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Old 10th Aug 2022, 6:41 pm   #1
Cracklemaster
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Default Radiomobile 1070XB Transistors

Hello everyone my first post here!

I’ve been working on a friends car with a Radiomobile 1070XB. The radio had not been used for quite a while and the tuning knob “slipped” and only moved in the central section on the indicator. The preset buttons were also very stiff and the bulb had expired. I decided to remove it and service it as best as I can. All of the above problems were sorted out and I ran the set for several hours on a bench with 12v car battery supply, connected to a spare car aerial and to the original 4 ohm speaker. The reception was poor but that was expected with no proper earthing and trimming. It all worked fine for hours on end and over several days.

Refitted the set to the car and the reception was excellent. I moved the car several times of the next few days and tested the radio as much as possible. Then all of a sudden it just went very quiet when switching between MW & LW, you can just about make out radio 4 on LW, but that is on full volume.

Removed the set again. If you introduce an audio input via the volume knob, the audio is perfect meaning the output side of the radio is fine. Looking inside there is no visible damage or burnt components, I noticed if you fiddle or even gently tap transistor VT3 you get a crackle relative to the volume knob setting.

Reading the excellent posts elsewhere on this forum it would appear these transistors change through the 70s each time with a minor change to the model number.

1070 has AF117 Germanium Transistors
1070X has BF184 & BF185 Silicon Transistors
Also having the metal cap with the fourth leg to shield it

My 1070XB has quite modern looking transistors with three legs (there is the hole in the circuit board for the fourth leg unused) I have downloaded the schematics for the 1070X and although it has a Radiomobile Service Bulletin about 1070XB and 1070XS differences it does not mention the transistors.

I have included the best photo I can get and the text on the transistor looks like E5465 or E5485, but wondered if anyone has any idea?

Thanks!
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Old 10th Aug 2022, 6:58 pm   #2
paulsherwin
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Default Re: Radiomobile 1070XB Transistors

Those are certainly silicon transistors. Any general purpose types are likely to be fine as replacements at AM frequencies (BC548, 2N3904 etc.) However, you should be aware that transistors of that type rarely fail, unlike the germanium AF11xs of the previous generation.

The numbers on the transistors are likely to be house codes, so not very informative.
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Old 10th Aug 2022, 7:45 pm   #3
AC/HL
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Default Re: Radiomobile 1070XB Transistors

I think they're Texas Instruments house codes, they also appear in the Thorn 3000/3500 series.
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Old 10th Aug 2022, 9:32 pm   #4
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Default Re: Radiomobile 1070XB Transistors

I've never understood why manufacturers used house codes for what are undistinguished general purpose transistors. I can't see any commercial advantage, and it just makes life more difficult for everybody. Motorola were notorious for this.
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Old 14th Aug 2022, 3:52 pm   #5
Cracklemaster
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Default Re: Radiomobile 1070XB Transistors

Thanks for all the replies, they are indeed Texas Instruments - you can just about make out the ‘TI’ printed in the corner. Nothing commercially available to match the numbers exactly, just a few transistors with a similar format E5 numbers.
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Old 15th Aug 2022, 6:07 pm   #6
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Default Re: Radiomobile 1070XB Transistors

As paulsherwin has said, any general purpose transistor should work here as a substitute. If tapping VT3 makes it crackle, I assume you have checked for dry joints? Transistorised car audio is prone to bad joints because of the large temperature changes that car interiors are subject too.
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