[Premium-Rx] SRT CR302A EJ KANB 301A

[John Graham 02]

>> Sorry, wrong title in the subject! <<

I too would be interested in any service information on this range of receivers. 

All I could find online is the CR300 product range brochure on the BAMA site at http://bama.edebris.com/manuals/srt/cr300 [this does  at least have a block diagram] and a couple of descriptive articles in Comunicaciones Eléctricas [vol 47, 1972 and vol 48, 1973], the Spanish edition of ITT's Electrical Communication [ITT was the parent company of Standard Radio & Telefon AB]. The Swedish ESR Resonans [2011 #1] has a 4-page article on the CR300 family by Karl-Arne Markström, SM0AOM in his Monadens Mottagare [Receiver of the Month] column. There is also a 4-page description in Golobin's 1985 book [in Russian!] on Professional Shortwave Radio Receivers.
There are also a couple of web pages with photos on the CR305A [Nixie tubes and switches] and the CR307A here: http://koti.mbnet.fi/~ijl/cr305a.html  [text in Finnish!]. This includes a scan of the block diagram.

I have an SRT CR307A, which is like the CR302A but with continuous tuning using an optoencoder and TIL311 LED displays; the 5MHz OCXO in mine is a Racal unit [yes, OCXOs are common in this type of receiver]. Like many marine receivers, the SSB is USB only. 
Interestingly, one of the 200kHz mechanical filters in mine is an E. German RFT type rather than the usual Telefunken ones although the receivers were built during the Cold War and have NSN numbers on all the modules [it's original, not a mod].

Unfortunately my receiver has a fault with the board that handles the continuous tuning, which only works at the "x1" rate but not the "x1000" rate. It should be quite easy to fix, except that the board is wire-wrapped, so virtually impossible to trace out the circuit. I may end up building a replacement board instead, or temporarily replacing the control of the most significant digits with BCD thumbwheel switches.

A CR304A - also very similar with continuous tuning and both LSB/USB - with full service manual sold on eBay.de a few days ago for EUR 636. The listing said item location London, but it wasn't listed on Ebay UK and when I contacted the seller I was told it was in fact in Hungary!

hope this helps,

John Graham.




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Message: 1
Date: Mon, 24 Jun 2013 02:02:42 +0200 (CEST)
From: "Peter Ratuschni" <zpz at gmx.de>
To: premium-rx at mailman.qth.net
Subject: [Premium-Rx] SRT CR302A EJ KANB 301A
Message-ID:
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Hello All,
yesterday I received a swedish HF receiver, a SRT CR302A. (This was for heavy but luckless repairing of the Eddystone.) SRT means "Standard Radio and Telephone".
The label "302A" was hidden by a sticker saying "EJ KAN B 301A". 
A switchs allows the following modes: A1.1, A1.2 (CW), F1.1, F1.2 (seems to be the FSK option), A2.A3 (AM), A3AU (USB), A3AL (LSB), A3B (DSB ?). Some more positons are possible which are not marked.

Does anybody knows about this unit? On the web there is only some very basic information.

There is a switch with 11 positions, going from AGC to Chan.A, Chan.B and numbers from 1 to 8. I am not sure what this is good for. It is not HF gain because manual gain control is done with a potentiometer below and activated with a push button.
The display consists of 6 nixie tubes in original but somebody swapped the 4 lower digits with big LED digits. That looks strange, but after a while I liked it. Then the tuning seems to be also modified. The original unit has a switch for each digit - you have to move to another switch if you want to change from i.e. 7,999.9 KHz to 8,000.0 KHz. So instead of a 100Hz step you can produce a step of 1 MHz. (First nulling the 4 lower digits and then incrementing the MHz-digit). I do not know if this is originally the same with every digit - on mine unit two switches were omitted and the 100Hz tuning knob is able to make a carry for 1, 10 and 100 KHz. The control of the LED digits is realized with a DIY pcb. 
The internal 5 MHz reference was a little surprise to me, as this seems to be a big OCXO. I do not know if this was usual for commercial receivers that time.

I fiddled around a bit with this heavy unit and found that I never heard CW so good at my location. The area is electromagnetically polluted in the sw range and I have only some indoor antenna wire. Of course, with wider filters I found nearly the same problems as with the other receivers.

b.r.
Peter




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