12-06-2021, 10:30 PM
Tonight I began working on the HQ-129 some more. I have decided not to use a can to replace the 3 section can electrolytic, but instead to mount 2 terminal strips and use individual 10 MFD 500V condensers. Cheaper, and will be easier to service in the future, and actually allows higher voltage condensers for even greater reliability.
To be able to get at things, I will need to remove various parts, including the headphone jack, so tonight I removed the knobs and the front panel. From the color scheme used this appears to be an early production HQ-129-X. Except for having the original antenna connection replaced with an SO-239, and a few other minor back panel modifications, it is pretty much unmolested, except for one puzzling modification. Someone added a 7 pin miniature socket in the back corner near V11, the OC3 voltage regulator tube. It is connected to a SPST switch on the front panel, also an addition, which is labelled "CALIBRATION". There was no tube in the socket when I got this radio, although all the other tubes were there. The original RF tube, V1, which should be a 6SS7 seems to have been replaced with a 6SG7 on purpose, since this number is written next to the socket under the chassis. I am rather puzzled about this socket, since there is no sign of a crystal to go with it if it is a calibrator modification. Here are pictures, and a schematic. If anybody has any ideas about it, let me know. I just bought a Hammarlund FS-135-C so I will be able to use that as an internal calibrator if I wish.
[Image: https://64.media.tumblr.com/d0ffbe7d814b...be77fa.jpg]
[Image: https://64.media.tumblr.com/cfc79603535a...d3772f.jpg]
[Image: https://64.media.tumblr.com/1c2c7be38ec5...a6c710.jpg]
[Image: https://64.media.tumblr.com/dd33d2c3e077...df03f6.jpg]
To be able to get at things, I will need to remove various parts, including the headphone jack, so tonight I removed the knobs and the front panel. From the color scheme used this appears to be an early production HQ-129-X. Except for having the original antenna connection replaced with an SO-239, and a few other minor back panel modifications, it is pretty much unmolested, except for one puzzling modification. Someone added a 7 pin miniature socket in the back corner near V11, the OC3 voltage regulator tube. It is connected to a SPST switch on the front panel, also an addition, which is labelled "CALIBRATION". There was no tube in the socket when I got this radio, although all the other tubes were there. The original RF tube, V1, which should be a 6SS7 seems to have been replaced with a 6SG7 on purpose, since this number is written next to the socket under the chassis. I am rather puzzled about this socket, since there is no sign of a crystal to go with it if it is a calibrator modification. Here are pictures, and a schematic. If anybody has any ideas about it, let me know. I just bought a Hammarlund FS-135-C so I will be able to use that as an internal calibrator if I wish.
[Image: https://64.media.tumblr.com/d0ffbe7d814b...be77fa.jpg]
[Image: https://64.media.tumblr.com/cfc79603535a...d3772f.jpg]
[Image: https://64.media.tumblr.com/1c2c7be38ec5...a6c710.jpg]
[Image: https://64.media.tumblr.com/dd33d2c3e077...df03f6.jpg]
