HMV Testing Soon

[Nowhere-Man]

Here I found a pic to show what the HMV looks like. You'll see three kind of cascaded tuning scales which is a nice feature of this set. Unfortunately the middle scale on my HMV has been cleaned by some "simpleton" who managed to totally erase the lettering. Somehow I'll have to make a transfer from a photo if and when the radio works.

This radio boasts the nowadays quite rare X78 Triode Hexode Mixer tube. It also has a KT61 output tube.

I decided to test just the mains transformer for the initial test so I removed the tubes. This is just in case the transformer has any issues. I imagine the radio hasn't been powered for possibly 15 - 20 years so I'll be treading carefully.

One unusual feature is it's very heavy on switch connections. There are switches to shunt capacitors across inductor coils and several aerial switches to bring the coils into circuit. Bands are MW, LW, SW.

It has an image rejection capacitor.

Should I be fortunate enough for it to work, it will need restringing and I'd need to work hard on the cabinet which is pretty sorry-looking and scratched.

I put the plug on today and will put it somewhere safe and test the transformer voltages soon.

[Nowhere-Man]

P.S. I have realised while working on my radios my boat was falling to pieces so I've been very busy on the boat. I've actually been experimenting with alternatives to welding via adhesives. So far this has been successful.

I also have a plan to use vintage electrical fittings on my seventies boat to make it appear as it would have been. Maybe it will be a new trend like vintage boat electrics...

[Ed_Dinning]

Try an ad here, I'm sure there are plenty of people with spare fittings available.
BUT, if you want them they should be accepted at YOUR RISK.

Ed

[Nowhere-Man]

I noticed some odd points of interest with my GEC and Ultra radios.

The GEC radio I have, for example, doesn't seem to run an AVG line from the AVG diode. The schematic shows it and the cathode taken to chassis potential. The AVG is then taken from another 1 Meg resistor that follows the volume potentiometer in series, being taken to the Mixer grid and IF tube grid. Or maybe I'm missing something? So far as I'm aware from the Chas Miller book it's more normal to take the IF amplifier to the AVG diode with a set bias resistor. I'll have to look at it again and see the logic behind it.

The HMV seems more orthodox.

[Terry]

That is unusual - but not unique, I think - for a design using a double diode.

However, don't forget that the method you describe is used (because it is the only way!) on valve portables because they only have a single diode.

[Murphyv310]

It's not that unique.
Every battery valve set and transistor radio only uses one diode for AVC.

[Terry]

It's not that unique.
Every battery valve set and transistor radio only uses one diode for AVC.

Yes, Trevor, I'm well aware of that but it was valve sets that were being discussed with one diode of a double diode not used.

I kept the discussion to single diode valve radios in an attempt to compare like with like.

[Murphyv310]

Hi.
I understand what you mean Terry.
Having read my fair share of journals and books over the years it's often found that's what written and what's done in reality are two separate entities.
A recent restoration on a European radio had the oddest AVC circuit, it used a single diode detector but the resultant DC was fed to a triode valve that varied the RF and IF valves cathode voltage! The set was complex but also skimped on other parts of the design. My Tandberg also only uses one diode for detection and AVC.