[R-390] Re: Racal RA.17 Receivers

Wed Jun 8 21:44:17 EDT 2005

Guday Roy My receiver is a RA17L   these radios are all very similar the
American radios had a 6AS6 as the third mixer the British radios had a 6F33
which is very hard to find these days and I have substituted the 6AS6 in my
radio it has different socket connections, the radios are easy to service if
you have the right gear , the ceramic bypass caps in the IF stage give a lot
of trouble and also the 100KHz IFT s are wound with Litz wire under tension
and after many years of heating & cooling  some strands give way and effect
the Q of the transformer and when you re align you cant obtain the shape in
the handbook, I have fixed these by disassembly and running solder up the
wires , you can get a good idea what is happening in the Wadley loop by
connecting a CRO probe to the O/P of the 3rd mixer and tuning the MHZ dial
you will see the one mhz pips going across the screen as you tune the VFO
from 40 to 70Mhz ,also the 40mhz filter and the 37.5 mhz filter need to be
swept ,I use a HP 141T and tracking gen and this combo does a great job , I
also have the ISB adaptor for this radio which has an input of 100KHZ and
splits off bath sidebands at 18KHZ and demodulates with 2 product detectors
,I have bought many pallets of these receivers at our AUST gov. surplus
auctions and have never found one that I couldn't fix , A very common prob
is an open circuit 100k resistor associated with the 6As6 screen or plate
,Icant remember , also here in Australia ,in the late sixties and early
seventies lots of hams in OZ made there own Ra17 rx s it was called the
Deltahet and I have scanned the articles into my computer if you would like
to see them ,Do you have broadband Roy? as they are a few Megabytes ,My
project of the hour is re manufacturing an ART 13 tx by Collins ,I have got
it all back together and its taken a fortnight,{ I am a  retired
Electrician }and I powered it up last night and its working ,today I am
going to align it
----- Original Message ----- 
From: "Roy Morgan" <roy.morgan at nist.gov>
To: "bernie nicholson" <vk2abn at bigpond.net.au>
Cc: <roy.morgan at nist.gov>
Sent: Wednesday, June 08, 2005 12:12 AM
Subject: Racal RA.17 Receivers


> At 09:30 PM 6/6/2005, you wrote:
> >Hi guys I have three 390a rx s and a 391 and I also have one of the last
> >racal Ra17 rx s made the Aust. army date code for manufacture is 9th
month
> >1974 , its a nice reciever and it is very slightly more sensitive than a
> >390A,  when evaluated with a signal generator  {The American RA17 RX s
Had
> >A FRAME grid tube in the RF section and the rest of the world got a
> >Cascade Double triode }
>
> Bernie,
>
> I appreciate your comments on the Racal RA.17.  I have here an RA.17 UC.
> This seems to be an "Americanized" version with features for panoramic IF
> adapters and/or external oscillator injection.  I am not sure what tube(s)
> are in the front end. I will go look soon.
>
> I am pretty sure I do not have the correct documentation for the thing. I
> wonder if you do?
>
> Mine has an intermittent in the front end, so I will need to take at least
> that section apart.
>
> Roy
>
>
> >BUT in practical terms the the 390A  outperforms it due to a FAR better
> >signal to noise ratio which is a function of the 2khz mechanical filter,
[
> >I am Talking SSB reception here ] if I wanted to listen to a broadcast
> >station the racal RA17 has nicer audio , the dynamic range of the 390A is
> >Much  better than Ra 17 around 20Db in fact , the 100Khz I F  in the Ra17
> >Just cant compete with the mechanical filter for ssb and neither can the
I
> >F  stage in the 390 rx  ,I know that the 390A project was to save money
> >and it achieved that end BUT  between the time of the original concept
and
> >the 390A project Mechanical filters were invented By Mr Adler at Zenith
> >radio Corp and it became possible to exceed the original performance
> >specsof the 390 with less stages and also to take advantage of more
modern
> >tube design , overall I see many advantages for owners of 390A receivers,
> >The tubes are Plentiful and easy to source, here in Australia 6AJ5 /6BJ6
> >/6082 ,are in the same supply status as rocking horse droppings and from
> >what I hear in the states people who have these tubes want an arm and a
> >leg for them , on the minus side with the 390A  there is an ongoing
> >problem whith the mechanical filters, the foam rubber packing inside the
> >filter with the passing of the years has De -materialised and also become
> >corrosive , especially the 4khz filter,I have replaced a couple myself in
> >the last few years  but I bought a few spare IF modules many years ago ,
> >summing up I would say that there is no BEST receiver it all depends on
> >what ones interests are, BUT if you want to work DX on forty meters at
> >night in amongst the broadcasters on SSB or CW the 390A is the way to go
> >!!!!!!!!!!!!!!!!!  PS  I wonder how much Collins Paid Zenith for the
> >Mechanical filter production licence??????????? Best Regards to
> >everyone  BERNIE N
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> - Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
> 7130 Panorama Drive, Derwood MD 20855
> Home: 301-330-8828 Cell 301-928-7794
> Work: Voice: 301-975-3254,  Fax: 301-948-6213
> roy.morgan at nist.gov --
>
>
>
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