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Historic Item repair

efiste2

Jul 30, 2013
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Jul 30, 2013
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I have an 1962 early warning reciever/carrier from the cold war and I have modified it discretely to be able to plug a 3.5 jack lead into it and it will play original warnings sounds from my PC. However from advice from this forum and others, it appears the AMPLIFIER circuits are no longer operating properly (the output is very quiet and the volume control hardly increases the output).
With it being a collectable item Id like to ask you learned chaps if you think that it could be repaired by an electronics expert, especially an expert who has the experience to know about older circuits etc etc. When I say repaired I mean repaired in a way that it works well but also still looks cosmetically correct on the inside. ie leaving the existing components in situ and some how hiding away the new ones needed for the repair.

heres what the unit looks like with the covers off to give you chaps an idea of how old the components are. (the upright circuit board is the receiver part of the unit and is no longer in use, so its the lower circuit board (the amplification board that is in need of attention)



I hope the above makes some sense.......Thanks
 

duke37

Jan 9, 2011
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The first thing to do is to get a circuit diagram (schematic) to know what the components do. It appears to be a transistorised amplifier from the 1950s

The most likely faulty components are the capacitors. These can be disemboweled and filled with newer, smaller capacitors.
 

efiste2

Jul 30, 2013
18
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Jul 30, 2013
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Thanks for the info, I have the schematic (below) im afraid im not sure how well it shows up using my image host on here, but the original is very clear......Just need to find an "old school" electronics expert local to me now.

 

duke37

Jan 9, 2011
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I do not have the CV transistor equivalents, possibly oc45, OC81D and two OC81.

You will not get much audio power out of this, about the same as a small transistor battery radio. The suppressor circuit should have its switch closed.

Measure the voltages on the transistors to start and measure the supply current. I would expect about 5mA with no signal going up to a few tens of mA at full blast.

You do not say where you are so it is a little difficult to give any indication of who can help.

If the volume control does little, perhaps the signal is not suitable.
 

efiste2

Jul 30, 2013
18
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Jul 30, 2013
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The volume thumbwheel also is the ON switch, ie to awitch the unit on you have to turn the thumbwheel from its starting position, as there is no other manual switch on the unit Im guessing S1 and S2 are both operated when the thumbwheel is turned from its starting position.
I have spoken at some length with telecom guys who operated these many years ago, and they reckon these units should be loud, after all it served as Nuclear Attack Warning.
To give you some more details (apologies for doubling up on my other thread) I am using the speaker output from my PC to play MP3 files into the Amplifier circuit of the UNIT.
I have connected the output signal wires from my PC directly across the speaker terminals of the UNIT and that is also very quiet, even quieter than using the normal input method, hence my assumption that the amplifier circuits are not performing.

My only other theory is that these units used to output a constant tick sound called the "CONFIDENCE TICK" which when the unit was "ticking" it proved that the telephone/carrier signal was working, However if there was an "ALERT" apparently the should increase the volume automatically as it sands out its WAILING siren noise.
Im not sure if that could be the problem or not, as I dont understand how it automatically adjusted the volume, howver playing the "TICK" MP3 file the output is still very low.
By the way your assistance is very much appreciated, Thank you!!!
 
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