All about CB radio

[Damo666]

Originally Posted by Techman

That's strange, a capacitor added usually drops it by three and three quarters rather than ups it by six and a quarter.

Flicking the switch on Channel 32 high band (27.755) on this Stalker 9 of mine takes me to 27.781, which is normally Channel 33 high band on other sidebander rigs I had many years ago. So on this, UK channels 1-27 read 15-40. It took some getting used to at first, because 16 is normally cgsnnel 1, 33 is 19, etc'.. and because high band has alphas & strange jumps/gaps, some of the lower UK 27/81 channels are jumbled up a little.

[Damo666]

Originally Posted by G0HZU_JMR

I can't remember how much difference it makes but if it was my radio I'd leave it as stock

I have several mk1 Cobra 148 GTL-DX radios here two of them are in very nice original condition (boxed) with no mods/changes anywhere and I think the lazy s meter is part of the charm.
I've got another one I converted to the 40m band and I left the s meter as standard on that one too.

I've got quite a few mk2 Cobra 148GTL-DX radios here as well including two original ones (boxed) that look even better than the mk1 radios. These are both standard too. I do still have my original mk2 148 that I bought as a student in about 1982 and this is very heavily modded. I learned a lot about PLLs and receiver and transmitter design from playing with that radio. It's a bit tatty inside and out but it still works well.

I decided to leave it (meter mod with 1N60), Jeremy, as it's not really a big issue - and the more untouched the rig is, the better.

I'm a big fan of the Cobra 148 MkII, and as a teenager back in the early 90s I always wanted one but could never quite afford one, so I had to settle for a Midland 3001.

As time progressed, I managed to save for some better rigs; Northstar DX990, Stalker 9, Superstar 3900, and a stint with a President Lincoln - all pretty good in their own way.

[SiriusHardware]

Originally Posted by Techman

That's strange, a capacitor added usually drops it by three and three quarters rather than ups it by six and a quarter.

It depends whether the capacitor is from one end of the crystal down to ground or, alternatively, in series with it. Sometimes you couldn't get enough bend in the preferred direction by doing it one way, but it would go far enough in the other direction doing it the other way.

The only really decent / acceptable way to retrofit 27/81 to a generic radio which didn't originally have it was to introduce an eprom programmed with code conversion tables between the channel switch and the inputs of the PLL IC - that way the awkward CEPT channel jumps and gaps were eliminated and the 40 27/81 channels were as indicated on the display, with only the addition of a crystal pull (as already discussed) needed to bring the frequencies into line.

For CEPT-only, FM only radios (Like Damo's Realistic TRC1010) it was theoretically possible to fit the 27/81 version of the same PLL family either instead of, or alongside the original PLL, and of course it could also be done the other way to add CEPT to a 27/81 radio.

The first approach is quite a 'heavy' modification which I wouldn't consider inflicting on anything which has survived for this long in its original form. The second option, for radios which were originally either CEPT or 27/81, was relatively non-destructive and reversible.

[Techman]

Originally Posted by SiriusHardware

The only really decent / acceptable way to retrofit 27/81 to a generic radio which didn't originally have it was to introduce an eprom programmed with code conversion tables between the channel switch and the inputs of the PLL IC.

That's what's in that Tristar that I pictured. I've just been looking through my pictures as I thought that I had some pictures of the 'innards' of it, but I couldn't find them.

I've actually had that radio for a very long time, probably something like 35 years. It's not changed in all that time and it was only recently that it went wrong and I had to repair it. The only other thing I've had to do was when it came out of retirement several years ago, was to re-set it onto frequency as it had drifted slightly low over the last 30 odd years. It's no 'prize winner', although it's not in bad condition and virtually in the same condition as when I first got it, as it wasn't new but probably no more than a couple of years old at the time. I swapped an old valve linear for it via a friend who knew the person, so I never actually knew the original owner, other than it was a 'ham' operator who wanted a 'basket case' linear to convert for amateur use and I'd been given this linear with a burnt out mains transformer. The radio was just the radio, no mic or bracket and possibly no power lead, but it has been a good radio over the years. It's probably true what you say about them, but I lived out in the 'sticks' and I seem to remember that I had it in the car at one time, too. I read a comment on the 'net' somewhere, that you never, ever see a mint, boxed Tristar777 for sale on the usual place, and I think that's true, as strange as this may seem. So the next obvious question has to be - do you still have the one that you bought brand new back in the day?

As to the recent fault, I was 'down' on USB having a chat with a group of locals, when I released the mic and found they were talking to each other over me. I thought 'that's strange', but then realised that the radio had stopped transmitting, apparently I just disappeared 'mid flow'! SSB being all peaks and troughs, it wasn't exactly being over driven, unlike the way this particular model thrashes itself on FM. Tests showed that the 2SC1969 RF output transistor had failed - I noted that it looked like it had been replaced before, but this must have been before I got the radio as I've never had to do any repairs on it before. I removed the transistor and tested it out of circuit and it tested fine, so I put it back in and the fault was still there. I removed the transistor again and this time it tested faulty with base emitter o/c. I've had this sort of intermittent behavior with these transistors before, so I wasn't particularly surprised by this.

Rather than use a genuine original 2SC1969 bought by me new probably over 35 years ago, I thought I'd see if I could get something that's obtainable today and make it work. I'd thought about having a go at a MOSFET conversion, but the ideal component for this job is starting to be 'faked' all over the place, too. I had read something on the 'net' where someone had mentioned that a particular supplier had some transistors that worked, but the delivery time was a few weeks. I think I've mentioned this in another thread about these transistors where I ordered a couple and when they eventually arrived I fitted one and it was perfect. I set the base bias and the radio seems to be outputting more power than it ever did before, although I have to admit that I'd never checked the bias with the original transistor when it was working. When I brought this radio out of retirement several years ago, I found that it had developed a strange fault whereby it would not transmit on SSB until it had been switched on for over an hour, or this could be speeded up by whistling down the mic for perhaps up to half a minute. I put this down to possible low voltage electrolytic capacitor problems and intended to look into it sometime, but the radio improved somewhat with use, although the fault was always there to some extent. However, since replacing the RF final transistor, this fault seems to have completely cleared. The original fault was only on SSB output, FM etc., was always fully there from switch on - I'm trying to work out how a failing final would affect SSB only, without affecting FM and AM, unless it's just a coincidence that the fault has cleared?

The transistor I fitted clearly has a stuck on label with its type number etc., so I would think it's some sort of 'non-original' although the supplier stated that they were 'originals', but no complaints as it works a treat and I've ordered more! I've also recently bought one of those 'Eleflow' copies that are 'said' to be very good. It 'looks' good and comes supplied with data, and although I haven't tried it yet, I have every confidence in it. However, I read a comment on another forum just recently (where I'm not registered, but just read now and again) where someone commented that they didn't particularly rate them but didn't enlarge on that comment.

This particular model of radio puts out the same power on FM as it does on peak power on SSB, and now being a good 20 watts, it's far too much on FM for its own good. It can be reduced by feeding the power for the RF output stage from the AM 'darlington', but I'm personally not too keen on this method. I think I'm going to just reduce the voltage with a fixed 'watty' dropper, a bit like the method used in the Ham multimode etc., but just with a fixed resistor rather than a pot.

Below, for your comments are, in the first picture, an original 2SC1969 from my very old stock and shown on the left in this picture, and the recent replacement that I fitted on the right in this picture. The second picture shows the same two transistors the other way up and the other way round. The third picture shows the faulty removed transistor:-

[SiriusHardware]

Originally Posted by Techman

So the next obvious question has to be - do you still have the one that you bought brand new back in the day?

I'm afraid not.

Although... I may still have the box in the loft, because for years I used to keep assorted computer cassette tapes in it.

I read through the rest of your post with great interest, but unfortunately I can't really add anything helpful because I haven't had to go down the road of coping with / trying out fake / alternative RF output transistors. When I was last actively involved in working on CB radios all the 2SC1969s around were genuine old stock, and I think Jeremy is in the same position so you are, in effect, sweeping that minefield for all of us. Good luck with that.

I have a glass jar containing a few spares that I bought back in those days and that little stash includes a 2SC1969, which unsurprisingly looks like your original genuine transistor. Have you tried peeling off the stuck-on label on the new transistor to see what lies beneath?

The 777 diagram names either the 2SC1969 or one I've never come across, the 2SC2050, as interchangeable alternatives for Q8, the output transistor. In other diagrams the 2SC1307 is frequently named as an alternative for the 2SC1969, but not in the one for the 777. This may be because it had quite high output power compared to some just as you say, so perhaps that narrowed down the range of alternatives?

A friend and I have just experimentally ordered some retro CB spares from Donberg, the Irish component company. (There should be an umlaut over the 'o', but I don't know how to get one on my UK keyboard).

They list quite a few Japanese transistors including the 2SC1969 - while I know Donberg have been around for quite a while, there's no way of knowing what extent they go to to verify the provenance of the parts they sell, so we're just going to try a few and see. The main problem with them is a minimum order value of £20, which is why this friend and I decided to club together to get a few spares.

The other place you can still get 2SC1969s from at the moment is Knights Electrocom - they state that theirs are genuine and price them accordingly, mainly, I think, to discourage anyone from buying them all up and then just reselling them. If you have a broken radio that you're fond of, I don't think £15 is an unreasonable price to pay to get it working especially if your own repair labour is free.

If your mysterious problem with no TX on SSB but normal operation on other modes came to me as a cold case with no other information given, I would probably reason that the same transistor can't be faulty in one out of four modes and OK in all other modes. Bearing in mind that SSB is unique in that you don't get any RF output when there is no modulating audio, I would have gone further back to see if there was a problem with the SSB audio drive path or the balanced modulator. There are sections of the circuit prior to the transmitter driver and output stages which are dedicated to SSB only, so I would have been looking there.

One of the last repairs I remember looking at was a 121 chassis with no TX output on SSB, funnily enough. If you've got a 121 chassis diagram (I'm sure you have) have a look at C176 which takes some of the audio from the output of the TA7205 audio IC, passes it on through R166 to RV12 (SSB audio drive level) and then on from there through L21 / C80 to the AN612 (balanced modulator).

Do you see anything odd about the way that capacitor is drawn on the diagram? On mine, it's shown with the negative end going to the TA7205 output and the positive end going to R166 / RV12, the audio drive level preset. In the example I had, C176 was fitted the way around that it was shown in the diagram, so the capacitor had slowly died due to there being a standing reverse DC voltage across it. It took a long time (many years) to die because the reverse current through it was limited by R166 and RV12.

When I replaced C176, I fitted it the other way around.

Now that I've pointed that out, you'll be looking to see if there is a similar capacitor in a similar position in the 125 (777) chassis. There isn't, unfortunately, but you could still have had an on/off problem with C81 (possibly C91 - it's a bit blobby on my copy) - it carries the SSB TX audio drive to pin 1 of the AN612 - maybe it was faulty but when the set had been on for a while, it 'reformed'?

[G0HZU_JMR]

and I think Jeremy is in the same position so you are

I do still have quite a few of the classic RF power transistors used in radios like this, some are from my old stash from 30 years ago and I did also design some HF/VHF wideband PAs at work in the early 1990s so I have quite a few of the classics like the MRF477, MRF479, 2SC2166, 2SC1969, 2SC1945 and 2SC1970 and 2SC1971. I'm pretty sure all of them are genuine parts as they were purchased about 30 years ago. I salvaged them from work when we had a huge stores clearout and I saved them from the skip. I really don't want to sell any of them though as I still have quite a few radios here that actually use these parts.

From what I've seen, the Eleflow parts do look to be reasonable clones of the old parts. I've never had one here to test though.

[G0HZU_JMR]

Do you see anything odd about the way that capacitor is drawn on the diagram?

My memory is fuzzy now but the AF ALC caps on the UKFM Cybernet 134 chassis were drawn backwards on some schematics and I can remember that this caused confusion to some people. I think that the PCB silk screen was wrong too. However, I recall that the caps were fitted 'correctly' by Cybernet at the factory although they looked backwards according to the schematic and the PCB silk screen. The ALC voltage was negative but the schematic and PCB artwork was backwards. I'm pretty sure I can remember this issue cropping up numerous times because people would spot that the caps appeared to be backwards in the PCB even though they were electrically correct.

[SiriusHardware]

In the case mentioned I disregarded the silk screen and just measured the polarity of the voltage across C176's pads, then fitted the new capacitor according to that measured polarity.

I think I remember that, as a result, the replacement capacitor was fitted contrary to the way the silk screening indicated. I think the original capacitor had been fitted as indicated by the silk screening, which was an entirely reasonable mistake to make.

I didn't know there had been similar craziness on parts of the 134 diagram, though - maybe I just never ended up working in those particular areas. I'm going to have a look at it later.

[G0HZU_JMR]

I can't remember for certain, and I haven't seen inside a 134 radio for decades but this issue did cause quite a stir in my area back in the day. The problem you may face (if someone has been there ahead of you) is that they may have swapped the parts to suit the silk screen! Assuming my fading memory isn't letting me down all the 134 radios I checked had the caps fitted correctly from an electrical point of view. i.e. backwards compared to the silk screen. It's wrong on some of the schematics too. It could be wrong on all of them for all I know. I only have a handful of old photocopies here from 30-35 years ago

[SiriusHardware]

I have several examples of 134 chassis radios here but they are unfortunately all stored at the moment, so it's not easy for me to have a look. I consider myself warned, though, thanks for bringing that up.

The only original Cybernet service manual I have here is the one for the Cybernet 3000, which interestingly has the 'Goodmans' brand name on the cover, implying that Goodmans were the importers / technical supporters of the Cybernet self-branded radios.

I had a similar service manual for the Cybernet 1000 / 2000 as well, but donated it to the friend who actually had a Cybernet 1000 and I've long since lost touch with him - I still have a copy of the diagram, which is enough to solve most problems.

Were you aware of / did you ever get to the bottom of the reason for the flaky channel LED displays on those? My example is ironically one which does NOT have that problem so I've never had the need / the incentive to find out what the actual cause was. I know you said you'd experienced some grief when working on those areas (not necessarily on Cybernet 1000 / 2000 radios).

[G0HZU_JMR]

No, I don't recall seeing any with a flaky LED display. I only saw a handful of the 1000, 2000 and 3000 radios. They weren't that popular in the areas I lived in during the CB craze so I can't help you much here I'm afraid.

I just had a look online at an RVC240 schematic and the AF LC caps are drawn backwards on that schematic. I wish I could remember for sure if it was wrong on the PCB silk screen as well. I don't recall swapping them round but I can remember lots of fuss about this back in the day. So some people probably have swapped them around to suit the schematic. When I lived in the midlands in the early 80s (i.e. back home during student vacation) I was part of a small clique of 'rig doctors' of varying skill levels and so stuff like this rarely went unnoticed. There was a network of rig doctors and our middlemen who fetched and delivered the radios.

When I was up north I operated alone as a rig doctorand I had some scary trips on my bike to houses in parts of Hull and Leeds. Look up the Bransholme estate in Hull

Back in the 80s this massive housing estate was home to dozens and dozens of CB operators and I met all types in the time I visited there. Some funny, some strange, some very scary and some lived in fairly grotty conditions. The guy who lived in a small two up two down alongside about ten German Shepherd dogs was particularly memorable.

His parting words to me as he went upstairs to fetch his broken CB were:

"Don't look the dogs in the eye, don't make any sudden moves, stay in the chair and keep absolutely quiet and you will be fine"

Then he left me alone in a room full of 'wolves' all giving me that dark angry stare that these dogs do so well. Before he said those words to me, my words to him had been "Can I come with you? Don't leave me alone with the dogs!"

[SiriusHardware]

Originally Posted by G0HZU_JMR

I was part of a small clique of 'rig doctors' of varying skill levels and so stuff like this rarely went unnoticed. There was a network of rig doctors and our middlemen who fetched and delivered the radios.

We had quite a similar situation here. All of us had originally been electronics hobbyists and had gone on to work as technicians / repair engineers. We were all around 20 years old then. Of our small group I was the only one who actually worked, at the time, for a domestic / brown goods repair business so most of my CB repairs came to me across a shop counter and I never found myself in the sort of mortal peril you described (that came later, when I went on to work on access systems and CCTV systems). I did quite a few CB repairs as 'homework' as well because it gave me a better opportunity to try them out and test them properly, and I was just really interested in them anyway so the more I saw, the better.

I lost interest in repairing CBs when it began to dawn on me that nearly all the sets I was getting had self-inflicted damage of one sort or another - best case scenario, everything twiddled, requiring patient and time consuming realignment - worst case, the same but with everything adjustable smashed and needing to be replaced first. For decades now the only CB radios I have repaired or maintained have been my own.

[Damo666]

My friend discovered yet more CB's while rummaging in the loft yesterday so has given me them; There's an Amstrad 901, Harvard 407 home base, Icom 1020, and another couple of Handheld's.

All are working OK apart from the Icom 1020 and Harvard.

The Icom motorboats on TX from anything more than the first few low channels & gets progressively worse as the channels climb. Receive seems fine.

The Harvard homebase Transmits fine, but on receive - after about 5 min's after switch on, audio sounds pretty grainy & off frequency. Sensitivity seems fine.

The Harvard appears to use the same PCB as the Amstrad 901 (PCMA0002F) and a visual inspection of the board doesn't show any glaring problems. It's also never been opened & tinkered with.

[SiriusHardware]

Is the Icom definitely a 1020 and not a 1050 (as in ICB 1050?). I don't remember a 1020 and can't seem to find any references to them online.

If you want to have a go to work through the faults on these it might be better to start a specific thread for each one, although neither of them are likely to be as straightforward as the squelch fault on your Pama GX19 was.

[Damo666]

My apologies, it's an Icom 1050 as you rightly said.

I was thinking about starting another couple of help threads, but I don't want to appear to be flooding the forum.

[G6Tanuki]

The Icom 1050 was one of the few CB27/81 rigs that *didn't* use the LC7137 synth chip, instead it used a more-traditional Motorola synth so it was easy to convert to the FM part of the 10M amateur band (29.6MHz). It was also quite easy to fit a 100KHz repeater-shift so you could work through the US repeaters on 10M when the band was open.

See http://www.worldwidedx.com/threads/i...radios.145191/ for details. All in all a rather nifty rig.

[SiriusHardware]

Damo666, Re; your concern about whether to post more threads about CB radio repairs:

I think the only thing which would raise concern would be if you started to turn up with a new broken CB radio every couple of weeks or so on a suspiciously regular basis, as it might lead some people to assume that you were using help freely given here to assist you in running a repair-and-sell business.

As long as it doesn't get out of hand, and your thread titles are sufficiently clear so that members who are not interested in the thread subject can avoid it, I don't think there will be a problem.

If you do decide to post threads about these two radios I would suggest tackling one at a time for reasons of clarity, apart from anything else, before moving on to the next.

What were the other handhelds, by the way?

[Damo666]

Originally Posted by G6Tanuki

The Icom 1050 was one of the few CB27/81 rigs that *didn't* use the LC7137 synth chip, instead it used a more-traditional Motorola synth so it was easy to convert to the FM part of the 10M amateur band (29.6MHz). It was also quite easy to fit a 100KHz repeater-shift so you could work through the US repeaters on 10M when the band was open.

I got chance to test this out properly this evening, & coincidentally, it happens to be on the 10M band; It transmits from 29.310 Mhz on Channel 1, upto 29.700 Mhz on channel 40 in 10 Khz steps. There's good sounding FM hash as heard on a working FM rig, but I have no 10M rig to transmit to it with.

The motorboating on TX has also ceased completely, so I can only guess it was perhaps due to a lack of use (left in the loft unused for years) and a Capacitor maybe reforming after the unit has been switched on a couple of times in my short testing?

There was a small envelope taped inside the rig containing a 3 legged crystal marked with "10M08AA", so I'm guessing this was the original crystal for the UK 27/81 frequencies. I've never seen a crystal marked in this way before, nor have I seen one with 3 legs.

I really want to get this back on CB frequencies, but the mod's I've found here on the 'net don't mention removal/swapping of a crystal to do the conversion.

[Damo666]

Originally Posted by SiriusHardware

Damo666, Re; your concern about whether to post more threads about CB radio repairs:

I think the only thing which would raise concern would be if you started to turn up with a new broken CB radio every couple of weeks or so on a suspiciously regular basis, as it might lead some people to assume that you were using help freely given here to assist you in running a repair-and-sell business.

As long as it doesn't get out of hand, and your thread titles are sufficiently clear so that members who are not interested in the thread subject can avoid it, I don't think there will be a problem.

If you do decide to post threads about these two radios I would suggest tackling one at a time for reasons of clarity, apart from anything else, before moving on to the next.

What were the other handhelds, by the way?

Good points & these were my thoughts - and because it was only a week or two ago that I requested assistance with the GX-19, I didn't want to push the limits per chance the community/moderators thought this was my game - which it most definitely isn't.

The Icom 1050 now "appears" to be functioning correctly, albeit it needs converting back to 11M, so that eliminates the need to publish another thread.

I've been a little vague with the Harvard 407 symptoms, so before I make a new thread I'll scrutinise it under test a little bit further very soon. Then I'll publish a thread properly headed so people can avoid it should it not be of interest.

PS - The Handheld's are a TRC-1013 & a Harvard 020 2 channel toy type affair.

[G0HZU_JMR]

There was a small envelope taped inside the rig containing a 3 legged crystal marked with "10M08AA", so I'm guessing this was the original crystal for the UK 27/81 frequencies. I've never seen a crystal marked in this way before, nor have I seen one with 3 legs.

The 10M08AA is a crystal filter and this would have been used in place of CF101 to improve the 'bleedover' performance of the radio. However, I wouldn't recommend the 10M08AA as it is too narrow and typically gives a harsh sound to the receiver. The 10M15A is a better filter. It looks the same but is wider and doesn't give the harsh sound of the 10M08AA.

The original radio would have used a ceramic filter here at CF101 and this was followed by the MC3357 mixer/FM chip. The ceramic filter was very wide and gave overload/bleedover issues in the MC3357 IF chip, especially when used on UK FM CB when it was busy. My advice would be to check to see if there is a 10M15A filter fitted here or the original ceramic filter.