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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 Today, 1:40 am   #281
SiriusHardware
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Default Re: Cybernet PTBM121D4X problems

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Originally Posted by John M1JWR View Post
Good news and bad news
10w fm 4w am and 10w ssb cant really do better than that
now the radio transmits on 21.390mhz on all modes and bands and channels
mod there apart from fm
i'm afraid somthing has died in the radio
pll ?
think in future i will stick to carburettors !!
It's a bit late to go into this tonight, but I think I see what has happened.

What I think you have managed to do is tune the early stages of the transmitter to (2 * 10.695) Mhz = guess what, 21.390Mhz

Nothing broken but the tuning, which is wildly out.

Rule #4: Be aware that simple RF power meters only show how much power there is. They don't care what frequency it is on.

To get the tuning back into the right region, use a receiver to monitor the output on the middle channel, middle band and initially tune to increase the indicated signal on the receiver, ignoring what is happening on the power meter. That way you can be more sure that you are tuning the coils to peak on the right frequency.
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Old Today, 2:06 am   #282
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

ahh yes i thought whats going on here, just to be on safe side i checked vco ch1 lo, its happy 4.19v and checked pll its happy with correct voltages and
checked c/changer side and voltages changed with channel.
was going to see if it rx'd next.
op error, part of the learning process.
now where's my vacume guages !!!
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Old Today, 2:17 am   #283
Techman
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Default Re: Cybernet PTBM121D4X problems

It sounds like the driver or output is perhaps going into oscillation. (I think I mentioned this before). I'm wondering if it's been doing this before and you have only just noticed it? If you remember I said that off peaking, or de-tuning the transmitter driver and output inductors (or coils) should be avoided, well this is a situation where slight 'off peaking' of one (or more) may be necessary. On AM/SSB, monitor the output with your frequency counter and watt meter and slightly adjust each of the inductors in turn and you may see it suddenly stop oscillating and return to transmitting on the correct frequency - some of these sets are prone to this. I'm still not convinced that there's not still an un-diagnosed fault somewhere in the drive, or perhaps it is just that the whole set was way out of adjustment in the first place.

You mentioned the 'swing' seems to be backwards on AM modulation - I think this is down to bad regulation and the audio level is making the supply rail 'dip' to this part of the circuit. Certainly they wouldn't think a lot to it on the old channel 6 AM, where carriers are wound down to a couple of watts and audio is wound up flat out and the whole lot fed into massive linear amplifiers! However, your set will probably sound quite nice to listen to on AM as it is. You can't really say that the audio on 6 is 'nice'. I'm sure you know about channel 6 AM, on what is now known as 'mid band', if you don't, then just look it up - there's nothing to be heard on there at the moment though.

As a note on those resistors with a '*', it's interesting to note that the same resistors, which are the same value but marked as R39 and R38 on the 059 chassis circuit diagram, are not marked with a '*'. The 059 board is not known for output stage biasing problems, whereas the 121 board is well known for issues with distortion and clipping of the output waveform.

As another note regarding R45 which is 4.7K, but without the point/dot shown on the drawing, I note that on the original Hi Gain and Concorde diagrams that the 'dot' is shown but is below the line compared with other similarly marked values, so it looks like the Intek circuit could be an early version with the 'dot' being mistakenly left out, but was corrected on later issues, having to be inserted lower due to spacing. Makes you wonder if there's any other corrections from this drawing onto the later ones - that is if they are indeed later.
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Old Today, 2:19 am   #284
Techman
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Default Re: Cybernet PTBM121D4X problems

Just seen post #281 - that's a good possibility I hadn't thought of.
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Old Today, 2:27 am   #285
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

techman did you get the links for the alternative circuit diagrames
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Old Today, 2:40 am   #286
Techman
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Default Re: Cybernet PTBM121D4X problems

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Originally Posted by John M1JWR View Post
techman did you get the links for the alternative circuit diagrames
No, sorry, they're actually original paper copy diagrams that I have from the original radio handbooks. I could probably sort out posting copies if necessary, or post a quick camera snapshot.
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Old Today, 2:45 am   #287
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

put them on post 275 they were done 10 years ago by an american
they look completely different to any original
they also mention the bias upgrades
ch6 am the super bowl

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