Knight-Kit 83-Y-135 Signal Tracer

Some time ago I restored a Knight-Kit 83-Y-135 signal tracer.

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This is the mostly finished project. I keep forgetting to take the “before” photos. 

I believe the knobs are original. Most photos of the 83-Y-135 show it with a lighter gray front panel with smaller red-ish knobs …

… such as this photo from, the Knight 83-Y-135 page at, F. Stephen Masik’s post on the Antique Radio Forum web site, 

Flinx’s blog post about his 83-Y-135 restoration, and in the scanned manual at the Boat Anchor Manual Archive (BAMA)

However, there are a few sources that show the older dark gray panel with larger knobs that appear similar to mine,

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such as this page from the 1962 Allied Radio catalog,

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the cover of this manual reprint from,


and photos from an eBay auction.

I essentially re-kitted the unit. I stripped everything off the from panel and the chassis and cleaned everything up. The front panel had some rust stains on it, 

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so I used some Dupont No. 7 auto polishing compound on it.

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I was able to remove the rust stains, but I faded some of the silk screen lettering pretty badly. 

If I recall correctly, I cleaned up the old hardware with a Dremel tool with a wire brush. It came out pretty nice.

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I did use the Dremel with wire brush to clean up the original binding posts. I think I just cleaned the plastic with Simple Green.

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I think they also cleaned up nicely.

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If you look closely, you can see the shouldered fiber washers that insulate the binding posts from the front panel.

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The original washers were in bad shape, so I replaced them with new. You can still buy them from Mouser, although they are made by Keystone rather than Waldom. I’m showing #6 washers here, but I just checked and I actually used #8 size, Keystone part number 3065.

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The back side takes flat fiber washers ...

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… again replaced by new ones. Despite the photo above, I actually used #8 size, Keystone part number 3372.

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Per the instructions, I used a shouldered washer on the front of the black (ground) binding post ...

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… but left off the flat washer on the rear, so that the binding post is grounded.

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A previous owner had replaced the Amphenol 75-PC1F connector with a bulkhead-mount BNC connector, but had incorrectly used a non-insulated connector. Grounding is critical in a high-gain circuit such as a signal tracer to avoid hum from ground loops. The original 75-series connector was insulated from the front panel by fiber washers. It was intended to be grounded to a terminal strip near the 6AU6 tube in the first stage of the amplifier.

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I installed a modern insulated BNC jack to restore the originally-designed grounding scheme.

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Knight didn’t supply star lock-washers for the terminal strips. I didn’t trust just the screw and nut to provide a good low-resistance ground connection, 

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so I fired up my Ungar iron with a 4039 element and tip and soldered the terminal strips to the chassis.

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I also soldered the mounting plate and tabs of the re-stuffed electrolytic to the chassis.

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The wiring instructions start at the usual place: wiring up the heater circuit, along with some  of the front-panel controls.

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We’re nearing completion.

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The wiring wasn’t too complex, so it was rather pleasant to rebuild the kit.

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Fortunately the eye tube is good.

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I described my method for making the probe in a previous post.

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I checked the wiring against the resistance chart in the manual before applying power.

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Why stick with one meter when you can use two?

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The finished restoration ...

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… in its new home on the bench.

© Steve Byan 2011-2019