UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio 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.

Reply
 
Thread Tools
Old 15th Jul 2017, 10:32 am   #41
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 59
Default Re: Sailor T128 Marine Transmitter.

Upon looking at the diagram with a clearer head, I can see that the -70V is likely "coming from" pin 10 of the power connector, which is stated -84V by design. I guess this is the grid bias, and must be kept fairly negative in order to check the electrons acceleration through the tube. (have I got this part of valve theory right?)

However, it seems odd that the test meter (which is a center zero dial) should be pegging hard left on the position 5 (Final Drive) setting. this at least doesnt seem right for a design. The meter is pegging negative because there is -70V across it in this position.

please help!
crestavega is offline   Reply With Quote
Old 15th Jul 2017, 10:39 am   #42
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 11,811
Default Re: Sailor T128 Marine Transmitter.

I've also been looking at the diagram and have come to much the same conclusion.

With the meter switch set to position 2 it should be possible to measure the negative bias voltage directly.

Regarding the meter "pegging" in position 5, it appear that there are diodes D603, D604 and D607 which will only conduct if the grid voltage goes positive. This should prevent the meter from pegging when the grid voltage is in its normal negative state. I haven't looked at this in much detail though.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 15th Jul 2017, 11:00 am   #43
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 59
Default Re: Sailor T128 Marine Transmitter.

At the risk of looking a bit like I am having an argument with myself here!!

I think I may have developed a theory - see attached diagram
there are diodes D603,D604 & D607 (highlighted orange) in the measuring circuit for S1002-position5.

I think the purpose of these diodes is to "block" the large negative grid bias from the meter, so that in the quiescent mode the meter will see 0V.

if one or more of these diodes has gone bad and shorty, the meter will see grid bias.

by extension, if this happens, there could be a low resistance path to 0V for the relevant grid(s), which case would presumably result in abnormally high anode current for the affected valves.
I am still seeing this *occasionally* on the middle valve (anode metal starts to get red hot) This only happens on keydown, which is I suppose because HT is only supplied to the caps on keydown.

please could more experienced eyes comment on the above leap of faith?
Attached Thumbnails
Click image for larger version

Name:	T128_gridbias_issue.jpg
Views:	25
Size:	63.6 KB
ID:	146208  
crestavega is offline   Reply With Quote
Old 15th Jul 2017, 11:14 am   #44
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 11,811
Default Re: Sailor T128 Marine Transmitter.

You're definitely going to have -84V or W.H.Y on the anodes of those diodes. If you've got -84V on the cathodes you have a problem.

The cathodes are all connected together, so you'll need to test them using the diode function of a DMM. or just disconnect one end of all of them and reconnect them one at a time.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 15th Jul 2017, 1:49 pm   #45
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 59
Default Re: Sailor T128 Marine Transmitter.

Thanks, yes indeed I will lift the diodes. In fact I think I will just replace them all. This set came off quite a small MFV and the PA heat must have convected damp salt air up through it. Quite a bit of corrosion around this area

Thanks very much for looking at my problem.
crestavega is offline   Reply With Quote
Old 17th Jul 2017, 7:57 am   #46
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 59
Default Re: Sailor T128 Marine Transmitter.

Predictably, D603 was the culprit. strange, because I had actually replaced that diode a few weeks back - purely because it looked bad.
This has fixed the problem of the final drive dial pegging hard left, and the problem of the anode starting to glow after a few seconds of tx.

However still not much RF coming out of the PA. Hmmm.
crestavega is offline   Reply With Quote
Old 17th Jul 2017, 8:02 am   #47
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 11,811
Default Re: Sailor T128 Marine Transmitter.

I assume you've selected AM, have the power level switch set to max and have a proper dummy load attached to the aerial connection?
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 18th Jul 2017, 9:57 pm   #48
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 59
Default Re: Sailor T128 Marine Transmitter.

Yes. I am using the TUNE function for Tx which sounds like just a full carrier. I have a dummy connected indeed. power level does not seem to make a difference.

May be a problem with drive. there is a test meter position (pre-drive - position 1) which cuts PA function and shows the RF Drive voltage, to enable the peaking of the drive signal:
I dont seem to see any needle twitch at all on this, so maybe there is not enough drive to make the PA work.
crestavega is offline   Reply With Quote
Old 19th Jul 2017, 8:12 am   #49
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 11,811
Default Re: Sailor T128 Marine Transmitter.

Being primarily an SSB transmitter, there's a lot of circuitry involved in generating the drive.

A check on the DC voltages around V501 is probably in order. Then it's time to get the scope out and check the two tone oscillator, SSB generator, double balanced mixer etc.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 19th Jul 2017, 9:11 am   #50
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 59
Default Re: Sailor T128 Marine Transmitter.

Yes, I do appreciate that the "brains" of this radio is in the small signal department. However, I am pretty sure that is all working. I can hear decent SSB, carrier, and the two-tone signal (not all at the same time!) on a nearby receiver, pretty well on the advertised frequencies. so I think I can safely say that it is working all the way through to the balanced modulator and probably beyond that.

as I understand it: the built-in test meter, in pre-drive position, sniffs the half-wave recitifed (D602) voltage from the QRP signal being applied to the PA valves.

P.8 of the original manual (Tunin-up main channels procedure), step 10, says to adjust the drive level for a peak on the pre-drive meter. Now I cannot get the meter to even twitch in this position so either there is no signal at all getting to the PA grids or there is something amiss with the sniffing line leading to the pre-drive meter.

I have put a small dc voltage on the anode of D602 and the meter moves so it's ok to there. Beyond that is 8.2pF C605. to test that properly I need to get out the sig gen and scope etc as you say.

I think it probably is pointing in the direction of a problem around the driver tube V501 as you hint, which I have not even investigated up to now (other than replacing a toasted resistor R515 I think it was.)
crestavega is offline   Reply With Quote
Old 19th Jul 2017, 9:53 am   #51
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 11,811
Default Re: Sailor T128 Marine Transmitter.

You say there is not much RF coming out of the PA. Have you actually measured this into a dummy load or are you going by the measurement of aerial current?

The drive is indeed sniffed by diodes, so a check of these would be a good idea. You've had problems with diodes before.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 20th Jul 2017, 12:27 pm   #52
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 59
Default Re: Sailor T128 Marine Transmitter.

I was just going by the aerial current actually.

I'll pop a bird on it but I am pretty certain just by feel that it's not "working". You get a feel for when equipment is actually pulling amps don't you?
crestavega is offline   Reply With Quote
Old 23rd Jul 2017, 8:02 am   #53
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 59
Default Re: Sailor T128 Marine Transmitter.

not a twitch on the bird.
strange, because the PA is definitely doing *something*. just very, very little.
the power reducer switch is acting strangely. listening to it on my nearby receiver, the best signal (best sound and strongest signal) is produced on mid and low settings with noticable flakiness and signal reduction on full pwr. that is possibly a clue.

could someone please explain to me where these terminals (see attached) are connected to?
the lines are left out for clarity (at least i assume thats why they appear open cct) and the manual assumes a level of intelligence that I obviously don't have, unfortunately.
( I have managed to deduce that a whole lot of individual LC circuits, L502 thru L533 are also omitted for clarity)

in other news, weirdly, I did start getting meter deflection in predrive position (ie, indicating that there is RF voltage on the driver line at the PA valves) without really doing anything. I just came to it one night and it was there. possibly there was a dirty contact on the test meter sw. Having said that, I am not certain how much voltage there should be on that line. the voltage table in the manual advises 4Vpp at TP14 (the input to the driver?) so I guess at least that..?
Attached Thumbnails
Click image for larger version

Name:	T128_L50x_LC_circuits.jpg
Views:	26
Size:	80.2 KB
ID:	146665  

Last edited by crestavega; 23rd Jul 2017 at 8:08 am.
crestavega is offline   Reply With Quote
Old 23rd Jul 2017, 9:33 am   #54
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 11,811
Default Re: Sailor T128 Marine Transmitter.

As far as I can see there are a lot more coils in the driver unit than are shown on the circuit diagram. 32 in fact, 2 for each channel. Shorting links have to be inserted across the points you show as described on page 8 of the manual.

The initial tuning procedure for each preset channel seems to be pretty elaborate and I wonder if you've carried it out for whatever crystal frequency you're using?

The PA also requires initial tuning to match the aerial and it's possible the aerial originally used with this set doesn't have the same characteristics as your dummy load, so PA tuning may be needed too.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 23rd Jul 2017, 9:45 pm   #55
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 59
Default Re: Sailor T128 Marine Transmitter.

the shorting links, of course they are. makes sense now.
thanks. very. much.

in all honesty I have not even had the freq counter out on the set. the fact that the tx is being resolved quite reasonably on a nearby sythesised rx just makes me think that the only problem is (probably) a fairly simple one, in the PA stage somewhere
I will go through the tuning procedure and see if that helps.

previous people back up the thread have said not to expect any smoke out of the chimney until the tuning is set up properly. I have had a go at it but only really tackled setting up the pi-tank output. I havent given it an honest effort.

still just feel that I am missing some fundamental fault on the PA.

the only reason that I attempted repair was because when I first fired the radio up I could tx voice & alarm across the bench. so I thought it was just the PA.
crestavega is offline   Reply With Quote
Old 4th Sep 2017, 11:17 pm   #56
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 59
Default Re: Sailor T128 Marine Transmitter.

How can I find a pinout for this old cylindrical "tin can" package of a MC1496 balanced modulator?

I am starting to think there might be a problem associated with the Motorola MC1496 Balanced Mixer in me T128 Tx....

on reflection this seems unlikely because it is pretty much the beating heart of the whole Tx, and the Tx is almost working - just low in power.
I am clutching at straws a bit, but I have arrived at this deduction by following the "Typical Voltages & Waveforms" chart in the manual (p50 of the T128 PDF at peel.dk)

TP14 was low at around 0.8V (should be 4 - 5V)
TP13 was correspondingly low at 0.7V (should be 3 - 4.5V)
TP12 was OK at 0.6V
TP11 was OK at 0.7-1V

TP11 & 12 are inputs to the MC1496 whilst TP13 is the output which goes to the driver.

was using a 50MHz CRT scope for the measurements.
I feel that I ought to check the power supply for the MC1496 but Im not too sure how without a pinout...
crestavega is offline   Reply With Quote
Old 5th Sep 2017, 7:31 am   #57
KeithsTV
Nonode
 
KeithsTV's Avatar
 
Join Date: Aug 2007
Location: South Bradford, West Yorkshire, UK.
Posts: 2,027
Default Re: Sailor T128 Marine Transmitter.

Here's the Nat Semi data sheet for the LM1496 which includes the pinout of the metal can version.

Keith
Attached Files
File Type: pdf LM1496.pdf (164.2 KB, 11 views)
KeithsTV is online now   Reply With Quote
Old 5th Sep 2017, 11:44 am   #58
Aub
Heptode
 
Aub's Avatar
 
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 810
Default Re: Sailor T128 Marine Transmitter.

The timestamps of the last two posts look strange?
__________________
Ignorance of The Law is No Excuse - but I didnt know that!
Aub is offline   Reply With Quote
Old 5th Sep 2017, 5:40 pm   #59
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 59
Default Re: Sailor T128 Marine Transmitter.

Strange?
I only get odd periods of time here and there to work on this project which has been infesting a large corner of bench for almost a year, I am afraid to say.

I got a few hours on it late last night and posted yet another cry for help at about a quarter past midnight.

a very helpful cove posted a help for me at about a quarter past breakfast this morning!!

with any luck I might get a chance to fiddle around with the balanced modulator tonight and might make another post....

the struggle contiuuuuuuuuums
crestavega is offline   Reply With Quote
Old 5th Sep 2017, 7:57 pm   #60
Aub
Heptode
 
Aub's Avatar
 
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 810
Default Re: Sailor T128 Marine Transmitter.

No, i wasn't questioning your working hours. I meant that i would have expected your post of 12.17 am to be 0017am , as Keithstv's post was 8.31am.

Cheers

Aub
__________________
Ignorance of The Law is No Excuse - but I didnt know that!
Aub is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 3:57 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 - 2017, vBulletin Solutions, Inc.
Copyright ©2002 - 2017, Paul Stenning.