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.  Here’s the view of Manhattan today  from East River State Park in Williamsburg, Brooklyn.  In the center is the Empire State Building

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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  15 amperes @ 5 volts. At 20 amperes forward current (Way outside its ratings) … Continue reading

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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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