A while back I posted a message asking for advice with an Eddystone
770U MkII restoration and since that time I have had a lot of guidance
from Graeme Wormald, Gerry O'Hara, Graham Gosling and more recently
from Chris Parry. Essentially I now have this receiver returned to a
high physical standard with cabinet and front casting re-painted
professionally.

I have worked my way through a number of basic problems starting with
a lack of audio resulting from a fault on the base of the first audio
amplifier, intermittant crystal calibrator caused by a dry joint in
the calibrator supply plug, no signal operation which was cured by
replacing V1 RF amp and V2 LO. This gave me decent operation on all
but Band 1, the top band operating from 390MHz up to 500MHz.

An examiniation of the turret showed that the Band 1 coil biscuit
substrate was decomposing into a powdery asbestos like substance. The
material was also swollen so that material was being shaved off by the
fixed metal turret contacts as the rotor was operated. However
although the electronic aspects of this coil look very basic no
component fault could be detected. My assumption (and it is only an
assumption) was that the substrate was in someway causing RF loss
possibly through damp ingress.

In time I was able to obtain a replacement coil and after fitting I
found that I now had operation up to around 425MHz. as tested using
the 2nd. and 3rd. harmonics of my modest AVO signal generator.
Retesting using a more sophisticated synthesised Marconi 2022E signal
generator simply confirmed this point of failure.

Unable to see any obvious fault or to make any headway using a
broadband scanner to detect for certain an LO (too many signals of
unknown origin) I remembered something about my other hobby with E-
type Jaguars. The myth was of a 150 mile per hour car and while the
press cars in 1961 did undoubtably achieve this speed the average car
did not.

I decided to obtain another set of RF amp and LO valves selected for
best gain etc. aware that very high gain LO valves can cause other
problems. Through Wilson valves I obtained two valves which had an
increase in gain of about 10% and on fitting the new higher gain LO I
found that I now had operation up to 440MHz.

So this receiver is now in pretty good shape picking up military air
traffic and civil air traffic up to Band 2 but only operating up to
440MHz. on Band 1. Adjustment of the turret coil biscuits in reality
is limited to the capacitive trimmers which seem to be pretty
broadband. Adjustment of the coils (in so much as they exist as coils
on Band 1) does not seem practical and I think the fact that the dial
scales were hand calibrated individually confirms this.

My feeling now is that either operation up to 500MHz. needs a
pretty "hot" LO valve of the original manufacture or the LO is
tracking above signal on Band 1 when on Bands 1 and 2 it should track
below and is giving out. I think that to confirm this one way or
another I would need a pretty good signal analyser which I do not have
and so for the moment I suspect I will have to box the receiver up and
leave it at that.

One last possibility would be for me to obtain a blank Band 1
substrate and transfer to it one by one the components from the old de-
laminating original coil. But if anyone out there has more idea's I
would be very happy to try them.

Mike