Mysterious RA17L EA76

[paolo67]

Hi everybody,

while inspecting the receiver closely, I found this small tube in the IF assembly. It is V24. The manual says that V24 has been fitted starting from s/n 3737, mine is s/n 7939. However, V24 is completely disconnected

Around V24, I found what I think are some inconsistencies on the manual. The schematic shows two components that are not referenced on the picture (Illustration 9), namely R91A and R97A. On the same illustration, C195B is referenced twice, probably one is actually C159B.

The two components are actually not fitted, this meaning that the receiver reflects the inconsistencies of its own manual and the whole thing is then consistent...

Because nobody has been there before, i.e. it is how Racal made it, it should not be just an error. Does anyone know more about this story? Would you recommend me to recreate the circuit and insert V24? If so, is there something to consider in terms of component positioning?

Thank you in advance
Paolo

[XTC]

Paolo,

See this thread for a very good explanation of what V24 does.

https://www.vintage-radio.net/forum/...ad.php?t=24298

In the circuit diagram I have, the diode is a GEX 54 germanium diode up to S/N 3737 and an EA76 in later S/Ns. Both variations are in the diagram, the GEX54 version in the main cct diagram and the EA76 version in a box. Both versions are essentially the same.

C159A is a 0.1µF cap and C159B is a 0.001µF cap and both are connected from the AGC line (the anode of the diode) to earth. R91A is a 470K resistor connected in the AGC line before the diode.

It looks as if the reference to C195B in the picture is a mistake and it should be C159B. These caps are wired in parallel on the tagboard next to the one associated with EA76. The picture I have shows the EA76 and MR8, the GEX54.

It's perfectly possible that your set was not wired correctly in the factory, and no one noticed. It's also possible that both the germanium diode and V24 were fitted, but only one was connected.

If there's no diode in the AGC line, I'd be inclined to wire it in so that the AGC works as intended, however, I think you ought to trace the circuit carefully to see whether the GEX54 has been installed or if someone has fitted another diode in the AGC line.

What's the serial number of your set? If it's around 3737, they might have fitted both either because it was easier to do that until their production process caught up - say they had a stock of tagboards with the diode fitted to use up, or because they had to continue with the germanium diode until a customer had approved the EA76 modification.

[paolo67]

Many thanks for your answer, this is great stuff.

I did not even noticed MR8. And, actually the AGC line to the 1st VFO assembly is missing on the specific illustration, the reason for this is also clear now.

The s/n of my unit is 7939. There is no solid state diode, but it seems that the EA76 was previously fitted and then deliberately excluded: I found where R97A is located and one side of it is floating.

Just to make sure I've got the point, I measured the AGC voltages after the two 10M resistors. Here the conditions:

System sw. AGC
IF Gain MAX
Preselector Wideband
Attenuator MIN
IF Filter 6.5k
Mode AM
Input signal 3.5MHz tuned for maximum RF signal, 50% 1kHz modulation

And this is what I've got (it might be slightly inaccurate as the sig.gen. output impedance is 50ohm):

+20dbm -10.00V
+10dbm -8.44V
0dbm -6.90V
-10dbm -5.05V
-20dbm -3.57V
-30dbm -2.38V
-40dbm -0.90V
-50dbm +1.68V
-60dbm +2.72V
-70dbm +3.17V
no signal +4.00V

I would say that the AGC is somehow working. If I would fit the diode, the negatives would not change (diode reverse biased), and eventually I would get lower values for the positives. BUT if it should get negative only for really strong signals, it seems that I should check the values for some of the R...

Makes sense?

[XTC]

The voltages on the AGC line you quote look right, but I haven't measured them and I'm not certain. Remember that the AGC line is very high impedance.

The AGC line goes into the 1st VFO UNIT but it controls the ECC189 cascoded triode RF amp.

See here for my experience of sorting one of these sets.

https://www.vintage-radio.net/forum/...ad.php?t=26092

I found that of the two 10M resistors, R81C and R81B, one was open circuit and the other measured 22M. I tried measuring them in circuit, but with those values, it was hopeless, and so I cut them out and replaced them with two new ones. I only found out what their actual values were when they were removed.

I found that some of the resistors in the RF amp were open circuit and others had impossibly high values. R23 seemed to have twice it's proper value in the set and was measured as being much higher when cut out. Obviously, it was unreliable! The fact that when I bought the set, there was a bag of valves inside, including six E88Cs (the non vari-µ version of the ECC189) should have told me something. I suspect that a previous owner had had a serious problem with the AGC /RF gain and the E88Cs were part of his attempt to work around it.

In general, the capacitors in these sets seem fairly reliable, but the resistors cause a lot of problems.

I'd advise you to replace those two 10M resistors with modern ones with a suitable voltage rating and then investigate the resistors in the rest of the AGC line and the RF amp. Replacing the resistors in the RF amp is a painful business, but you really have to check them and make sure they are about the right values to get the AGC system working properly. Then rewire the AGC line to include the EA76. Check that the EA76 isn't faulty first.

Pete.

[Skywave]

Originally Posted by paolo67

. . . Because nobody has been there before, i.e. it is how Racal made it, it should not be just an error.
Paolo

Hi Paolo,
I hope you don't mind if I ask, but how can you be really sure that "nobody has been there before" - unless you acquired this receiver in an obviously unused, virgin, 'never-been-out-of-its-shipping-crate' condition' ? By now, the vast majority of Racal receivers of this ilk will have some active service under their hoods - and therefore maintenence - including unauthorised, strange mods.

Just curious.

Al.

[paolo67]

Well, after some "familiarization time" with the thing, it is possible to recognize "virgin" areas from "rework" areas:

- solderings: rework always leave some sign of it, sometimes small sometimes more evident. One thing that characterizes this receiver is that the end of each component is well wrapped around its connection point, being a tube socket contact or whatever else. It is VERY difficult to recreate the same conditions when reworking - for me of course - not even mentioning when the component is buried under other elements

- components: brands, types, "aging". Rework with NOS capacitors of the same brand - and age - or 10% carbon type resistors would be inappropriate IMHO. Certainly possible, but not really likely. I own a '51 R390 non-A that looks like it have been reworked long time ago to fit a 390A IF deck: same type of insulation for the extra wires including coaxials, additional transformer of that age, uniform dirt and dust. I cannot be sure of course but...

- maintenance: I always thought that these receivers were designed as "modular" in order to make service easier and quicker (maybe not just for that but ALSO for that...). Faulty unit? Just replace the whole subassembly with no additional alignment effort. Was component-level rework so common in your opinion? I think it is more an enthusiasts, non-professionals affair

If rework is so well done to be indistinguishable from the original, I would just try to imagine who could have done that. It must be someone that really loved it, and in this case I would trust his work 100%.

The EA76 story gave me the opportunity to discover that either I don't have the right version of the manual - although "RA17L" is written both on the manual's cover and the receiver's tag - or the manual is not exactly accurate: there are mismatches between the schematics and the pictures in terms of missing/extra components, and missing wires. After some deeper investigation, I found that the previously missing components are actually located very near to the tube, and there are outstanding signs of rework. I would say that the manual I have - taken from BAMA BTW - is "minimalist" if one considers the complexity of this thing.

Bottom line: I trust the manual unless there is something such as the above suggesting that I shouldn't. In this case, I asked the experts because it looked intact and the manual was not that helpful...

I would be curious to hear from you and others how you proceed when working with something new...

[paolo67]

BTW, I just realized that there might be something lost in translation: I am not saying that the whole receiver is as Racal made it, but there are areas in it that I recognize as virgin, never been reworked. The area with the two 10M resistors etc. looks like that

Paolo

[Skywave]

Originally Posted by paolo67

BTW, I just realized that there might be something lost in translation: I am not saying that the whole receiver is as Racal made it . . .
Paolo

Ah-Ha! Sorry, Paolo - that is indeed what I thought you meant. [If that was what you had meant, there was a string of suggestions that I was going to make; obviously irrelevant now].

Al.

[Skywave]

Paolo: "I would be curious to hear from you and others how you proceed when working with something new..."

I'll try to be concise & compact in answering your Q, (since this is drifting OT a little).

In my employment, I frequently have to re-work / modify radio equipment. However, such comparison here with an item of vintage equipment is not valid. It is much easier to disguise re-work on modern & surface-mount equipment than something like the Racal you have.

My personal approach towards repairing vintage items like the RA-17 is to use original components where the design dictates. Otherwise, a more modern - and hopefully more reliable - components goes in, provided that it is suitable for the task that it performs. With new equipment, there is far less latitude, but then the parts are much easier to source.

Two different scenarios; two different approaches.

Al.

[Skywave]

Originally Posted by paolo67

I would say that the manual I have - taken from BAMA BTW - is "minimalist" if one considers the complexity of this thing.

I trust the manual - unless there is something (such as the above) suggesting that I shouldn't. In this case, I asked the experts because it looked intact and the manual was not that helpful...

Hi.
I've looked at the manual available from that Site (BAMA) & I must say that I cannot agree with your opinion that it is "minimalist". To me, it seems very comprehensive, although I do accept that it does not give the detail that you require on the unusual placement of the EA76 and associated components in your particular RA-17L.

Seems to me that provided the correct components are fitted in this region of the cctry. & wired correctly to the rest of the set, their unusual placement in your RA-17L is of small consequence: the important point being 'does the AGC cctry. work as designed?' And your measurements imply that it does.

The only conclusion that I can come to is that the relocation of these components is probably a late Racal modification that is not covered in the manual from the BAMA Site. I note that the serial number of your RA-17L makes it quite a "late build". Perhaps that is the reason.

Persevere with it Paolo - the RA-17 is a fine receiver but maintenance on these is not a quick task - but the results are usually well worthwhile.

Incidentally, if your phrase "I asked the experts" includes members of this Forum, then I for one, am truly flattered

I look forward to being able to help you further.

Al.

[paolo67]

I can rephrase the Q and make it more useful: certain types of components are more likely to 'fail' than others. Among them, paper type capacitors and carbon type resistors, that seem to be widely used in the set. Maybe also the electrolytics: we know how to handle them, however.

The Q then is: what would you consider as the best modern replacement for them? 'Modern' implies reasonably easy to source...from RS for example

Paper type cap.: metallized polyester? polystyrene? Maybe it depends on their place in the circuit...any rule of thumb?

Resistors: thick film/metal film seem to be obvious choices. Do you see any problem with them, provided they have all the necessary voltage ratings etc.?

I would just focus on the above: each 'category' of components deserves its own analysis IMHO.

Please help me on this: I am not trying to make it just working, I want it to work perfectly and, if not possible, to understand why...

[Skywave]

The best advice I can give you on the topic of 'suitable choice for component replacement' is to have a good look at past Threads on this Forum (where this Topic has been widely discussed), including the read-only archive sections.

Since this is not related uniquely to your RA-17L problem, I shall say no more on this.

Al.

[XTC]

Paolo,

Manuals and RA17 variants.
==========================

See the bottom of this WWW page for a list of RA17 variants.

http://www.recelectronics.demon.co.uk/ra17.htm

It's quite likely that this isn't a complete list.

Racal made a lot of variants for particular customers. If say, the Swiss Post Office ordered 30 sets, it's quite likely that they wouldn't have wanted to pay for a special manual in addition but there may have been a type-written addendum covering the differences. When the sets were retired and sold off, they may have gone one way and the manuals and addenda another.

I've got a set which has an RA17L label, and appears to be an RA17L, but the IF filter ranges and front panel markings for the filter control are those of a MKI/MKII and it looks as if this was done in the factory, rather than a MKI/MKII IF strip was added after the set was released from the factory. Also, the RF gain control is disabled when the set is switched to AGC. It doesn't look like anything mentioned on the recelectronics site.

Some of the resistors in the RA17L diagram are in parallel, presumably to cope with the wattage. In some later sets, single higher wattage resistors were fitted, apparently in the factory. These mods are not covered in any manual I've seen.

The manual commonly available in the UK is the RA17L manual. I go to the radio rallies in the UK, and look on the WWW and I haven't seen manuals for odd variants. Mauritron seem to have a fairly comprehensive collection of manuals for all sorts of kit and offer RA17, RA17L, RA17W and RA117E manuals, but they don't seem to do manuals for RA17N, RA17K etc.

It's perfectly possible that your set was a special for a particular customer, or was just never wired properly in the factory and the problem was never spotted. The easiest course seems to be to wire it as a standard RA17L.

Replacing caps and resistors:
=============================

I find the paper caps in RA17s don't seem to cause problems. If I have to replace paper caps in vintage equipment, I prefer Ero MKT1813s.

The resistors are definitely a problem in these sets. I replace them with metal film 2 or 3 watt (350 to 500V rated) or 0.6W metal film, if I'm sure the voltage and wattage are adequate. The 0.6W are a lot smaller than vintage carbon 0.5W and can look out of place.

Sometimes, there's so much dismantling involved that you may as well replace everything in that section of the set while you are doing the job. If resistors are fairly easy to change and appear to be within 20% of their stated value, I leave them, unless the value is critical.

It's a matter of personal judgement, but certainly, I'd avoid NOS components.

Dealing with something new to you.
==================================

I suppose it depends on the value of the item and the complexity, and how much you want to keep it authentic, how much time you have and how patient you are. It's worth looking and asking on the WWW, if you have doubts or don't understand something. There are some places on the WWW where you find a huge amount of knowlege about particular things like Tektronix scopes, I'm thinking here about the Yahoo! Tektronix group.

There are also magazine articles dealing with specific sets, which can be well worth tracking down before starting work.



Pete.

[paolo67]

Pete,
thanks for this and many compliments for your special unit, this is very cool.

The RA17 is a milestone in the history of radio, and all the variants are an evidence - if another one would be necessary - of the incredible concentration of organized knowledge and experience the Racal UK labs should have been.

This page is also interesting: manufacturer's mods

http://www.recelectronics.demon.co.uk/info.htm

The year code of my unit is UH, should mean Aug. 1963. Not sure if some of the mods are later, but one thing I now understand is that I should source and read more literature, and this means not limited just to what is on the WWW.

BTW, I wired a NOS Philips EA76. Gets red quickly and very hot, this is what I measured (using a >10M inp. impedance Fluke, left the receiver and the 8640A as they were...):

+20dbm -9.61V
+10dbm -8.37V
0dbm -6.90V
-10dbm -5.12V
-20dbm -3.62V
-30dbm -2.50V
-40dbm -1.26V
-50dbm -0.30V
-60dbm -0.06V
-70dbm +0.02V
no signal +0.10V

So the positives are gone. The two 10M resistors are fine, up to there all seems to be as designed now. R23 is 90ohms in circuit, will dismount the subassembly anyway and investigate more.

The fact is that I sometimes hear overloading and can't explain why. Actually, S2 - the preselector switch - must be mechanically bad. Checked it with the sp.an. and a second, higher freq. and gain peak appears on all bands depending on some sort of S2 miscontact that disappears when slightly moved...When receiving, this touch-up eliminates the overload.

I might have been not so lucky with the paper caps then. Pics of some I replaced:

dielectric leaks, the nice aluminium colour is gone...

http://img176.imageshack.us/img176/5...2053uy4.th.jpg

badly burnt by a resistor, this one is 50% of its nominal value

http://img257.imageshack.us/img257/4...2054fp9.th.jpg

Believe it or not, I choose exactly the same brand and series!!! I feel much better now... Many, talking of recapping the '390, recommend the Orange Drops. They're just too difficult to source for me here in Italy.

On resistors, thank you for the hints, this is brilliant. I'll definitely switch to your approach.

Please apologize if I eventually hurt someone's sensitivity by defining the manual "minimalist", definitely wasn't my intention. What raised my attention was the paragraph on the 40MHz filter alignment, because its performance seems to play a relevant role in defining the performance of the whole set. BUT, I didn't consider that the assumption was to allow alignment WITHOUT the wobbulator. Under these conditions, any attempt will not result in an in-spec alignment and actually the message was: do not try because you don't have proper equipment. Unexceptionable. Funny enough, look at this:

http://www.pdp-11.nl/racal/misc/wobb...obbulator.html

Who doesn't wish to own one?

Paolo

[Skywave]

Originally Posted by paolo67

. . . . Please apologize if I eventually hurt someone's sensitivity by defining the manual "minimalist": definitely wasn't my intention.
Paolo

Hi Paolo,
Since I was the one who queried your "minimalist" comment, I guess that remark is primarily aimed at me.
There's absolutely no reason to apologise. None at all.
I was simply taken aback by your comment - since compared to other communications radios that I have owned & serviced over the years, the Racal manual, IMHO, sets a good example of doing it right.

As for the absence (in the manual) of procedures for re-alignment of the 40 MHz filter, I can only assume that the original Racal thinking was 'this section will only ever require infrequent adjustment - if at all - and if it does, the organisations who buy this receiver will either:
(a) have the money to buy the specialist test jigs and / or
(b) have trained staff and appropriate alternative laboratory equipment to do the necessary work'.

During the '60's and '70's, where I was employed, option (b) was quite common. But then there were literally hundreds of these receivers in use every day, 365 days / year.

These days, for myself, I would choose a quality spectrum analyzer with tracking generator - or better still, a fully-featured network analyzer, like an HP.

Best regards,

Al.

[XTC]

Paolo,

It's good to hear that you've sorted out the AGC problem and I'm sure the measurements you've recorded will be useful to others in the future.

From what you say, it sounds as if you have a problem with S2. It could be something which can be solved with contact cleaner, you may have to tweak a contact carefully, or it might be a dry joint.

Cap and resistor replacements are a matter of judgement. There isn't a right answer, there are some good answers and some not so good answers. I haven't found problems with the paper caps in RA17s, but they're paper caps and they will develop leakage. Once again, in some positions leakage or short-circuit failure can be acceptable, and in others, it would do a lot of damage or cause a lot of work.

I thought that the manual, especially the fault finding section, could have been better, but it isn't bad either. I've come across a lot of other kit which wasn't exactly as represented in the manual. Some HP and Tek manuals are incredibly good, but there are still vague parts, like referencing matched transistors with a Tek/HP part. Since Tek and HP no longer supply these parts, it would be useful to know what criteria they were matched for.

I'd have thought that with an S/N of 7939, your set was built around 1970. Look at the date on the meter and the dates on the electrolytic caps; these are unlikely to be definitive, as the meter could have been changed. I'm not so sure that the letter date codes are completely regular. .

The 40MHz filter has been discussed on this forum before, and the general view was that it rarely needs adjustment. When you think that the manual was written for sets within their projected design life of maybe 10 years (not 40 years and being kept in sheds etc.) it's reasonable. There are a few other areas of the set which were set up in the factory and they're not covered in the manual either; you're just told to leave them alone.

If the 40MHz filter does fail, it may not be a simple procedure to set it up even with a CT501. I've only seen one CT501 for sale and it sold on ebay for £200, no doubt with a hefty shipping charge in addition. One way of looking at it is that could be £200 towards a spectrum analyser with tracking generator which might well prove to be a generally more useful piece of equipment.


Pete.

[paolo67]

All,

thank you again for your support.

I removed the 1st VFO assembly, did some serious cleaning at every contacts plate of S2 and that problem is now gone. Checked every component around the RF amp and decided to overhaul the entire area as too many resistors were out of spec, sometimes by more than 100%. It took quite a lot of time and patience...

Now the impression is that there's much more gain but also much more noise. This might be normal as I live downtown in Milan and the dipole on the roof catches loads of QRM with any of my other receivers, especially at daytime.

I am now sure that the AGC at the RF amp stage works fine, and I would never have ever succeeded without the help of the forum, so I will never thank you enough. BUT, this is not then the reason for the issue that eventually got even worse: overloading, and lots of spurious responses.

I am now collecting data, will search the forum first and eventually will open a new thread, hoping that you will still bother...Want to repeat every measure as I cannot believe it: apparently, 20MHz signals break through!!

Paolo

[Skywave]

Good to hear from you again, Paolo.

Yes, please do come back! The RA-17 - although a fine receiver - is a complicated beast! It's only by exchanging notes, comments, etc. can we share each others experiences and knowledge - from which all RA-17 users can benefit.

As such, this Forum is an excellent vehicle for that job.

Al / Skywave.

[Don Collie jnr]

Originally Posted by paolo67

Hi everybody,

while inspecting the receiver closely, I found this small tube in the IF assembly. It is V24. The manual says that V24 has been fitted starting from s/n 3737, mine is s/n 7939. However, V24 is completely disconnected

Around V24, I found what I think are some inconsistencies on the manual. The schematic shows two components that are not referenced on the picture (Illustration 9), namely R91A and R97A. On the same illustration, C195B is referenced twice, probably one is actually C159B.

The two components are actually not fitted, this meaning that the receiver reflects the inconsistencies of its own manual and the whole thing is then consistent...

Because nobody has been there before, i.e. it is how Racal made it, it should not be just an error. Does anyone know more about this story? Would you recommend me to recreate the circuit and insert V24? If so, is there something to consider in terms of component positioning?

Thank you in advance
Paolo

Hi Paolo, I had a Racal Ra117 a while back and did a lot of work on it replacing components. There are 3 small capacitors just after the demodulator diode that were marked "300" [I`m going from memory here],
and were *meant* to be 300pF each. They turned out to be 30pF. It might be a good idea to check them [although the rig still worked...]
.................................................. .............................................Don.

[paolo67]

Thanks Don for this. I'll definitely check them, I think I remember where they are, three in a row just below one of the two 100kHz transformers

Paolo