Photos uploaded to Post 10.

Yeah Carl Looks like a repair in the late 50s by a small service shop. Replaced grid coupler cap to the 42. Had run out of pigtail electros so pressed a twistlug can he had on the shelf into service. Understandable....

Paper coupling cap has since gone leaky and cooked the 42's cathode resistor.

There were quite a few small radio makers in the 30s that didn't subscribe to the ARTS&P system. Kinda slipped under the radar.

I am pretty sure this will be a real nice restoration. Nothing I can't tidy up hey.

So 1938 according to the date stamp.

Check the valve for a heater cathode short, that can also fry a cathode resistor.

How can a heater-cathode short (rare enough anyway) fry a cathode resistor, Marc?

The most it could do is apply 6.3V AC to the 42's 400 ohm cathode resistor, which results in a dissipation of less than 0.1 watt.....

If the valve was, say, a 6M5 with a 150 ohm cathode resistor, it would dissipate 0.26 watts.

Still no fry, even in the worst case of the heater-cathode short being at the hot end of the heater circuit.

Hi Fellows,

The marking in the twist cap is for an electro, the values suggest a filter cap on the HT. At 40 mfd that would place a real load on the 80 at warmup.

The nearby Ducon paper is possibly the grid coupler cap for the 42.

I get the feeling that this is a small builders chassis rehomed into a home built cabinet,
maybe a console unit which was too large for the lounge room?


Cheers, Graham

Gfr53

You will note a earlier comment by myself that there is evidence of a different escutcheon in the form of a larger ring mark on the woodwork. Maybe a existing cabinet from another radio.

Recapped this one today and blow me down it works and is a extremely strong performer.

This post seems to be jinxed. Every time I have tried a reply either the site was not working, or the NBN here had yet another "Hissy Fit", was shut down, or going at the speed of a tired snail.

Technically the heater shorting to cathode should not damage, but can affect bias adversely. The loss of bias can make its own arrangements. Normally with an open Rk everything heads for B+ voltage & a low voltage Cathode bypass cap will be destroyed (punched through).

Unfortunately we do not know what malady took place inside the valve to send it all short

Yes, a H - K short will remove bias if the valve is cathode biassed. But how can the cathode then head towards B+ when it's tied to the heater line (normally grounded) by a heater-cathode short?

And if it's not grounded, the heater line will be shorted to the cathode and not affect the bias in any way.

I suspect that if you see such general mayhem around this area, the H - K short would have happened later as a result of the valve being seriously stressed or maybe the cathode resistor going O/C, allowing a much higher voltage than intended onto the cathode.

There is no issues with this set what you thought was a burnt resistor is just a resistor with a blob of wax on it. This set works . All it needs is a tidy up .

Badly explained: The point with rk open is that if there is a cap of low voltage normally an ecap on an OP tube or often, on 2nd detector it will punch through and become a short, rarely do they explode. They can be destroyed by AC as well, as they conduct it.

If the cap shorts and the resistor is good naturally it wont burn. If there is no cap & there is a malfunction causing the tube to become a diode, then Rk, or the backbias resistor can cook. Never heavy up a back bias resistor, better it burns on overload than the transformer. In the majority of cases where this has happened & the backbias has been fried there will be a shorted filter cap, or a shorted valve & it often presents as heater cathode short: That may be debris from a grid fail.

Not all faults follow the book. Never trust an old electrolytic anywhere to be good.

This has been recapped today. With success I might add.

This radio had a problem with volume . It would go low and then normal and stay stable. I cleaned and tightened the valve sockets and this seems to have fixed the problem. The 80 socket was very loose. It's amazing the difference . It's a 80 year old set playing very strongly.