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Old 11th Feb 2017, 4:32 pm   #1
dtvmcdonald
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Default Racal RA17C tips

I just won a Racal RA-17, US version, on our EBay. It should be here next week.

I have the online manual and a full schematic I pieced together from three partial ones I found on the net. Its Ok, but not exactly a perfect scan. Does anyone know of a really good one online, perhaps across the pond?

Reading the manual it mentions "three tools to undo knobs". These will, of course, not be there. I've been bit by this before (R-390A among others). Does anyone know what they are? The parts list shows some plain Allen wrenches ... are these them?

This is my fifth boatanchor and it may well, at 67 pounds (it has no cabinet), be the lightest or second lightest.

Oh yes ... is this old enough to be not metric? The manual has metric overall dimensions in parentheses and lists the Allen wrenches in inch sizes. Are British pre-metric screws the same size as ours? (I think I'd rather it be metric, if not same as as ours, at least all stores here carry all metric sizes.)
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Old 11th Feb 2017, 5:00 pm   #2
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Default Re: Racal RA17C tips

No, pre-metric british radio screws were usually "British Association" BA threads. These were actually defined in metric units, but they aren't the same as the M3, M4 etc series now in use. The hexes of nuts were also BA sizes.

The knobs on all the RA17 family I've come across (inc the RA117 which was a synthesiser compatible version primarily for America) all came off with imperial sized Allen keys.

David
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Old 11th Feb 2017, 5:28 pm   #3
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Default Re: Racal RA17C tips

you need a good hard 1/16" allen key - not the usual diy superstore rubbish.

Cheers,

Colin.
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Old 11th Feb 2017, 9:25 pm   #4
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Default Re: Racal RA17C tips

I restored an RA-117 and needed two allen keys, 1/16" and 3/16". Mine was (I think) a british unit and some of the screws were marked as unified threads

TC
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Old 11th Feb 2017, 10:31 pm   #5
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Default Re: Racal RA17C tips

I guess the third tool must be a wee plain screwdriver to get the BFO pointer off. It's a bit fragile.

While the knobs are all off, you might be as well gently checking their skirts to see if they need gluing back on.

Cheers,

Colin.
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Old 12th Feb 2017, 1:03 am   #6
Craig Sawyers
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Default Re: Racal RA17C tips

Worth looking up the Yahoo group RacalRA17forum@yahoogroups.co.uk

It is not the most active group, but there is a lot of expertise on restoring an RA17 of any variety in there

Craig
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Old 12th Feb 2017, 9:34 am   #7
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Default Re: Racal RA17C tips

All.

I have had over 25years experience of repairing and restoring Racal valve equipment and I have observed the following with regards to the various allen keys required:

3/16" is required for the main tuning knobs and RF knobs etc. I use a Draper T handled tool.

For the winged knobs I use an Xcelite 99-21 Allen key with the 99-1 handle. The code 99-21 equates to 1/16". However, I have also found some winged knobs require the use of 2MM Allen key as well.

The remaining Allen key is an Xcelite 99-20, which equates to .050". This is used for the tiny locking screws on the 1st VFO.

Also I have found the following sizes are useful as well:

5/32" and 1/8" are used the removing the countersunk screws which secure the handles to the front panel.

DTVmcdonald.

What version of RA17C did you win? The Racal catalogue lists 18 versions of the C potentially for the American market. The C16 series was for the Dutch market.

Regards

Rob.
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Old 12th Feb 2017, 11:24 am   #8
Craig Sawyers
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Default Re: Racal RA17C tips

I'd forgotten you were on this list Rob!

All the best

Craig
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Old 12th Feb 2017, 3:37 pm   #9
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Default Re: Racal RA17C tips

I think the one I'm getting is an RA-17C-12

These seem very common over here.
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Old 18th Feb 2017, 12:54 am   #10
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Default Re: Racal RA17C tips

I got the set. Its in pretty good shape except one corner of the front panel and the adjacent handle are seriously askew. A big clamp and wrench should fix this. Its not clear whether the panel will have to come off to do this.

The screws holding the top are US standard 6-32 ones.

All controls work, but all free rotary ones bind a bit against the panel.
Is this normal? Are they free-spinning like Hallicrafters or National, are somewhat stiff like an R390-A kilocycle control. I will test tubes tomorrow.
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Old 18th Feb 2017, 4:00 am   #11
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Default Re: Racal RA17C tips

The two tuning knobs turn against friction, Greater on the kilocycles knob than on the megacycles one. This isn't flywheel tuning like an AR88. The kilocycles knob has to turn a worm gear reduction stage for the capacitor as well as driving the sprockets and spools of the film-strip scale.

There are no clicks on the megacycles knob. the markings on its scale are guides, so turn to the wanted black block under the cursor line, then finely adjust a little for best signal.

David
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Old 20th Feb 2017, 5:40 pm   #12
dtvmcdonald
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Default Re: Racal RA17C tips

What's the general view on recapping these? My general inclination puts this right on the border of "replace all paper and electrolytic caps" versus not based on age. I have not yet been able to get it on my bench to look at the bottom, and won't until Wednesday. Remember its a US model. Do these use a different brand of cap than the UK ones? Where are they made ... in the UK? Only three tubes were bad, one of them a slightly wrong type (the first RF amp).
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Old 20th Feb 2017, 6:52 pm   #13
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Default Re: Racal RA17C tips

Well that depends on what you are trying to achieve. If you want it to work, then changing the capacitors is an essential. Probably some resistors as well. Possibly other parts.

If you want to look exactly as it was made - inside and out - then replacing parts with anything other than originals will knock that goal on the head. However, its hardly a rare item, and Racal manuals giving pretty exact descriptions of the parts fitted can be found - so you are hardly destroying a piece of history if you decide to go for the "make it work" option and do functional replacements rather than exact replacements.

I've pointed out a number of times that to bore out original capacitors and fit modern bits inside - and then start swopping resistors out for modern ones that don't look anything like the originals is a quite bizarre way to behave. Trying to hit both targets simultaneously is like to trying to score goals at both ends of the field simultaneously......

Richard
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Old 20th Feb 2017, 7:11 pm   #14
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Default Re: Racal RA17C tips

As well as considering recapping [ and being from the "Use it don't look at it" school I don't fret about non-original appearance parts here] you should be aware that a good proportion of the high-value resistors - the type with a white cylindrical ceramic body and the 'insides' held in place by a pink or terra-cotta-coloured cement at the ends - will have gone a lot-higher than they were originally specified to be.

Screen-grid feeds, grid-feeds from the AGC line, what's badged as a 47K resistor could easily be 150K if your radio's seen lots of use. Result: low gain in the IF strips and susceptibility-to-crossmodulation in AGC-controlled stages (specially where you have a few-hundred-Kilohms grid-feed-from-the-AGC-line resistor decoupled to ground by a leaky paper-capacitor, so the actual grid-voltage becomes anybody's guess).

I'l happily replace the old ceramic-bodied resistors with modern 2-Watt metal-film equivalents - safe in the knowledge that they'll stay on-value for the next 50,000 hours of radio use.

When I played with these radios, replacing the valve HT-rectifier with a couple of silicon-diodes each with a 200Ohm surge-limiting resistor was also seen as "a good thing" - it both reduced heat inside the cabinet and also 'stiffened' the HT rail so it was less-likely to suffer voltage-wandering when you adjusted the RF/IF gain.

Later RA1x7-series receivers used silicon HT rects anyway, so this could be considered a "works" modification??
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Old 20th Feb 2017, 7:57 pm   #15
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Default Re: Racal RA17C tips

Some owners have replaced the valve rectifier with solid state and disconnected the reservoir capacitor to convert it to choke input filtering.

To get back some of the voltage lost by this modification they have bypassed the resistor that generates the AGC negative bias voltage. They make up a small voltage doubler on the heater supply to generate the new AGC negative bias.
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Old 20th Feb 2017, 9:37 pm   #16
dtvmcdonald
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Default Re: Racal RA17C tips

This is a US model that already uses a silicon bridge rectifier. It has a 47 ohm resistor in series. There is of course no transformer center tap.

So I will do a full recap. I have all but the 0.01uF film ones and the 32 uF electrolytics in stock. I'll use 47 uF instead and adjust the 47 ohms to get the correct voltage; we're a bit high here and I'll adjust the taps to get the filaments right.

Thanks.
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Old 21st Feb 2017, 10:18 am   #17
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Default Re: Racal RA17C tips

The one area in a RA-17 that will require a substantial rebuild will be the 2nd. VFO. It's not a particularly difficult job. The ventilation provided for it is poor. Inside, there is a tag board with Rs and Cs on it: it's usual to find many Rs that have been substantially cooked. I've even seen a tag board which was almost reduced to ash. Oh yes - and the mixer valve can go noisy, too.

Al.
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Old 22nd Feb 2017, 12:20 am   #18
dtvmcdonald
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Default Re: Racal RA17C tips

I got the thing on my workbench today and opened up the bottom.

Arggggghhhhh ... its been got at. With wire cutters. All paper and
electrolytic caps are gone. One wiring harness has been cut in two (nearby) places.
A few other wires are cut at random. That's the bad news. Restoring it
will be a logistical nightmare. The manual is not clear which cap
goes to which tag board terminal, and some (but so far I've not found many)
wires are cut at more than one end.

Does anybody had good either "before" or "after" photos to
complement the B&W manual.?

The good news, so far, is that no unique parts look missing or destroyed.
The power transformer has the proper resistance. The unique mechanicals
work flawlessly. The perp didn't use his cutters on the switch wafers or thing like
RF choke pies. It will take a couple more days to decide if
I will restore it, which I will if I find no showstoppers. I've never
done a recap except one or two caps at a time to avoid just this
logistics nightmare.

The other good news is that the price was right, at least for me.
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Old 22nd Feb 2017, 5:45 pm   #19
dtvmcdonald
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Default Re: Racal RA17C tips

Where on the radio is R119? Its the bleeder used when in standby, so perhaps the
switch area? Its not on the pictures in the manual or at least I don't see it. The big
power supply resistors are there, and not too far off value, but look rather cooked
so need replacement.
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Old 23rd Feb 2017, 12:30 am   #20
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Default Re: Racal RA17C tips

Two questions:

On the wires connected to the two grids of the 12AT7 in the audio area (which come
from shielded wires) there are, right at the pins, two little doughnuts about 3mm
in size. If this was RF I'd say they were ferrite beads ... but it isn't. What are they?
This area needs a complete rebuild.

Second: the instructions for removing the 2nd VFO are clear except that they
refer to a "boss" which is supposed to be loosened but not removed.
I'm totally at a loss for this, maybe its a Britishism? There are too many
things that could cause a fall-apart disaster! Help is needed.
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