[Hammarlund] HQ-150 Question

[Dan Martin]

Have an HQ-150 here with a very noisy high band, 18-31 mHz.  Only the highest frequency band. No others. Lots of loud pops, snaps, and crackles while rapidly tuning up and down the band. LO signal on scope shows sharp variations and spikes in amplitude up and down corresponding to the snaps and crackles. Noise is main tuning cap movement driven. Radio sits quiet on a fixed frequency. Try tuning around and it gets real noisy fast.  I could post a video w/audio if this system could take the bandwidth.

I have rotated in several 6C4’s (oscillator) and 6BE6’s (mixer) without change. I’ve put in place the 6C4 and 6BE6 from my excellent performing HQ-140, to no avail.  I’ve cleaned, Deoxited, and even used metal polish to a shiny mirror gleam the C1 cap wipers and contact disks. No change. I’ve preemptively replaced C89, C6, and C29 caps without change. All associated resistors in and around osc. grid circuit check OK. Pin voltages of mixer and osc. OK. I’ve checked and tightened the screws mounting the cap sub-assembly to the chassis.

Have simply run out of ideas and need help and comments.

I have worked on HQ-140’s/150’s extensively and currently have one of each. These are excellent radios and among my very favorites. Treated right and aligned well the single conversion HQ’s are wonderful.

Comments? I’m dead-ended. Need more ideas.

Thanks in advance.

Dan
WB4GRA

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