Heathkit SG-8 article in Newsletter

[Gary Albach]

Gerry, just read your article in the current newsletter describing the repair of the Heathkit SG-8 signal generator you received in the Mystery Box raffle. Those new knobs look very spiffy! If you still have the old knobs, and want to use them again, you can repair them using one of the cyanoacrylate gel glues, such as LePage Gel Super Glue. Several of the knobs on my high school SG-8 and its matching C3 Condenser Checker were cracked, but I was able to repair them using the superglue gel after cleaning the broken parts with a toothbrush and Windex.

Your article prompted me to revisit a presentation I gave a couple years ago in Edmonton on improving the waveform of the SG-8. Unlike the competing low-priced generators of the time with similar circuits (e.g the Eico 320) the designers of the SG-8 chose to overdrive the oscillator and the modulator to distort the waveform and hence produce the harmonics that extend over 200 MHz on the dial. Apparently back in the 1980s there was a group of hobbyists dedicated to improving the waveform of their SG-8s, and it was Peter Bertini in the US who kindly told me their favorite tricks. They placed a 4.7k resistor across the lowest frequency rf oscillator coil (Band A), lowering its Q-factor to produce more of a sine wave, then reduced the amplitude of the drive on the modulator section of the 12AU7 by adding a 200pF capacitor to ground. (The Eico 320 achieves the same result by using a smaller coupling capacitor but for some reason this doesn’t work in my SG-8 – maybe there is just too much stray capacitance.) The resistor across the coil throws the dial calibration off a bit, but with a frequency counter this isn’t a big deal. The attached photos show the circuit and the waveforms before and after the modifications. The output waveform is still not a perfect sine wave but it is a big improvement over the original. You mention in your article using the SG-8 as a transmitter for music around the house; I never tried cleaning up the waveform on Band B, the broadcast band, but I would think these same tricks would be effective there as well, and might improve the audio quality.

Attachments:

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   Heathkit-SG-8-original.jpg
   

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   Heathkit-SG-8-with-changes.jpg
   

[Rhonda]

Hi Gary:

I remember that presentation you gave to the club.

I have come into quite a few radios that will need repair so the SG-8 will get quite a work out this summer. And before I do that, I’ll have to clean off my test bench and send you those battery boxes I built. I also have the Eveready 427 done up as well for you to try. Just been really busy to get everything into parcels.

Glad you made it back from “way down under.”

Stay frosty,

Gerry

[Gary Albach]

Hey Gerry – one last thing about the SG-8, I found mine to be quite ‘leaky’ through the output attenuator switch, and maybe radiating through the cabinet as well. Had trouble at times getting the output down low enough for the more sensitive receivers.
I’m going to be in Edmonton May 12-14th, so maybe I could pick the battery pac up from you? Really looking forward to trying it in a variety of my T/Os and clones so we can report its performace in different radios. And seeing how the 427 turned out – I will need several of them for the little Rogers-Majestic/Motorola lunchboxes. I think Radar may still have paper labels for these batteries.
Have finally warmed up. Antarctica this time of year is getting a little chilly!
Cheers,
Gary

[Rhonda]

Hi Gary:

If you are driving into Edmonton, definitely we can meet up and you can take the goodies back with you. The one battery eliminator is heavy so if you are flying, parcel post is the best way to get everything to you.

Please let me know. I am also working on May 14 so if we can meet up in the evening on May 12/13, that would be good. And if you are around for Saturday, our club is looking to have their spring workshop that day at Bill Elmer’s place.

Cheers,

Gerry

[Steve Dow]

Hello Gary,
I have owned, and now do own Heath SG-8 signal generators, as well as Eico of the era. I read with interest
about the attenuator and cabinet leakage. When CB radios first were available in Canada, they were tube models and
service needed a fairly low level signal to peak the sets. One trick we used back then was to insert a bit of folded paper
between the two solder glob contacts of the Amphenol RF connector. On 27 MHz, by tightening or backing off the
ring of the connector, the RF level could be really reduced right down into the noise level.

The first CB sets that were sold at the original House of Stein Electronics store on Granville Street were Raytheon
and later, Lafayette and AGS. Those of course were tube sets. Back in the very early 60’s I was running the
service department, in the mezzanine floor of the store at 1005 Granville Street.

Across the street was the Belmont Hotel. On the roof was a giant neon clock that could be seen for miles. Below the
eves was a horn loudspeaker connected to an amplifier with a microphone next to an electric Westminster chime clock sitting in
machine room for the neon display.

To demonstrate the CB radios, I had installed a fairly large aerial on the brace frame that supported the House of
Stein illuminated sign. The Raytheon CB was on a shelf in the optics and radio department. Mr. Wagner , the specialist
selling those items would call on the CB, and make contacts to show customers the operation. His call sign was
XM11-099, and my two call signs were XM11-123 and XM11-124. I believe the year was 1963.

One day the police came in and asked if we had heard any unusual radio traffic. Someone people had reported hearing
something that sounded like emergency calls on Granville street as far down as Georgia Street.

Eventually, the Belmont hotel became involved, because the clock chiming on the roof was heard for a distance with the
noise. It was the clock speaker, and the voice was from our CB transmitter.

I went up to roof location and found the amplifier system for the chime system. It had been installed years before
by a firm called Radio Service Engineers. This was a Vancouver firm that manufactured and installed sound systems
in British Columbia.

The fix was simple. A routine low pass filter in the microphone line and replacement of some very old connectors.

I remember the incident was reported in the Vancouver Sun.

Forty years after, far from Vancouver, I collected vintage PA system components, from school garage sales, manufactured
by Radio Service Engineers.

Steve Dow

[Gary Albach]

Hi Steve – sorry for the long delay time here in responding but boy, you sure took me back with memories of Granville Street electronics stores before the downtown reconstruction. I moved there in 1970 and used to visit the stores on Granville and on Main Street. I love your story of broadcasting CB calls down Granville Street from interference with the PA system on the Belmont Hotel. LOL!
Wish I’d know your trick of putting a bit of paper in the Amphenol connector – a really great idea!
Cheers,
Gary

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