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Greetings, Just got an RA6790/GM which works great on AM. CW and SSB is garbled and distorted. Ran a BITE test with no faults found. It has 5 filters installed. Selecting between them on CW makes no difference. Any ideas? Regards, Patrick

Hi Would anyone have a copy of the user manual for the PRC-6990 which is the UK version of the Racal MSHR transceiver. I need to find the pinouts of the side and top accessory connectors and how to program scan. Tony

My MA-937 power supply unfortunately did not come with a case/shell. It looks to be the same form & fit as the case for the TRA931x. If anyone has an empty case laying around that needs a purpose, please let me know. Thanks! Mike KD7VRG Tucson, AZ

Hello All, I recently acquired a TR-967. Unfortunately the previous owner left Duracell batteries in the pack for a "while". Even thought the batteries were still within their expiration date, they leaked and destroy the box. Therefore, I am in need of one or two. Any leads or other info, i.e. "it's the same as the battery box for XXX radio, or a BA-yyy will work", would be appreciated. Thanks in advance, Gene K1NR PS: Apparently this is a well known issues with Duracell these days.

Anyone have it to share? Thanks Can be contacted from QRZ MW6ABC

Group. I have for sale 3 of the above items for sale, these are new old stock asking ?33 each. plus pstge Jeff G8XXI

Hi, I currently have on my bench a Racal Syncal 30 aka TRA931. I'm currently involved in looking into alternative PA transistors since good 2N5070s are nearly impossible to source these days. I currently have a pair of 'experimental' transistors in place and the set is happily generating 20W on all frequencies with a very slight drop (about 2W below 2MHz). What is a bit alarming is that the set will happily deliver 20W (in the High position) even when AM is selected. Oddly, although the manual specifically states that the o/p is nominally 5W on AM (and understandably too), there is no mention in the circuit description of how this reduction in output power is achieved. Looking at the wiring associated with the Mode Switch, it looks like the Mute pin (66) on the synthesiser might have something to do with it, but poking around in that area has proven inconclusive. Can anyone shed some light on this? Regards, Ian, GM0UHC www.chavfreezone.me.uk

Hi everyone, I have a question for the technical guru's. When I tune in AM stations using SAM on my WJ8711, its quite obvious that is generating and reinserting its own carrier. There is a momentary heterodyne if the AM signal changes in frequency suddenly while it adjusts to the correct frequency. The RA6790, while it performs fabulously well as an AM receiver, does not show any evidence of this happening at all. It also doesn't perform as well as the WJ on selective fading. Why then is it widely believed that it has full time synchronous AM? Cheers, Peter - VK2AN

Does anyone have one of these, or pictures of the inner workings? I pretty certain I worked on the design of this unit but can't find any information online to jog my memory. -- Mike G8GYW

Hi chaps, I've just received one of these 6 band VHF filters today. It physically bolts onto the TA970H VHF RF amp and also the MA989/E frame. What I need to know is whether it can handle the TX power of a 3W TRA967 transceiver on its way to a TRA970 VHF RF amplifier.

Hi Friends, I am new (only here, unfortunately I am all but new...) I am trying to restore initially at least one of three RA.1217 I have here. They are probably the most difficult equipment I worked on. Is there someone willing to give me some suggestion? Thanks, Gianni from Florence, Italy

Hi Everyone, I have done an alignment on this receiver and it is working really well, but the only slight gripe I have is the hang AGC time constants. On the Long setting, it is incredibly long - at least 4 seconds, however Medium is so short that the AGC "pumps" noticeably on SSB signals. I thought it should be a simple matter to adjust some resistor values to something more useful, like maybe 1 second for Medium and 2 or 3 secs for long, but it is proving to be much more difficult than I thought. According to the manual, R45 (330K) on the A4 board sets the LONG time constant, and the parallel combination of R45 and R146 (27K) should set the MEDIUM time constant. I have changed R45 to 220K and it does seem to have shortened the long time constant, but changing R146 to a much higher value has no effect whatsoever on the medium time constant. In fact, removing the resistor altogether, still has no effect on the medium time constant? Does anyone have any information on what is going on here? Please note also, that I want to keep the "hang" AGC and not disable it as per the article by Dallas Lankford. Cheers, Peter - VK2AN

RA1778 Tricks of the Trade - VMARS AM net resolved as SSB - using AFC carrier phase lock, full carrier AGC and selectable USB/LSB side band - eliminating co-channel QRM. Not quite its intended use, but handy as the Vintage net's 'drift the night away' 73-Graham https://youtu.be/vdIwBHLOoes?si=5ibtYZyzBVBw22q7

I saw a post about the hex files for the 6790 with LF and 1-10-100kc tuning but cannot find it now for some reason, I would like to find those files. Thanks W5DTW -- This email has been checked for viruses by Avast antivirus software. www.avast.com -- MOGMAN

For anyone who is interested, I thought I would do a quick write up of how to change the AGC time constants on the RA6790/GM There are two separate stages that control AGC on this receiver, a "hang" AGC section and a normal AGC decay section on the main IF/AF board, A4. The hang AGC holds the AGC constant for a period of time then the decay takes over with an RC time constant. This works as follows: FAST AGC setting In this mode, hang AGC is disabled by Q2, and the AGC decay is set by R55 (1K) and C52 via R65 and R64. You probably should leave this as is. MEDIUM AGC setting In this mode, both hang AGC and AGC decay are active. Q10 turns on and the hang AGC time constant is set by the parallel combination of R146 (27K) and R45 (330K) and C42. The AGC decay is set by the parallel combination of R52(47K) and R53(10K) and C52. SLOW AGC setting In this mode, both hang AGC and AGC decay are active. Q10 turns off and the hang AGC time constant is set by R45 (330K) and C42 only. The AGC decay is set by R52(47K) and C52 only. Suggested Mods. In my receiver, the SLOW AGC setting was very slow - somewhere around 4 seconds. The MEDIUM setting, however was too fast at less than 0.5 second. I have adjusted the values as follows to give around 1.5 seconds on MEDIUM and around 3 seconds on LONG with a longer decay to avoid the abrupt AGC cutoff. I ended up with the following values - but feel free to vary these as you like. R45 - 180K R146 - 180K R52 - 82K R53 - 100K Another possibility is to fit small trimpots so the times can be easily adjusted. The receiver is now much more pleasant to listen to on SSB and CW signals, especially when using MEDIUM AGC. Cheers, Peter - VK2AN

Hi all, I saw on https://radiohistory.uk/RacallistB.htm that the AATU BCC540F and G can accept PWM data from the RT on a PRM 4790 and BCC39. But has anyone published the differences between these two models? Is G just later then F and perhaps more desirable because it is more recent? Or are there some other differences to know about? Thanks 73 Eugene W2HX My Youtube Channel: https://www.youtube.com/@w2hx/videos

I have a paper copy of the two volume 1778 maintenance manual which is missing the Parts List which should be Chapter 25. Does anyone have this, as a pdf maybe? The only on line version of Vol2 is also missing this Chapter. I am about to start again on the big wiring job on mine where the Hellerman sleeves have decayed and thus ruined a lot of the main wiring loom. 73 - Dan ac6ao / g3ncr