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 Post subject: Audition Transistor Radio
PostPosted: Oct Wed 25, 2017 1:03 am 
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Location: Sheridan, Wyoming 82801
I'm looking for a schematic for a "Audition Spice Chest Radio 906". It is a Transistor made in the 60's I think. The problem is that after it plays for about 5 min. the volume begins to gradually drop off and the monitored battery voltage drops at the same time. Thanks for any Help :roll: ..


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 Post subject: Re: Audition Transistor Radio
PostPosted: Oct Wed 25, 2017 1:47 am 
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Have you measured the current draw? I would bet it's creeps up pretty high when the radio has been running for a while.


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 Post subject: Re: Audition Transistor Radio
PostPosted: Oct Wed 25, 2017 1:57 am 
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Harv, it would be best to replace all of the electrolytic capacitors one at a time taking note of their polarity.
The values should be marked on them.

Nowadays I use 50V rated capacitors as replacements, occasionally 35V
The lead spacing, diameter and height of today's 50Volt electrolytic capacitors are comparable in size to the lower voltage rated ones of the 1960's - 1970's +
See this... viewtopic.php?p=2666406#p2666406

I've never seen a schematic for this model or any other of Woolworths offerings.
Image
https://www.radiomuseum.org/forum/japan_757.html#8
Japanese manufacturer code 705 unknown.

Image
https://www.ebay.it/itm/AUDITION-AMERIC ... Sw~y9ZBRm3

oh... the last Woolworths store closed its doors here in 1984
Greg... :)


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 Post subject: Re: Audition Transistor Radio
PostPosted: Oct Wed 25, 2017 4:26 am 
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Greg, Thank you very much for your reply. I will replace those capacitors and let you know. I'll have to order them so it will be a while. Harv.


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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Wed 01, 2017 7:29 pm 
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Location: Sheridan, Wyoming 82801
Hello Greg. I have replaced the Electrolytic caps. The radio still plays nicely for about 5 min. then slowly loses volume. Supply voltage goes down with it.
Have you ever has a problem like this ?. With no schematic I suppose I'll just have to shotgun it. Thanks, Harv.


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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Wed 01, 2017 7:48 pm 
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It may be a bias problem caused by a leaky driver or output transistor.

Greg.


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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Wed 01, 2017 7:55 pm 
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insert a milliammeter in series with the battery's line, see what current is, if it stays steady then you might look at the bias caps if it decreases then look to a bad transistor. if it increases then you have a cap or transistor that is shorting.

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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Wed 01, 2017 9:07 pm 
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Harv, here is a typical (broadcast band) 3V eight-transistor schematic for Hitachi TH-841
The voltage and current measurements should give you something to go by, bearing in mind that your radio has a 6 Volt supply.
http://www.kevinchant.com/uploads/7/1/0 ... th-841.pdf

Greg.


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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Wed 01, 2017 11:02 pm 
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OK Greg and Radiosmoker, that sure gives me something to go on and thank you for your help !!.


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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Sun 05, 2017 8:21 pm 
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OK, I finally got back to this radio. The current starts out in the milliamp and will slowly climb to the amps. before I shut it down. There are four transistors clamped together that get very hot. There are only four standard type caps so I will replace those.
Now my questions for you fellows about the transistors :.
I tried crossing these 2SA numbered transistors and got NTE136 and so on. They are Germanium I suppose and expensive, $7 to $11. Do you use or know of other transistors I can use that are less expensive ?. Thank you for tour help.. Harv.


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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Sun 05, 2017 9:00 pm 
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If the Transistors are heating up, there's an obvious short somewhere. I doubt that anymore than one of them, if that, is the culprit.

Inspect the circuit for any solder bridges, change the E-Caps, and spec the resistors.

While it's on, check the base and emitter voltages of each Transistor. There should be about .2 volts difference between them, and their voltages should be in the 1 -2 volt range. The collectors should be right about at the supply voltage.

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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Mon 06, 2017 1:12 am 
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Location: Sheridan, Wyoming 82801
Thanks for the reply and tips Fifties. In case I do end up with any bad transistors is there any type you would recommend ?. I figure there must be suitable replacements with more modern transistors.


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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Mon 06, 2017 4:48 am 
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probably most any small signal amplifier Transistor will work, some better than others. If you have to go that route, adjusting the base bias resistor would peak it. Of course you'll have to determine with your meter if they are NPN or PNP Transistors. I'm sure there are tutorials on the net for that.

First however, if you do what I suggested, we can then go from there. After replacing the Electrolytic's, if the Transistors still heat up, checking each Transistor's element voltages would be next.

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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Mon 06, 2017 5:29 am 
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Joined: Nov Wed 12, 2014 6:06 pm
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Location: Sheridan, Wyoming 82801
OK, I'll check out the transistors because as I stated above, I have replaced the e-caps. I may as well replace the standard caps as well. Thanks, I'll get back to you.


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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Mon 06, 2017 8:19 am 
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I don't think there is a reason to replace the disc caps. Check the Transistor voltages and post your results.

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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Mon 06, 2017 2:52 pm 
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Joined: Nov Wed 12, 2014 6:06 pm
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Location: Sheridan, Wyoming 82801
will do...


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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Fri 10, 2017 2:04 am 
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Joined: Nov Wed 12, 2014 6:06 pm
Posts: 103
Location: Sheridan, Wyoming 82801
I found the bad transistor. There were four transistors connected together in what I'm guessing is a heat sink. I had felt for any heat several times if I could get the radio to play long enough. Finally I took the screw out and removed the sink. Then turned on the radio and crossed my fingers that it would play long enough to show any heat if it was going to. I kept touching each transistor and sure enough one of them started to get hot. I found four new 2SB156 transistors on ebay very reasonable. I get back to you after I put the transistor in and give it a good run. Thanks, Harv.


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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Thu 16, 2017 5:11 pm 
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Joined: Nov Wed 12, 2014 6:06 pm
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Location: Sheridan, Wyoming 82801
Well, I still have the same problem. I have replaced two of the bad transistors, all the e caps, pulled and tested most of the other components. There are four transistors together in a heat sink. two get hot after the radio is turned on for a short time. Now I suspect that the black wire from the batteries had been hooked up in the wrong place causing the problem. I need a picture of the bottom side of the board to confirm the correct hook up. No schematic is available.
Thank for help and tips !!. Harv.


Last edited by Harv Hunt on Nov Sun 19, 2017 6:27 pm, edited 1 time in total.

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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Thu 16, 2017 5:13 pm 
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Joined: Nov Wed 12, 2014 6:06 pm
Posts: 103
Location: Sheridan, Wyoming 82801
egg (Greg), I sent a P.M. Harv.


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 Post subject: Re: Audition Transistor Radio
PostPosted: Nov Sun 19, 2017 6:25 pm 
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Joined: Nov Wed 12, 2014 6:06 pm
Posts: 103
Location: Sheridan, Wyoming 82801
If anyone has one of these I would sure appreciate if you could take a picture of the solder trace side of the board. I have to see if the Black-Neg. Power wire is hooked up in the correct place. Thank you..


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