table model AM BC radios.... :-)

By the way, talking about overload. The issue of crystals breaking has been
mentioned a few times, but how do I measure what the crystal "sees" for
current and what is tooo much???

Seriously, folks, the websites for International Crystal, Corning
Frequency Control division, etc., all give specs on various sizes
and cuts of their quartz crystal units. Few really "measure" the
crystal drive levels since that can be done analytically...if one
knows how to do this. If not, there are several hints on the
various crystal unit websites for approximating that, such as
typical circuits.

The best approach at the beginning is to take advice from others
on what works and what doesn't...such as the old, old FT-243
holder crystals can take more power dissipation (thicker slice of
quartz) than most of the smaller HC-6 holder units. The newer
SMD quartz crystal units have very low power specs and should
not be used with most vacuum tube circuits because of that.

Having been in the electron-pushing racket for better than a half
century and bridging the tube and transistor eras, I've never
experienced any quartz crystal physically "breaking." If a
quartz crystal circuit stopped working, the quartz unit just sat
there without a sound, same as it did when it worked OK. :-)
Only the oscilloscope trace knew what was in the hearts of
such circuits...

Len Anderson
retired (from regular hours) electronic engineer person

By the way, talking about overload. The issue of crystals breaking has been
mentioned a few times, but how do I measure what the crystal "sees" for
current and what is tooo much???


It's not easy to measure crystal current, since it's RF current at the crystals
frequency of oscillation. Most AC milliameters will stop working at about
10Khz, and the lead length and impedance will probably throw off your
oscillator.

One "trick" we used in the old days, which also sometimes saved the crystal
from destruction, was to put a low current pilot lamp in series with the
crystal. Seems to me it was a #49, but you'd best look it up. My recollection
was that this was a 60ma bulb. In normal operation it should not glow visibly.

Doug Moore KB9TMY

By the way, talking about overload. The issue of crystals breaking has been
mentioned a few times, but how do I measure what the crystal "sees" for
current and what is tooo much???


It's not easy to measure crystal current, since it's RF current at the crystals
frequency of oscillation. Most AC milliameters will stop working at about
10Khz, and the lead length and impedance will probably throw off your
oscillator.

One "trick" we used in the old days, which also sometimes saved the crystal
from destruction, was to put a low current pilot lamp in series with the
crystal. Seems to me it was a #49, but you'd best look it up. My recollection
was that this was a 60ma bulb. In normal operation it should not glow visibly.

Doug Moore KB9TMY

In article ,
"Paul_Morphy" writes:

" Uncle Peter" wrote in message
news:vQnbc.9210$pM1.6556@lakeread06...

I suggest he put all his radios on a shelf, and get a cell phone. No
dangerous
RF levels, no deadly voltages...

NOT

Gee, Unc, have a tough week? : I don't want him to give up radio, I just
don't think an Ameco AC-1 is worth the trouble.

But he does think it's worth the trouble.

I didn't want one when I was
15 and they were new, and I wouldn't waste my time fiddling with one now.

Nobody is saying *you* should. But your're saying Uwwe shouldn't. See the
contradiction?

73 de Jim, N2EY

In article ,
"Paul_Morphy" writes:

" Uncle Peter" wrote in message
news:vQnbc.9210$pM1.6556@lakeread06...

I suggest he put all his radios on a shelf, and get a cell phone. No
dangerous
RF levels, no deadly voltages...

NOT

Gee, Unc, have a tough week? : I don't want him to give up radio, I just
don't think an Ameco AC-1 is worth the trouble.

But he does think it's worth the trouble.

I didn't want one when I was
15 and they were new, and I wouldn't waste my time fiddling with one now.

Nobody is saying *you* should. But your're saying Uwwe shouldn't. See the
contradiction?

73 de Jim, N2EY

In article , Uwe
writes:

I will just have to fiddle a bit more
with the pi network (since at the B+ voltages suggested here my plate
current would be way high) and I will have to live with the chirp.

Are you getting a "dip" in plate current? If not, the coil is probably too
large or too small. Unless you get a real dip, the output network isn;t right.

I have used a very similar transmitter with 350 volts on the plate, and the dip
is clean and pronounced.

Nobody
has complained yet anyways and maybe the chirp is worse in my receiver than
on the air, as someone here suggested. By the way I use a Icom R75 for a
receiver and switch the antenna off during transmit-still plenty of a signal
seems to get into the receiver anyways.

It is quite possible that the receiver is being overloaded by the large signal
and creating a chirp.

73 de Jim, N2EY

In article , Uwe
writes:

I will just have to fiddle a bit more
with the pi network (since at the B+ voltages suggested here my plate
current would be way high) and I will have to live with the chirp.

Are you getting a "dip" in plate current? If not, the coil is probably too
large or too small. Unless you get a real dip, the output network isn;t right.

I have used a very similar transmitter with 350 volts on the plate, and the dip
is clean and pronounced.

Nobody
has complained yet anyways and maybe the chirp is worse in my receiver than
on the air, as someone here suggested. By the way I use a Icom R75 for a
receiver and switch the antenna off during transmit-still plenty of a signal
seems to get into the receiver anyways.

It is quite possible that the receiver is being overloaded by the large signal
and creating a chirp.

73 de Jim, N2EY

in article , N2EY at
PAMNO wrote on 4/5/04 18:59:

In article , Uwe
writes:

I will just have to fiddle a bit more
with the pi network (since at the B+ voltages suggested here my plate
current would be way high) and I will have to live with the chirp.

Are you getting a "dip" in plate current? If not, the coil is probably too
large or too small. Unless you get a real dip, the output network isn;t right.

I have used a very similar transmitter with 350 volts on the plate, and the
dip
is clean and pronounced.


Jim, the original docs I got for this tx call, at 40 m, for a 15 turn coil
on the coil form provided with the kit, which I hear was 1.25" diameter.
If I use the formula for air coils this turns out to be roughly a 22
microhenry coil.

The coil which works best with my tx is 8 turns on a 1,125" ceramic core.

To get guess work out of it I just bought and built a L/C meter and
measured my coil to have 2.7 microhenry. So I am way off, but it works, sort
of.

The air caps are 36 to 420pf at the plate and 15 to 728pf at the antenna, so
that seem right.

All this happens with B+200V and 35 mA plate current.


Older ARRL handbooks give typical values for pi network for 50 Ohm antenna
loads and my values are in range for the caps but my coil is too small.

The ouput voltage on my antenna measured with a scope is up to 75 volts peak
to peak, with a 50 Ohm load that would mean I get more out of the tx than I
put into it and I am not of the sort who says this might happen.

So my conclusion is, and tell me if this sounds right, that I have an
antenna which is far from 50 ohm resistive at 40m and that that makes
everything weird.
The dips in plate current are nearly imperceptible and they are not aided by
my 250mA full scale meter. They may be 2 or 3 mA.
I tune with the help of my scope.

73

Uwe

in article , N2EY at
PAMNO wrote on 4/5/04 18:59:

In article , Uwe
writes:

I will just have to fiddle a bit more
with the pi network (since at the B+ voltages suggested here my plate
current would be way high) and I will have to live with the chirp.

Are you getting a "dip" in plate current? If not, the coil is probably too
large or too small. Unless you get a real dip, the output network isn;t right.

I have used a very similar transmitter with 350 volts on the plate, and the
dip
is clean and pronounced.


Jim, the original docs I got for this tx call, at 40 m, for a 15 turn coil
on the coil form provided with the kit, which I hear was 1.25" diameter.
If I use the formula for air coils this turns out to be roughly a 22
microhenry coil.

The coil which works best with my tx is 8 turns on a 1,125" ceramic core.

To get guess work out of it I just bought and built a L/C meter and
measured my coil to have 2.7 microhenry. So I am way off, but it works, sort
of.

The air caps are 36 to 420pf at the plate and 15 to 728pf at the antenna, so
that seem right.

All this happens with B+200V and 35 mA plate current.


Older ARRL handbooks give typical values for pi network for 50 Ohm antenna
loads and my values are in range for the caps but my coil is too small.

The ouput voltage on my antenna measured with a scope is up to 75 volts peak
to peak, with a 50 Ohm load that would mean I get more out of the tx than I
put into it and I am not of the sort who says this might happen.

So my conclusion is, and tell me if this sounds right, that I have an
antenna which is far from 50 ohm resistive at 40m and that that makes
everything weird.
The dips in plate current are nearly imperceptible and they are not aided by
my 250mA full scale meter. They may be 2 or 3 mA.
I tune with the help of my scope.

73

Uwe

"Uwe" wrote in message
...

The dips in plate current are nearly imperceptible and they are not aided
by
my 250mA full scale meter. They may be 2 or 3 mA.
I tune with the help of my scope.

The pi network should be able to match a wide range of impedances but it
would help to connect a known resistive load. Five, 2-watt, 270-ohm
resistors in parallel would be close enough. If you're getting a dip in
plate current the circuit is resonating somewhere, and you say you've worked
people, so it's putting some rf on the band.

See if you're getting two dips. A lot of those pi networks would resonate on
the operating band with the plate tuning cap almost completely meshed, but
there was enough range in the cap that it would also tune to the second
harmonic. If your LC meter is right you may be dipping at a harmonic, not
the fundamental.

OTOH, if your calculation of what the original coil was is correct, the
plate tuning capacitor should resonate when its value is about 20 pF -- for
a 22-uH coil. That doesn't mesh with the range of your plate tuning cap. A
2.7 uH coil would resonate with the plate tuning cap at about 185 pF, which
seems more reasonable.

This is one of those rare occasions when a grid-dip meter is handy. Is there
a ham club in your area? Someone may have one to lend. Meanwhile, hook it up
to a dummy load and see what you get.

There's something else you could try, but I don't know how well it would
work. With the AC-1 unplugged you could connect your receiver antenna to the
top of the plate tuning cap and adjust the plate tuning cap while listening
for a peak in the noise level. That would tell you the circuit was
resonating at 7 MHz. If NG, try 20 meters and 10 meters.

In the olden days I had a 6BE6 connected inside my Viking Valiant, such that
it turned on and bridged the receiver antenna input when transmitted rf
appeared at the grid. When the key was up, rf from the antenna passed into
the receiver. This allowed for full break-in CW, and I could dip the plate
tuning cap just by listening to the noise level. Real handy when moving
around the band in a contest. You would probably pop the front end of a
solid-state receiver doing this, so don't try it. The circuit was in an old
Radio Handbook, which was edited by Bill Orr, W6SAI. That's what made me
think that you could try this with your receiver, but exercise appropriate
caution.

You know, I think you can get coil forms to fit your rig from Antique Radio
Supply, and also maybe Ocean State Electronics (oselectronics.com). You
could even make one for 30 meters. Ocean State has a power transformer in
their catalog that may do for a power supply for your rig, too. Or look for
an old tube-type hi-fi receiver in a thrift shop or at a tag sale. If you're
going to do, you may as well do it! :

73,

"PM"