S-100 Mullen TB-1 TB-2 TB-4 extender

This page last updated July 25 2024. Copyright (c) 2024 Herb Johnson all rights reserved. This Web page covers the Mullen brand S-100 extender cards with logic probe circuits. Look for other S-100 extender cards I sell, on my S-100 items for-sale Web page. Later I'll add a Mullen S-100 relay board.

For sale: Mullen TB-1 TB-2 or TB-4 boards are not common and may not be found with the probe, or the probe may be damaged from age. I have a few of the boards, probes, and various parts for the probes. Ask me for details and prices. They won't be cheap, they are rather attractive and useful. Details of the Mullen boards and probes are below, so you'll know more about specific features and parts. - Herb

Mullen TB-2 TB-4 S-100 card and probe

Here's a Bob Mullen TB-2 extender and logic probe card. It has a simple logic circuit that displays H and L for logic states, and a wire probe. Note the +8V and +16 and -16V power lines can be disconnected from the extended S-100 connector. A later model TB-4, included a RESET button for the /RESET S-100 line. The button simply connects the /RESET line to ground.

I have copies of the Mullen manuals also. Here's the TB4 schematic and board layout. Also, here's the TB4 manual and circuit operation description.

As the manual explains, the logic probe 7-segment, displays either H for high, L for low, O for open (voltage between logic high and low), or P for pulse (a brief logic signal). a local switch acts to "catch" the P pulse display and hold it, otherwise the P is displayed for less than a second.

Mullen TB-1 S-100 card

Here's a Bob Mullen TB-1 extender card I recently acquired. This particular board is unpopulated, it was sold as a kit. Here's the solder side. It has a simpler logic circuit than the TB-2, here's the schematic. I'll try to find a full manual. It has red yellow and green single LED's to indicate logic high open or low. Here's an assembled TB-1, from the mfe archive links below. Likewise, an assembled TB-1 from s100computers.com I found a closeup of the probe connector on-board, here's that connector and probe cable and LEDs.

Mullen probe

The probe looks to be a simple multimeter-type probe with metal tips. The cable is possibly #18 test probe (flexible multistrand) wire. But it's late 1970's technology that's hard to find in this particular configuration (and good condition) half a century later. That's why I detail these features in this section.

The test probe end, is a "phonograph needle tip" with a removable .058" diameter steel pin that's very sharp. The pin is held by a collet that has a threaded knurled cap to compress the collet. Here's a closeup of the Mullen tip. The plastic handle is about .362 inch diameter (but may have shrunk). These probes were used in the era for VOM or voltmeters or multimeters. Most vintage multimeter probes will not have the exact same mechanics, most are a solid tip and solder end.

A manufacturer of test probes from the 1970's, HH Smith, is still in business in the 2020's. In their current model 699 probe kit, they include several probes including a needle-tip, with a knurled cap on a knurled collet. Here's a photo of an older HH Smith kit of tip parts; see the right-hand corner of the bag. Note the Mullen probe has a smooth based collet; the modern HH Smith is knurled. You may not care about this cosmetic difference, but knurling makes it easier to extract the collet from the plastic handle.

HH Smith provides other tips and two handles for their modern probe set; it retails at $70 in 2024. HH Smith specifies a #18 wire for their probe kit: that has about the same diameter as the wire on the Mullen probe. Vintage probes, of course, are found by happenstance.

The end that plugs into the Mullen board, is a "standard phone tip" 1-inch brass pin, with a .156" diameter tip, which has a solder-cup to hold the wire end. This part is still available in 2020's as a Keystone brand 1601 tip. The modern HH Smith kit I describe above, has a solid pins that screws into their custom cable.

Resources

A few S-100 manual archives have Mullen board photos and manuals. the deramp.com mfe archive has the Mullen extender and the Mullen relay boards.

John Monahan at s100computers.com has some photos and manuals for Mullen.

I'd call the following Web page, a tribute to Bob Mullen from one of his colleagues.

This document copyright © 2024 Herb Johnson.