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Old 1st Dec 2021, 6:02 pm   #1
vintage_8bit
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Default RA17L Serial No = N 3392

Hi All. I've just got started on the restoration. I'm used to pre 60's domestic sets so this is going to be quite a challenge for me.

VFO 1 has had suspect R's & C's changed. Moving on to VFO 2, I found an extra 0.1uF cap not on my circuit diagram. It also looks non original. Please see images below. The red circle on the circuit diagram is where its fitted. Has anyone any idea why this has been done? Colin
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Old 1st Dec 2021, 6:17 pm   #2
Craig Sawyers
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Default Re: RA17L Serial No = N 3392

From C129 to the top of the primary of L60. 0.1uF C129A, Mod(ification) 9

And the coax from SK4 goes to the top of L60 directly.

No idea why.

Craig
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Old 1st Dec 2021, 6:20 pm   #3
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Default Re: RA17L Serial No = N 3392

Isolating HT from the inner of PL4/SK4, presumably someone got a bite and an amendment was issued?
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Old 1st Dec 2021, 6:31 pm   #4
Craig Sawyers
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Default Re: RA17L Serial No = N 3392

OK - here's a plausible reason. Suppose in the original version there is a short between variable capacitor vanes (not actually an uncommon fault in an RA17). That would short the top of L60 primary to ground and put 240V at the other end - and blow up the coil.

The modification means that any vane short has no catastrophic effect.

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Old 1st Dec 2021, 7:17 pm   #5
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Default Re: RA17L Serial No = N 3392

Thanks for the replies. I will leave the mod in place then. Is there a readily available documentation of any mods that I could download? Colin
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Old 1st Dec 2021, 7:34 pm   #6
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Default Re: RA17L Serial No = N 3392

Connectors like PL4 are handy for inserting test signals or taking a look at what comes out. Finding that HT comes out could be a bit of a surprise, and expensive in test equipment as well. Keeping RF connectors near ground is good housekeeping.

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Old 1st Dec 2021, 7:34 pm   #7
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Default Re: RA17L Serial No = N 3392

Apparently EMER E727 has all the info, the royalsignals web site shows they have a copy.

I've never had any luck obtaining documents from that site but here it is anyways (look for Item no: 1128):

https://www.royalsignals.org.uk/uk-c...lth-rx-tx.html

Lawrence.
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Old 1st Dec 2021, 8:43 pm   #8
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Default Re: RA17L Serial No = N 3392

Thanks Lawrence. I have made a request for the document.
David. Looking at the circuit it looks like isolating PL4 from the H.T. will mean that V9 has no H.T.?
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Old 1st Dec 2021, 9:17 pm   #9
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Default Re: RA17L Serial No = N 3392

Could that capacitors circuit connection be as per the schematic in here (C129a, isolating the tuning capacitors from HT DC without interruption to V9's anode supply):

http://www.radiomanual.info/schemi/R..._serv_user.pdf

?

Lawrence.
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Old 1st Dec 2021, 10:22 pm   #10
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Default Re: RA17L Serial No = N 3392

Ill have a good look tomorrow & check again my interpretation of the mod. Hopefully Ill have that download as well. Colin.
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Old 1st Dec 2021, 10:32 pm   #11
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Default Re: RA17L Serial No = N 3392

It might be a mod to allow the use of an external synthesiser or crystal oscillator for the third LO?

The synth wouldn't have much tuning range before the 'kc/s' knob would need re-peaking.

The RA117 has an external LO switch, but it also has an extra IF at 1.6MHz in place of the 2-3 MHz tracking filter.

All sorts of specials and mods can be found based on RA17s.

David
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Old 2nd Dec 2021, 11:18 pm   #12
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Default Re: RA17L Serial No = N 3392

I managed to download the document E 727 thanks Lawrence.

Armed with the document I had another look at the extra capacitor. It is wired as the E 727, & not as I thought initially. The cap is wired in series with C129, & the H.T. is still on the plug & socket to feed V9.

The EMER confirmed Lawrence & Craig's thoughts as to prevent damage if the vanes of C129 short.

The cap is quite leaky so it will be changed along with the Hunts caps.
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Old 3rd Dec 2021, 1:21 am   #13
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Default Re: RA17L Serial No = N 3392

See the schematic for the RA17-C12 ... yes, its to isolate the capacitor vanes from B+.

Your diagram is not the same as the RA17-C12
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Old 3rd Dec 2021, 12:02 pm   #14
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Default Re: RA17L Serial No = N 3392

(dtvmcdonald) Yes, looking at the RA17-C12 schematic, C127,C128, & C129 are all isolated by C129A. With my RA17-L only C129 is isolated as per E 727. Colin
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Old 28th Dec 2021, 1:41 pm   #15
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Default Re: RA17L Serial No = N 3392

I usually, take lots of photos & make drawings when I disassemble anything. So why can't I find where 2 wires go?.

I'm now re-fiting the 1st VFO & not sure which way round the (orange from V7 anode) & (red from R51 /52) wires go. The pair go to pins 3 & 4 on the input to the 40MHz B.P.F. If I could identify the pin numbers on the B.P.F. all would be well. Colin.
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Old 28th Dec 2021, 5:44 pm   #16
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Default Re: RA17L Serial No = N 3392

Ok. When I turned the set over I found I had marked up the filter board with the colours. So orange goes to the left & red to the right on my previously posted image. Colin.
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