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Old 14th Dec 2015, 11:05 pm   #101
Wendymott
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Default Re: Eddystone 888A.

Hi Al and the rest of the collective. Good news first.............. I have located the fault.................Bad news second............... The Contact on the Wavechange switch is "Wiped out".......
I found this as I rotated the switch, I got the expected output, but quarter way through rotation between idents...see photo. Now as you can all imagine.....this is going to be a night mare to replace that wafer.. even if I could get one..........so.. for the time being... 15M is off the menu.
Thanks..all of you for your comments and suggestions.

So much for a "cheap buy" on ebay... haa haa.
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Old 15th Dec 2015, 12:42 pm   #102
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Default Re: Eddystone 888A.

That looks like it will be a real pain to gain access to!

I have in the past replaced the contacts on those kind of Yaxley-switches by drilling out the rivet and fitting replacement contacts (salvaged from another switch) with a ?10BA? screw/nut.
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Old 15th Dec 2015, 1:50 pm   #103
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Arrow Re: Eddystone 888A.

Hi Wendy. Re your report on your discovery about the switch. Is it that the fixed contact is loose to the paxolin? I see that someone has been in there and done some component replacement: I wonder if that someone was a bit heavy-handed?
The total removal of the w/c switch assembly will, in reality, be impractical. So some type of fix in-situ will be required. I'm sure that there is a way - time for some lateral thinking . . . I'm thinking . . .

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Old 15th Dec 2015, 3:01 pm   #104
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Default Re: Eddystone 888A.

Hi guys........... The switch contact seems to have dis integrated...As mentioned earlier one or two valve base pins were also broken, thus suggesting metal degradation.
I did consider fitting a Reed relay across the broken switch, and selecting on the 15M range, however there is no switch point where I can use an energising voltage. The only part of the switch with ht that could be "potted" down is the anode windings of the mixer coil, but....and here's the annoying bit... it is the anode connection to the wiper, not the HT feed, I could have potted the voltage down to a drive transistor and no one would be the wiser, but .............. I have decided that 15M missing is not worth the effort.
But thanks to You Al and Tanuki and others for your help and suggestions. I am now going to recase the 888 and sit in a darkened room..
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Old 15th Dec 2015, 10:28 pm   #105
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Arrow Re: Eddystone 888A.

Seems to me that you now have the following choices:

1. Sell it on: effectively using the reverse procedure (and description) as when you purchased it. With a bit of luck, you might even break even.
2. Scrap it for salvage parts / spares. (Recently I had to do that with a 770R Mk. 1: that's one Eddy, which you do not want to go anywhere near!).
3. Be really brave and do the necessary dismantling in order to replace the broken wafer. Sounds a daunting prospect, I realise, but consider these points in so doing:
(a) this receiver was built by hand, so it can similarly be un-built by hand and then rebuilt - by hand. In many areas in the 888 / 888A, Eddy. could have done a much better job as regards component and wiring placement: now's your chance;
(b) there is a lot of documentation and experience available when (not if) you get stuck. This very forum being one good example;
(c) you'll gain a lot of really useful experience in taking it to bits and putting it back together again - and gain some real credo & prestige for such a successful and difficult repair;
(d) whilst it's in bits, you can do a real overhaul, especially cleaning those areas and parts that are impossible for access without a total strip down.

With time, care and attention to detail, you could end up with an 888 which is as good as new.

Al.
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Old 16th Dec 2015, 11:26 am   #106
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Default Re: Eddystone 888A.

Hi Al. I was just discussing the very same suggestion on the phone with a mate of mine...What I did was.... fit a reed relay across the contact and the wiper, use rectified heater voltage, and a small switch at the rear, in the small eventuality that I would listen on 15. Not nice I know, not in the spirit of the true restorer.... but it works for me. As it happens I received a PM asking if I would be willing to do a write up for the forum... which is 50% complete.
IF and I say If.. a full switch assembly came available, it would be worth totally stripping..... but I cannot see that happening...
As long as 40 and 80 are working ok, its being re assembled.
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Old 18th Dec 2015, 5:06 pm   #107
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Default Re: Eddystone 888A.

Hi Peeps.. Just out of interest... well to me anyway...... I replaced the first local osc with a NTE312 Fet....... similar to a 2N3819..... Shunted the anode load with a 1m/H choke, potted the HT down to 12V, and fitted the fet onto a B7G plug. Worked ok on all bands except 160M. Reviewing the schematic given to me by Tanuki, it shows a 47K as the gate bias, the resistor in the eddy is 22K. Replacing this to 47K.... voila.... I am a bit worried that on 15M the tuning range has changed considerably, i.e 21.5Mhz is now where 21.3 was..... and 28Mhz is very nearly off the scale LF end... This is what David suggested may happen as the original components would be chosen with the valve's internal capacitance in mind.
It may be a none starter in the final receiver.
Since then more of the wavechange switch has become faulty..... so the 888 is now cased up until I get some replacement wafers and bits.
When the switch shaft is removed I may look at re wiring the Osc base to a 6C4.
The fun of radio.
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Old 18th Dec 2015, 6:28 pm   #108
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Default Re: Eddystone 888A.

The main worry is that the mixer may be a bit light on LO drive.

David
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Old 18th Dec 2015, 7:35 pm   #109
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Default Re: Eddystone 888A.

Is there any room to fit a flag to the switch shaft which could operate an optical sensor to drive the reed relay to do the old contact's job? It wouldn't necessarily need to be on that part of the shaft in the picture.
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Old 19th Dec 2015, 6:35 pm   #110
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Default Re: Eddystone 888A.

Hi David. I will do comparative checks before I fully commit...... Hi Chris. I really did think of that...but I discounted it.....however... today I was given some ceramic wafers of a similar physical size... not to use as a replacement, but for the contacts.... AND.... bonus.... the rivets when removed with a tiny grinder are still long enough to peen over on the composite wafers.
Getting giddy.......will start on this sunday.
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Old 23rd Dec 2015, 11:17 pm   #111
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Default Re: Eddystone 888A.

Well Peeps.... It is happy time at G8BZY's QTH... The 888S is reasonably "on song"...There are still one or two "niggles" to sort, but the main chassis is working on 10,15,20,14 and 7. I still have to change the Mixer input switch wafer, or 15M switch leaf, but either way it means a near complete dis assembly.....but at least I have a great starting point now.
The FET 1st Vfo oscillator is now working well with a NTE312 running at 6.5V DC. It is a big shame that I cannot derive 6.5 from the heater supply, as that is 3.0.3 V, thus I had to pot down from 150V. The pot resistor is 14.4K to allow 6 m/A for the VFO and 4 m/A for the zener. Just a bit warm but outside the Diecast case. The injection voltage mirrors the Valve version very well. Initially the FET died as I was using 12V dc and the P P voltage was too high.
A Cautionary note.... do NOT Monitor the frequency with a X10 scope probe on the drain of the VFO, the capacity of the probe "Pulled" the frequency low by about 1.5 Mhz on 28 Mhz.... obviously due to the small capacitance already in circuit. Took me a few minutes to find that one.
I would guess that Eddystone, when manufacturing these receivers did not pre align the front end with a spectrum analyser with tracking generator or a POLYSKOP.
10, 15 and 20 have a reasonable peak that tracks the whole scale, but 7 , 3.5 and 1.8 have very poor responses, with 7 and 3.5 having "Double" humps and 1.8 nothing at all.. I will attempt to get 7 and 3.5 a better single hump response.
Well thats it till after Dec 25th.
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Old 24th Dec 2015, 12:59 pm   #112
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Default Re: Eddystone 888A.

Could you not get the "HT" for your FET VFO from the output-valve cathode? This approach was used commercially to provide 'HT' for solid-state UHF tuners in some valve/transistor hybrid TVs, and I used the same approach when fitting transistor BFOs to various valve 'all-wave' receivers.

You may need to raise the value of the existing cathode-bias resistor a bit to account for the 'stolen' milliamps.
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Old 24th Dec 2015, 3:57 pm   #113
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Default Re: Eddystone 888A.

Nice one Tanuki..... I will try and report back.
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Old 24th Dec 2015, 6:18 pm   #114
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Default Re: Eddystone 888A.

Hi Tanuki... The voltage at that point is 4.9V. If I raise the cathode resistor from 150R to 220 R... theoretically it should raise the voltage to 6.4... which is what is required...unfortunately the valve must be a little "tired" and could only manage 5.4V
The VFO needs at least 6.2V to stop the 80M range from "squegging" ..... I am happy with the arrangement, for now, even though I am loosing a little power in heat. As they say... you never get something for nothing... even at Xmas.
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Old 24th Dec 2015, 6:55 pm   #115
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Default Re: Eddystone 888A.

Hi Wendy - I only offered it as a possible suggestion - it's always worth experimenting. Given that you've got a working solution anyway, stick with it!

[Hmmm... 4.9V. That's USB-level power. Could you drive a frequency-synthesizer from it? Or am I tempting you to the dark side?]

~~G6Tanuki (and Archie the dog...)
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Old 25th Dec 2015, 11:52 am   #116
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Default Re: Eddystone 888A.

Hi Tanuki... There is that "Huff n Puff" synth.....which I built, but I found the software in the PIC seemed to be faulty....With the 888, I think the stability is quite good, "not done any measurements yet".... but due to the tuning range spread over the whole dial, the main culprit, the mechanical expansion of the tuning cap, will be negligible. However the 750 is another problem altogether, as a general coverage receiver..the amateur bands are miniscule thus the tuning ratio is much larger.
Regarding the "dark side", I am all for making things better, whatever the technology, I am not a purist. "Woof" to Archie
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Old 25th Dec 2015, 2:13 pm   #117
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Default Re: Eddystone 888A.

The 888 should be fair on stability, but it involves high frequency VFO operation. The later EA12 fixed that with crystal-oscillator first conversion into a tuneable IF, so you see the same band spread on all ranges and the 100kHz intervals on each range line up directly above each other on the scale.

I'm not too bothered about using an 888 as the basis for playing around with different circuits. To turn it into a high stability receiver for the sub/cw/psk filled amateur bands would probably also need something doing in the filter area as well as tuning stability.

I've kept my EA12 in original form, and it's not too bad on the amateur bands. CW is quite effective, but close SSB stations are a problem without a crystal SSB filter. Tuning stability is fine. Fun to take on the air occasionally.

I have an RA1217 which is another interesting period receiver. It has good SSB filters and CW filters, along with good stability and tuning scale resolution. As a 1960s transistor-based comms RX is suffers a lot from overload and intermodulation effects. Also fun, but not when the bands are heaving and signals are strong.

25 years ago I got myself an ICOM IC765. This is a corker of a transceiver and can fully hold its own with some of the very best. Mine's been sitting in pieces on the dining table for some time. A couple of 4000 series CMOS parts need replacing, but these sets are available at fair prices and deliver serious performance. I must get round to sticking it back together.

Sitting in the shack at the moment is an IC7700. This is one of the latest and greatest, but it serves to show how little progress has been made over the old '765. It looks terrifying to the uninitiated. If I want a set to be seen in public, the Eddystone is the attention-getter and the AR88 comes not so close. I do a few radio events for the scouts and special event stations etc, so I need to take equipment which will do the job and equip,ent which can get people interested.

The EA12 is the same as turning up anywhere on a horse... horses can upstage any Ferrari.

David
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Old 25th Dec 2015, 2:49 pm   #118
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Arrow Re: Eddystone 888A.

Quote:
Originally Posted by Wendymott View Post
The VFO needs at least 6.2V to stop the 80M range from "squegging"
A full-wave bridge rectifier across the 6.3 v.a.c. common heater cct. + R/C filter (plus a voltage regulator?) may provide a solution. I seem to recall that the heater feed for the noise limiter is unique to that valve, so spare power capacity may be available. Now the reason for that valve to have a separate heater supply is well-known & makes sense, but it might be worthwhile to try the experiment of re-wiring that heater supply from the 'common' 6.3 v. supply, thus freeing up that original 6.3 v. to power the aforesaid bridge rectifier, etc.

Oh, and yes: Merry Christmas!

Al.
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Old 25th Dec 2015, 2:55 pm   #119
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Default Re: Eddystone 888A.

Quote:
Now the reason for that valve to have a separate heater supply is well-known & makes sense
Not to me, could you please explain?
 
Old 25th Dec 2015, 2:58 pm   #120
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Arrow Re: Eddystone 888A.

From memory: the cathode of the valve is substantially above ground potential. Therefore, due to capacitive coupling, heater-cathode, there is a possibility of impaired S/N ratio if the heater is connected to the common 6.3 v. supply.

Al.
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