04-11-2020, 06:56 PM
A good afternoon so far
All the paper caps were replaced. A number were themselves replacements, including some Sangamo types with plastic bodies but they still measured leaky. One or two of these were quite poorly soldered - sometimes just touched on to the connecting terminal. After that, I replaced the wires to the bulb sockets, which had frayed, and looked tatty. As yet, I've done nothing with the original electrolytics, so I decided to remove the old replacements, tidy things up a little and fit some temporary smoothing caps in order to enable a test power up.
Test one: Dim-bulb in series with the power, no rectifier in the socket. The bulb did its usual number of glowing a little, then dimming as the valve heaters come up to temperature. All valves showed the glow
Test two: Dim Bulb, rectifier added, B+ monitored. The bulb behaved as before, and B+ rose, approached 300 v then fell as the circuits started to draw current. All good news. I played with the volume control. Not much going on, I thought, but eventually I realised there was a slight hiss and hum from the speaker. Crackles when the wave change switch was operated. A hint of changing noise when the tuning was moved, but no stations. Tuning up the Heathkit signal generator, I could hear the modulated signal as it swept through close to the IF, which should be at 460 kHz. Great!
Test three: Direct power. Without a knob on the waveband switch, it is hard to know the position. tuning around, I first heard the Morse Code output from my shortwave beacon, 13.555 MHz - aha! this is band C !. I switched down a band, and heard some noise, holding the short antenna lead. Then down again to broadcast. Stations and stations! Great volume, and the speaker is of nice quality.
Next thing will be to apply the golden screwdriver and attempt an alignment. That should be fun, as there's no service sheet, so I'll have to work out which trimmers are for which waveband and whether they are oscillator or aerial circuits, and for which end of the band. That's OK, I like these sort of challenges.
For now, I'm really happy that we have a working radio on the bench
Cheers
Ed
All the paper caps were replaced. A number were themselves replacements, including some Sangamo types with plastic bodies but they still measured leaky. One or two of these were quite poorly soldered - sometimes just touched on to the connecting terminal. After that, I replaced the wires to the bulb sockets, which had frayed, and looked tatty. As yet, I've done nothing with the original electrolytics, so I decided to remove the old replacements, tidy things up a little and fit some temporary smoothing caps in order to enable a test power up.
Test one: Dim-bulb in series with the power, no rectifier in the socket. The bulb did its usual number of glowing a little, then dimming as the valve heaters come up to temperature. All valves showed the glow
Test two: Dim Bulb, rectifier added, B+ monitored. The bulb behaved as before, and B+ rose, approached 300 v then fell as the circuits started to draw current. All good news. I played with the volume control. Not much going on, I thought, but eventually I realised there was a slight hiss and hum from the speaker. Crackles when the wave change switch was operated. A hint of changing noise when the tuning was moved, but no stations. Tuning up the Heathkit signal generator, I could hear the modulated signal as it swept through close to the IF, which should be at 460 kHz. Great!
Test three: Direct power. Without a knob on the waveband switch, it is hard to know the position. tuning around, I first heard the Morse Code output from my shortwave beacon, 13.555 MHz - aha! this is band C !. I switched down a band, and heard some noise, holding the short antenna lead. Then down again to broadcast. Stations and stations! Great volume, and the speaker is of nice quality.
Next thing will be to apply the golden screwdriver and attempt an alignment. That should be fun, as there's no service sheet, so I'll have to work out which trimmers are for which waveband and whether they are oscillator or aerial circuits, and for which end of the band. That's OK, I like these sort of challenges.
For now, I'm really happy that we have a working radio on the bench
Cheers
Ed
I don't hold with furniture that talks.