Hi all.

Recently I had to repair a HMV five valve radio, type 65.
The set is a gift for my ex and needed a bit done to get it running and make it safe.

New knobs were available and are of excellent quality. A new power cord had to be fitted due to the original being of rubber insulation which was cracking and falling off leaving bare wires. Paper caps were changed, and resistors replaced as necessary. Then valve pins were straightened and sockets cleaned with an application of CRC2.26 Controls were also cleaned, and the main electro reformed.

Alignment was a little strange, trying to determine the pointer set position, and work out where the various frequencies were to be on the scale.
Note: 600kc/s is directly over the station marking for 4AT, and 1500kc/s over 3AK. The pictorial diagram of the chassis shows the alignment points.

After alignment there was an intermittent problem as the set would go intermittently dead. I tried cleaning the earthing fork on the tuning gang, and replacing pin one on the 6AN7 valve socket, before finding that the problem was a vibration sensitive capacitor, decoupling the screen grids of the 6AN7 and the 6BA6.

I thought that the two caps in the white plastic cases were polyester, but wrong. Furthermore, when removed and measured on a capacitance meter tapping the cap would produce one of three readings/values. This is for a 0.047μF cap.
1. open circuit. 2. correct value. 3. double rated value 0.1uf

The set is ready for delivery. Naturally I will have to explain how to drive it. Turn it on. Wait about thirty seconds for sound. Adjust the tuning if necessary. Re-tune the station after the set has fully warmed, if necessary.

Please be careful when replacing the mains lead. The switch contacts are REALLY close to the metal work.

Wayne.

the problem was a vibration sensitive capacitor

Interesting, but why not just replace the culprit?

I am suspicious here. If the cap is in the detector first audio area that area is tends to have a lot of radiation. That means with modern caps you can get induction and volume control leads are the worst. I often need to add shielded wire in that area.

Some times it pays to shrink tube the end of the mains wire at the switch, or put insulation paper on the chassis, or around the switch.

If its a white UCC cap and has a band indicating "outside foil" and has not got "Polyester" written on it. Its a fair bet it paper & will leak like a sieve.