Heathkit Q Meter ..test coil??
Daniele
Tubes are new, sockets have been cleaned,
apparently no resistors are off tolerance,
filter caps replaced..
Time to check calibration, the manual
talks about a test coil.. anyone having an idea
of how to do it or do calibration without it??
It seems that all controls are working,
i can drive the meter to marks,
the only trouble i'm getting is the pointer
going under zero when switching from CAL to Q..
I guess something about the trimmer but before
moving it i'd have the test coil fot next use..
Uh... what's so 'special' in that odd 5000mmF cap??
(seems to measure 6.5 megohms...)
Daniele
http://www.tuberadio.it
Pete Bertini
"Daniele" <a...@tuberadio.it> wrote in message
news:o6VTm.2292$4d....@twister2.libero.it...
Daniele
The 5000 pF capacitor is a sandwich mica. The
reason they used that design is to eliminate any
inductive reactances. That is why the cap has wide
and very short leads.
Heath uses the RF voltage developed across the
mica cap. for the injection voltage into the tuned
circuit. The capacitor has to be high enough in
value so it has as little effect on the tuned circuits
efficiency as possible. It sounds like you might
have some moisture in the capacitor, there should
be no resistance reading. Maybe placing the cap
in an oven at 140 degrees for a few hours might
help?
The calibration coil is a small coil with banana
plugs that Heath supplied with the Q meter so
the builder had a reference to calibrate it against.
If it is missing, you will need to have a friend
measure the Q of another coil, and then you can
use the known coil to calibrate your meter.
I can send you a photo of the coil, but there isn't
much to see.
Peter
nesesu
Daniele, I have the coil for calibrating mine. I would have to look at
it to recall the design, but I could probably make a duplicate and
measure it's Q then send that to you. Do you have a source for bananna
plugs to put on it?
Please let me know if you are interested in this.
Neil S.
Daniele
PB> The 5000 pF capacitor is a sandwich mica. The
PB> reason they used that design is to eliminate any
PB> inductive reactances. That is why the cap has wide
PB> and very short leads.
yes, i arrived myself to the means of the sandwich
shape. What i was really wondering was about the definition
of 'special', thinking about some sort of special dielectric..
PB> Heath uses the RF voltage developed across the
PB> mica cap. for the
PB> injection voltage into the tuned
PB> circuit. The capacitor has to be
PB> high enough in value so it has as
PB> little effect on the tuned circuits
PB> efficiency as possible. It sounds
PB> like you might
PB> have some moisture in the capacitor, there should
PB> be no resistance reading.
PB> Maybe placing the cap
PB> in an oven at 140 degrees for a few hours
PB> might help?
I agree about the presence of moisture..
btw, using a modern sealed mica cap, would
have any negative effect in good working
readings?
Daniele
http://www.tuberadio.it
Daniele
n> Please let me know if you are interested in this.
done :)
Daniele
http://www.tuberadio.it
Bill M
>
> I agree about the presence of moisture..
> btw, using a modern sealed mica cap, would have any negative effect in
> good working
> readings?
> Daniele
> http://www.tuberadio.it
I don't think so. No higher in frequency than the QM-1 goes I would
think that a typical silvered mica dipped cap would be as good as the
calibration cap. They have pretty good Q but the pf value tolerance
isn't very precise.
I calibrated mine via some sample coils which a HP4342A? owner measured
for me. The QM-1 does a reasonably good job when calibrated that way.
I wouldn't claim accuracy better than 10%, though, but thats plenty
enough for my uses since I'm typically *comparing* coils. I don't use
the QM-1 for *measuring* inductance or capacitance. Its somewhat
obsolete for that purpose anyway.
-Bill
Pete Bertini
"Daniele" <a...@tuberadio.it> wrote in message news:qxeUm.2769$degrees for a
> PB> might help?
>
> I agree about the presence of moisture..
> btw, using a modern sealed mica cap, would have any negative effect in
> good working
> readings?
> Daniele
> http://www.tuberadio.it
>
On second thought... That high a resistance probably
has no effect at those frequencies. The reactance of
the capacitor should totally swamp out the extremely
small effect of several megohms resistance.
If I was going to replace a missing one, I'd do something
like paralleling ten 50 pF surface mount capacitors
in a donut configuration. Etched PC board with
two concentric copper rings. Outside ring
would be the ground return side for one end
of the SM caps, the inside copper disc
would be the terminal post connection and where
the other ends of the SM caps connect. That
would provide a very low impedance capacitor.
But, I'd think you would want to have some standard
inductors on hand before making modifications.
Pete
Jim Mueller
<snip>
btw, using a modern sealed mica
> cap, would have any negative effect in good working readings?
>
> Daniele
> http://www.tuberadio.it
It probably would have a negative effect. If an ordinary capacitor would
work, they wouldn't have gone to the expense of a custom job.
--
Jim Mueller wron...@nospam.com
To get my real email address, replace wrongname with dadoheadman.
Then replace nospam with fastmail. Lastly, replace com with us.
HankVC
I had one of those Heathkit Q-meters which I liberated from a
bankruptcy auction in the early 1960's. Heath provided a test coil
with inductance and Q marked on it, as I recall. Until I was able to
get hold of a Boonton 260-A Q meter, I used the unit quite often, and
it's probably still soldiering on somewhere. The 260-A came with a
set of standard coils, so I haven't really considered alternative
methods of calibrating one of these units. I later picked up another
260-A "junker" that supposedly had a burned-out thermocouple, but
found that there was just a solder joint problem, so got it working,
and picked up a Boonton 250-A RX bridge to complement the Q-meters.
I may be living in an obsolete world, but when I worked for James
Millen in the 1950's, a Boonton 160-A was the design lab workhorse.
If I didn't know all the good things that could be done with a
Q-meter (I'd never seen one), by the time Wade Caywood and Dick
Freeman got what they knew through to me, I've always either wanted
one or had one on my test bench. If you've got coil problems in RF or
IF stages, a Q-meter is still, in my view, "the thing to have." And
the little Heath unit, while not a Boonton or a Marconi (also a good
Q-meter if you can find one with companion oscillators), will do a
first-class job determining the capacitance needed to resonate a sick
IF with bad capacitors in the base, tell you very quickly if you've
got all the strands of Litzendraht connected at the terminations, and
a host of other things.
I'd suggest downloading the 160-A and 260-A manuals from the Bama
mirror. They give good information both on how to use the instrument
and methods for calibration with and without a known reference
standard coil. I think that some of the parameters given are specific
to those designs, but can probably be drawn on to devise methodologies
for the Heath unit. I would also not overlook the manuals for the
Marconi, which may be more readily available in Europe than here in
the states. As I recall, the Marconi circuit was closer to the Heath,
with a similar injection circuit (no thermocouple on the injection
resistor). Compared to the Boonton and Marconi manuals, the Heath
manual only gives cursory information. My recollection is that my
familiarity with the Boonton and Marconi units made it pretty simple
to get the Heath unit calibrated on all its bands.
On dealing with the leakage across that injection capacitor, I'd make
sure the unit is squeaky-clean. A Q-tip and some lacquer thinner
cleanup might clear the leakage. Offhand, I don't know how badly 5-6
megohms would affect the calibration. I'd also check out the Mouser
catalog for a suitable 5000 pf. replacement and try one in the
circuit.
Hank
Pete Bertini
"HankVC" <hvan...@nyx.net> wrote in message > On dealing with the leakage
> sure the unit is squeaky-clean. A Q-tip and some lacquer thinner
> cleanup might clear the leakage. Offhand, I don't know how badly 5-6
> megohms would affect the calibration. I'd also check out the Mouser
> catalog for a suitable 5000 pf. replacement and try one in the
> circuit.
>
> Hank
It's a fixed compression mica, similar to the style used in early
solid state RF power amplifiers. Design was chosen to minimize
stray reactances, just as done in the small value resistance injection
system used in the Boontons.
IIRC, my VHF Boonton Q meter uses a weird inductance type
injection technique? They are neat instruments.
Pete
Pete Bertini
"Pete Bertini" <radioco...@cox.net> wrote in message
news:5z9Vm.2034$on6...@newsfe19.iad...
>
>
> It's a fixed compression mica, similar to the style used in early
> solid state RF power amplifiers. >
I just looked them up; I was thinking of "metal cased micas."
Unelco makes them, but the 5000 pF value is a bit
elusive. You'd have to parallel a few modern values to get to
5000 pF for the injection cap value.
Pete Bertini
Here's a good website to bookmark;
it gives info on making your own
Q Meter standards; and there are some discussions about
possible improvements that could be make to the QM-1.
Peter
nesesu
Peter, now that I have made the coil for Daniele, it would be
interesting to read the website and see what it has to say.
So, could you post the pointer to the website?
I was checking the Q of the new coil as well as the Heath coil that
came with the QM-1 by A: the readings on the QM-1 and B: by using the
formula of dividing the Cf by the 3dB bandwidth. Comparison of the
results varied widely, so I am not sure what to make of that.
Neil S.
Pete Bertini
"nesesu" <neil_su...@telus.net> wrote in message
news:96c70149-7a04-4ee4...@o9g2000prg.googlegroups.com...
Neil S.
Wow, I am getting senile. Here is the link:
http://www.noding.com/la8ak/m1.htm
I suspect there will be a wide range of variation between test coils,
unless one has a pretty well calibrated Q-Meter to verify them
against.
The Heath QM-1 Test Coil might be affected by moisture? Mine
looks to be enclosed in a fiber cylinder. I wonder how close
it has retained it's original accuracy?
Pete
Daniele
actually i didn't gave too much attention to it,
i prefer work on the QM for the original
circuitry and than look around for upgrades.
Yesterday evening i was talking with a friend
(an electronic engineer into smd technology)
asking about the idea to use SMD caps in parallel
on a wafer in round shape; in his opinion, even if smd
appears to be all the same caps, they will resonate
differently each other, this would make interference
on results more than using a single 5K cap with short
pins. His suggestion is to use a selected poly film
cap and short wires. Value needs to be in the range
4.95-5.05, he says the meter itself has probably more
class error than the difference created by the
work of the new cap.
*NEWS from him:
- he is going to finish a sort
of plug and play VU meter based on an EM83;
all needed is in SMD, power supply and preamp,
all into an octal socket with transparent pvc tube,
time to finish building it depends on pcb sockets
arrivals from china...
- he has a good lot of blue LCD display, he
offered to use them for something radio-servicing-related
gear. I've introduced him the idea for something
useful for alignment, something which can incorporate
a signal generator 165-185Khz | 440-480Khz | 10.7mhz
and an 'oscilloscope' to monitor bandwidt, a sort of very
portable gear that could eliminate oscilloscope and
signal generator on the bench when aligning. If someone
has other/better idea for using LCD Display feel free
to share it.
Back to the QM: cleaned up controls, now it works
fine, zero adjust too; needs only calibration
(and here many thanks to Neil aka Nesesu for
trying to make a calibration coil) and to resolve
the question about that special cap.
I believe mine is the early version
in light green/yellow case with red marks
and with the zero adjust knob in bullet shape.
The interesting thing is that mine was sold
here in italy, the back shows a label in italian
for the mains. I know where it came from
and i can be sure it has never been internally touched,
the strange thing is that miniature tubes have
the radio fee label used from '30 to WWII end
(with fascist symbols) while the set seems to be
mid '50s. 9 pin tubes never seen that label since
that label was no more in use after 1945-1946 while
miniature tubes have been start to be used around
1952-1953 (here); that's strange, seems that those tubes
have been kept secretely in stock for years...
Daniele
http://www.tuberadio.it
PB> Peter, now that I have made the coil for Daniele, it would be
PB> interesting to read the website and see what it has to say.
PB> So, could you post the pointer to the website?
PB> I was checking the Q of the new coil as well as the Heath coil that
PB> came with the QM-1 by A: the readings on the QM-1 and B: by using
PB> the
PB> formula of dividing the Cf by the 3dB bandwidth. Comparison of the
PB> results varied widely, so I am not sure what to make of that.
PB> Neil S.
PB> Wow, I am getting senile. Here is the link: