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Heath IG-18  IG-5218
Heath IG-18  IG-5218
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Old 9th June 2021, 07:33 PM   #61
Pizzigri is offline Pizzigri
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Thank you Jack,
hopefully there's going to be enough interest to spark some ideas. The IG18 and brethen are really nice and the discrete switched networks make them really interesting... a modernization of the circuit can make this generator a really nice lab tool

Is anyone interested in updating/designing the PCB?
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Old 10th June 2021, 06:33 PM   #62
jackinnj is offline jackinnj  United States
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Heath IG-18  IG-5218
I can certainly do it -- but which design.
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Old 10th June 2021, 07:54 PM   #63
mickeymoose is offline mickeymoose  Canada
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I have a box labelled "Dismantled IG18" on the shelf. Whenever I walk by it winks at me, the sexy thing!
I'd give the design of a set of pcb's a go if there is a consensus of a good design. E
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Old 10th June 2021, 08:22 PM   #64
jackinnj is offline jackinnj  United States
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Heath IG-18  IG-5218
IG18-SL -- based upon the HP339A.

Might want to use a compound amplifier instead of 1/2 of a 2134 on the output.
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Old 10th June 2021, 08:52 PM   #65
Pizzigri is offline Pizzigri
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Quote:
Originally Posted by jackinnj View Post
I can certainly do it -- but which design.
OK so I have been looking around at all viable projects, starting from the venerable regreening of the IG18 article of the 70s.
I think that the design with the highest potential is the Super IG18SL design, by Steve Lafferty Modifications: Heathkit IG-18 Audio Generator
and
http://www.tronola.com/IG-18SL_Construction_Notes.pdf

Larry Burk designed a PCB in Eagle and the files are downloadable form Tronola website.
The basic design is there, however Dick Moore experimented with the design - and I believe much improving it - with more current and still available parts (especially opamps).

There are three separate parts of this project which i believe the interested parties here could address:

1- updating the power supply to something actually modern. The PS is somewhat present in Lafferty's board and I think it should be redesigned as it involves powering the device with a tranformer wired for 240V but connected to 110, which is very unpractical for us living this side of the ocean. So something based on the ubiquitous LM317 and LM337 pair would be optimal I think (Dick mentions this in his writeup).

2 - redesigning the PCB to account for double layer and actual components used for the more modern opamps that need less ancillary discrete components (something that Dick Moore pointed out in his writeups here:IG-18 #3, the IG-339A
and here:
IG-18 #4, the IG-339B
possibly avoiding any Tantalums and resizing the layout so the parts actually fit on the board...

and finally, 3 - debating and finally choose the best and easiest solution for the multiplier network.
Use the existing tuning network of the 18/5218, as Dick Moore did admittedly simplifying things and also making it cheaper, just adding the AGC caps. Point here is to avoid the uber expensive switch from Mouser, and possibly the purchase of 8 expensive precision caps, discarding the ones already inside the IG18.

All switches for the frequency use 1/2 W and 1% resistors, would using 0.1% improve things? Dick Moore also suggests changing the attenuator network to reflect HP 339, but I am not knowlegeable enough to evaluate cost/benefits.

Hopefully we could also come up with a BOM that we can use with the whole project.
In the end, I would like to acknowledge the work of Steve Lafferty and the late Dick Moore R.I.P., and also I will ask Mr, Lafferty if he would be interested in hosting eventually any update we could come up here on his site, as a follow up on his excellent work.
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Old 10th June 2021, 08:53 PM   #66
Pizzigri is offline Pizzigri
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Quote:
Originally Posted by jackinnj View Post
IG18-SL -- based upon the HP339A.

Might want to use a compound amplifier instead of 1/2 of a 2134 on the output.
Exactly! That was what I was referring to.
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Old 10th June 2021, 08:59 PM   #67
jackinnj is offline jackinnj  United States
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NG0 MLCC were found by Scott Wurcer to have lower distortion than polyester and polypropylene.
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Old 10th June 2021, 09:12 PM   #68
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Ok, although I'm scared what prices could uF size caps could cost in MLCC.
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Old 12th June 2021, 03:12 PM   #69
jackinnj is offline jackinnj  United States
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Quote:
Ok, although I'm scared what prices could uF size caps could cost in MLCC.
Wima MKP are radial, available in 50/63 and 100V. Would need to parallel the multiples of (4.7uF || 270n), (470n || 27n) etc. to get within 1%
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Old 12th June 2021, 04:28 PM   #70
Pizzigri is offline Pizzigri
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Well, I was looking at the schematic from Lafferty's page and attempting to figure out how Dick modded the design, and also how the Eagle PCB that is suggested fit in all of this. And I had a crazy idea...

basically, to make the whole design in SMD, and moving the AGC and multiplier networks on the PCB itself, using the original Heathkit switch just to select the combinations to reach the optimal cap values (i.e. paralleling them on the PCB and using whenever possible, precision SMD parts). It would simplify a lot the build and avoid going crazy with difficult to find rotary switches and routing lumps of paralleled caps.
Still, something that i dont think I can do although I am trying to understand how DipTrace works (and it will NOT import the Eagle file that's on Tronola's page). Would anybody be interested?
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