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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 5th Nov 2017, 9:38 pm   #21
Phil G4SPZ
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Default Re: Never assume anything!

Once I was coming to the end of a long restoration job on a 1939 Ever Ready all-dry battery portable. I'd duly identified the four battery connections with labels showing "HT" and "LT" and was preparing to make the connections and switch on.

Then I got interrupted.

When the interruption was over, I realised I was running short on time. Red was HT positive, I assumed. You can guess the rest. There was a brief bright flash from all four valves, followed immediately by a sickening feeling and some muttered profanity. That cost me around 25 for a set of scarce valves.

So in addition to not assuming anything, I'd advise avoiding interruptions!
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Old 5th Nov 2017, 10:46 pm   #22
Boater Sam
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Default Re: Never assume anything!

Ouch I don't do many battery valve sets. I have a habit of wiring 2 silicon diodes in series to ground on the LT positive and a fuse wire in series. Then if the HT gets connected, hopefully the filaments may survive.
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Old 5th Nov 2017, 11:01 pm   #23
Phil G4SPZ
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Default Re: Never assume anything!

I believe that's the crowbar variant of the circuit known as an "idiot diode", Sam. A good tip, and one that this particular idiot should remember!
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Old 30th Nov 2017, 4:35 am   #24
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Default Re: Never assume anything!

Decades ago, HeathKit earned the nick name "GriefKit" here in the States.

Some of their kits had mis-marked resistor color code stripes, and some of the diodes had the cathode band marked on the anode.

Made for interesting times, I tell you. Soured me on their products, too.
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Old 30th Nov 2017, 8:20 am   #25
Phil G4SPZ
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Default Re: Never assume anything!

That's sabotage! On a serious note, though, I have been caught out by mis-marked components in the past. I now never fit any component without having checked it first.
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Old 30th Nov 2017, 2:07 pm   #26
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Default Re: Never assume anything!

Quote:
Originally Posted by FrankB View Post
some of the diodes had the cathode band marked on the anode.
I once found a diode wrongly marked, presumably it got turned over somehow before the marking stage in manufacture and survived batch testing.
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Old 30th Nov 2017, 5:11 pm   #27
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Default Re: Never assume anything!

I can remember booking lots of overtime due to a miss marked reel of capacitors.
The pick and place machine was not fancy enough to test components before fitting them. It just carried on fitting the wrong part until the reel ran out.
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