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Old 20th Sep 2010, 5:55 pm   #1
Nick G8GRA
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Default Deaf RACAL RA117E

Folks,

I have a deaf RA117E receiver. When tuning the first VFO, ther is no "hiss" on any of the 1 MHz segments. To get 10dB S/N I have to inject some -50dBm.

I have a Mauritron manual, but there is little test data for me to verify where the problem is.

Has anyone any experiance in these nice old receivers?

Nick
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Old 20th Sep 2010, 8:28 pm   #2
Skywave
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Arrow Re: Deaf RACAL RA117E

Hi Nick,

There are quite a few members here who have experience of repairing the RA-17; I'm not so sure about the RA-117.
However, what does spring to mind, though, is this Q.:
"Is the 1MHz xtal osc. producing the requisite level of O/P and on the right freq.?"
Since if this is wrong, then very little of the R.F. 'processing' circuitry will be working correctly . . . . typically manifest as an absence of 'hiss' on any of the 1 MHz segments, 1st. VFO

Al. / Skywave.
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Old 25th Sep 2010, 9:39 pm   #3
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Default Re: Deaf RACAL RA117E

First thing to try - pull the 1st VFO/1st mixer unit valves and stick them back in, then the 1MHz osc and harmonic gen valves and the 1MHz crystal - dirty pin contacts are quite common. Do this one valve at a time with the power on and the set warmed up. I presume the HT link at the rear is attached and clean?

Do you possess a decent oscilloscope, signal generator and/or sweep generator? A diode probe is kind of useful too if you want to make sense of the test points above the chassis and don't have a 100MHz plus scope.

They aren't bad to work on provided you have a strong back, strong bench and can see them as a collection of separate radios all stuck together.

Good Luck,

Colin.
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Old 7th Oct 2010, 3:04 pm   #4
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Default Re: Deaf RACAL RA117E

Hi Nick.

Ref your email on your deaf racal RA117E receiver, have you had any joy locating the fault as of yet??

I have been repairing/servicing Racal RA17/117 receivers for over 20 years (with an occasional short break) so if you need any assistance just let me know.

Regards

Rob
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Old 8th Oct 2010, 9:57 pm   #5
amornummi
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Default Re: Deaf RACAL RA117E

A low gain set I repaired was due to one of the little tubular 5n bypass caps being o/c. It was on the 1r7 megs if stage decoupling the top end of a tuned cct.

Inject test signals at ( I use a scope probe) at 100kc/s 1.6 megs 3/2 megs. On the top mounted boxes I wrap thin tinned wire around appropriate valve pin.

Another stock fault is in the RF amp, the two 100K HT to gnd go o/c, so no anode current, check with AVO down valve socket.

G3TSA
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Old 20th Oct 2010, 8:38 am   #6
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Default Re: Deaf RACAL RA117E

I have a RA117E. Great when they are working but very complicated. So many reasons for loss of signal. However, one problem that I have had more than once is the failure of V3 the ECC189.
Also I was told that the silvered mica caps in the filters tend to drift in value and was advised to change them all in both filters without disturbing the pre-set capacitors. This did improve things for me.
Still got more drift in the VFO than I should have and in spite of changing all the component in the calibrator it still isn't very reliable, works when it wants to.
Don m5aky
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Old 24th Oct 2010, 2:25 pm   #7
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Default Re: Deaf RACAL RA117E

if you are mucking about in the RF amp, be very careful not to break the co-ax from the preselector range switch. Replacing it is a real pain.

I've seen the 100k grid bias resistors on the cascode amp o/c too - yesterday in fact, on a 17L - they are a bit awkward to get at so you might want to replace them with higher rated items. Check all the resistors while you are in there - they will probably all be high in value - and replace the cylindrical paper caps with nice mylar (petp) ones.

If you are stuck for a cv5339 rf amp valve and don't want to pay grossly inflated prices, get a cheapo Russian 6n23p. Purists may shudder but it will work well enough. No need to get the "EV" special quality type - audiophools have inflated the price of these too.
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Old 24th Oct 2010, 4:02 pm   #8
MichaelR
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Default Re: Deaf RACAL RA117E

It is a long time since I worked on this set but as has been suggested by other posts it will be necessary to identify which section of the receiver the loss of gain is occurring. ( it may be more than one section if the receiver has never had any work done to it ).

There is no easy way to trouble shoot a receiver of this complexity.I almost had to rebuild the set I had , resistors ( especially inthe IF module) were high everywhere to gether with failing caps, however once sorted the set became very lively. It is one of the best comms receivers I have ever owned.

I would methodically work through the set stage by stage and draw on the experience of the forum such as Racal Rob, you might as well take this as an opportunity to put the whole set right and refurbish it. I only suggest this approach because as you are aware the set is so heavy and cumbersome you do not want it on the workbench so often.

Regards
Mike
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Old 24th Oct 2010, 5:48 pm   #9
Colinaps
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Default Re: Deaf RACAL RA117E

I'd go along with all that - if you have one of these dc-to-light scanners, you have a very useful piece of test gear. A scope is pretty much essential too.
Wrap a piece of wire round your finger to make a probe that can be lowered over an uncovered valve - you can use that to see/hear if the 1st and 2nd VFOs are VFO-ing and you should be able to hear the 100kHz oscillator and its harmonics. Without any one of these three, you won't have a chance of seeing the 37.5MHz product at every MHz point.

If you can find the Army manual, (join the WS19 yahoo group) it goes into more detail about setting up the filters but DON'T touch the 40MHz set unless you have a half decent sweep generator. You can roughly tweak the 37.5 filter if you have a way of measuring the frequency and amplitude of the filter output and the 1st VFO is good and stable. Sadly,many are not!

Cheers,

Colin.
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Old 25th Oct 2010, 10:33 am   #10
Nick G8GRA
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Default Re: Deaf RACAL RA117E

Folks,

Thanks for your advice so far.

I have to confess I am stuck because I don’t have any test data to measure RF levels or required voltages.

The 30,000 foot view for me is that the 117 and the 17 has two major components, the Wadly loop to convert 1 MHz bands to the second major part, a 2-3MHz receiver.

The problem I have is that I have no test data to fix the receiver as I keep repeating.

The annoying problem is that I have another 117E that I was going to use as a reference comparison to fix the faulty one; it had a duff 1.7MHz oscillator that I have fixed, but is deaf to!!!

There is quite some gain in the RF front-end amp (of a working receiver I must add), but injecting a signal into the 2-3MHz BNC socket still shows a deaf receiver.

Again, I have to add I have no test data to know what is good or bad.

Collinaps:


Thanks for your advice but there is something more sinister going on because having tried your suggestions it still doesn't work.

The test equipment I have for this restoration project are:

* Schlumberger Stabilok 4031
* Tektronix TDS380 (400MHz 2Gs sampling 'scope)
* HP 8595E spectrum analyser with sweep generator (9kHz to 6.5GHz)
* HP E4418A power meter for the low power stuff.

All of the above are in calibration.

RACAL Rob

Thanks for your offer. Derby is not that far off from North Wiltshire so a "Grand Day Out" might be possible if I can get an "Exit Visa" from my wife!

I have to confess I have walked away from the project for the last few weeks because of exasperation.

I also have two MA79G's that have not been switched on for 6 years so there may be more issues in the future.

Regards,

Nick
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Old 29th Oct 2010, 6:19 pm   #11
Colinaps
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Default Re: Deaf RACAL RA117E

Hi Nick,

Well, you're doing better than I am for test kit since the work went all "outsourced". Now I'm worried about sounding patronizing!!

Until you get to the 2nd VFO, it's all much the same as a 17l, just with different valves. You should be able to see your 1MHz harmonics ok, and you should be able to check the bandpass filters with your tracking genny between test points, at the very least, you can look with the speccy to see that the BFOs and the 1.7MHz osc are ringing ok.

I have a nice pdf of the manual but without any of the drawings that I found on the net somewhere; it's more legible than most because it seems to have been made from a Word doc - I'm happy to email it to you if that's any help - and there's a complete manual on the VMARS website.
For the dreaded filter alignment, look here: http://www.recelectronics.demon.co.uk/ct501.htm
which shows you what to look for at the test points.
A set of x10 scope probes will suffice to protect your speccy and tracking genny from nasty HT floating around the test points. If you have any way of checking their input capacitance, good and well, go by the book; if not, hope for the best.

Refer to the 17L manual to make sure you understand any differences in valve numbering etc - I have a 117 in the shed waiting for inclination and opportunity to coincide but haven't done one for several years. Several 17 and 17Ls though...


Cheers,

Colin.
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Old 15th Nov 2010, 2:02 pm   #12
Nick G8GRA
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Default Re: Deaf RACAL RA117E

Colin,

Thanks for the support so far. Apologies if I appear to be a "Clever D" with the test gear but I used to run my own business and kept the kit. But is no good having an array of test kit if you cant fix anything!!

I was trained at Pye Telecommunications in the late 70's, moved to Lucent Technologies and am now at SunGard Public Sector. I have been in radio all my working life and that is why I am so frustrated with these two 117's.

Any idea what the 1MHz oscillator RF output level should be?

There was a bizarre fault with the 1.7MHz oscillator. The output on the anode was about 35mV so I changed all the components on the terminal strip and it came up to 35V. But tuning the anode inductor the ferrite slug would come out still not reaching a peak. I put an extra 10 turns on it and it would then resonate with an output of almost 50V.

But still it acts as a very large paperweight and not a receiver!

The front end seems to be okay as the pre-selector works and I get something like 35dB gain. For 4.5mV input I get something like 280mV out of the 30MHz LPF in the box.

Regards,

Nick
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Old 18th Nov 2010, 6:15 pm   #13
amornummi
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Default Re: Deaf RACAL RA117E

For a start , unplug the black coax which goes into the 100kc/s if filter box.
Check there is about 200 volts coming out of filter box , and still there when 22k to ground.
Put plug back in , as hammers 6BE6.
connect , you should hear your fluorescent lights .
Touch a couple yards wire onto the 1 st if amp grid , you should get lots of noise.
If so then you know the 100 k and audio is ok.
The 100k filter seems lossy if you make 50 ohm measurements,but works ok .In circuit, I think about half the input voltage comes out,less on xtls.
Put your test set (100 pf in series) into the 3 to 2 mc/s convertor input - works ? = tuneable if is ok
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Old 20th Nov 2010, 4:29 pm   #14
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Default Re: Deaf RACAL RA117E

Hi Nick,

Did you have any doings with the old L700 in your Pye days? I've spent many happy hours trying to get two watts out of the brutes, and changing e'lyitcs in the IF and BB units!

My 117 isn't fit for power just yet but my 17L that's on the bench makes about 4V p-p of 1MHz at the port on the back panel. A rough and ready probe, as described earlier dangled over the harmonic generator shows 1MHz spikes with a decaying HF "ringing" in between.

Cheers,

Colin.

Last edited by Station X; 21st Nov 2010 at 10:20 am. Reason: 40V changed to 4V.
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Old 28th Nov 2010, 4:08 pm   #15
Nick G8GRA
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Default Re: Deaf RACAL RA117E

Amornummi


Thank you for your help and I will be having a go at your suggestions this afternoon. My wife has released me from domestic duties so I can "play with radio's" now.

I have ordered some 100kHz resonators and will build a simple 100kHz signal generator to test the last IF stage. I can build this to give a precise output level and put it into a 50R variable attenuator.

I don’t have fluorescent lights and if I did they wouldn’t be very well calibrated


Colin

Again, thanks for your valuable input. One receiver gives 4V pk/pk as you say, whilst the one I am working on gives 2.5V pk/pk. Both measurements are high-Z into the 'scope.

I took the xtal out of the 2.5V 117 and cross-coupled the 1MHz from the 4V one to no avail. I need to bring the 2.5V up to 4V, but I don’t think that will be a showstopper at the moment unless you think otherwise.

As to the L700, yes, lots of experience, but some 25 years ago. I worked on the commercial 1.5G and Home Office 1.8/2.3G systems both in the Cambridge factory and deployment within the UK and overseas. The most unusual one I worked on was for an African administration who were licensed for a 72 channel system at 450MHz – what a ridiculous waste of spectrum! Never mind, business is business.

I still have the full L700 maintenance manual for all variants. It has the cct diagrams, tuning instructions, component lists etc. You can have it if you want it; I have no need (we use Westica digital now).

It was basically a 450MHz TX with a varactor multiplier after that to get to the required band and some serious filtering – I would call it a duplexer, but Pye Telecom liked the term "branching filter".
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Old 28th Nov 2010, 9:27 pm   #16
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Default Re: Deaf RACAL RA117E

I have had IF screen decoupling cap cause "deafness".

David GM8JET
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