This week I have been restoring a 1949 KB ER30 radio.
These are a 6 valve largish radio and they have a 10 inch speaker driven by a 6V6GT output valve.
The valve line up is 6K8GT 7R7 6SL7GT 6V6GT 6X5GT and a 6U5G tuning indicator.
The radio was generously donated to the KB Museum by Leslie Wertheimer from Cheshire, and was kindly brought to me, first by forum member "Boater Sam" to Miky's do, then from there to the NVCF by "Keiths TV", where it was handed over to me.
These radios are not particularly rare, a few examples of the KB ER30 (not this one) can be seen in the Radio Museum;
https://www.radiomuseum.org/r/kolsterbr_er30er_3.html. This example will feature in the KB Museum website when finished.
The KB service information is available here;
http://www.kbmuseum.org.uk/kb_servic...KB_ER30_kb.pdf
This example is in better external condition to my original one so was a welcome addition to the collection in the KB museum.
On examination on the workbench I was surprised by the size of the mains transformer, I didnt remember it being as big as that. It seems to be a universal replacement and as well as the necessary windings for this radio it also appears to have 4v and 5v windings. It has been squeezed in (only just) between the magic eye and the OP valve.
I checked to see which valves were fitted and found the double triode, 6SL7GT, was substituted with a 6SN7GT, and when I checked my other ER30 I found that also had a 6SN7GT fitted, maybe KB changed the spec.
I next checked the OP transformer primary and that seemed OK at something over 400 ohms. Next was to try and reform the double smoothing electrolytic, surprisingly they appeared to reform very quickly on my home made reformer, but I found they had no ability to keep a charge so it was released from its clamp and 2 temporary replacements were tacked in. A new 32 + 32 uf capacitor has been ordered from Cricklewood via Ebay. The V5 cathode bypass capacitor was reforming OK but I decided to replace it with a new one as it seemed daft to leave one original component in when all the other capacitors would be new replacements.
Some other work had previously been done in the past to replace some capacitors, there were a couple of Mullard mustards in place of the audio coupling caps C19 and C21 on the V4 anodes. But the remaining 5 waxies and a tiny brown hunts were all to be replaced with new ones.
There is a label to warn service engineers that if the plugs to back panel are removed from the chassis then the ground to the speaker is disconnected leaving the output transformer with no load.
At first switch on the HT rose to about 120v, there were sounds of static on the workshop speaker and all seemed OK, so the lamp was switched out and the HT rose to about 170v still rather low. I switched off and looked for another 6X5 rectifier. I fitted this and the HT rose to about 210v. I plugged in the aerial and the set was receiving loads of stations on all 3 bands, it was very lively, and could really have benefited from a further reduction drive on the tuning capacitor.
Long wave was very surprising, its coverage was almost into MW, covering from 142 to 410 kHz, and I was picking up a number of navigational beacons at the high frequency end. One on 363 kHz was giving out an identity signal of ". . . _ . _ . ."
RTE on 252kHz was coming in very loud and clear, as well as R4 and a host of French stations. MW was crowded with stations, Gold on 1548 was unusually loud and clear and Caroline on 648 at the other end of the band was also very clear with no noticable background noise.
The magic eye had only a faint red glow from the heater. So I borrowed the very good one from my other ER30.
Altogether an excellent performing radio, a credit to the KB design engineers, and it will sound even better when it is back in the cabinet and connected to its 10 inch speaker instead of the 4 inch workshop speaker.
Hope the new smoothing capacitor arrives soon so I can hear the radio as it should sound, back in its cabinet.
Mike