Test Equipment Anonymous

I've been threatening to pick one of these bridges for a while and the first rally of the year for me was the opportunity.

I had to rebuild the outer range multiplier selector knob as the plastic had crumbled around the centre. I had most of the pieces, as they'd been held captive by the design of the knob and the case so I reassembled the 3d jigsaw of plastic, superglued them in place and then poured a load of epoxy resin over the whole lot. I also lubricated and cleaned the switches, cleaned up the front panel a bit (not finished…). There was one switch contact that wasn't making but turning the switch with a little pressure applied to the back of the contact seems to have cleared it.
The only modification I did was to add a PP3 battery clip as the previous owner had soldered a PP3 to the power leads.
The amplifier board probably needs some new capacitors and has had a GET transistor replaced with an ACY type at some point but it all appears to work.



Why do I want this old and obsolete instrument? I wanted to sample the "fully manual" way of measuring parts, the switches and potentiometers are quite lovely to use and you don't get that with a T7-H

The TF2700 is a lovely bit of kit; I had one for many years, and paid £70 for it in 1993. They go for peanuts now. I gave mine to a colleague when I replaced it with a computer controlled impedance analyser that could go to 200kHz. I've now replaced that with one that can go to 8MHz.

It was intended to run off a PP9 battery. You might want to go back to that as I have personally seen/heard three PP3 alkaline explode unprovoked. Not serious explosions, but it would be unfortunate if one destroyed an unobtainium transistor. PP9s still appear to be old-fashioned Leclanche cells made of six stacked cakes internally and don't even ooze, let alone explode.

You can significantly improve a TF2700 by replacing its main range resistors with 0.1% types (originally 0.5%), and the outer range switch resistors also with 0.1% types. If you now use the instrument to measure a stack of (say) 100k resistors with the range multiplier switch set to zero (forcing the measurement to be made by the inner potentiometer), you can plot the results, fit a straight line to it and determine by how much the inner dial needs to be rotated on its shaft. Doing all this can bring your uncertainties down to 0.25% or better.

If you need to measure decent capacitors (polystyrene, polypropylene, PTFE, air) accurately, a TF2700 is excellent. It's only when you start investigating lossy components that you need a fancy impedance analyser. Treasure your TF2700.

synx508 wrote: ↑Mon Apr 20, 2026 4:06 pm The only modification I did was to add a PP3 battery clip as the previous owner had soldered a PP3 to the power leads.

Zenith enabled me to not be able to pass one of these up at W-s-M rally a couple of years ago. Meter is a bit naff, but usable.

I just poke the PPx battery clips out of the back panel, and use croc clips to attach them to a bench PSU.

Crude? Of course!
Functional? Yes.
Reversible? Yes, in 30s.
Quick and simple? Yes.

Sufficient job done.

EC's concept of improving the resistors is tempting.