The AM Forum

I have my Hammarlund HQ 129 almost finished on the recapping so I can proceed to alignment. And actually I also have an HQ-140 and a Hallicrafters SX-16, all of which have one thing in common. The IF must be aligned to the crystal frequency and not just by the published IF frequency. The 2 can be off from the other. I have no sweep generator. I have a very nice Hickok 288X military version, and a frequency counter to keep it accurate. I have a Tek 2215 scope, and various VTVM's and LCD multimeters. Is there a way to determine what the frequency of the crystal in these radios actually is with this gear? I could align these rigs with an accurate 455 or 465 signal, as the case may be, but since the crystals  in these rigs may or may not be on-frequency, that means the crystal phasing controls will be of little reliability. Thank you.

It's pretty simple to blow a bit of tiny RF thru the crystal, near the supposed freq.

Monitor the output of it with your scope, adjust the gen freq for max trace on the scope.

You'll know where it is then.

Proceed to align from IF input at that freq.  ADJ LO to make it jive with dial indication.

73DG

Thank you. "Blow RF through the crystal"? How? I'll do it, and with gratitude for a new important thing I will have learned.

Hi,

I don't have an HQ-129 but did once align my HRO-50,
which should be a similar single-crystal IF filter circuit.
Check that the 'phasing' capacitor is half-meshed before starting.
This should correspond to the 12 o'clock position of the phasing knob.
Connect your signal generator, set to a low level output,
to the input side of the crystal filter, either using a X10 scope probe
or an added 1 Meg Ohm resistor in series with the standard
signal generator probe. Using your scope with a X10 probe
connected to the output side of the filter, tune the signal generator
slowly to determine the peak output frequency. (On my HRO-50,
it was actually peaked at 457 Kc with a nominal 455 Kc crystal filter).
The use of a X10 scope probe or a series 1 Meg resistor is to isolate
the added capacitance of the probe's coax from the receiver circuitry.
Then when doing the IF transformer alignment,
have your signal generator set to the frequency you determined
to be the peak freq of the crystal filter. With the rcvr on,
use an A.M. modulated signal (say 1 Kc modulation)
and adjust each of the the IF transformers for peak audio output
of the receiver.  Do this part with the rcvr AGC turned off
and the signal generator rf output set to its lowest hearable
speaker level  You may have to disconnect your counter
at this point, to ensure a low-enough signal level,
depending on the shielding of the counter and signal generator.
Have fun!

73

Inject your generator signal thru a few pF cap to pin 8 (6K8), and tune for max E at pin 4 of V4 6SS7 with the phasing cap C21 set mid-scale. 

Now you know the true freq of the crystal, if you have a way to read that.

Leave the gen set there, and peak the IF cans T1 & T2 for max output.

Shift your scope/SA to pin 3 of V6 (6H6), and tune for max again.

Pull all test gear, connect an antenna, and set dial for WWV on 5 or 10, adjust LO for dial agreement.

Hammy has a procedure for top & bottom ends of the bands, that is always proper to do as in the manual.

You'll be close enough, and a tiny tweak for the real world operation might pick up a dB or 2.

If your switches are noisy, a tiny amount of DeOxit applied with a toothpick will usually fix that right up.

A hint is sub a 5R4 for the 5U4, it will provide plenty of B+, with an amp less filament draw. 

Don't sub a SS rect replacement, the B+ will be high enough as it stands without the extra 10-15V.

73DG

Hi,

I forgot to mention that you should have the crystal filter set to
its sharpest position while checking for the frequency of its peak
response.

I like W7TFO's suggestion of substituting a 5R4 for the 5U4,
to reduce filament drain.

73