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 Valve Signal Generator
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 Return to top of page · Post #: 1 · Written at 9:03:22 PM on 16 January 2014.
Art's avatar
 Art
 Location: Ipswich, QLD
 Member since 22 October 2013
 Member #: 1437
 Postcount: 886

Hi Guys,

I picked this up for $10 today, and can't believe it works!
It needed a new valve which I happened to have an a collection I got recently...
then it worked.
I grounded it to a portable radio, and sat the other clip near
the ferrite loop (AM radio),
and it's either 400 or so kHz out, or 80 kHz out from what I can tell,
one is an harmonic.

Image Link

I'll clean it up and see what I can do anyway.


 
 Return to top of page · Post #: 2 · Written at 1:09:23 AM on 17 January 2014.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 4013

They sold lots of LSG-11s. I have one and it stays on frequency very well.

I'll hop in before Marcc does on a point of safety. The LSG-11 was shipped with capacitors connected on each leg of the mains to earth, that is active to earth and neutral to earth. The metal case of the unit is earth.

These are "death caps" inasmuch as if the cap on the active leg fails short circuit then the case can be at mains voltage and thus potentially lethal.

In my case those caps had been removed by a previous owner and not replaced. I will replace them with Class Y mains capacitors.

If yours still has them in place then you need to make sure they are the correct type for safety purposes.

The user manual contains the schematic. You can get it here:

http://bama.edebris.com/manuals/leader/lsg11/.


 
 Return to top of page · Post #: 3 · Written at 2:20:51 AM on 17 January 2014.
Art's avatar
 Art
 Location: Ipswich, QLD
 Member since 22 October 2013
 Member #: 1437
 Postcount: 886

Thanks that's nice to know, because I do like it, and it's cleaning up well.

I think it wants a BNC socket because I don't know how to disassemble the plug on the original test lead.

Anyway, I will take heed with the caps, the larger multi section electrolytic I've seen is 2 x 10MFD.
May also be something else in there.

I assume you put the high rated caps back in the same and
all it means is you are less likely to die?


 
 Return to top of page · Post #: 4 · Written at 8:21:09 AM on 17 January 2014.
Maven's avatar
 Location: Canberra, ACT
 Member since 23 August 2012
 Member #: 1208
 Postcount: 581

Is that socket marked "xtal" an output of crystal freq, or an input for external crystal?

Maven


 
 Return to top of page · Post #: 5 · Written at 10:07:13 AM on 17 January 2014.
Scraps's avatar
 Location: Blue Mountains, NSW
 Member since 10 March 2013
 Member #: 1312
 Postcount: 401

They're quire versatile, the xtal is for a crystal input 1-15Mhz. It can output a modulated or unmodulated signal from 120Khz -130Mhz and up to 390Mhz on harmonics with either 400Hz, 1000Hz of external AF. It also has a AF output which I've found handy for injecting signals. Apart from my Fluke meter and soldering iron it's probably my most used tool.

I replaced all the caps last year including the two on the mains as suggested by GTC, which fixed an AF problem (no 400 Hz) but it still has a small problem that can be only be seen on a scope. The waveform on the low RF setting is clipped and not the perfect sine wave I'd expect. I might get back to chasing this one day but for now it doesn't affect it's performance. I also replaced the 2 core flex with an earthed lead and anchored it properly. At the time Marcc suggested a gland installed backwards will work on this as there isn't a lot of clearance between the chassis and case. I also fitted a BNC as I couldn't find the right plug to make up a lead. From what I can gather they are a very old style of microphone connector, Amplion I think.


 
 Return to top of page · Post #: 6 · Written at 12:02:54 PM on 17 January 2014.
Art's avatar
 Art
 Location: Ipswich, QLD
 Member since 22 October 2013
 Member #: 1437
 Postcount: 886

Hi again Guys, my mistake, the two caps that connect each side of mains to earth
look like our modern disc ceramic caps. one of them appears to be switched in circuit only when the unit is powered on by the switching pot.

Just on my first play I placed the alligator clip near the AM radio's loop antenna.
I heard on YouTube what is supposed to be heard on a radio when you sweep through a band,
but my understanding, the modern AM radio has digital display, and I know what station it's on. It seems the sig generator must me misaligned unless I'm not understanding it properly.


 
 Return to top of page · Post #: 7 · Written at 12:32:36 PM on 17 January 2014.
Art's avatar
 Art
 Location: Ipswich, QLD
 Member since 22 October 2013
 Member #: 1437
 Postcount: 886

If the death cap fails short and the chassis becomes live,
isn't the idea of the appliance being earthed all about providing a better path to earth so you don't get electrocuted?


 
 Return to top of page · Post #: 8 · Written at 12:34:08 PM on 17 January 2014.
Scraps's avatar
 Location: Blue Mountains, NSW
 Member since 10 March 2013
 Member #: 1312
 Postcount: 401

Unless they've been replaced, those caps won't be Y types and as mentioned before are a deathtrap. From memory the broadcast band is covered by band B and C on the LSG-11. An alligator clip close to the aerial might not be enough. With about a 1k resistor in series try connecting it directly to the aerial terminal. Have the RF Hi/Lo switch set to low and the RF fine just above minimum and try sweeping the band again. Increase the RF fine in small increments, you shouldn't need to go much above about 1/3 for this to work. If you don't have an aerial terminal you might have to make up a loop and set the RF Hi/Lo to Hi. With a capacitor in series it can also be connected directly to the mixer grid.

Do you have a scope to actually check the output?


 
 Return to top of page · Post #: 9 · Written at 12:57:19 PM on 17 January 2014.
Art's avatar
 Art
 Location: Ipswich, QLD
 Member since 22 October 2013
 Member #: 1437
 Postcount: 886

Yes I do, but the signal generator is out of commission for now.
Even if it was safe it's still do dirty and rusty to do much with.


 
 Return to top of page · Post #: 10 · Written at 1:06:39 PM on 17 January 2014.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 4013

isn't the idea of the appliance being earthed all about providing a better path to earth so you don't get electrocuted?

Yes, but that assumes that the earth path is intact and very low resistance from the instrument case back to the earthing rod. There are people in cemeteries who discovered that not to be the case.

The electrical safety point we are making is that there should be no possibility of the metal case becoming live and these old caps contravene that.

When working with mains electricity, too much care is barely enough.


 
 Return to top of page · Post #: 11 · Written at 2:28:53 PM on 17 January 2014.
Art's avatar
 Art
 Location: Ipswich, QLD
 Member since 22 October 2013
 Member #: 1437
 Postcount: 886

Ok I understand. I do want to do my own earth, but this is only a rental house.


 
 Return to top of page · Post #: 12 · Written at 2:48:38 PM on 17 January 2014.
Art's avatar
 Art
 Location: Ipswich, QLD
 Member since 22 October 2013
 Member #: 1437
 Postcount: 886

Nice to find a plug that is so easily serviceable,
so the socket on the panel doesn't need to change.
Pity it won't clean up so easily
Image Link


 
 Return to top of page · Post #: 13 · Written at 5:01:14 PM on 17 January 2014.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 4398

The plug will clean up with a 3M scourer laced with a potion of Ajax and ammonia. Elbow grease works every time.

The place I am working at is filtering the site with the circuit diagram so I cannot comment on the condensers except to state the obvious:-

1. If the condensers are wired across the switch contacts and the condenser shorts out it will merely switch on the radio, if the short can handle the load.

2. If the condensers are wired across A and N and it shorts then the supply voltage will make it go 'pop!'.

3. If the condensers have a metal case and these are tied to an earthed chassis, supposedly for the protection of users, then yes, subject to what GTC said, it will or should trip the relevant fuse or circuit breaker in your switchboard but perhaps only if it is an RCD (safety switch). If it is a standard 20A MCB or rewirable fuse then there is a possibility that the fault current won't be high enough to cause a trip and there will be fireworks inside the radio instead. Whether the fault current is high enough to trip a protection device depends on a lot of factors and it shouldn't be taken into account that such protection will work every time it is needed.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Brad.

A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 14 · Written at 10:03:06 PM on 17 January 2014.
Art's avatar
 Art
 Location: Ipswich, QLD
 Member since 22 October 2013
 Member #: 1437
 Postcount: 886

I will get pics up when it comes down to putting it back together.
Better to be safe than sorry. I'm not trying to cheat out of a couple of caps, just want to understand things better.
Obviously I've got to learn how to use this.
A user manual would be handy also if anyone has one.


 
 Return to top of page · Post #: 15 · Written at 10:13:30 PM on 17 January 2014.
Art's avatar
 Art
 Location: Ipswich, QLD
 Member since 22 October 2013
 Member #: 1437
 Postcount: 886

In case you missed that Brad Image Link it's another Jaycar spring Smile


 
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