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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 3rd Sep 2017, 5:21 pm   #1
n_highfield
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Default Drake SSR-1

Just acquired one of these for no better reasons than it was only twenty quid and I have never had a Wadley loop receiver before.

I looked around the internet before it arrived and there are apparently two versions - one all bipolar and with a slightly odd system for the 1 MHz harmonic generator of an astable multivibrator directly synchronised to a 10 MHz crystal osc. The other version with mosfets in the local oscillators and a rather more sanitary harmonic generator using a 7490 decade counter between the crystal and astable oscs.

Curious to know which type I had, I pulled the cover off as soon as it arrived; neither - yes to bipolar local oscs but a 'kludge' board on the back of the harmonic gen with the 7490 on it!

NHH
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Old 3rd Sep 2017, 7:21 pm   #2
John KC0G
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Default Re: Drake SSR-1

Nick,

I had not realised that there were multiple versions. Thank you for the education.

John Wilson bemoaned the fact that the Lowe SRX-30, Drake SSR-1, and Century 21 receivers were all very similar, and came from the same manufacturer, in his article "The Non-Phase Lock Loop", ie the Wadley loop, in Short Wave Magazine, February 1998, pp 12, 12, 16, 17. The Standard 6500 also came from that manufacturer.

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Old 3rd Sep 2017, 9:10 pm   #3
n_highfield
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Default Re: Drake SSR-1

the SSR-1 manual http://gmcotton.com/ham_radio/misc%2...ver_Manual.pdf has the bipolar version. While the alignment instructions available on BAMA has the mosfet version, as does the Standard C6500 manual available on mods.dk.

The alignment instructions invite one to "rock" VR1 (which adjusts the free-running frequency of the astable) to determine the points at which the lock frequency changes above and below 1 MHz and set it half way between the two. There is a hand written note to the effect that VR1 is not present on all sets indicating the change to a divider type circuit.

The reason for the change becomes clear on reading this http://www.qsl.net/pa2ohh/06ssr1.htm seems like temperature effects could easily shift the free-running speed of the astable sufficiently for it to lock on to the wrong increment of the 10 MHz crystal osc. Presumably the kludge board was an interim measure until the main board could be redesigned, but why didn't they just use a 1 MHz crystal osc?

Interesting stuff I think, or perhaps I'm just easily pleased!

NHH
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Old 6th Sep 2017, 5:11 pm   #4
John KC0G
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Default Re: Drake SSR-1

IMHO, definitely interesting stuff!

The web page by PA2OHH is interesting reading. I did not know that the circuitry of the XCR-30 Mk II and SSR-1 had so much in common. Perhaps one should not be surprised. Trevor Wadley had made the design of the XCR-30 Mk II as simple as it needed to be to do the job. The early version of the XCR-30 Mk II used discrete transistors in the audio p.a. stage. The later version, like the SSR-1, used an i.c. amplifier.

The SSR-1 had a poor reputation when it was on the market. The comments in various editions of the World Radio and TV Handbook were far from complimentary. PA2OHH makes the reasons clear, not least of which was that it was a portable design in a base station's clothing to be used as a base station.

There was a further stage of development. Lowe with the SRX-30D, and Century with the 21D models offered a digital frequency display. The Century 21D manual be found online. The display used two long since obsolete MSM5525RS counter chips, one for the MHz digits and the other for the kHz digits. The arrangement was quite clever. The 21D also used SL1641 mixers. I assume, but do not know, that the SRX-30D was very similar to the 21D

73 John
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Old 13th Sep 2017, 7:40 pm   #5
n_highfield
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Default Re: Drake SSR-1

Thanks for that John - a little more insight!

BTW, I see the XCR30 use a 1MHz crystal oscillator http://www.qsl.net/pa2ohh/06barlowdiag.gif - I remain puzzled by the 10MHz and divider arrangement on the later variants.

NHH
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Old 13th Sep 2017, 8:30 pm   #6
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Default Re: Drake SSR-1

10MHz crystals are often cheaper than 1MHz.

It could all come down to something as unsubtle as money or rationalising parts usage.

David
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