07-07-2018, 10:20 PM
More today, mostly fiddling with alignment, but one other important step forward.
Following the datasheet calls for set-up of the 2nd, then the first IF. When I try injecting a signal as specified, this kills the stage completely. Instead, I found a "gimmick" insulated wire wrapped loosely around the same point, I was able to inject and hear 455 kHz from my generator. This wasn't working quite as expected, as the adjustment of the second IF still showed rather little response - but there was enough pickup from the first stage that it did respond, and I could tune the first IF.
Jiggling things around a bit, I find it is possible to get first and second IFs to peak up, although I do feel this could be improved upon. There are also periodic crackles from the radio after switch on from cold, so I may investigate for "silver Mica disease".
Aligning the front end is very rudimentary on this radio, and seems to fall in just fine, although there is one anomaly. The 31 m "Spread Band" is derived from the 6-18 megahertz band using padding and trimming capacitors. However, the oscillator trimmer has to be adjusted to maximum to meet the set point. It is in parallel with a tubular ceramic (82 pf) and I wonder if this has drifted in value over the years.
All this fiddling around had, until today, ignored one thing - terrible audio from the speaker. For one thing, the surround had detached from the frame, making for a big "slap" on heavy bass accents. But also, the voice coil was rubbing. Looking closer, there were two screws adjacent to the field coil. These secured clamps that held a plate to which the spider is attached. A little adjustment restored clean movement to the voice coil, and lovely audio.
Cheers
Ed
Following the datasheet calls for set-up of the 2nd, then the first IF. When I try injecting a signal as specified, this kills the stage completely. Instead, I found a "gimmick" insulated wire wrapped loosely around the same point, I was able to inject and hear 455 kHz from my generator. This wasn't working quite as expected, as the adjustment of the second IF still showed rather little response - but there was enough pickup from the first stage that it did respond, and I could tune the first IF.
Jiggling things around a bit, I find it is possible to get first and second IFs to peak up, although I do feel this could be improved upon. There are also periodic crackles from the radio after switch on from cold, so I may investigate for "silver Mica disease".
Aligning the front end is very rudimentary on this radio, and seems to fall in just fine, although there is one anomaly. The 31 m "Spread Band" is derived from the 6-18 megahertz band using padding and trimming capacitors. However, the oscillator trimmer has to be adjusted to maximum to meet the set point. It is in parallel with a tubular ceramic (82 pf) and I wonder if this has drifted in value over the years.
All this fiddling around had, until today, ignored one thing - terrible audio from the speaker. For one thing, the surround had detached from the frame, making for a big "slap" on heavy bass accents. But also, the voice coil was rubbing. Looking closer, there were two screws adjacent to the field coil. These secured clamps that held a plate to which the spider is attached. A little adjustment restored clean movement to the voice coil, and lovely audio.
Cheers
Ed
I don't hold with furniture that talks.
