That would make sense. I was a mainframe computer tech for 20 years and the numbering system we used to locate the correct logic pin amongst the thousands of pins on a logic board never included I or O to avoid confusion with ones and zeros.

The only problem with this is Chris's radio and my 1972 radio are both July radios but start with a J. Interestingly both are July radios and both start with JH.

The only problem with this is Chris's radio and my 1972 radio are both July radios but start with a J

I guess it's the date of the "youngest" (i.e. most recent) component that is closest to the set's manufacturing completion date.

The OP transformers might have been an early example of a 'just in time' supply chain, obviously not a system they employed for their caps

You're on the right track with the transformer date codes.

It is the second letter that indicates the month not the first. It seems that aside from the Kxx on the 11-90, all the 11-99 radios have Jxx date codes. The second letter is the month and the number is the year.

I checked one of my radios again (it's already in bits) and the date code is JB9 i.e. Feb 1969. This was for s/n 16310 which I already had estimated was a Feb/Mar 1969 radio.

The other examples given also seem to match up well. Chris's JH5 matches August 1965. A couple of the examples are out give or take a month that that would be expected as parts are often sitting around for a while.

It is the second letter that indicates the month not the first.

Perhaps the first letter denoted supplier, or maybe factory?

The Miniwatt valves also have a date code printed in tiny figures near the base.

Example:

C7D = C, Hendon Works. 7, 1967 & D, April.

A 7 or more year run for the last of the Krielser valve mantel sets is a pretty good innings. There ought to be plenty of survivors out there.

A 7 or more year run for the last of the Kriesler valve mantel sets is a pretty good innings. There ought to be plenty of survivors out there.

I'll say. One is lucky to get an appliance to last that long these days let along be manufactured for that long. There was an article on Today Tonight last Monday relating to Australia "becoming a throw away society" with some emphasis on the lousy quality of fridges and the equally lousy customer service when it comes to trying to get spare parts when things do go wrong. The story is unfortunately about 25 years old because that is how long the world's major electrical and electronics companies have operated their 'planned obsolescence' policies so that people just keep buying more junk to fill the rubbish tips with every few years.

The programme showed one bloke who owned an electric Kelvinator Silent Knight that was 55 years old and still ran perfectly and all the plastic fittings on the door were still in good condition. He'd even had a new door seal fitted as this would have been the only weak point with these fridges and with a good door seal even a fridge like this will still operate with reasonable economy. His only problem would be a gas leak - the ammonia gas used as a refrigerant in these old beasts is no longer made. The fact is, assuming a gas leak doesn't develop, a well looked after Silent Knight like that one should run for 100 years, just like the radios we all collect.

Well mine is 6V4 rectifier, serial 15774.
Haven't found any dates on any parts of mine.

It also has that couple of drops of white paint that is probably on every second old radio.

Cleaned Up:
Image Link

Funny thing, mine had a bum 6N8 valve, but I had a spare.
As it was, it worked, but was so quiet I had to hold the speaker to my ear
unless I touched the antenna terminal.
It seems no wire antenna was good enough to make it good
unlike any other AM radio I have here in the same location.

With the 6N8 replaced, it's a performer!
Can someone explain what this valve is doing in the circuit?
http://www.kevinchant.com/uploads/7/1/0/8/7108231/11-99.pdf

Without swapping valves, I might have just thought it was a
bad model radio that needed an awesome antenna,
and wouldn't have been impressed with it,
except it has been mentioned in this thread that it is anything but deaf.

The pentode part of the 6N8 is an intermediate frequency amplifier; the diodes detect the audio through R5 to the volume control, and provide automatic gain control voltage to the grids of 6AN7 and 6N8 through R4 the 2.2Mohm resistor.

Thanks, then perhaps it stands to reason it is able to pass
a signal without amplification when the valve was bad?

I should have at least noticed it was sitting between two IF formers.
So the amplifier would have still been fine.

Since a signal, albeit quiet, was being detected, the diodes were probably OK. It seems likely the problem was therefore a weak pentode amplifier.

Hi Guys. This thread, with regard to serials and dates, prompted me to check my 11-99 that get used daily in the kitchen and sign up with my answer. Mine has a serial # 46591. The code on the mains transformer was not hard to decipher - it says "25 APR 1974"

1974! You currently hold the record for the most recent 11-99. I amazed they were still in production by then and going by the serial number progression, still selling.

My interest in radio started in the early 70's and I was always saving up pocket money to buy my next one (most I've still got) but I don't ever remember seeing these for sale. I'm sure a brand new valve radio would have caught my interest. It's possible I had seen them and assumed they were solid state, valve technology wouldn't have been a strong selling point for a radio in the 70's.