I am new to Valve Radio restoration and I am interested in getting an RF Sig Gen. I am only going to restore/repair the odd radio as and when they become available.
I would be grateful of suggestions on what and where suitable units are available.

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Clive

Hi Clive,

I too am new to this, and was also thinking about a signal generator. I noticed on eBay they are selling digital signal generators for about 25 dollars. Granted they are new tech, but they are cheap and would cover the right frequency ranges for testing AM sets.

http://www.ebay.com.au/itm/191223704530

Anyone see any issues using one of them?

Regards,

Damien

A signal generator should have a frequency range from about 105 kHz up to about 30 MHz to cover IFs, the normal broadcast band and short wave bands.
It should have good control over the output level, from microvolts up to, say 100 millivolts and generate a modulated signal.
Other aspects, in no particular order are, good shielding, good frequency stability, option of internal or external modulation, etc. The device referred to does not appear to do anything like this.
Harold

The critical things are stability & accuracy. The one I use is not particularly accurate but is stable, so I calibrate it with a frequency counter.

Now as has been touched on. I have a Function Generator that can generate several different waveforms at a variety of frequencies, all of which are useable in radio & amplifier repair. But this cannot modulate an audio tone for use in calibration.

So, unless the Signal Generator is capable of being modulated with a tone of 400, or 1000Hz, it is not what you need. Beware that you are not buying a "Pig in a Poke". Many selling on sites like Flea Bay, have no idea of what they are selling, its function, or how it works.

I have a surplus couple of rough ones (valve) One is a Leader LSG-11(overhauled) with paperwork & original Box. There is a photo of it, I think on this site.

Marc

Dear Clive.
I can highly recommend the Leader LSG-11.
It is what I have used for years.
Just make sure that you turn it on five minutes before using.
Wayne.

Thanks Wayne, It looks like I have secured a LSG-11.

Thanks also to all who have replied to this thread.

Clive

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Clive

The LSG-11, as manufactured, has a pair of capacitors as mains noise filters (C18 & C19 in the linked schematic), known as "death caps" -- so called because if they short internally they connect the metal case to the mains.

If they haven't been already, they need to be replaced with modern mains rated Class Y capacitors.

http://i268.photobucket.com/albums/jj8/dneprrider/test/f9dad8bd.jpg

About Y caps here:

http://powerblog.vicorpower.com/2013/06/what-are-y-capacitors/

LSG-11 is not alone in this & it beggars belief that something like that was able to get into the country without an earth on the metal case/chassis.

I have two or three devices here where I have made modifications to their cable anchorage and added grounding as they are absolutely intrinsically unsafe, with a cap to an ungrounded chassis from the mains.

Note that there are "X" and "Y" caps for mains, one is for permanent. Most will have Standards association approval stamps on them and a voltage rating around 275V AC, not a DC one.

You can cut the cap out, but with a metal case and a transformer ground it.

AC/DC radios & Hot chassis radio's (many European & Early American) special case no earth can be fitted & treacherous bordering on lethal.

LSG-11 here was modified after I got it and was part of its major overhaul.

Marc

Amendment: Today I went to the Radio Club meeting, a must do as Pres & VP are away & I as a PP won the chair.

An LSG-11, no book or test leads, followed me home. I note it has a three wire cable, but unit's functional condition is not known at this point and there is no way I will plug it in to find out, before I check it.

Marc

Oh dear! I am pedantic about never plugging in an unknown. I am sending Brad a photo for here, showing my point. This is the LSG-11 I brought home today.

This is what has happened hopefully from just inferior cord anchorage ... like none. The outside of the mains cable is plastic. The core is rotten rubber, so the slightest twist in the cable has seen it short & start to burn first.

The mains transformer is the same resistance as the other one & 500VDC has not gone to ground. The larger NP caps are of an interesting type, however a random leakage check on three that were out of, or able to be switched out of circuit says they are paper, & one was shorted.

So I have taken a commercial risk & changed them & the electrolytic. Now I can put a mains cable on it & power it. Caps on mains removed.

Marc

I've bumped into VIR flex meltdowns a few times over the years.

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A valve a day keeps the transistor away...

Brad, Thanks for posting photo. As many radio sets, much test equipment, domestic appliances and even houses pre plastic wiring can have rubber wire. This should serve as a reminder that it is still out there and by now most of it has passed its use by date. Of the four grades some Radio manufacturer's seem to have used the worst one & The stuff during & post War seems to be the worst.

I refurbished a family Breville 730 a couple of years ago, that was never initially powered as the rubber wire to the dial lights had bare conductor in places, Astor JJ two for repair one in day both same, rotten rubber, they keep coming.

But for the new & over zealous, what is in the photo, is but one example, of why you look before you leap & never power it until you do look.

Marc

Audio modulation is a good thing if it doesn't come with all siggens.
The LSG11 needs a small preamp between it and modern line level devices.
Then you are safe if AM radio is ever discontinued!