Substituting valves

[G8HQP Dave]

Adding a resistor in series with the EZ81 cathode so that the HT voltage is the same as it would have been with an EZ80 is not too daft, but almost certainly unnecessary as domestic sets were designed to cope with some voltage variation. I would be more concerned about the EZ81 greater heater current. The other stuff about extra current messing up MW is simply untrue.

[jonnybear]

Originally Posted by jsbhavsar

Ohh yeah Dave. I have never taken that valve set again to him. Besides, he was pretty old in 2002 to attend to valve sets and maybe impossible now. He had attended this Ekco set just for curiosity because he had all the valve testing equipment from his Philips job. I still believe he was right in replacing the power cord and volume control ON OFF switch. I understand that EZ80 had become weak but he should have waited to procure EZ80 than go for EZ81. I still remember him saying "I did something to the pin base", however, I just dont recall what was that. Whether he changed pin connections or did he simply add a resistor to reduce current ahead is not clear in my mind.

All this sounds a bit like the old articles by DB in TELEVISION magazine, ref Snoddies repairs

[turretslug]

That extra 0.4A drawn by the EZ81 heater over the EZ80 is getting beyond what I would think of as insignificant- as well as extra heat in the vicinity of the rectifier, that elderly mains transformer will be getting a bit warmer, too, and it's always wise to keep half-century old components from getting avoidably stressed.

Not strictly concerned with the thread title, but is it possible that something was mis-connected/omitted in the attempt to connect a ferrite rod and subsequent reversion?- it need not have stopped the set working completely on MW but could quite feasibly have left it performing rather poorly.

Good luck with your investigations- it sounds as if it was an excellent, high quality set in its day.

[jsbhavsar]

Yes turretslug, the National Ekco A731 radio was kind of "world receiver" along with its younger brother A730; both were released in 1959-60 in India. It was collaboration with Ekco UK wherein the kit+components arrived from UK, and got assembled in Mumbai downtown. I still do not get why Ekco UK or National Ekco India carefully or carelessly avoided the "ferrite rod aerial" in both the sets. It would have definitely helped the MW and MSW bands if not all. Either they were too sure of tuned RF stage to boost the MW performance or the theme of these "world receiver" sets was more focussed on SW reception for expats.

Here is the advertisement preserved by Mr P Rajan from those days about the two sets. If you observe, the A731 (with tuned RF stage) is 26% more costly than the A730 (no tuned RF stage). In those days, Rs 625/- would have been eight months salary of an average clerk or accountant and three months salary of an engineer.