06-30-2018, 10:28 PM
Progress today. I replaced the capacitor on the bandswitch for a film type 5600 pF part. I found elsewhere that the originals were paper, so this seems a fair swap.
With one or two last thinker items, it was time to pop all the valves back out, and set up the dim bulbs tester. The usual routine - check voltages, then everything but the rectifier. This all came together nicely, and power was applied without drama, until I saw that the 6SQ7 wan't lighting up. There was then a diversion as I wiggled it, saw the dial lamps and dim bulb flicker, and realised that the octal base was loose. I disassembled the valve from the base, and carefully tinned then resoldered all the pins. This may still be a problem valve, but I have a spare.
From there I added the rectifier, and monitored HT. It came up nicely, and then I moved the clip to the return from the speaker field coil. 0.28 Volts. The cause was found to be at the socket on the speaker - one of the connectors on the cable had not seated properly and pushed out of the back. Easy fix - connection and voltages appropriate, but drooped noticably as the emission came up on the output valves - expected with the dim (now brighter) bulb in circuit.
At this point, with everything looking just fine I cut the bulb out and applied direct mains power. Still no drama, and a feint buzzy hum from the speaker that responded to the volume and tone controls. An intermittent noise was traced to a dry solder joint. Alas, no stations on AM or shortwave. Switching to the phono input and adding the customary finger to the input terminal showed that the audio stage is working nicely - good and strong with plenty of volume.
At this point, it was getting a bit late, so diagnostics were somewhat cursory. I grabbed a portable AM/FM/SW radio and twiddled the RCA listening for signs of oscillator Success on the SW bands, and at seemingly appropriate frequencies, but nothing on the AM broadcast band (Medium wave to we of UK origin).
So, we have a solid audio stage, an oscillator on some bands, but no stations, and no oscillator (I think) on AM. So on to diagnostics! It's possible the repaired 6SQ7 is not working, amongst other things unknown.
Cheers
Ed
With one or two last thinker items, it was time to pop all the valves back out, and set up the dim bulbs tester. The usual routine - check voltages, then everything but the rectifier. This all came together nicely, and power was applied without drama, until I saw that the 6SQ7 wan't lighting up. There was then a diversion as I wiggled it, saw the dial lamps and dim bulb flicker, and realised that the octal base was loose. I disassembled the valve from the base, and carefully tinned then resoldered all the pins. This may still be a problem valve, but I have a spare.
From there I added the rectifier, and monitored HT. It came up nicely, and then I moved the clip to the return from the speaker field coil. 0.28 Volts. The cause was found to be at the socket on the speaker - one of the connectors on the cable had not seated properly and pushed out of the back. Easy fix - connection and voltages appropriate, but drooped noticably as the emission came up on the output valves - expected with the dim (now brighter) bulb in circuit.
At this point, with everything looking just fine I cut the bulb out and applied direct mains power. Still no drama, and a feint buzzy hum from the speaker that responded to the volume and tone controls. An intermittent noise was traced to a dry solder joint. Alas, no stations on AM or shortwave. Switching to the phono input and adding the customary finger to the input terminal showed that the audio stage is working nicely - good and strong with plenty of volume.
At this point, it was getting a bit late, so diagnostics were somewhat cursory. I grabbed a portable AM/FM/SW radio and twiddled the RCA listening for signs of oscillator Success on the SW bands, and at seemingly appropriate frequencies, but nothing on the AM broadcast band (Medium wave to we of UK origin).
So, we have a solid audio stage, an oscillator on some bands, but no stations, and no oscillator (I think) on AM. So on to diagnostics! It's possible the repaired 6SQ7 is not working, amongst other things unknown.
Cheers
Ed
I don't hold with furniture that talks.
