Hi Gerry,

Thanks for the reply. I have taken this restoration and repair on as a hobby
project after completing my two E-type Jaguars and found working on the 770U
turret tougher than anything on the E-Types. I have worked my way through
various audio and Xtal calibrator faults and cleaned the turret contacts
to get the receiver working. I have replaced the front end valves to ensure
correct gain (from Wilson Valves) and now have a situation where I have all
bands working except Band 1, the highest frequency band.

I have examined the coil biscuit several times. The base material on which
the assembly is formed looks different to that of the others in that instead
of being a solid looking grey material it looks rather like crumbly white
asbestos and is swollen in thickness. I think this may be through having
been stored in a damp environment. TheBand 3 coil has a little of this
appearance
but not nearly so bad. This swelling in width has meant that as the turret
is rotated the rigid parts of the contacts on the turret side have started
to "machine" away a thin layer of the coil biscuit material. Never the less
I can see no electrical reason as to why the coli set would not work.

My signal generator is an Avo 135 which works up to 240Mhz. however I have
been able to use the 2nd and 3rd. harmonic output to feed into the aerial
input to check the receiver successfully up to and including Band 2. So while
I see a signal at the top end of Band 2 I cannot see the same signal at the
same frequency at the bottom end of Band 1

I have carried out DC checks at the anodes and cathodes of V1 RF Amp and
V2 LO. These show a variation in some ranges which is possibly to be expected
and others with no obvious explanation On all ranges but Band 5 the V1 anode
volts are 119. On Band 5 it is 149. Same with Cathode volts on V1 all are
0.7 except for Band 5 which is 4.6. So far I cannot see a reason for these
higher voltages yet Band 5 is working.

On V2 LO All anode volts are around 0.35v except for Band 1 which is 56.
I think this may be because the anode is fed by a small inductance on the
Band 1 coil pack instead of a resistor which is the case on the 5 bands.
Cathode volts are 1.7 on Band 1 and around 0.85 to 1V on all others. Its
a mystery that has me stuck at the moment. I am thinking of getting on with
the cabinet restoration while I think it over.

I have had a 940 from new in 1968 but more recently bought an as new 830/7,
EA12, 770R MkII and of course the 770U MkII. Never had anyproblem with the
940 all of this time both sides of the Atlantic except for getting the cabinet
off in the 1970's in Boston to change to 110volts. I have read and enjoyed
all of your projects. A lont time ago as an apprentice Radio and Television
Engineer (1960 - 65) I repaired many 405 line TV turrets but have seen nothing
like the one on the 770U or R. I am afraid I moved on from Radio and TV to
scientific instruments and sales and marketing management by 1969 so its
a lont time since I did any fault finding. I have limited test equipment,
the sig gen, Avo 8 and a 120Mhz scope. I hope to find another coil for Band
1 and if Icure the fault source enough equipment to carry out a full alignment.

Thanks for your input any further advice appreciatted.

Regards,

Mike Cassidy




.
>-- Original Message --
>To: <eddystone_radio_users@...>
>From: "Gerry O'Hara" <gerryohara@...>
>Date: Wed, 26 Jul 2006 00:53:34 -0700
>Subject: RE: [eddystone_radio_users] Eddystone 770U MkII
>Reply-To: eddystone_radio_users@...
>
>
>Hello Mike,
>
>Did anyone respond to your posting? - I thought someone would have by now.
>I am not at all familiar with the 770U, but the symptoms you describe would
>indicate that audio and detector stages are functional, the 5.2MHz and 50MHz
>IF stages are functional and that the fault(s) are in the RF circuitry.

>If
>the fault is present on all ranges, the symptoms would suggest the first
>suspect to be the 1st local oscillator (not oscillating) - do you have any
>way of 'listening' for the oscillator to check this directly?, eg. a
>receiver covering the oscillator range (or part of it), frequency meter,
>GDO
>etc. If the fault is present on all ranges, then the fault could be the
>valve (6AF4A) or one of the few passive components associated with it, psu
>problem (stabilizer), the valve socket or even a dry joint, rather than
in
>the coil packs (turret). If the fault is only on one or more ranges (but
>not necessarily all), suspect components in the turret or its contacts.
>Have you checked the voltages in the RF/LO section, including whether the
>stabilized supply (VR150) is working ok? (see Appendix A in the manual
>attached for the set's voltage table), also, check the mixer diode, D1
>(GEX66). Note that the turret includes some passive components that adjust
>the HT2 voltage to the RF section depending on the band in use (R89, R91
>etc). Also check that the AGC is functioning (put a VTVM or similar high
>impedance voltmeter across the AGC line and feed a signal into the IF and
>see if you get a reasonable voltage - not sure what this should be on the
>770U, but my 770R can give -10v on a strong signal. If no AGC, check C30
>and V11b.
>
>If you cannot find a UK source for new valves (unlikely), eg. Wilsons (tel:
>01484 654650) or The Tube Shop (tel: 0870 9220404, or
>http://www.Tube-Shop.com), the RF valves can be obtained from AES
>(http://tubesandmore.com) : the 6AF4A is listed at US$4.25 and the 6AM4
at
>US$3.05 (2004 catalogue - check latest prices on the web site) - even with
>postage from the US this is pretty cheap. Also, try a search on Ebay.
>
>Let me know how you make out and/or if someone more knowledgeable has been
>able to help.
>
>73's
>
>Gerry
>
> _____
>
>From: eddystone_radio_users@...
>[mailto:eddystone_radio_users@...] On Behalf Of superconjacko
>Sent: July 16, 2006 4:40 AM
>To: eddystone_radio_users@...
>Subject: [eddystone_radio_users] Eddystone 770U MkII
>
>Hello, I am currently restoring a 770U MkII which although having a
>scratched cabinet (currently at the paintshop) looks for the most
>part untouched. Having sorted out lack of audio through dirty valve
>contacts I am now trying to deal with the more serious problem which
>seems to be an RF stage failure.
>
>Taking Ted Moore's advice from a very early newsletter I have
>decided to replace V1 and V2 before going any further. Can anyone
>advise me of a suitable reliable source or dealer who can supply me
>with the valves I need (also same for a 770R MkII).
>
>Seperately can anyone comment on what I have found so far. No output
>of course but appropriatte signals out when using a signal generator
>to feed in the first and second IF frequency at the first and second
>IF. Feeding in any signal at the aerial point (up to the limit of my
>signal generator)gives no output when the receiver is tuned to that
>frequency except that when the first IF freq of 50Mhz. is applied to
>aerial input I get a tone out. Presumably through some form of break
>through.
>
>Pressing the calibrate button give a very low level constant tone
>but no calibrate points. Since this signal is fed via the RF stage I
>have taken this as confirmation of an RF stage fault. I note that
>the calibrate circuit given in the MkII diagram differs from that
>shown in the addendum sheet in the manual. Does anyone have any
>knowledge of this.
>
>And finally I see that someone has lifted a small 50pf coupling
>capacitor which feeds into the AVC circuit presumably disabling
>same. Does anyone know if this is carried out for some specific
>reason.
>
>Hope for some input, Regards, Mike
>
>
>
>
>
>



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