Archive for the ‘Radio Frequency’ Category:

2020-02-17 I Bid On A Boy’s Radio, Lost

From FB group Vintage Transistor Radios Last week I bid on a boy’s radio, $26 which lasted up until near the end. But as usual I was outbid at the last minute. I think the demand exceeds the supply, and the prices go up too high. Looks like I’ll be getting one that no one

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2020-02-14 Zenith Royal 400 S/N Z551549 Replaced Capacitors, Driver Transformer

Zenith Royal 400 s/n Z551549 I soldered broken orange wire to battery holder. Replaced all four electrolytic capacitors. Silent speaker and nothing from earphone jack. I checked the voltage at the collector of the driver transistor, it was zero. One pin of the driver transformer primary measures 5.8 V, the other pin measured 0. Checked,

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2020-02-06 Royal 500H Alignment

From FB group This Zenith Royal 500H radio has the extra 8th transistor for the RF amplifier, so it should have excellent sensitivity and be able to pick up those weak stations. Most of the problems with old radios are with the electrolytic capacitors, but the Zeniths all use the carbon composition resistors and they

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2020-01-30 Royal 200 Silicon Conversion, Part 3

Also to FB group Vintage Transistor Radios I finally drew the line and said I’m finished fiddling with this Zenith Royal 200 and put it back together. I got it without knobs or handle, and with all the transistors missing. It’s not pretty, and the speaker cone is warped and sounds bad. This is the

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2020-01-23 DIY Variable Capacitor 90 to 3400 pF

The beginning isn’t clear about how it looks. First, scroll to end and look at the photo. https://www.randombio.com/capacitor.html

2020-01-20 Costs of Radio Assemblies and Parts

From FB group Vintage Transistor Radios A thought occured. Do you think that Motorola may have had a lot of parts for tube sets and they decided to use them up by putting a transistor chassis in them? If you break down a radio into its assemblies and/or parts, which of them has the highest

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2020-01-18 More Zenith Royal 200 Conversion to Silicon

Continued from post 2020-01-15 I dug through my drawers and boxes of transistors and found a bunch of MPSA56 PNP general purpose on tape, and put them into the LO and mixer. I think they helped slightly – they are lower minimum fT than the 2N3906s. I adjusted – optimized – the trimpots I had

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2019-01-15 Zenith Royal 200 Conversion to Silicon

My Zenith Royal 200 conversion to silicon transistors is going slowly. Right now I’m working on getting a good sine wave out of the local oscillator (see photo). The waveform had high frequency parasitic ringing every other cycle. I put a 100 ohm resistor in series with the collector lead and it helped some. I

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2020-01-10 Corrosion and Damage On Diode Leads

This photo is a detector diode that was broken during replacing the electrolytic capacitors.  The lead on the top was twisted, apparently putting stress on the glass package.  I replaced it with a 1N270 germanium diode. comment from fb group Vintage Transistor Radios Did you notice that the leads are magnetic? They stick to the

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2020-01-06 Two Similar Transistor Radios

I posted this a few days ago.https://m.facebook.com/groups/606087512820068?view=permalink&id=2638214152940717 Now I’ve replaced the capacitors in another one very similar, a DE LUXE. It’s not quite as complete and in as good a shape as the Encore. What surprised me was that some of the electrolytic capacitors were bad (measured open) and the symptom was no sound whatsoever

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