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Old 8th Dec 2015, 6:45 pm   #81
G6Tanuki
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Default Re: Eddystone 888A.

"I used a digital receiver to listen to the local oscillator which is a very easy way to get the end points spot on - on most receivers anyway. Even easier than a frequency counter apart from the mental maths involved. "

Agreed 101% - when frobbing around with this sort of thing I find a modern digital-synthesized receiver to be much more useful than a frequency-meter: you program one memory of the 'test' receiver to the "lower set-point" of the receiver-on-the-bench's intended LO when tuned to the lower alignment-frequency, and another memory to the LO 'upper set-point' alignment frequency.

Also program the 'test' receiver to CW.

Then it's dead easy: set your test-receiver to the lower-set-point memory, tune the receiver-on-the-bench to its lower-set-point on the dial, and twiddle its coil slug until you hear the whistle on the test-receiver.

Switch to the higher-set-point memory, tune the receiver-on-the-bench to the appropriate calibration set-point on its dial, and tweak its capacitor until you hear the whistle.

Repeat this a few times: because you've stored the two points in your test-receiver's memories it's quick and easy to toggle between them.

My current 'test' receiver is a Yaesu FT897D and out-of-the-box its calibration's a lot more-accurate than any of the surplus 1980s/1990s H-P or Rohde&Schwartz frequency-counters/sig-gens I've had in the past.
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Old 8th Dec 2015, 7:51 pm   #82
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Lightbulb Re: Eddystone 888A.

Hmm: it seems that this problem with Eddystone receivers whose local oscillators won't tune over the appropriate freq. range is more common than I thought. Since the most difficult item to source & replace is the associated coil; knowing that coils can change their nominal inductance (for various reasons) as the years go by; that it does seem that it is the higher freq. bands which seem to be affected most - where the inductances are relatively small - all leads me to suspect that it is these coils where the trouble lies. In which case, there are two possibilities: not enough inductance or too much. Not too sure what to do about the first case, but the second should be treatable by replacing the dust-iron slug with one made of brass. Perhaps a 0 BA or a 2 BA screw (with the head removed and a slot filed, thus permitting adjustment) may provide an answer.

Wendy: fancy running that idea up the flagpole to see if it flaps?

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Old 8th Dec 2015, 9:01 pm   #83
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Default Re: Eddystone 888A.

Before proposing solutions we need further insight into the problem.

Are the LO coils losing or gaining inductance? [which would imply issues with the ageing of the cores] or is there some kind of issue with their encapsulation that's causing their residual capacitance to vary outside what the designers at Stratton&Co. originally expected?

I've experienced a slew of issues over the years with the various waxes used to impregnate RF coils: they age in 'interesting' ways which can introduce unpredictable losses, detuning, and unpredictable-"Q".

Others have followed my suggested cures with success - see https://www.vintage-radio.net/forum/...d.php?t=114061

Could be worth removing the problematic coils, melting-off what wax you can, and sticking them in a warm negative-pressure desiccator for a few weeks to dry them out and then measuring their inductances.
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Old 8th Dec 2015, 11:09 pm   #84
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Arrow Re: Eddystone 888A.

Quote:
Originally Posted by G6Tanuki View Post
Before proposing solutions we need further insight into the problem.
Yes indeed: the more unknowns that we can safely eliminate, the narrower the list of suspects. However, you seem to agree with me that the coil is now the primary candidate. My suggestions of changing the coil slug should confirm if a change of inductance is the cause, thus proving (or otherwise) that the coil is defective. Moreover, that test is simple to arrange. Removing that coil will be a tricky and a delicate task, so you need to be very sure that the coil is defective, prior to removing it.

As for a "negative-pressure desiccator", I don't think there are many people here will have one of those. With suspect dampness in a transformer or coil, most people seem to settle for a warm airing cupboard.

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Old 8th Dec 2015, 11:59 pm   #85
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Default Re: Eddystone 888A.

Well gentlemen.... the "can of worms" is getting larger by the day....I admit I did not consider the inductance value changing, only the "C"'s..... I have had the coil out that many times, I am sure it can find its own way out now....as its the 15M coil with very few turns, I think that a rewind is in order.....the sealing medium is wax, it may have had some negative effect on the coil. Also the core is always innermost, thus maximum inductance.
So Al, Tanuki, and others, I will look at that scenario in the next couple of days as I am busy weds.
Thanks for the continued interest and support.... I will report back......
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Old 9th Dec 2015, 12:33 am   #86
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Default Re: Eddystone 888A.

Quote:
Originally Posted by Skywave View Post
As for a "negative-pressure desiccator", I don't think there are many people here will have one of those.
We chemists talk of little else, and could not be without them, though the term 'vacuum oven' is preferred

B
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Old 9th Dec 2015, 12:58 pm   #87
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Question Re: Eddystone 888A.

Wendy - re your post #85. So you've successfully removed the coil - and several times too. From memory of the RF box ass'y., I thought that doing that would be a really tricky job - and perhaps it was - so well done!

When the coil is out, do you have the kit to measure its inductance? Knowing that value and the value of the capacitors associated with it will enable the tuning range to be calculated, albeit approximately.

Al.
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Old 10th Dec 2015, 12:55 am   #88
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Default Re: Eddystone 888A.

Hi Al. Yes I have a decent LCR meter, at least it confirmed the values of the "errant" caps..I will try that tomoz... at some stage...
The next problem was very little BFO injection... I compared it with the 750 and the RF was way down.. about 30 db....looking in the BFO can, I spotted that pin 6 should be grounded, "G3" it was totally unsoldered... Plus one cap was soldered to a heater pin rather than the pin next to it.... It looks like this set was a "Friday afternoon" jobby.
Still it ok now.... just 15 to sort out now... I hope.
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Old 10th Dec 2015, 1:07 am   #89
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Default Re: Eddystone 888A.

Keep at it, Wendy - you'll get there eventually. Fixing radios and other bits of non-functional electronics is just a manifestation of Real Life: nothing really worthwhile is achieved without a struggle: the 3 P's apply. And those are the Things that we value the most.

Al.
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Old 10th Dec 2015, 7:41 pm   #90
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Default Re: Eddystone 888A.

Quote:
Originally Posted by Wendymott View Post
The next problem was very little BFO injection... I compared it with the 750 and the RF was way down.. about 30 db....looking in the BFO can, I spotted that pin 6 should be grounded, "G3" it was totally unsoldered... Plus one cap was soldered to a heater pin rather than the pin next to it.... It looks like this set was a "Friday afternoon" jobby.
Still it ok now.... just 15 to sort out now... I hope.
It wouldn't be the first: History shows a range of Racal RA17/RA117/RA217-type radios with components soldered to the wrong tags, not soldered at all, or sometimes components [in the bandpass-filters] completely missing! I'm entirely happy to embrace Eddystone's gear as being just as subject to this shoddy workmanship.

[In the 1980s one of my roles was doing murderously-rigorous software audits for the aviation industry: you'd be amazed at the amount of simplistic "If it's not X it must be Y" code I found. That's the equivalent of finding a 4.7-Ohm resistor on a circuit panel where the requirement was a 470K-Ohm one]

Never trust the original assembler of *any* radio!
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Old 10th Dec 2015, 9:04 pm   #91
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Default Re: Eddystone 888A.

HI Al and Tanuki. I had not come across or even expected such shoddy workmanship on what would have been an expensive piece of kit.....In my TV production days... (80's) we had quite rigorous QC control, and the QC inspectors were a law unto themselves only answering to the MD.... not even I as Technical Manager has power to over rule, but advise. And.. I admit... we sometimes got it wrong.
Back to the Iron.... kept hot.
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Old 10th Dec 2015, 9:36 pm   #92
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Default Re: Eddystone 888A.

Believe me - when you were a manufacturer pushed to get a batch of receivers/transmitters/data/crypto-devices out of the doors to a deadline, quality-assurance became a bit of a handwaving-issue: if the customer was .mod.uk or .gov.uk then you'd sometimes be paid-by-delivery even if the stuff delivered was 'marginally' functional, and you cleared-up the more-obvious failures after you'd got paid!

RA17/117 bandpass-filters are quietly known for having various capacitors [particularly those initiating/terminating the filter chain] either unsoldered, or missing entirely!

I'm familiar with an Eddystone 730/4 whose BFO was wired in a way which could never possibly have functioned; nevertheless it was issued to me [as school CCF Signals Sergeant in the 1970s] by CoD Donnington workshops.

Last edited by G6Tanuki; 10th Dec 2015 at 9:42 pm.
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Old 12th Dec 2015, 11:34 am   #93
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Default Re: Eddystone 888A.

Don't take ferrite cores on trust!
There are different grades and some are delicate to magnetic fields.

At least one sort used by Pye could be ruined by a pulse of current through the associated coil (short to deck of the associated transistor collector for e.g). Many were also ruined by the magnetic field from a well known type of thermostatically controlled soldering iron which was allowed to come too close.

It was amazing what simply swapping all the ferrite cores could do for front ends multipliers etc that would not tune.
The problem was finding supplies of known good ones. I was lucky. Neosid happened to have an office on the other side of town!
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Old 13th Dec 2015, 11:42 am   #94
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Default Re: Eddystone 888A.

Hi Jon..... Thanks for that input.... I will swap a core from say the "Top band" range and see what happens....watch this space.
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Old 13th Dec 2015, 8:45 pm   #95
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Default Re: Eddystone 888A.

Hi Wendy: Don't assume that the magnetic characteristics of the cores in the top-band stages are the same as those in the upper-HF-band stages!
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Old 13th Dec 2015, 8:58 pm   #96
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Default Re: Eddystone 888A.

Heating and slowly cooling magnetic cores can be very therapeutic.

David
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Old 14th Dec 2015, 12:09 am   #97
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Default Re: Eddystone 888A.

Hi Peeps... Ok Tanuki, but it changed NOTHING... I even added one turn to the coil and effectively no effect.. However..............I removed the Local osc valve V3 and did what I should have done on day one...... fed a signal from the tracking generator, to the ant input and monitored the output on the spectrum analizer at the grid of the mixer. On all bands except 15... perfect expected results. On 15.... no tuning at all, thus after all this I conclude the Beehive to be S/C or VERY Leaky. This would obviously damp the tuning, and give very weird results, also the sensitivity on that band was 40 db down... Thus.. I have ordered 2 x beehive trimmers from ebay, and expect delivery on weds., I am not even looking for any more suspects. I have things to do tomorrow (Mon) anyway. Watch this space..
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Last edited by Wendymott; 14th Dec 2015 at 12:11 am. Reason: added info
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Old 14th Dec 2015, 1:00 am   #98
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Question Re: Eddystone 888A.

Wendy - now I'm totally confused! By what you've just written, it seems that you've now concluded that the fault lies in the preset adjustments for the variable-frequency tuned circuit at the 1st. mixer grid. However, up to now - and based on what you have reported during your investigations prior to your last post - I (and, it seems, a few others here) have been making suggestions on the understanding that the fault was in the variable frequency 1st. local oscillator, i.e. that that oscillator will not track correctly. Hence, I (and a few others) now seem to have been barking up the wrong tree!

Can you clarify things for me, please? Have I mis-read some of your previous posts?

[Just an afterthought: beehive trimmers - like any other component - can fail of course. But, in my experience, a total failure of a beehive trimmer is a very rare occurrence].

Thank you.
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Old 14th Dec 2015, 8:46 pm   #99
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Default Re: Eddystone 888A.

Hi Al. Ooopppssssss.. Sorry for any confusion I have caused. The problem certainly lies in the Second stage tuning on 15M. The fault appeared to be mis tracking, where setting the L at the LF end, for a signal peak.................. then setting the tuning at the HF end and peaking the Trimmer for "maximum smoke", caused the LF end to require another adjustment of "L" to peak the signal, add infinitum... until I had no adjustments left and still no proper peak.
In my investigations, I removed the Local osc valve V3, and fed in a signal from the spectrum analyser tracking generator, and monitored the grid of the mixer. There is no tuning "hump" at all.
The beehive cap is the only component I have not replaced. Even I am not convinced its to blame, the only other possibility is that the "shorting" contact of the bandswitch is not clearing the contact, and is killing the signal.
I will know later tonight either way... as I can "borrow" a trimmer from another coil, and also check the switch contacts.
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Old 14th Dec 2015, 9:46 pm   #100
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Arrow Re: Eddystone 888A.

Quote:
Originally Posted by Wendymott View Post
The fault appeared to be mis-tracking, where setting the L at the LF end, for a signal peak.................. then setting the tuning at the HF end and peaking the Trimmer for "maximum smoke", caused the LF end to require another adjustment of "L" to peak the signal, add infinitum... until I had no adjustments left and still no proper peak.
O.K., Wendy - I understand this whole saga a bit better now: thanks.

Now I don't want to go on and on about this, nor do I wish to cause you any embarrassment, but from the above extract, you do say:

"The fault appeared to be mis-tracking".

It is the local oscillator which tracks the signal circuits, not the 'other way round'. It was your way of describing the observed fault conditions that threw me (and others here) on to the wrong foot and caused a string of suggestions about possible faults on that L.O.

Anyway, let's move on. I (we?) now have a much clearer idea of what the fault actually is - and where the cause of the problem lies. So keep at it - I know you'll get there in the end.

Al.
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