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Old 3rd Dec 2018, 11:54 pm   #141
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

hopefully ive got it near enough right, the results are as follows all on am
basically tiny tweaks on sig gen around the basic frequency given until it peaks
on radio, when adjustment is made use the fine control until no more improvement can be got.
results are with fine on its lowest, i have assumed anti clockwise position and
hi signal is around 2 oclock on fine control.
dont seem to get it any better than the following
ch30 lo 26.855 lo sig s7 hi sig 9 to +30
ch20 mid 27.205 lo sig between s7.5 and s8 and hi sig s9 to +30
ch10 hi 27.525 lo sig s7.5 and hi sig s9 to +30
i did a test with it as there is a kind of tone on ssb for its squelch issue as
i can peak it at s5 on ssb the squelch mutes it at s4 and below, when i get it
to s5 only a slight turn on squelch knob will mute it.
also took note of power consumption on psu with tone on and radio in rx
fm uses 285ma am uses 290ma and ssb 327ma
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Old 4th Dec 2018, 1:17 am   #142
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Default Re: Cybernet PTBM121D4X problems

You seem to have got it quite well balanced. Unfortunately it's hard to say whether the figures are reasonable or not in terms of overall sensitivity because the generator doesn't seem to be able to put out precisely measured amounts of RF signal. Because of this, you can only really use it to make relative / comparative measurements rather than absolute measurements.

For example, connect the generator to the 777 which I assume you think is working well. Try generating a signal in the middle of the middle band on the 777 and then turn the generator output down, down, until the 777 is indicating exactly S1.

Then, without changing the output level or frequency, connect the generator to the Colt. Can the Colt 'hear' the signal as well as the 777 could? Ideally, it should indicate S1 as well, but there are possible variables - the S meter on the Colt may very well be adjusted differently for a start, so the actual sensitivity could be near-identical, but one meter might be adjusted to read higher than the other. On the other hand, if the Colt just doesn't hear the signal at all then it is still more deaf than your 'gold standard' radio.

When tuning the receiver, did you adjust anything other than T9-T10-T11?
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Old 4th Dec 2018, 2:11 am   #143
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Default Re: Cybernet PTBM121D4X problems

Will try on 777 tomorrow night
did not adjust anything apart from those 3 coils
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Old 4th Dec 2018, 1:08 pm   #144
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Default Re: Cybernet PTBM121D4X problems

OK, give that a go and with any luck the Colt will actually turn out to be roughly as sensitive as the 777 now.

If not, the fact that the front end coils needed retuning means that we can't now assume that any of the tuning is still correctly set, so it may be necessary to check the I.F section tuning as well. Prior to that, you first need to be sure that the channel frequencies are dead on.

Do you have enough TX output on all bands (AM/FM) to allow you to measure the TX frequency?
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Old 5th Dec 2018, 12:01 am   #145
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Default Re: Cybernet PTBM121D4X problems

Did a fairly comprehensive test on all 3 bands, i left sig gen on whilst i swapped
radios to try and make sure it stayed where it was, the only adjustments i made were between bands and the fine control when i tested on that perticular channel.
the colt is pretty much bang on frequency wise. i sorted that at the weekend,
it was pretty close to start with.
the results are as follows with 3 positions on fine control as there is sometimes
a small peak at the 2pm position plus full anti clockwise and full clockwise.
27.525 777 anti/c s8.5, 2pm + of +30 c/wise s9 to +30
colt 320 anti/c s7.5 both 2pm and c/wise read s9 to +30
27.205 777 anti/c s8.5 2pm s9 to +30 c/wise + of +30
colt 320 anti/c s8 2pm and c/wise s9 to +30
26.855 777 anti/c s8.5 2pm line before + of +30 c/wise s9 to +30
colt 320 anti/c s7.5 2pm line before + of +30 c wise s9 to +30
did find a funny thing with 777 when i switched it on and it was still on ch50
i could hear the sig gen on it and an s7 signal and the sig gen was on 27.205
ive heard the 777's are a bit iffy image rejection wise, i soon lost it when i switched band down 40 channels to ch10 mid then went up to 20.
overall i looks like not a lot in it
the colt does tx on all bands but very low on both am and fm less than quarter of a watt flat out !
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Old 5th Dec 2018, 12:21 pm   #146
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Default Re: Cybernet PTBM121D4X problems

OK, If I am interpreting your results correctly it doesn't seem too bad.

You can try, if you wish, also adjusting T12 in the same cautionary fashion as the others to see whether that is already on-target or not. If it turns out to be well out, it might pay you to run carefully through the T9-T10-T11-T12 chain all over again. On the other hand you might take the view that if it isn't broken, don't fix it. It's entirely up to you how much time you want to devote to it. You certainly don't seem to be short of patience.

I did remember there's a minor issue with the SSB squelch threshold, I think we'll leave that until later and maybe make some headway on the transmitter when you're ready.
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Old 5th Dec 2018, 12:57 pm   #147
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Default Re: Cybernet PTBM121D4X problems

Forgot to mention, I actually owned a 777 from new, back when they were still a current model. Worst radio I ever owned, in terms of poor immunity to off frequency signals. I did a swap-loan for a while with someone who had a radio with a 121 chassis - far superior receiver. He said he wouldn't be able to live with the receiver on mine. So your observations on that 777 are not untypical, unfortunately.
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Old 5th Dec 2018, 11:35 pm   #148
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

Can confirm t12 did the trick, rather small adjustment needed, checked on
each band on min fine, each band is gap between s9 and +30 on meter on min
and either on or a smidge over the first green line in +30 area.
signal dosent go below the gap between the s9 and +30 no matter where you
have the fine setting, so that sounds good.
looks like i am ready for the next bit
the only cybernet i ever had new was a rotel 240, cant remember when, around '82/'83
had a multimode 2 around that time but mostly colt black shadows, 485 and 320fm
i also had a hygain v, ugly thing, for a short time, its a time when you had one for a
short time then moved it on, had also a 148 cobra, diddent like it, deaf as a post !!!

Last edited by John M1JWR; 5th Dec 2018 at 11:42 pm.
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Old 6th Dec 2018, 12:40 am   #149
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Default Re: Cybernet PTBM121D4X problems

First a few voltage checks: In TX mode, AM, what do you have on wire terminal (18)? (BTA, which is the transmit-only regulated supply voltage).

In -RX- mode, AM/FM, what do you have on Q9 (RF Driver) collector and base and on Q10 (RF Output) collector and base?

In -RX- mode, USB/LSB, what are the same measurements?

The collectors should be a little over 6.8 volts on AM/FM and approximately the full supply voltage on USB/LSB.

Now, back to your scope:

Set the probe to the x10 position if it has one, and the input mode switch (AC/GND/DC) to AC. Centre the trace.

In FM TX mode, take the scope probe to the base of the driver Q9 and adjust the volts / div dial until the signal (a thick band) is roughly one division high. Because your scope is quite high-frequency capable you should be able to see the RF signal as an actual waveform if you wind the time/division dial up towards the high end, but don't worry if you can't. It's only the vertical height of the signal we are concerned with at the moment.

Now take the scope probe to the collector of the driver, the signal there should be a lot bigger (vertical size) than it was on the base.

Repeat for the output transistor Q10 - scope the signal on its base, adjust the volts / div so that the signal looks quite small (say 1 division high) and again move to the collector, once again the signal on the collector should be bigger than it was on the base.

If both these checks are OK, then the driver and output are probably OK. If either of the devices has a much smaller signal on its collector than on the base, the device may be defective.
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Old 6th Dec 2018, 1:55 am   #150
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

Have done voltage checks
tx pin 18 am tx 7.3v
q9 and q10
am rx c.8.08v initally starts higher and goes down to settle on that. b.0v
fm rx c 13.61v b 0v
usb and lsb c 13.61v b 0v
also did in tx incase you may ask
q10 am c 6.76v b 0.56v
fm c 13.46v b 0.56v
usb c 13.47v b 0.56v
and q9
am c 6.76v b 0.75v
fm c 13.41v b 0.75v
usb c 13.42v b 0.75v
emitter was 0v throughout tests
bit late for scope now will set it up for tonight as its a bit of a rigmarole,
hope you get something from these so far
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Old 6th Dec 2018, 2:09 am   #151
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Default Re: Cybernet PTBM121D4X problems

That's interesting, as the Colt looks to be a 'high power FM' variant of the 121 chassis where (as in the Hy-gain V) the finals run on the raw supply voltage in FM TX mode.

Only in AM mode do the finals run on the output from the emitter of the AM Darlington.

DC voltage measurements done in the presence of large amounts of RF are likely to be rough at best, that's why I asked you to do them in RX mode and not in TX mode, as you might reasonably have expected.

So the next thing is to do those scope measurements to see if the driver and output are amplifying. You might want to keep the scope a bit handier for a while.
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Old 6th Dec 2018, 11:43 pm   #152
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

did checks with scope
on driver transistor at 5m v/div signal is three quarters of a division up and down
of centre line on base.
on collector at 50m v/div it is 3 divisions up and 3.5 divisions down
lesser settings on collector fill the screen
on final its a bit different
on base 20m v/div gives 1 division up and down of centre line
on collector on .1 v/div gives 2 divisions up and 1.5 divisions down
lesser settings on both fill the screen.
on a side note it looks like the original transistors in there
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Old 7th Dec 2018, 12:57 am   #153
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Default Re: Cybernet PTBM121D4X problems

OK, looks like both devices are amplifying their input signals, which is obviously a hopeful sign. Try some tuning. Use FM mode as it is the 'simplest' transmitter mode with the output stage running on full supply and producing constant output.

Obviously, all tuning to be done into a dummy load with a power meter in line, never into no load, and never into an aerial.

FM TX, try tuning T4 and T5 to see if they are already correctly set or whether you can make some improvement.

If adjusting them slightly clockwise or anticlockwise only reduces what little power you have, set them back exactly as you found them.
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Old 7th Dec 2018, 2:25 am   #154
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

as with the rx section a fair amount of adjustment needed to gain some output
power, so gained some dizzy heights !!!
i used channels 20 on lo mid and hi bands
on ch 20 lo its now upto 2.75w
ch20 mid 2w and on ch20 hi its 1.5w
as an overall spread on ch1 lo band its 3.5w and ch 40 hi its half a watt
dont know if its a good sign, the heatsink around tank area was getting rather warm.
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Old 7th Dec 2018, 10:27 am   #155
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Default Re: Cybernet PTBM121D4X problems

Not quite the dramatic improvement we would have hoped for. For the time being focus on peaking it up on the middle channel of the middle band, you can sort the top end / bottom end balance out at the end.

Try adjusting T6 next, if that makes an improvement as well run through T4-T5-T6 several times again.

For the output stage heating problem - possibly the output stage bias could be set too high - I will look into how to check that.

Also, have a look at the output coils near Q10, in particular L12 (if I am remembering the right one). There was a tendency on the 'high power FM' variants of that chassis for one of the output coils to overheat, which would then burn the varnish off the wire causing shorted turns on the coil. If this has happened it is usually quite visually obvious. If the coil is damaged you can remove it, remove the damaged wire from the former and rewind it with new varnished wire of the same thickness (same number of turns, of course - take photos of the original winding).

Or, since you have a donor set you can try the same coil from that one. I stress that if the original coil does not look damaged it probably isn't.
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Old 7th Dec 2018, 12:12 pm   #156
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

There appeared to be a lot of adjustment in t6 for hardly any gain,
i have been over t4 t5 t6 3 times more, very little extra output.
i have peaked them for now.
L12 is very hard to see because of the heatsink, though from what i can make
out varnish is present also on the plastic part above the wire coil, i looked
at the other two coils and they appeared to be the same.
did not see any varnish below coils on bottom plastic part.
work time, i will be back later on...
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Old 7th Dec 2018, 1:21 pm   #157
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Default Re: Cybernet PTBM121D4X problems

If it does not look obviously burnt, it's OK.

May have to consider the possibility that the output or driver are faulty after all, but I'll think of a few more things to check.

Can you try gently adjusting T2 / T3 further back - these are in the output path from the Synth VCO and the signal splits two ways after that, in one direction towards the receiver and in the other towards the transmitter. As before, leave them as you find them if you see no improvement over their current position.
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Old 7th Dec 2018, 11:35 pm   #158
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

discovered a crack in the screw part of t2 and it wont adjust
time to swap out of other radio
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Old 8th Dec 2018, 2:21 am   #159
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Default Re: Cybernet PTBM121D4X problems

Carefully take the whole coil out and look at the bottom, you should see an unbroken slot. If you can, unscrew the core out through the bottom, then put it back in the top end with the unbroken end upwards and refit the coil. Don't try to dig or drill the broken core out, you will almost certainly wreck the coil.

Considering the amount of meddling this radio has obviously had, you have been lucky not to encounter any cracked cores before now.

Last edited by SiriusHardware; 8th Dec 2018 at 2:30 am.
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Old 8th Dec 2018, 2:34 am   #160
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

well thats that adventure, have swapped the coil from scrapper, making sure it was the right way round, switched on and the same power output is displayed on the meter, i only got a tiny peak out of those two coils so i will assume they were correct.
i removed the broken slug as i would assume the coil itself may be ok, just
incase i get one with a shot coil and a good slug, you never know.
whilst the iron was out i have removed the 2166 and 1969 out of scrapper as they were from memory good, they are still attached to their heatsinks.
one day i will post a pic of the scrapper was scrapped, i got it for a tenner a
few years ago for spares, i did a sort of repair in the area with superglue and
it worked and output was good, until repair started to come apart again.
as for spares, invaluable !!
just seen your post i will do that and keep as a spare
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