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 17th Oct 2016, 12:57 pm   #21
GW3OQK Andrew
Pentode
 
GW3OQK Andrew's Avatar
 
Join Date: Apr 2011
Location: Swansea, Wales, UK.
Posts: 105
Default Re: Sailor T128 Marine Transmitter.

That will be OK. I can't see what the HT on the driver is, but presumably less than 800v.
Andrew
GW3OQK Andrew is offline   Reply With Quote
Old 14th Feb 2017, 1:02 am   #22
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 64
Default Sailor T128 confusion

Please could someone help
regarding my Sailor T128 (attempted) restoration, and with reference to its manual

http://peel.dk/SP/pdf/Sailor%20T128%...20(Manual).pdf

there is a "test switch", shown on p.52 of the PDF.

in sections C (iv) and C(v), (p.10 of the PDF), there are instructions to set the test switch to position"TRANSMIT". I cannnot find a position marked TRANSMIT.

this test switch and its functions are summarised in Section D (p10-11) of the PDF. None of these functions are specifically labelled as "TRANSMIT" however, the final paragraph of this section states "leave switch in position 10 Ik3 before reassembling tx"

Is it a safe assumption that position 10 is the TRANSMIT position?
crestavega is offline   Reply With Quote
Old 14th Feb 2017, 8:24 am   #23
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 12,118
Default Re: Sailor T128 Marine Transmitter.

The test switch merely sets what the meter measures. There is no TRANSMIT position as such, so it's safe to assume that the document should read position 10.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 14th Feb 2017, 9:43 pm   #24
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 64
Default Re: Sailor T128 Marine Transmitter.

indeed, closer inspection of PDF p10-11 (section D) shows the exact function of the test sw. the Pre-Drive position "automatically cuts screen grid voltage" which presumably (?) effectively stops any effective PA work.
crestavega is offline   Reply With Quote
Old 15th Feb 2017, 8:52 pm   #25
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 64
Default Re: Sailor T128 Marine Transmitter.

I set up dummy load and had a tentative transmit on my T128 this afternoon. seems to sort of "work", with a pleasant sounding clear audio on a nearby rx.

The unit has not been tuned in a long time so clearly requires setting up as per the manual, which I will get around to.

meatime, I wonder if any more experienced hands can advise me about this -
the middle TT22 valve of the three in the PA, upon key-down, starts to glow noticably hotter than its neighbours, and there is a hint of blue glow around the base.
does it mean that the bottle has gone "soft" or is this a normal symptom of an un-neutralised pa?

also was somewhat perturbed that the aerial amps needle was not moving at all. although I have not actually checked the movement of the meter.

Last edited by crestavega; 15th Feb 2017 at 9:09 pm.
crestavega is offline   Reply With Quote
Old 16th Feb 2017, 10:06 am   #26
GW3OQK Andrew
Pentode
 
GW3OQK Andrew's Avatar
 
Join Date: Apr 2011
Location: Swansea, Wales, UK.
Posts: 105
Default Re: Sailor T128 Marine Transmitter.

Cresta, I don't worry about blue glow at all. If the anode glows red it would be a different matter. You are not going to get any aerial current until you get round to doing the setting up. Good news you can pick up some signal from it.
Andrew
GW3OQK Andrew is offline   Reply With Quote
Old 16th Feb 2017, 10:31 am   #27
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 12,118
Default Re: Sailor T128 Marine Transmitter.

The test switch enables the cathode current of each of the three PA valves to be checked individually. Any problems are likely to show up as large differences in cathode currents.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 16th Feb 2017, 3:08 pm   #28
Aub
Heptode
 
Aub's Avatar
 
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 820
Default Re: Sailor T128 Marine Transmitter.

Have you tried swapping the valves around? Does the glow stay with the middle position, or move with the valve?

73's

Aub
__________________
Ignorance of The Law is No Excuse - but I didnt know that!
Aub is online now   Reply With Quote
Old 16th Feb 2017, 10:18 pm   #29
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 64
Default Re: Sailor T128 Marine Transmitter.

in swapping the valves around, indeed the problem stays in the middle position.
Andrew - I think yes, the anode is glowing red hot shortly after keydown (at least, it is the outer plate(s) of metal inside the bottle so I presume that would be the anode).also, the test meter shows the nr.2 kathode current pegging hard on tx. (Ik1 and Ik3 are similar at half scale deflection)

So hopefully that indicates just that the PA settings need balancing up....

thanks very much for helpful commentary.
crestavega is offline   Reply With Quote
Old 5th Jun 2017, 10:09 pm   #30
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 64
Default Sailor T218

back on this somewhat recalcitrant T128 transmitter.
I seem to have a problem with the cathode current of the middle (nr.2) tube. I was trying to neutralise (?) the PA tubes, per the manual. Believe that I am supposed to adjust kathode kurrent for 35mA.

Initially, Ik2 was pegging hard over 100mA on Tx, and I discovered that the adjustment VR P605 was failed opencircuit, as was the 22 ohm R807 between kathode & ground. I replaced these and got a more sensible Ik2 = 55mA but adjusting P605 did not change the current.
The problem is defninitely in the position, not the bottle.

occasionally, the valve in this position also starts to glow alarmingly red on Tx.

I am convinced that the PA stage is just not "working"; there is no aerial current, and I can just hear & see that the tubes are not loading up with Tx drive. I am working straight into a big oil filled dummyload. I can hear the signal on frequency, with convincing sounding audio mod on a nearby Rx.
Attached Thumbnails
Click image for larger version

Name:	T128_PA.jpg
Views:	53
Size:	60.2 KB
ID:	144014  
crestavega is offline   Reply With Quote
Old 5th Jun 2017, 10:14 pm   #31
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 12,118
Default Re: Sailor T128 Marine Transmitter.

Threads merged.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 6th Jun 2017, 8:11 am   #32
Keith
Hexode
 
Keith's Avatar
 
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 372
Default Re: Sailor T128 Marine Transmitter.

Looking at the circuit, the most likely suspect would be the grid coupling capacitor for the middle PA valve. Worth checking for leakage or just replacing.
__________________
Keith Yates - G3XGW
VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm
Keith is offline   Reply With Quote
Old 7th Jun 2017, 12:07 am   #33
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 64
Default Re: Sailor T128 Marine Transmitter.

I am beginning to understand perhaps. please can you advise me if I am correct that C805 (highlighted in red on attached snippet) is the Grid Coupling cap. in question here?
this is apparently a 400V 4.7nF ceramic.
am I right in thinking that the purpose of this cap is to pass RF from the previous driver stage onto the control grid of the PA tube, but to galvanically isolate this grid from the (presumably high?) dc voltage associated with the anode of the 12HG7 drive tube.
if high dc bias was to get onto the grid, I can see that excessive current could flow in the PA tube.

I have to confess that I cannot see where the 12HG7 driver valve gets anode volts from. presumably there is a good reason for specifying a 400V cap in that position though.
Attached Thumbnails
Click image for larger version

Name:	isthistheGCC.jpg
Views:	42
Size:	68.1 KB
ID:	144076  
crestavega is offline   Reply With Quote
Old 7th Jun 2017, 7:42 am   #34
Keith
Hexode
 
Keith's Avatar
 
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 372
Default Re: Sailor T128 Marine Transmitter.

Yes, that's the one. It's the transmitter equivalent of "that" capacitor! The anode of the driver gets its HT via its tuned circuit.
__________________
Keith Yates - G3XGW
VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm
Keith is offline   Reply With Quote
Old 7th Jun 2017, 4:46 pm   #35
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 5,047
Default Re: Sailor T128 Marine Transmitter.

100% agreed: plenty of otherwise-good 1980s/1990s Japanese ham-radio "hybrid" valve/transistor transceivers have suffered a PA-valve meltdown when the coupling capacitors have gone soft.
G6Tanuki is offline   Reply With Quote
Old 7th Jun 2017, 10:32 pm   #36
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 64
Default Re: Sailor T128 Marine Transmitter.

how do ceramic disc capacitors go "soft"?
crestavega is offline   Reply With Quote
Old 8th Jun 2017, 6:20 pm   #37
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 64
Default Re: Sailor T128 Marine Transmitter.

Pulled it out and meggered it, showing 60MOhm at 500V, probably OK?
crestavega is offline   Reply With Quote
Old 8th Jun 2017, 7:14 pm   #38
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 5,047
Default Re: Sailor T128 Marine Transmitter.

Quote:
Originally Posted by crestavega View Post
how do ceramic disc capacitors go "soft"?
They go leaky and can sometimes fail S/C catastrophically (putting driver-stage-HT on the PA grid is not a recipe for happiness).

Remember that the capacitor has to handle the sum of the driver-stage anode voltage, the PA-stage negative-bias (whether derived from a separate source or by grid/cathode rectification of drive) *and* the peak RF voltage-swing.

If your radio uses grid-rectification-bias for the PA, and the capacitor goes open-circuit (or loses significant capacitance) then there could be insufficient RF drive to the grid to generate the necessary grid-bias and the affected tube will then draw an excessive anode current.
G6Tanuki is offline   Reply With Quote
Old 8th Jun 2017, 9:34 pm   #39
Keith
Hexode
 
Keith's Avatar
 
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 372
Default Re: Sailor T128 Marine Transmitter.

Another possiblity would be a reduction in the effective cathode resistance for that valve. You mentioned that R807 had gone o/c. Was it replaced with the correct value? Or maybe the parallel capacitor is low resistance? You also say that P605 no longer controls the Ik for the valve. I can't quite read the circuit in that area but it must be a clue.
__________________
Keith Yates - G3XGW
VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm

Last edited by Keith; 8th Jun 2017 at 9:40 pm. Reason: Further relection...
Keith is offline   Reply With Quote
Old 15th Jul 2017, 1:13 am   #40
crestavega
Tetrode
 
crestavega's Avatar
 
Join Date: Apr 2014
Location: Kirkwall, Orkney, UK.
Posts: 64
Default Re: Sailor T128 Marine Transmitter.

I have replaced capacitors on me T128 and now getting sensible kathode kurrent on all tubes. however I still don't seem to have any serious work being done by the PA.
I have discovered that the "Final Drive" voltage seems to sit at -70V. Im not sure this is right
I discovered this on the built in test meter, which in position 5 (Final Drive) pegged hard over left in standby. no change on Tx.
The manual states that in this position, the test meter will show deflection when the grid voltage of one of the tubes becomes positive wrt Earth.
I think the grid is supposed to sit at slightly negative potential in order to stop excess anode current? yet sitting at -70V seems like it will choke the valve from doing anything...?
I must confess I am a bit stumped as to where that -70V is coming from.
One thing I did notice is that from cold, this voltage is 0V but seems to creep down to -70V as the filaments heat up.
cheers
Tris
Attached Thumbnails
Click image for larger version

Name:	T128_-70V_mystery.jpg
Views:	26
Size:	87.0 KB
ID:	146202  
crestavega is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 8:19 am.


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.