Monthly Archives: July 2011

UTC FJ-125 transformer

A gorgeous part in search of a project! There are about a dozen of these, new and in original boxes sitting around the shop. The FJ-125 weighs 10 kg and is just under 18 cm long. It has a single … Continue reading

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Tung Sol’s 7241 & 7242 monster triodes

Both have 100 watt maximum plate dissipation. The 7241 has a maximum DC plate current of 1.2 amperes and the 7242, 0.9 amperes. So you are thinking about OTL (output-transformer-less) circuits, huh? Do not let anyone fool you, both of … Continue reading

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Daven VH-795-G attenuator

This has three decks and can give you attenuation from 0 to 111 db in 0.1 db steps. Unlike the Hewlett Packard and General Radio equivalents each deck has 11 steps. The VH-795-G has 600 ohm input and output impedance. … Continue reading

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Finally cooler in New York City

Today it’s overcast and much cooler in NYC.

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Using a 1B3GT vacuum diode as a HV capacitor

If you connect the filament pins (2 & 7) together a 1B3GT, or similar vacuum diode makes an excellent HV capacitor capable or at least 15KV. Filament power is not applied. You can then use it as the upper cap … Continue reading

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Hewlett Packard 320A passive distortion analyzer

An interesting box rarely seen today. Internally, it’s just an attenuator and a tunable bridged T network. Operation is simple: Select 400 Hz or 1 KC. Apply signal to the input terminals at corresponding frequency. View residual on a ‘scope. … Continue reading

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Tung Sol 7791A hydrogen high voltage diode

From the sublime (866) to the insane: Tung Sol 7791A hydrogen diode. Current rating: is 8 peak/2 ave. amperes and 25000 peak inverse voltage. Filament eats

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More tubes to test – 3B28 Xenon rectifier

The 3B28 has the same pin out and filament voltage (2.5 volt @ 5 amps) as the 866 but is filled with Xenon gas rather than mercury. Peak inverse anode voltage is 10000 volts at peak plate currents of 1 … Continue reading

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Testing an RCA 866 rectifier tube

Here’s an ancient RCA 866 (non-A, S envelope) being given a quick test on Triplett 3444A tube tester. At the top of the envelope you can see the characteristic blue glow of mercury vapor. Not a good idea to stare … Continue reading

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Hot time in Brooklyn

Thermometer says it’s just about 100 degrees

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