This Sprague TO-4 Tel-Ohmike Capacitor-Resistor Analyzer is from the bench of a retired Radio/TV repair technician. It is an excellent candidate for restoration.

Recent Service: The original power cord had brittle, crumbling insulation so I installed a new 2-prong power cord. While inside, I also replaced two leaky capacitors to bring the unit back to a basic functional state.

Functionality: The unit powers up normally, the 1629 "Magic Eye" tube has good brightness, and both the Resistance (R) and Capacitance (C) bridge circuits function as they should (see the last couple of pictures).

What It Needs Next: While the unit is functional, it is still an unrestored instrument from the 1950s. To make it a reliable, daily-use tool for your test bench, you should expect to replace the remaining original capacitors, replace some brittle rubber under-chassis wiring, clean the switch contacts and pots, and perform a calibration. You can find a rebuild kit with all the necessary capacitors here on eBay for a reasonable price. A free pdf of the manual, including schematic, is available on the BAMA website.

Cosmetics: The faceplate is clean with sharp, readable lettering. The knobs are original. The leather handle is missing. The metal cabinet shows light wear with no dings or dents.

Shipping: Item will be carefully packed for shipping.

From our AI coworker: Why you might want a Sprague TO-4 Tel-Ohmike Capacitor-Resistor Analyzer on your bench while doing tube equipment repair and restoration:

Electrolytic leakage at rated voltage — the killer feature. A DMM can't apply 250–450 VDC bias to a power filter cap; the TO-4 can, up to ~600 VDC. This is the single biggest reason restorers keep one on the bench.

Capacitor reforming — combine the leakage test with the built-in meter to monitor leakage current dropping in real time as a dried-out electrolytic re-forms.  No separate bench supply needed.

Power factor measurement — gives a practical read on electrolytic quality at 60/120 Hz, which is exactly the ripple frequency in tube power supplies.  A low power factor tells you the cap is still good for filtering; a high one means it's time to replace.

Capacitance range 1 pF – 2000 μF — covers every cap value you'll encounter in tube gear, from small coupling caps to large filter caps.  The 2 μF reference bridge cap means the measurement is self-contained (no external standard needed).

Insulation resistance — useful for checking tube sockets, wiring, and chassis-to-element isolation on old equipment.

Built-in analog meter — multiple ranges for leakage current, voltage, and resistance. The momentary button switches between current and voltage views, so you can watch both during a reforming session without a second meter.

Magic Eye (1629) null indicator — provides a sensitive, easy-to-read null for the AC bridge, making capacitance comparisons quick.

SAFETY WARNING & DISCLAIMER: This is a vintage piece of electronic test equipment manufactured in the 1950s. It is capable of generating lethal high voltages (up to 600V DC). It is being sold strictly as a vintage collectible, restoration project, or for parts. The seller assumes no liability or responsibility for any damages, injuries, or electrical shocks resulting from the plugging in, testing, restoration, or operation of this device. By purchasing this item, the buyer acknowledges they possess the technical knowledge required to safely handle high-voltage tube equipment. Sold AS-IS with no returns.

Brand	SPRAGUE
Product	Capacitance Meter
MPN	TO-4
Country of Origin	United States
UPC	NA

Vintage Sprague Tel-Ohmike Model TO-4 Capacitor-Resistor Analyzer WORKS

Specifications