Archive for the ‘Receiver’ Category:

2019-10-07 Zenith Royal 500H Troubleshooting

I got this from eBay, it doesn’t make any sound at all. It has a small crack in one corner but the case is otherwise okay. The screw on the bottom is corroded but the battery holder is in halfway decent shape. It needs a bit of cleaning, the metal is a bit tarnished but

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2019-06-12 Plug-in Coils Pros And Cons

from FB group Regenerative Radio… Jun 13 I’ve thought about using plug-in coils, but I’ve had experience with Grid dip meters and there are a few important issues that must be dealt with. One is, what happens to the unused coils when the equipment is not in use. They get separated from the equipment and

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2019-06-11 Selenium Rectifier Burned Up, How To Replace

from FB group Vintage Transistor Radios Jun 12 Bob Kirsch has the right idea, but the single replacement diode *must* be rated for 400 V peak inverse voltage or more. A 1N4007 is cheap and readily available. I assume you’re in a country where the AC line voltage is 120 VAC, because the rectified DC

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2019-04-09 Event Horizon Telescope Hoopla Tomorrow

There has been a big media buildup to the scheduled release of the “picture” of a black hole. This was synthesized from data taken by multiple radiotelescopes around the world, and processed by supercomputers. More information. Update Apr 10 evening – As I had expected, the media made quite a big issue out of a

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2019-04-05

from FB group Vintage Transistor Radios April 6 I clicked on the link and I looked at the schematic. I’m surprised that in 1959 they had a radio that used the OTL amplifier to drive the spkr. I remember OTL was used in the early ’60s for Hi Fi amps, but I didn’t think that

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2019-03-31

from FB group Vintage transistor Radios April 3 Are all ‘polyvaricon’ tuning capacitors the same? They’re all about the same size. Charles Vesser Japan Industry Standard… The few that I have examined were 140 pF antenna and about 70 pF oscillator. In parallel give 210 pF. They’re probably made to match up with the loopstick

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2019-03-22 Tuned Circuit For 702 kHz

from FB group Building Transistor Radios Stoffel van Aswegen I used the free Android app ElectroDroid to do these calculations. For 702 kHz, a 220 pF fixed capacitor (NP0 or C0G) and a 230 microhenrys coil are needed. The standard ferrite loopstick is 230 uH, but you can wind your own on a coil form

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2019-03-19 Radio Alignment Questions

From FB group Building Transistor Radios Mar 20 Bob Kirsch Any recommendation for doing a complete alignment? Documents? I used a HP sweep gen decades ago but I don’t have one now, just an old signal gen. I thought about building a sweep gen but I need to get a few parts. I have bought

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2019-02-05 Floating Detector Diodes Are Not A Good Design.

from FB group Building Transistor Radios 2019-02-05 Graeme Heal Aaron Cake has a lot of good circuits and projects. But this one uses the ‘floating detector diode’ with no DC return path, so the circuit will only work if the diode’s leakage current provides the discharge. That means the diode must be germanium, not silicon,

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2019-01-27 Replacing Corroded Battery Contacts

From FB group Building Transistor Radios 2018-01-27 Many of the radios I’ve acquired were so corroded that I had to replace metal parts. I used tin can lids to make replacement battery holder contacts. The steel is springy enough to hold cells in place. Scissors can cut the steel, and it can be drilled and

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