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 Leader SG 11 power transformer
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 Return to top of page · Post #: 1 · Written at 5:01:21 PM on 22 March 2019.
Normf's Gravatar
 Location: Erowal Bay, NSW
 Member since 19 June 2018
 Member #: 2256
 Postcount: 78

Purchased a Leader SG 11 signal generator on ebay a few weeks ago, was working OK.
Went to use it today and no power, traced to an o/c primary on power transformer. This has 100v + 6.3v secondary windings.
Does anyone know where I can obtain one of these.
Have included some photos

Leader LSG-11
Leader LSG-11
Leader LSG-11
Leader LSG-11


 
 Return to top of page · Post #: 2 · Written at 5:51:31 PM on 22 March 2019.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5262

Does anyone know where I can obtain one of these.

Probably easier just get another LSG-11, working or not. They must have sold lots of them because they tend to pop-up all over the place.

My LSG-11 has recently decided to die. It's now in the fix-it queue. Hopefully it's not the transformer.


 
 Return to top of page · Post #: 3 · Written at 6:19:14 PM on 22 March 2019.
Normf's Gravatar
 Location: Erowal Bay, NSW
 Member since 19 June 2018
 Member #: 2256
 Postcount: 78

Thanks GTC
Do you have any details on calibrating these units, mine was slightly out of calibration.
The transformers in these units are smaller physically than in the Tech TE 20D which would require similar current capacity.
Done a quick search none available at present, if anyone knows of a cheap one available let me know.


 
 Return to top of page · Post #: 4 · Written at 7:11:05 PM on 22 March 2019.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 5502

Photos uploaded.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 5 · Written at 8:07:30 PM on 22 March 2019.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5262

Do you have any details on calibrating these units

As for calibration, there's noting adjustable in the LSG-11 -- it's a 'poverty pack' SG. I always connect a frequency counter whenever I'm using any analogue signal generator and use that as the "dial".

Mine was always pretty much bang on versus the dial, and stayed that way over a long period of time. When I first bought it (second hand) I ran it for 24 hours and it had minimal drift according to my digital frequency counter, which is why I have kept it.

Given its construction, it's also a very good RFI generator.

BTW: if the original death caps are still across active and neutral to case, then you need to eliminate them, either altogether or replace them with Y-class capacitors.

You probably already have it, but the user manual is available here: https://www.kevinchant.com/uploads/7/1/0/8/7108231/leader_lsg11.pdf


 
 Return to top of page · Post #: 6 · Written at 8:43:02 AM on 23 March 2019.
Normf's Gravatar
 Location: Erowal Bay, NSW
 Member since 19 June 2018
 Member #: 2256
 Postcount: 78

Thanks GTC
Mine has been refurbished with new caps and supposidly new valves, has a .001μF disc ceramic between neutral and earth.
Should I replace this?
I have been using a cheap frequency counter to set the frequencies I need when aligning a radio,
Find it quite stable after being turned on for more than 1/2 hour.
What do you use as a dummy aerial?


 
 Return to top of page · Post #: 7 · Written at 11:37:40 AM on 23 March 2019.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5262

has a .001μF disc ceramic between neutral and earth.

The correct capacitor type these days for line to earth is class-Y (class-X is for across the line). The danger with such installations is if the cap fails short circuit then line voltage will appear on the chassis hence the nickname "death caps". Modern mains rated caps are designed to fail open circuit. Although yours is on the neutral, that depends on the plug being wired correctly. In mine I got rid of them completely.

BTW: the original selenium rectifier is another weak point. They tend to fail short circuit and burn out the transformer secondary.

I use indirect coupling -- a loop of wire close to the antenna is usually sufficient. Use a .001μF cap for IF stage.


 
 Return to top of page · Post #: 8 · Written at 1:04:32 PM on 23 March 2019.
Johnny's avatar
 Location: Hobart, TAS
 Member since 31 July 2016
 Member #: 1959
 Postcount: 320

A very slim chance of finding an original transformer.
It’s a fairly simple constructed one, if it were mine I would pull it apart with a view of either repairing or rewinding.
Failing that, a smallish transformer from a 1960’s valve radio, and use only half of the Center taped secondary.
JJ


 
 Return to top of page · Post #: 9 · Written at 3:28:38 PM on 23 March 2019.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 571

Agreed, pull it apart and look for one of those "fuses" taped into the outer section of the winding or a bad solder joint between the external lead and the copper wire.
Fred.


 
 Return to top of page · Post #: 10 · Written at 4:58:05 PM on 23 March 2019.
Normf's Gravatar
 Location: Erowal Bay, NSW
 Member since 19 June 2018
 Member #: 2256
 Postcount: 78

Thanks JJ and Fred
Was considering that as a possibility, as you can see by the photos it is fairly small unit.
Going by what someone has written on the circuit diagram it is dropping 30v across a 3k resistor to give the main ht of 75v.
so that's only 10mA, doesn't seem enough.


 
 Return to top of page · Post #: 11 · Written at 3:56:23 AM on 24 March 2019.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 571

While you are waiting for a replacement from somewhere.
This will work electrically but may be a room problem in the chassis as a permanent fix.

Use a second small transformer to feed the 6 volt line.
Size it to deliver the amps needed for the filaments plus a bit for the HT drain.
So you need a small 240 to 6 unit from Altronics or Jaycar.
The fresh 6 volt supply will then use the 6 volt winding on the original as a "new" primary and drive the 100 volt winding.
The original 240 leads are taped off.

If you had any 240 to 6 volt from an old radio you could clip lead up a test, taking the usual OHS and safety precautions regarding live leads ect. In my workshop that means lay it out on the bench with jumper leads but keep your fingers out of it!
Fred.


 
 Return to top of page · Post #: 12 · Written at 8:09:57 AM on 24 March 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3702

I have had a run of SG11's & had one surplus new valves & restored. Not all are made by the same mob & have oil filled caps; All of which are best used to decorate the inside of a bin. They are as bad as wax paper. It was exchanged for cost of repairs and I got the dud, which has also cooked the transformer.

I have serious issues with the thinking & how these and several other items like it got into the country? Earth the chassis: It and the cabinet are metal.

If you are not worried about original you can use an LR8 regulator and a TIP 50 to bring the voltage down and it will be regulated. Maximum input for LR8 is 450VDC. I use one as the voltage stepper for a capacitor reformer.

I also have a Tech -20D (and its & SG11's data) Inherently non adjustable. I also use a counter, but do not calibrate with the tone ON. I also tap the audio & use it as the external sync for a CRO: Much more stable. A CRO is used as the measuring device when calibrating

Marc


 
 Return to top of page · Post #: 13 · Written at 8:40:45 PM on 25 March 2019.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1291

This, running into a full wave voltage doubler (2 diodes, 2 caps) will easily get your 75v at 10mA.

https://www.altronics.com.au/p/m2855l-powertran-30v-240v-150ma-centre-tapped-ei-core-transformer/

This little guy will run your heaters:

https://www.altronics.com.au/p/m2835l-powertran-6v-240v-150ma-ei-core-transformer/

Two transformers, sure, but they are little ones.


 
 Return to top of page · Post #: 14 · Written at 6:15:05 PM on 28 March 2019.
Normf's Gravatar
 Location: Erowal Bay, NSW
 Member since 19 June 2018
 Member #: 2256
 Postcount: 78

Thanks Ian
Found I have a 240 to 30v trany about the same physical size as the transformer in the SC-11.
should have a 6v trany for filaments, Will try that out


 
 Return to top of page · Post #: 15 · Written at 5:33:20 PM on 30 March 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3702

If you have a small transformer with a bit of a rating. SG11 "B" would not draw a lot of current, so you could (and I have done it) use the LV secondary as the primary & drive it with the other transformer. There may be a suitable one in say a 500mA to 1A wall wart.

Do not use switch mode.

Marc


 
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