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 Circuit Diagram for Dick Smith Q-1312 RF signal generator
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 Return to top of page · Post #: 1 · Written at 12:02:36 PM on 18 July 2019.
Keith Walters's avatar
 Location: Sydney, NSW
 Member since 16 January 2008
 Member #: 219
 Postcount: 48

I have two of these I rescued from the DSE Engineering Department when they closed down.
The both used to work, now neither one does.
I opened up one and I suspect it has a faulty 2SK55 JFET as the voltages on that don't look right.
I had a brief go at tracing out the circuit but what I've drawn thus far doesn't make a whole lot of sense.
Does anybody have any experience with these, or even better a circuit diagram?


 
 Return to top of page · Post #: 2 · Written at 5:13:19 PM on 18 July 2019.
Arty41's Gravatar
 Location: Brisbane, QLD
 Member since 18 September 2010
 Member #: 118
 Postcount: 289

A mate of mine Noel Everding and I used to know a guy that worked for Dick Smith "Steelo" who might be able to help Smile-


 
 Return to top of page · Post #: 3 · Written at 8:06:45 PM on 18 July 2019.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5263

I see from period advertising (Jan 1986) that it had a mate: the Q-1310 AF sig gen.


 
 Return to top of page · Post #: 4 · Written at 8:48:33 PM on 18 July 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3711

I have resorted to taking a photo of the PC board, sorting it out in an image editor, printing it and then playing join the dots.

Some of the early FETS became a short if they lost gate voltage.

They're easy to understand. You apply a source, open the gate & the whole lot goes down the drain.


 
 Return to top of page · Post #: 5 · Written at 9:57:56 AM on 19 July 2019.
Labrat's avatar
 Location: Penrith, NSW
 Member since 7 April 2012
 Member #: 1128
 Postcount: 269

I think I have the circuit. I will look for it this weekend.

Wayne.


 
 Return to top of page · Post #: 6 · Written at 3:06:29 PM on 19 July 2019.
Keith Walters's avatar
 Location: Sydney, NSW
 Member since 16 January 2008
 Member #: 219
 Postcount: 48

GTC:
"I see from period advertising (Jan 1986) that it had a mate: the Q-1310 AF sig gen."

Yeah, got two of those as well. THEY still work....
I'm actually working on a 1935 Sparton 666 6 valve superhet..
It has an unusual IF of 345kHz.
Before I had a circuit I'd assumed it was 455kHz and tried to align the IFs using a small 455kHz generator I have.
Not only wouldn't it peak up, but when I tried to screw the trimmers back in again, I found that the nuts had fallen off and I had to dismantle the IF cans to put them back on!
I've only just got round to replacing the rubber mounts for the tuning capacitor (which had turned to black slime after 80-odd years). It was a hell of a job getting it back together; never seen so many earth straps!
Then, when I pulled out my trusty DSE signal generator to finish the job, I found out it wasn't so trusty any more and had stopped working. Well never mind, I'll just drag out the backup- oh crap; that's stopped working as well!
In the end I resorted to the old(/new) trick of working out the oscillator frequency for a known station, setting the tuning knob so the oscillator produces that frequency (using a frequency counter) , and then peaking up the IFs (making SURE I'm peaking them to the correct station!)
Now that I have that all that sorted out it really performs; whether using the 2 inches of wire hanging out the back, or connecting a 30 foot antenna, it sounds much the same.


 
 Return to top of page · Post #: 7 · Written at 3:11:34 PM on 19 July 2019.
Keith Walters's avatar
 Location: Sydney, NSW
 Member since 16 January 2008
 Member #: 219
 Postcount: 48

"A mate of mine Noel Everding and I used to know a guy that worked for Dick Smith "Steelo" who might be able to help"

Rudolph Transfield I presume? Smile
I remember your name; everything else escapes me these days Sad


 
 Return to top of page · Post #: 8 · Written at 3:14:06 PM on 19 July 2019.
Keith Walters's avatar
 Location: Sydney, NSW
 Member since 16 January 2008
 Member #: 219
 Postcount: 48

Labrat:
"I think I have the circuit. I will look for it this weekend"

Thanks. I seem to remember there was a circuit in the back of the manual.
I still have all the Dick Smith project files on a portable Hard drive somewhere.
I wish I knew where!


 
 Return to top of page · Post #: 9 · Written at 9:42:54 PM on 19 July 2019.
Arty41's Gravatar
 Location: Brisbane, QLD
 Member since 18 September 2010
 Member #: 118
 Postcount: 289

Hi Keith, my e-mail address is open .


 
 Return to top of page · Post #: 10 · Written at 1:32:00 PM on 20 July 2019.
Labrat's avatar
 Location: Penrith, NSW
 Member since 7 April 2012
 Member #: 1128
 Postcount: 269

Hi Keith.
I have what I believe to be the manual for this generator, but your e-mail address is hidden.

e-mail me with your e-mail address, and I shall send the circuit to you.

Regards

Wayne.


 
 Return to top of page · Post #: 11 · Written at 10:08:30 PM on 22 July 2019.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5263

I resorted to the old(/new) trick of working out the oscillator frequency for a known station, setting the tuning knob so the oscillator produces that frequency (using a frequency counter) , and then peaking up the IFs (making SURE I'm peaking them to the correct station!)

I vaguely recall being shown that technique by an old hand, but it was many moons ago now.


 
 Return to top of page · Post #: 12 · Written at 12:41:30 AM on 23 July 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3711

I have mentioned it before, but there are traps with counters. I have an early EA, DSE kitset one and a Fluke. Both will give the wrong frequency if fed modulated RF.

One must be rather cautious if coupling to RF coils & resonant circuits as any change in loading, capacitance etc. can throw them off frequency.

The IF frequency is independent of the mixer oscillator. So one injects a low signal at IF frequency into into the signal grid of a Pentagrid & calibrates it first. After that you sort out the oscillator & antenna coils & padder if fitted.


 
 Return to top of page · Post #: 13 · Written at 9:37:26 AM on 23 July 2019.
Keith Walters's avatar
 Location: Sydney, NSW
 Member since 16 January 2008
 Member #: 219
 Postcount: 48

"Both will give the wrong frequency if fed modulated RF."

You don't measure the Intermediate frequency, you measure the oscillator frequency.
Take the example of 1170 2CH. 1170 + 345 = 1515kHz.
You monitor the oscillator frequency and adjust the tuning knob until the counter reads 1515kHz.
Then you adjust the IF coils for maximum output on 2CH (Using a different radio if necessary to make sure you are peaking 2CH!)
If the local oscillator is set to 1515kHz, then 2CH must be producing a beat of 345kHz.
(With a 455kHz IF the frequency would be set to 1170 + 455 = 1625kHz)
Attaching the frequency counter may shift the oscillator frequency, but that doesn't matter, it will just mean that the antenna coil alignment will be a little off. With a strong enough signal, that won't matter.


 
 Return to top of page · Post #: 14 · Written at 9:43:15 AM on 23 July 2019.
Keith Walters's avatar
 Location: Sydney, NSW
 Member since 16 January 2008
 Member #: 219
 Postcount: 48

Thanks to Labrat for the circuit.
As he says, there was one line left off the "Curcuit Diagram", but once you figure out where that went, it's easy to understand how it works.
More importantly, the voltages on the oscillator definitely indicate that the FET is FUBAR Smile


 
 Return to top of page · Post #: 15 · Written at 10:14:26 AM on 23 July 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3711

After a refit on a superhet I normally hook an Oscilloscope to the OP and go for alignment to ensure that part is working before worrying about the front end. That picks up distortion & faults not seen & the oscilloscope can then be used as a signal tracer.


 
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