Work continues on my old Hammarlund HQ-100. I give background on the rig and explain the electrical trauma it likely suffered. Following Dave K8WPE's dictum that we can still learn a lot from old receivers, I dug into this one. I wanted to fix a long-standing S-Meter/AVC problem. This led me to an interesting troubleshoot, with at least one "waste of time" detour. Eventually I found the fault in one of the coils in the grid circuit of the RF amplifier. The coils had been smoked years ago, perhaps by a lightning strike. I came perilously close to permanently losing 10-30 MHz. But I figured out how to fix the smoked coil. So my S-Meter/AVC problem was fixed. I really like listening to this thing. There is still a lot of nice material on the SW bands. There are some very nice broadcasts in Spanish.
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You can see where the coil burned. Wire remained intact, but the insulation burned creating a Primary to Secondary connection.
I just very carefully lifted one of the coils way from the other, eliminating the unwanted connection.
Here's my homebrew "RC Printed Network" Z2 module. This was unnecessary -- the original was good. I put the original back in.
Electric Radio magazine recently ran a two part series on the HQ-100. I have ordered these issues of the magazine.
After separating the coils, I hope you used something like "Q-Dope" or "Corona Dope" to secure the coils and provide some insulation. These products are like many products, you don't need them often but when you do, you really need them.
ReplyDeleteI hear you David, but those coil wires are VERY fragile. They are 60+ years old, and they have been burned. Not wanting the perfect to be the enemy of the good, once I got the DC short resolved, I carefully put the coil back in its case (as shown) and reconnected. It might go bad sometime in the future, but it probably won't. And if it does, I'll know where to look! 73 Bill
ReplyDeleteWhat issues of Electric Radio magazine?
ReplyDeleteER 380 and 381. I have them now.
ReplyDelete