CR100 /8 Re-alignment

[Daventry 5XX]

Hi All

I've made some progress in the battle to breathe new life into my CR100

I now have an output on all 6 wavebands, but the frequencies are way out of alignment.

Not surprising when you look at the screws in the coil assemblies, nearly all the locking nuts are loose and many of the screws are wound out so far that they are almost hanging out.

Clearly the phantom bodger has got at it.

My next job is to try to re-align them, but I only have a 100MHZ scope, a couple of geriatric sig. gens and a good quality (fluke) multimeter.

I have never attempted to re-align anything as complicated as this before,( I have done a couple of radios), can I do it with the tools at my disposal or do I need to raid the piggy bank and go on E bay ?

Can I find the necessary info. to do the job on this site or do I need to look elsewhere ?

Any advice would be most welcome

Cheers

Alan

[PJL]

I made a crude wobbulator but can't remember if it was for fun or essential! What I do remember is you must align the IF to be centred on the crystal filter.

[lesmw0sec]

Not familiar with this set, but you could probably get by with what you have, if you can borrow a frequency meter to check the accuracy when doing the I.F. in particular, bearing in mind what PJL has stated.
Have you searched for a manual on it? That should give you some pointers, but beware that the manufacturers often spec. test instruments to give the perfect results easily. You can often work around with different kit.

Les.

[Top Cap]

Ideally you should have removed the cover from the Xtal unit and hopefully discovered the actual crystal frequency written in pencil by some thoughtful soul back in the 1930's-40's.
It is not a light task to do this and others have found it possible to get close enough using a frequency counter and fine tuning a signal generator with the receiver set to 100Hz bandwidth, searching for the peak.
Having found this frequency and noting it on the counter, then it is best to align the i.f. transformers to this as otherwise one detects the wrong feel as the bandwidth control is rotated through its ranges. Just keep an eye on the counter to make sure the signal generator keeps at the noted frequency.
RF Stages: Now remember that the receiver was NOT aligned to the scale when manufactured. The angular position of the tuning capacitor was set to a particular point then the receiver was tuned to crystal markers and a vertical line drawn on the scale which was pre-printed with horizontal lines and rough positioning of numbers for the frequency points e.g. 1.2, 1.3, 1.4 etc.
This now poses some questions. Is the original scale still able to show the correct frequencies if the upper and lower points on each band are aligned? You might get away with it but over the years the tuning gangs value across the band(s) may have changed as well as the local oscillator tuning components.
I would certainly recommend trying this first anyway, as if you can get the band edge frequencies in, then yes there is a good chance the others may come into line too.
What is the condition of the scale? Some are so badly rust coloured as to be not usable. I have had a few like this and so another scale was contemplated. I hope to attach a zip file with 3 drawings, all done with MS Paint and for good reason as this program allows one to easily shift sections of the drawing by one pixel at a time. The first drawing is a mark up drawing, you have to print at the right size to emulate the one already fitted, cut it to size and fit temporarily to the drum. I have test printed this on my printer SET TO 100% and it comes out with a drum scale approximately 9 inches in length. I do not have a CR100 here to check with but hopefully it is about right. With this, you add your own vertical lines using an accurate marker generator, making sure the line you make meets with the dotted scale below, this will serve to get the right position on you final print. The other 2 drawings show how/where the vertical lines are added but of course your CR100 will be different. (They all are I don't think there ever was two B28/CR100's with the same scale!)
One useful trick for doing the local oscillator alignment is to listen for it on a digital receiver set to CW where it should appear 465 kHz above what the dial setting is. So if you wanted to mark the scale at say 1.8 Mc/s on Band 4, tune the CR100 until a beat note is heard at 2.265MHz on the digital receiver. (Hope I have got that right it has been a long day and I am very tired)
This method is excellent at the top end of Band 6 where it is very easy to align to the wrong setting by accidentally selecting the image frequency just 930kHz away. Listening for the Local oscillator ensures you pick the right point.
These are just some of my ideas, no doubt someone more knowledgeable will come up with some better ones, Good Luck though, there is something about these receivers I have always loved, I just don't know why.

[Daventry 5XX]

Hi Top Cap

No need for me to remove the cover from the Xtal unit, many years ago some kind person stuck a label on the outside with the frequency written on it.

Its been measured at 463.60 kcs.

Looks like I need to invest in a frequency counter before I go any further

many thanks for your help and advice

Alan

[turretslug]

Alan, I don't know how serious a type of frequency counter you're looking for or how much construction is your thing, but for the price of two pints of beer (including delivery), I've been most impressed with one I recently purchased from eBay, item 251548136454. It's a bare, assembled PCB but easily housed. Below 10MHZ, it'll give 10Hz resolution, more than adequate for one of your "geriatric sig. gens"- in fact, it'll do 10Hz above 10MHz, you just lose the MSD. Handily, an IF offset can be preset in 100Hz steps, so when the job's done, you can set it to 463.6 and use it with the CR100- you'll need a simple buffer amp to "sniff" the LO, though. The consumption is quoted at 90mA but I found that, when set to plentiful intermediate brightness, around 30-40mA consumption resulted. Mode is set by two PCB buttons- it comes without instructions but if you can get to grips with the average digital watch, this'll be no headache. Other display colours are available by searching "frequency counter", but at slightly varying prices, and not sure if all offer UK delivery.

Mods, I had a good read through the eBay rules, I've no vested interest here and as it's a quantity stock "Buy it now" item, there's no "egging on" motivation.

Agree with TC, it may be a comprehensive coverage set but the crystal filter is about the most complex/"unusual" aspect of it, everything else is much the same as domestic set practice of the era, just more of it!

Good luck, Colin.