KB NR40T radio.

[crackle]

I have just finished restoring this radio, it is a KB NR40T an export model.

All the brown hunts and the couple of wax caps were changed and the electrolytics reformed. But during further close inspection of the chassis I found this rather stressed 10k resistor connected across the aerial and earth sockets. Its value was intermittent, ranging from infinity to 2k.

I wonder how this could have happened, there is no sign of leakage on the transformer primary. The solder was removed by me.

Mike

[Cobaltblue]

Hi Mike I wonder if someone used the old "mains aerial" dodge and the cap went leaky or they didn't, fit one at all

Cheers

Mike T

[crackle]

That is possible Mike, the poor resistor could have been dissipating nearly 6 watts.
It does not look like it was designed for a mains aerial.

I was interested to find that the RF amplifier valve was bypassed for MW.

Mike

[Cobaltblue]

That's a fantastic looking set by the way don't think I ever met one in the metal.

Cheers Mike T

[crackle]

Being an export model I think they are pretty rare, I have only ever seen one other and that is Paul K's. There are no British stations marked anywhere, other than "London", and that is only marked on the SW bands.
I think this one was a real case of "my one is bigger and has more wave bands than yours".
All the bands are very lively, at night, except the 13 & 11m bands, they are rather quiet.
This one originated from North Norfolk on the coast, so it was possibly used by someone to listen to the Trawler band.
This radio dates from 1957, I would think this was one of the last large woodies that KB produced, other than radiograms.
I cant believe nobody else bid on it.
Mike

[crackle]

More photos of the dial here; http://www.kbmuseum.org.uk/kb_images/nr40t/nr40t.htm

Mike

[turretslug]

Distinctive set- curious construction with two chassis modules and joining bars, makes me wonder if this was to suit radiogram construction with chunks in different places or even a console with a double-deck arrangement. The way it is would help isolate the hot bit from the oscillator bit!

[Cobaltblue]

The construction is similar to the GR40 a set I once started a thread about

Cheers

Mike T

[Heatercathodeshort]

Maybe a lightning strike cooked it. Being an export model it was probably used with an outdoor aerial. Just a thought.

[turretslug]

Something rings a bell about there being a post-war HMV multi-band (export?) set that had a similar "tombola drum" tuning scale arrangement and a split chassis arrangement, but can't think of the chassis number. (6BE6, 6BA6 etc.)

[Synchrodyne]

The split chassis construction would appear to derive from the earlier FR20T model, where it was required to accommodate a large tuning scale drum.



Eight bandspread bands suggests that K-B designed and made its own front end, both mechanically and electrically. The proprietary bandspread front ends, such as from Weyrad, seemed to have six bandspread bands. Eight was logical, in that all of the HF broadcasting bands from 11 through 49 metres were covered.

A self-oscillating mixer using the relatively noisy 6BE6 seems to have been a less-than-stellar choice for this kind of receiver. Assuming that Brimar sourcing was a given then it had the 12AH8 triode-heptode available from 1949. And I think that the later 20D4 “super-duper” triode-heptode was available by 1957.

The 422 kHz IF was one of two BREMA post-Copenhagen recommendations, the other being 470 kHz, which seems to have been the more used of the two. 422 kHz might have been unusual for an export model, but on the other hand 470 kHz could be problematical in areas that used 10 kHz MF channel spacing, so perhaps 422 kHz was better in that respect.


Cheers,