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Old 23rd Feb 2017, 1:36 am   #21
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Arrow Re: Racal RA17C tips

I don't recall reading anything about a 'boss' in the manual about the removal of the 2nd. VFO: perhaps it refers to the kc/s knob; perhaps there's something different, mechanically, in the N. American variant. OTOH, these days, when I have do to such a removal, I rarely refer to the manual anyway. What I do recall (British versions, RA-17 Mk1. and 2; RA-17L; RA-17W) is that the tuning coil for the osc. in the 2nd. VFO is secured to the rear of the sub-chassis of that VFO: do not loosen or adjust the fixing which secures that coil! Doing that will throw the calibration badly out.

The first time I had to remove a 2nd. VFO, I didn't have a copy of the manual - so I had to work out how to remove it using eye-sight and cut-'n'-try: it wasn't that difficult. What is tricky is replacing the kc/s film strip, but to remove the 2nd. VFO, doing that is not necessary.

Al.
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Old 24th Feb 2017, 3:05 am   #22
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Default Re: Racal RA17C tips

I figured out the "boss".

I also measured the resistance of about 30 easily reached and
"isolated" resistors.

Maybe 20% were in tolerance! Some were in fact low ... unless
mica or ceramic or (!) air (!) caps are seriously leaky (like 250 k).

I've never ever seen any radio or TV with such an array of bad resistors.

I read a thread here that said something like "The Racal 17L is a great receiver
after all the paper caps, all the electric caps, and all the resistors are replaced".
Apparently they meant it.

Doug McDonald
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Old 24th Feb 2017, 8:56 am   #23
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Default Re: Racal RA17C tips

The need for anti-oscillation measures like ferrite beads isn't a matter of what frequency the stage is intended to handle, but rather depends on what frequency it could create problems at.

Right at the grid pins is right where ferrite beads would need to be. Resistors could have been used, but beads sort of suggest it was a later addition to fix a discovered problem.

The 12AT7/ECC81 is usable at VHF, though better VHF valves soon came along.

David
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Old 24th Feb 2017, 9:24 pm   #24
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Default Re: Racal RA17C tips

Unfortunately, many 1950s British resistors and capacitors could be a bit of a sorry shower and are the Achilles' heel of many otherwise fine pieces of gear. Philips of Holland could produce some excellent components in this era but with military approval and procurement there's a combination of needing to make a show of supporting national industry and sticking with the devil that's known.

I'd heard (and there's always an element of the story getting distorted as it passes down the ages) that Racal had originally wanted to license-build a Collins receiver (possibly the R388?) but that Collins had insisted on the use of US components- perhaps they were worried about reputation damage? This stumbling block supposedly was a factor in the genesis of the RA17, using Dr. Wadley's conversion topology.

Good luck with the set, it must have been disheartening to uncover its state but there are folk here who thoroughly understand the theory and practice of this classic.
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Old 25th Feb 2017, 2:53 am   #25
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Default Re: Racal RA17C tips

I'm continuing investigating it.

The power switch is broken (broken bat). There are no same-size
replacements at all in the US. All ours are either 15/32 inch or 12mm
(which in fact fit the exact same hole).

I can of course mount one of ours with a washer.

Do switches of this size exist over there? It appears to be
exactly 15mm.
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Old 25th Feb 2017, 5:16 pm   #26
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Deleted ... connection found

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Old 28th Feb 2017, 3:04 pm   #27
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Default Re: Racal RA17C tips

I noticed something odd recently.

Stuck between the casting and the side plate, near the power transformer and
rectifiers (top hat silicon, all working fine) was a plate of plastic,
about 4x18 cm with rounded corners. It had glue residue on one side. I have
not removed the side plate to see if it had been glued either to that or the casting.

Is this a known object, perhaps used as some sort of insulator?
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Old 14th Mar 2017, 11:20 pm   #28
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Default Re: Racal RA17C tips

Could be the transparent window on the escutheon kHZ scale?. After you've done all recapping and other things... I guess you have to realign the receiver and as far as i know this is a hell of a job....and you need full skills and specific measuring equipment...

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Old 16th Mar 2017, 7:23 pm   #29
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Default Re: Racal RA17C tips

The plastic part is not transparent. It was at one time glued to something.

The set is on the back burner for a while. I'm working on my WWII military iconopscope camera now that I found a second iconoscope for it. With two 'scopes acting identically I tried harder to find a circuit fault and eventually found a leaky metal can HV oil cap that was bad. Both tubes now work nicely.

I've got seven weeks to work on the Racal before picking up a Marconi 702. When it rains British rain, it pours!
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Old 2nd Apr 2017, 7:46 pm   #30
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I got the iconoscope camera working nicely with TWO of my three iconoscopes.
Then I got fed up with the AGC even with mods on my R-390A and
just finished playing with it and now with my own design it works passably.
In other words I procrastinate.

So tomorrow its on to the Racal. What do you people do for bad toggle switches,
other than a parts set? I took it apart and I possibley could
fix it with some delicate lathe work, but I'd have to make a jig to
hold it first. Barring those hopes, its either a mismatched switch or
one (speaker on-off) that does not work.
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Old 10th Apr 2017, 12:52 am   #31
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Default Re: Racal RA17C tips

I was able to get back to the Racal today after time off to verify that my 15GP22 is dying.

I decided to open up a box to see if the capacitor exorcisor left any, and they
did in the calibrator. I've never seen a paper or film cap like these .. are they oil or PCB?
They have this these white flakes on the ends and some
fell off and corroded the aluminum in places. 70% of resistors are bad.

Are the mica caps tuning the coils likely to be bad? They are tightly twisted
on and undoing them looks difficult.I suppose I could measure the
tuned circuits frequency and Q.
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Old 10th Apr 2017, 1:57 pm   #32
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Default Re: Racal RA17C tips

I shouldn't worry about the calibrator till last - they can be a pain to set up and a well lined-up radio works fine without one!

SM caps are usually ok but I have seen a few go O/C in the BPFs and 100kc/s IF strip.

Colin.
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Old 11th Apr 2017, 1:07 am   #33
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I finished the calibrator. It was of course easy, but every paper cap and every
resistor was very bad. The coils and mica caps are probably good because
the Qs were high and the frequencies quite close. The 100 kHz was spot on
and the 900kHz was close.

One thing I noticed that will, if it follows through on the rest
of the set, make things much easier compared to North American practice:
the part leads are only wrapped 3/4 turn around the tag pins and not at
all around the valve socket pins, rather than the US practice of two or three turns.

Now on to a very hard part: the power supply/audio . This is a nightmare
because it will have to be remade from the start: almost every wire has been cut
so I have no idea what connects where and will have to trace the wires.

All the power resistors are good and will be left in place for now.
In the future I will mount them above the chassis where the rectifier goes in the
European version.
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Old 11th Apr 2017, 7:38 pm   #34
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Default Re: Racal RA17C tips

Factory reconditioned sets had the big green WW resistors replaced with aluminium bodied chaps fixed to the side of the chassis. Unless you plan leaving the thing in standby for extended periods, the originals will probably last for a few more decades.

Colin.
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Old 12th Apr 2017, 5:37 am   #35
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Default Re: Racal RA17C tips

I finished the power supply and audio. I had to use the original plan
of modern (i.e. 1970's style but newly made) power resistors above the chassis,
because the 10K one broke on unsoldering. I don't like the look of the 165 Ohm one.
so I replaced it with a 100 Ohm 10 watt, a 50 Ohm 5 watt, and a 15
Ohm 2 watt carbon in series.
After my next Digikey order I will replace this with two 330 Ohm ones in parallel.
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Old 13th Apr 2017, 3:58 am   #36
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Today I did the AGC system and the first IF amp area. The two 10 meg
resistors were 10.5 and 11 meg .. quite remarkable, so I left them in.
Several 2.2K decoupling resistors were also good enough to leave in.

Now I need help!

Next is the 2nd IF-detector area. Two nightmares. First the leads to the two coax
cables terminating in the ceramic standoffs nearest the front panel have their
connections removed, so I would have to trace them out, and in any case I don't
know what parts were cut off them. Does anybody know?

2nd, and this might matter because of lead dress, there are four clamps
(in groups of 1, 1, and 2) there that presumably held capacitors. One is probably
the 1 uF AGC cap, but I have no idea what the other three were as I see no
more high value caps in that area. Does anybody know what was where?

I got the cut harness open ... its less disgusting than expected, and only one wire
will have to be replaced rather than simply rejoined ... plus one coax extended.
But the vandal broke the ceramic standoff that holds the filament wire. I will install
a terminal strip where one capacitor clamp was, to hold it.
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Old 15th Apr 2017, 4:42 pm   #37
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Last night I tried turning it on. Nothing disastrous happened: no smells.

It generated static but no reception. A test indicted the 1 MHz xtal oscillator
was dead. Careful examination found a couple of unobvious clipped wires.
Fixing these and a couple of mildly out of tolerance resistors fixed it.
But still no reception. Tests found no 2nd VFO output. So
I had to take out the two big modules. The 2nd VFO was in modestly poor shape.
Most Hunts caps were seriously cooked. A couple were actually open. Several
resistors were bad, and one 220pF mica. However, somebody had gotten in there
before, looks like in the late 60s or 70s, as there was one pristine and new-looking
(but leaky!) Hunts cap and several US-style mil-grade 1% resistors which
were all still within 1%. Several old resistors were within 15% in non critical
places and I left them.

Next up is first VFO. This also was worked on in the 60s-70s time frame.
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Old 15th Apr 2017, 7:05 pm   #38
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Default Re: Racal RA17C tips

Are you looking for one of these?

David
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Old 16th Apr 2017, 12:31 am   #39
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Yes, that's the part I need. Do you have one for sale?
I don't know this board's sales etiquette.

Doug McDonald
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Old 16th Apr 2017, 12:34 am   #40
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I got the 2nd VFO redone and both installed.


I got response from the megaHz knob, but no signals. This
ws traced to a missing B+ jumper on the back panel. Adding that
got signals, at least in the 5-10 MHz region. Accuracy is still
very good indeed, compared to my high class synthesizer.

The IF bandwidth works too.
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