Re-greening the Heathkit IG-18

richiem · 10th October 2010, 10:53 PM

I've just finished updating Reg Williamson's greening of the IG-18. With just a handful of parts, I'm happy to say that performance is significantly better than stock and along the way I found that some changes for the better are slightly counter-intuitive and different from Reg's experience.

While a major replacement of the guts can yield an outstanding oscillator (see IG-18 #2 -- simple changes can give very good performance.

I've got 0.007% THD at 1kHz with feedback set for a 5V output, and about twice that for 10V out, with good stability at all frequencies. It's here for those interested:
IG-18 #1

JimT · 11th October 2010, 04:01 PM

Thanks Dick,

Re-greening has now become one of my projects for this winter.

PS: If you get time, a final schematic would be nice.

Thanks
Jim

Damon Hill · 04:50 PM

Would you like to take a crack at Heathkit's lesser-known audio generator, the IG-1272? Uses a JFET along with three incandescent lamps, and has a bipolar supply, but seems generally similar to the IG-18. My measurements suggested distortion is down around .02%.

(Waves atcha from the east side of Puget Sound)

richiem · 11th October 2010, 06:05 PM

@ Damon Hill -- I've never seen one. Do you have a pdf of the circuit? 0.02% seems a bit high for an elaborate AGC circuit. I'd love to see the circuit if you have it or can scan it.

I'm about to post some general observations about RC oscillators to my site which rounds up stuff I've discovered trolling around for info. Stay tuned.

Damon Hill · 16th October 2010, 03:21 AM

At one time there was a schematic online, at Bama I think; some company bought the rights to the manuals and it was taken offline, as I understand.

So, I'll have to see if my old scanner is still working and get something posted this weekend.

It's quite different from the IG-18; all pushbutton and no square wave output, but there is a sync output on the back.

richiem · 16th October 2010, 05:56 AM

Thx, Damon -- if you can do it, that would be great. I've seen pix of it, but know nothing about it.

davygrvy · 20th October 2010, 03:53 AM

This thread reminded me of one of those back-burning projects I have to try: AN43

See figure 47 for a 0.0003% wien-bridge circuit from Jim Williams.

richiem · 20th October 2010, 08:10 AM

@davygrvy -- I have one mostly breadboarded and space-wired -- all that's missing is the common-mode suppression amp. Once I get the HP334 greening done and written up, I'll go back to play with that.

richiem · 20th October 2010, 08:13 AM

@JimT -- final circuit diagram is down the list of to-dos. In the meantime, my web page has the few parts changes that are needed and is specific enough to get you going:

IG-18 #1

jackinnj · 20th October 2010, 11:50 AM

Quote:

Originally Posted by davygrvy

This thread reminded me of one of those back-burning projects I have to try: AN43

See figure 47 for a 0.0003% wien-bridge circuit from Jim Williams.

There are also some circuits replacing the integrator with Linear's true RMS converters --

Krohn Hite uses a a FET AGC in their 4400 -- it's the only oscillator which comes close to the Audio Precision. They run from about $300 to $700.

11th October 2010, 04:31 PM	#3
Damon Hill diyAudio Member Join Date: Mar 2001 Location: Auburn, WA (somewhere between Seattle and Tacoma) Blog Entries: 1	Would you like to take a crack at Heathkit's lesser-known audio generator, the IG-1272? Uses a JFET along with three incandescent lamps, and has a bipolar supply, but seems generally similar to the IG-18. My measurements suggested distortion is down around .02%. (Waves atcha from the east side of Puget Sound) Last edited by Damon Hill; 11th October 2010 at 04:50 PM. Reason: corrected faulty memory after reading schematic

20th October 2010, 03:53 AM	#7
davygrvy diyAudio Member Join Date: Mar 2007 Location: Richmond, CA Blog Entries: 1	This thread reminded me of one of those back-burning projects I have to try: AN43 See figure 47 for a 0.0003% wien-bridge circuit from Jim Williams. __________________ Think out of the box

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10th October 2010, 10:53 PM	#1
richiem diyAudio Member Join Date: Sep 2010 Location: Grapeview, WA	Re-greening the Heathkit IG-18 I've just finished updating Reg Williamson's greening of the IG-18. With just a handful of parts, I'm happy to say that performance is significantly better than stock and along the way I found that some changes for the better are slightly counter-intuitive and different from Reg's experience. While a major replacement of the guts can yield an outstanding oscillator (see IG-18 #2 -- simple changes can give very good performance. I've got 0.007% THD at 1kHz with feedback set for a 5V output, and about twice that for 10V out, with good stability at all frequencies. It's here for those interested: IG-18 #1

11th October 2010, 04:01 PM	#2
JimT diyAudio Member Join Date: Oct 2004 Location: Waterloo	Thanks Dick, Re-greening has now become one of my projects for this winter. PS: If you get time, a final schematic would be nice. Thanks Jim

11th October 2010, 06:05 PM	#4
richiem diyAudio Member Join Date: Sep 2010 Location: Grapeview, WA	@ Damon Hill -- I've never seen one. Do you have a pdf of the circuit? 0.02% seems a bit high for an elaborate AGC circuit. I'd love to see the circuit if you have it or can scan it. I'm about to post some general observations about RC oscillators to my site which rounds up stuff I've discovered trolling around for info. Stay tuned.

16th October 2010, 03:21 AM	#5
Damon Hill diyAudio Member Join Date: Mar 2001 Location: Auburn, WA (somewhere between Seattle and Tacoma) Blog Entries: 1	At one time there was a schematic online, at Bama I think; some company bought the rights to the manuals and it was taken offline, as I understand. So, I'll have to see if my old scanner is still working and get something posted this weekend. It's quite different from the IG-18; all pushbutton and no square wave output, but there is a sync output on the back.

16th October 2010, 05:56 AM	#6
richiem diyAudio Member Join Date: Sep 2010 Location: Grapeview, WA	Thx, Damon -- if you can do it, that would be great. I've seen pix of it, but know nothing about it.

20th October 2010, 08:10 AM	#8
richiem diyAudio Member Join Date: Sep 2010 Location: Grapeview, WA	@davygrvy -- I have one mostly breadboarded and space-wired -- all that's missing is the common-mode suppression amp. Once I get the HP334 greening done and written up, I'll go back to play with that.

20th October 2010, 08:13 AM	#9
richiem diyAudio Member Join Date: Sep 2010 Location: Grapeview, WA	@JimT -- final circuit diagram is down the list of to-dos. In the meantime, my web page has the few parts changes that are needed and is specific enough to get you going: IG-18 #1