[Hammarlund] HQ-150 Question

[Richard Knoppow]

    I have never worked on an HQ-150 but since no one seems to have 
addressed your problem I downloaded the hadbooks and schematic from 
BAMA. It looks like a later relative of the HQ-120 HQ-129-X.  If its 
doing this on only one band it should not be too difficult to isolate 
it. There are three sections that are switched, the antenna, the RF to 
mixer transformer and the LO. One of those has to be the problem. If you 
have a scope I would look at the output of the RF stage and the LO to 
see if the noise if coming from one of them. Could be a lot of things 
like a bad silver mica cap, they can be very noisy.
    Sometimes it is very easy to overlook something. If you put it away 
for a couple of days it may become obvious.
    I also find the schematic confusing. I would have a couple of fairly 
large prints made and trace out the top band circuits. May be helpful. I 
use colored pencils or hiliters.

On 7/29/2024 5:57 PM, Dan Martin via Hammarlund wrote:
> 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
> 
> Sent from my iPhone
> 

-- 
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998