UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Amateur and Military Radio

Notices

Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

Closed Thread
 
Thread Tools
Old 17th Dec 2018, 3:12 am   #261
John M1JWR
Pentode
 
Join Date: Nov 2018
Location: Carlisle, Cumbria, UK.
Posts: 244
Default Re: Cybernet PTBM121D4X problems

i am afraid it either starts at 1.80 and climbs to 2.90 area or after microscopic
adjustment it starts at 2.70 and climbs to 3.85 area
i am afraid i am unable to get that setting at all
the meter is on 20m on the scale that says A with a line next to it and 3 dots under the line
John M1JWR is offline  
Old 17th Dec 2018, 12:49 pm   #262
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Cybernet PTBM121D4X problems

Try a different way.

Reinstate the Q10 emitter solder connection.

I'm assuming your bench power supply shows current as well as voltage - is it a digital readout?

If so, try this:

In SSB TX mode, zero modulation:-

Adjust RV2 for minimum voltage on Q10 base.

Slowly adjust RV2 in the other direction while watching the current drawn from the power supply. At first the current should change only by a small amount if at all, but when you get to the threshold point at which Q10 turns on, the current should start to increase more rapidly as you continue to turn RV2. Back RV2 off to the point just before that happens and note the current being drawn.

Then, adjust RV2 further until the current drawn is ~35mA more than it was at the Q10 switch-on threshold. If that works, that should put the bias adjustment in about the right area.
SiriusHardware is online now  
Old 17th Dec 2018, 1:36 pm   #263
John M1JWR
Pentode
 
Join Date: Nov 2018
Location: Carlisle, Cumbria, UK.
Posts: 244
Default Re: Cybernet PTBM121D4X problems

Was on with somthing else when you posted and that was experimentation with power outputs.
I got the emitter setting so as it was 3.30 ish on key up and would stop climbing
at 3.90'ish it was as good as i was going to get as it was doing my head in !
soldered back down and checked voltage on base on ssb tx it was 0.63.
i then backed off rv4 and set up the outputs that way and got it fairly even
across bands, with no rv4 in the picture full output is 2 and quarter watts on am and fm.
and around 2 watts on usb, thats all nothing more to give.
bring rv4 into the picture on fm and outputs went up, i was on 20 hi band at this
time and was 8w flat out, i thought ive had more than this.
the other two bands were much higher, low band was 14w.
looks like set up with rv4 out of the picture dosent really work.
there is more but work time now will report that later.
John M1JWR is offline  
Old 17th Dec 2018, 2:16 pm   #264
Techman
Dekatron
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
Default Re: Cybernet PTBM121D4X problems

Quote:
Originally Posted by John M1JWR View Post
ssb as its full voltage like fm so i went to rv4, then ssb output went upto 12w there was a little more but i left it at around 12w. this is the interesting bit, at that point i went back to fm it was now 15 or 16w, so i had to turn it down with l8 l12 etc to 10w spec the other two modes went down aswell so at the minute fm is 10w ssb about 10w and am is around a watt lower than before.
Just a reminder of where you were in post #248 - Personally, I'd avoid de-tuning inductors for power reduction. Get everything peaked up properly and as evenly as you can across the bands and then go from there.

So it looks like either the original output or driver were faulty in some way, even though those second set of readings were within what would be expected using a DVM on diode test and close to the replacement transistors. Either you disturbed something while changing the transistors and accidentally cured the fault or one or both of the original transistors had just given up working at HF frequencies - a bit like a bad fake. That's the trouble with using a DVM for tests like this, that's why I would have to use an analogue meter such as an AVO as it would have probably shown up leakage that you're not seeing with your DVM. I think if it were me I'd have to swap the original transistors back into the set one at a time to verify that it actually really was one of them that was at fault and that it wasn't just a coincidence, but that's up to you and if you've got time to 'play'.

As for the bias setting, just put a link on the mic socket, or put a shorting link on a spare mic plug to key up the radio with no audio, I always have a linked out mic plug for the purpose (they're cheap enough so not worth messing about). I agree that in theory, measuring the current in the emitter is the correct way to make the adjustment, but setting between 0.6 and 0.7 v on the base has always worked well enough for me, although I'm certainly going to have a play with the 'current' method sometime when I've got another one to set.
Techman is offline  
Old 17th Dec 2018, 2:51 pm   #265
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Cybernet PTBM121D4X problems

John, possible bad choice of words from me earlier - when I said with RF ALC 'backed off' I meant 'Set so it does not reduce the output power at all'. Then, as Techman says, peak the RF chain coils for best output and balance across the bands. I agree that reducing power by detuning is never the ideal method.

When you have the RF output as high as possible and as balanced as possible, only then bring the ALC back into play to reduce the FM output power to whatever you consider 'proper'.

Bias setting shouldn't be as hard as it seems to be, I wish I had an example here to play with. I never had trouble with the current setting method in the past. Maybe it depends on the type of meter used?
SiriusHardware is online now  
Old 17th Dec 2018, 11:07 pm   #266
John M1JWR
Pentode
 
Join Date: Nov 2018
Location: Carlisle, Cumbria, UK.
Posts: 244
Default Re: Cybernet PTBM121D4X problems

Yes looks like that meter isent equipped for that set up
i even tried on the next setting up 200m and reading was completely different
it had no relation to any numbers that we were looking for and did not match
the numbers on the setting below.
i might have been for me to understand that having no rv4 and setting up to the max.
i expected adjusting rv4 after that would bring them all up together, it was not
the case, they all went up but band wise, unevenly.
the other funny thing that happened was that after rv4 was turned up again
and then re lined the fm side, i switched to am and it was around 5w, i was able
to turn am up another watt to around 6w with the cans in the tank area
when i turned back to fm that adjustment did not affect fm output at all,
logic would've said that would have gone up aswell.
overall i found that when you turn rv4 up it dosen seem to lower fm output
at all, its approx in that 2pm area looking from the back of the radio.
will have another go shortly
John M1JWR is offline  
Old 18th Dec 2018, 12:55 am   #267
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Cybernet PTBM121D4X problems

As you may remember I originally didn't expect the RF ALC to have any bearing on the FM output since it looked like the pull up applied through R47 in AM/FM modes was supposed to disable or at least de-sense the RF ALC, so this has been a journey of surprises. Unfortunately it has been decades since I physically worked on these myself so all the little sequences of tweaks and nudges which used to be second nature to me are very dim memories now, although just working through this has brought a bit of it back.

I think we are at the point where, as the only person with a set in front of you, you are going to have to try to muddle your way back to the point where you had 15W on FM, 12 on SSB, and 4W on AM as that was a reasonably respectable outcome.
SiriusHardware is online now  
Old 18th Dec 2018, 1:05 am   #268
John M1JWR
Pentode
 
Join Date: Nov 2018
Location: Carlisle, Cumbria, UK.
Posts: 244
Default Re: Cybernet PTBM121D4X problems

Ok put back rv4 to around half way mark fm is nice and even across all bands
at 12w am is 4w and ssb is 11w, re adjusted rv4 a little and for once it did not
do much, however another problem now exists.
ssb is a full carrier, dont know what ive done there
John M1JWR is offline  
Old 18th Dec 2018, 2:02 am   #269
John M1JWR
Pentode
 
Join Date: Nov 2018
Location: Carlisle, Cumbria, UK.
Posts: 244
Default Re: Cybernet PTBM121D4X problems

Its ok sussed it, over did t6
John M1JWR is offline  
Old 18th Dec 2018, 10:30 am   #270
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Cybernet PTBM121D4X problems

Normally a permanent carrier in SSB TX would be caused by maladjustment of the balanced modulator presets RV5 / RV6 but if it isn't broken, don't fix it - if you're happy with it, leave it there. If you feel tempted to make further adjustments in future take good clear photos of all the adjustment settings before moving anything, and then at least you have a setup you can come back to.
SiriusHardware is online now  
Old 18th Dec 2018, 12:04 pm   #271
John M1JWR
Pentode
 
Join Date: Nov 2018
Location: Carlisle, Cumbria, UK.
Posts: 244
Default Re: Cybernet PTBM121D4X problems

Yes, i havent touched those two pre sets, dont intend to.
there was a time last night when i was getting rather confused with it,
loosing the battle, it got to a stage no matter how you peaked everything
it would never get to that 12 fm 5 am and what ever it was on ssb no matter
what ever i did, and these were small peak type adjustments, rv4 was backed off
to its half way point and it diddent really have any affect or at least it
diddent appear to have.
it was getting to a stage where hardly any of the specified cans/coils were
making any or very little adjustment at all, de sensed themselves.
so i thought go for an acceptable minimum and go back at a later date ie
10 fm 4 am and around 8 ssb, we know its done 15 fm (not good) 12 ssb and
6 am but never at the same time, its probably all down to either me being thick
and not understanding how this is done and maybe a bit of the radio taking
the michael,though a million miles from where it was originally.
so anyway thats where it is now around 10 fm 4 am and 8 ssb approx,
its a large,for me hurdle to jump over as we approach the finish line in this
marathon as there was only what appeared to be one fence to go.

Last edited by John M1JWR; 18th Dec 2018 at 12:12 pm.
John M1JWR is offline  
Old 18th Dec 2018, 1:02 pm   #272
John M1JWR
Pentode
 
Join Date: Nov 2018
Location: Carlisle, Cumbria, UK.
Posts: 244
Default Re: Cybernet PTBM121D4X problems

Link to concorde 2 service manual
http://www.cbradio.nl/ham/Service_Ma..._Homer_ENG.pdf
John M1JWR is offline  
Old 18th Dec 2018, 1:06 pm   #273
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Cybernet PTBM121D4X problems

Well, the effect of RV4 is to set the maximum RF output power limit, so, let's say that RV4 is set so that it will start limiting at 10W output, and you are starting off with about 6W and busy tuning up...

Once your tuning efforts get the output power up to 10W, further tuning in the right direction will seem to have no beneficial effect because the RF ALC will limit the power to 10W regardless.

The way to avoid that is to have the RF ALC completely 'switched off' by having RV4 turned fully towards 0V while you tune up - only when you are happy with the tuning do you then bring the ALC back in to limit the maximum power on FM / SSB (For reasons already explained, the AM power should only ever be about half of the FM / SSB power, no more).

That's the theory, but it seems to keep not working for you in practice, so, I would carry on doing what works for you in real life rather than on paper.

Well done finding the service manual, but it's a shame it does not include the main board layout. If it did, I think it would be fairly poor, so nothing lost. Even the one in my second-edition Export manual is quite poor with the green side traces almost invisible in places.
SiriusHardware is online now  
Old 18th Dec 2018, 3:48 pm   #274
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Cybernet PTBM121D4X problems

I've just had a little read through the CII service manual to see what it has to say on the subject of the RF ALC circuit. Here it is:-

Quote:
"The transceiver is also equipped with the RF ALC circuit utilising the RF output induced at the input of L-13 (In the SSB mode only). The minus voltage detected through D10 is applied to the DC plus bias circuit (pin no.7 of IC-3, TX mixer) thus reducing the gain of the TX mixer as high level RF signal is observed at L13. This circuit is disabled in the AM or FM mode of transmission".
That's what I was expecting originally, but we should bear in mind this manual is for the Concorde II which has low levels of power output on AM and FM, whereas this Colt has much higher output power on FM.

It goes on to say how important the Audio and RF ALC circuits are for proper operation but then never ever mentions how / when to set RV4, or RV2 (the output bias level) for that matter.

Last edited by SiriusHardware; 18th Dec 2018 at 4:18 pm.
SiriusHardware is online now  
Old 18th Dec 2018, 10:56 pm   #275
John M1JWR
Pentode
 
Join Date: Nov 2018
Location: Carlisle, Cumbria, UK.
Posts: 244
Default Re: Cybernet PTBM121D4X problems

http://www.cbtricks.com/members/rick...1d4x_Part2.pdf

http://www.cbtricks.com/members/rick...1d4x_Part1.pdf

Alternate schematic
John M1JWR is offline  
Old 18th Dec 2018, 11:16 pm   #276
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Cybernet PTBM121D4X problems

Yes, quite nice, I have seen a few redrawn CB circuit diagrams, possibly by the same author. Did you see the notes about transmitter output bias at the bottom of the diagram in the first link in your post above?

The author suggests changing R44 from 10R to 18R although the same effect could be achieved by lowering the value of R43, and that resistor has an asterix next to it on the diagram, meaning 'the value of this component may vary'. They are also suggesting a bias current of 50mA - hard to say who is right when the official Ham International service manual doesn't even mention it.
SiriusHardware is online now  
Old 18th Dec 2018, 11:24 pm   #277
John M1JWR
Pentode
 
Join Date: Nov 2018
Location: Carlisle, Cumbria, UK.
Posts: 244
Default Re: Cybernet PTBM121D4X problems

i seen these before its shown on you tube, swissradios, he is a collector.
anyway to put the rv4 thing into mechanics speak, rv4 is a type of guvnor
when its set to whatever the rest of the carburettor is adjusted to it
so to speak
John M1JWR is offline  
Old 18th Dec 2018, 11:39 pm   #278
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Cybernet PTBM121D4X problems

Using that analogy, I would call it a 'Rev Limiter'.
SiriusHardware is online now  
Old 18th Dec 2018, 11:54 pm   #279
John M1JWR
Pentode
 
Join Date: Nov 2018
Location: Carlisle, Cumbria, UK.
Posts: 244
Default Re: Cybernet PTBM121D4X problems

yep i understand that
try a bank of four carbs on a motorbike, after all the fiddleing/adjustments, then
you have to syncronise them, i find that much easier than this.
with carbs you get vacume guages.
its the syncronising of this rf output ie getting the modes to the correct power
output at the same time thats the difficult bit.
i will have another wee go with rv4 in a slghtly different place and see how i
come on, then i will get back to you.
John M1JWR is offline  
Old 19th Dec 2018, 1:11 am   #280
John M1JWR
Pentode
 
Join Date: Nov 2018
Location: Carlisle, Cumbria, UK.
Posts: 244
Default Re: Cybernet PTBM121D4X problems

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 !!
John M1JWR is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 10:18 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.