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Repurpose of old radio
Repurpose of old radio
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Old 31st January 2019, 11:06 AM   #11
Printer2 is offline Printer2  Canada
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Basically strip most of the wiring/components out and rewire. I have a dc radio that I gutted in my amp thread. Not using it yet but I cleaned up the chassis to use for a guitar amp. How about backing up with the camera to get an overall view of the working bits/
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Old 31st January 2019, 11:43 AM   #12
Rasped is offline Rasped  Denmark
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Quote:
Originally Posted by PRR View Post
This is NOT a safe candidate for a guitar amp. <snip>
Oh bugger.

I will built it safe for the ground up then. Thanks for the heads up. For future reference, how do I spot those radios? I have some other radios that are from the mid 50s, will they have the same problem?

Last edited by Rasped; 31st January 2019 at 11:45 AM. Reason: question added
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Old 31st January 2019, 12:23 PM   #13
DF96 is offline DF96  England
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Look for valves with names starting with U or 10. That indicates 100mA heater, which almost always means no mains transformer. Rarer is 150mA heater chain, indicated by valves starting with H or 12. AC-only sets with a mains transformer will usually have valves starting with E or 6.

Look for a mains transformer. However, a few sets had a transformer for the heaters and still had direct connection for the main supply rail so the presence of a transformer is not conclusive. The absence of a transformer is conclusive.

Google the set, and read what you find. If it says AC/DC then it will have a live chassis.

Consider the age and size of the set. Generally, the smaller and later the set the more likely it is to be live chassis.
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Old 31st January 2019, 12:49 PM   #14
Kay Pirinha is offline Kay Pirinha  Germany
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Don't get too dissapointed! Get a 230/230 V isolation transformer of appropriate power (look at the back wall for the radio's power consumption!), remove anything from the chassis that doesn't belong to the AF amplifier (i.e. leave just the last UCH4 and both UBL1's with their periphery), replace the one way UY1 rectifier by a silicon bridge, replace the mains filter capacitor, add another gain stage, using the IF or converter tube, add a tone control between this stage and the AF amplifier, leave the series heater chain, but feed it from the isolation trannie's secondary, and replace the ballast resistor by an appropriate capacitor to reduce heat and power consumption.
Remember that you've got a PP output stage after all!
Best regards!
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Old 31st January 2019, 01:07 PM   #15
Rasped is offline Rasped  Denmark
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Guys

I am genuinely scared by what you're saying.
I have to admit that I have converted 3 newer radios (from the 50s)... and played them with my guitar. Obviously not fried yet, but I will stop playing them for sure until I have made absolutely sure they are safe.

How was it even legal to construct death machines like this?

Am I correct when I think this schematic shows a safe circuit?
Powersupply is top right corner
Click the image to open in full size.

On closer inspection... probably not. Looks like the filament is powered directly on 220v as well... damnit.
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Old 31st January 2019, 04:17 PM   #16
DF96 is offline DF96  England
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These radios were perfectly safe when used as radios. Many TVs in Europe used a similar system. People repairing them or fiddling with them would be aware of the dangers and act accordingly.
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Old 31st January 2019, 04:34 PM   #17
Kay Pirinha is offline Kay Pirinha  Germany
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Rasped,
would you please upload your picture here? I absolutely don't want to create a Microstuff account just for having a look at it.
Best regards!
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Old 31st January 2019, 04:52 PM   #18
Rasped is offline Rasped  Denmark
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Quote:
Originally Posted by DF96 View Post
These radios were perfectly safe when used as radios. Many TVs in Europe used a similar system. People repairing them or fiddling with them would be aware of the dangers and act accordingly.
I will be careful now.

Quote:
Originally Posted by Kay Pirinha View Post
Rasped,
would you please upload your picture here? I absolutely don't want to create a Microstuff account just for having a look at it.
Best regards!
There you go. Sorry about that.
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Old 31st January 2019, 05:17 PM   #19
Kay Pirinha is offline Kay Pirinha  Germany
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Yes, this is also a AC/DC radio with a live chassis. Do you own it? 'Cause it's also got a PP final stage .
Best regards!
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Old 31st January 2019, 05:21 PM   #20
Rasped is offline Rasped  Denmark
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Yes, I own that one as well. Linnet Laursen 5812.
Capella FM-AM 5812 Radio Linnet & Laursen LL A/S; Kobenhavn,
Twin 8 inch speakers. Has a nice clean sound. I modded it to have a bit more gain, so it is a bit of crunch when cranked and playing a humbucker guitar through it. Well... not playing it again before it has been modded with an isolation transformer already figured out where to mount that. Do you think a 50w transformer is enough?
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