05-01-2022, 05:34 PM
I've been reading through the manual on the HQ-129-X and have figured out that I have to redo the alignment and reset things to the actual IF frequency determined by the CRYSTAL in the crystal filter which may not be exactly 455 KC. I looked at the method outlined in the manual, which would equipment I do not have, and then figured out my own way of doing it. Here is a schematic so you can follow along...
[Image: https://64.media.tumblr.com/18a5dd7cb768...73ef9d.jpg]
The first order of business is to figure out the actual frequency of the crystal in the crystal filter. To do this I first pulled out the 6K8 so it would not be generating any spurious IF frequency to mess things up. Next I fed a modulated signal starting at 455 KC into the circuit at pin 4 of V3, and hooked the probe from my scope to pin 8 of V4. I set the crystal filter to the second notch and tuned my signal generator up and down until I had the highest output on the scope and by ear from the speaker. I then tuned the adjustments on the crystal filter until the signal got its loudest, then turned the crystal filter to its maximum setting, and again tuned everything to the maximum, again starting by re-tweaking the signal generator VERY carefully for maximum output from the scope and speaker, then re-adjusting the crystal filter adjustments.
Once that was done, I checked the output frequency with my Tecsun PL-600. It turns out the crystal is 453 KC. I left the signal generator set exactly as it was, and then re-inserted the 6K8 tube, but did not attach the grid cap, but instead fed the signal from the signal generator through a 220 mmf condenser into the grid cap. I then re-adjusted T1, T3, T4, & T5 to 453 KC. It didn't take much adjustment at all. Tonight I will go over the full alignment of the set, and tweak all RF and oscillator adjustments so that everything aligns right.
With the crystal filter adjusted, and the IF reset to the new frequency, there seems to be much less drop off of signal now when using the crystal filter, which makes sense, since I had set the IF to 455 when I aligned the transformers before, and the crystal filter was just enough off to begin to really squash that when set to its tightest notch.
So, for those of you who ever have to do it and don't have a swept signal generator, there is a method for checking the frequency of your crystal filter and adjusting it, so you can set your IF to the right frequency.
[Image: https://64.media.tumblr.com/18a5dd7cb768...73ef9d.jpg]
The first order of business is to figure out the actual frequency of the crystal in the crystal filter. To do this I first pulled out the 6K8 so it would not be generating any spurious IF frequency to mess things up. Next I fed a modulated signal starting at 455 KC into the circuit at pin 4 of V3, and hooked the probe from my scope to pin 8 of V4. I set the crystal filter to the second notch and tuned my signal generator up and down until I had the highest output on the scope and by ear from the speaker. I then tuned the adjustments on the crystal filter until the signal got its loudest, then turned the crystal filter to its maximum setting, and again tuned everything to the maximum, again starting by re-tweaking the signal generator VERY carefully for maximum output from the scope and speaker, then re-adjusting the crystal filter adjustments.
Once that was done, I checked the output frequency with my Tecsun PL-600. It turns out the crystal is 453 KC. I left the signal generator set exactly as it was, and then re-inserted the 6K8 tube, but did not attach the grid cap, but instead fed the signal from the signal generator through a 220 mmf condenser into the grid cap. I then re-adjusted T1, T3, T4, & T5 to 453 KC. It didn't take much adjustment at all. Tonight I will go over the full alignment of the set, and tweak all RF and oscillator adjustments so that everything aligns right.
With the crystal filter adjusted, and the IF reset to the new frequency, there seems to be much less drop off of signal now when using the crystal filter, which makes sense, since I had set the IF to 455 when I aligned the transformers before, and the crystal filter was just enough off to begin to really squash that when set to its tightest notch.
So, for those of you who ever have to do it and don't have a swept signal generator, there is a method for checking the frequency of your crystal filter and adjusting it, so you can set your IF to the right frequency.
