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 Post subject: Recap transistor radios?
PostPosted: Feb Fri 15, 2013 2:41 am 
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I picked up a GE C3300A clock radio, which is a transistor radio from 1965. It works, no hum. Does it need to be recapped?
http://www.radiomuseum.org/r/general_el ... _3300.html

I haven't opened it yet. It says, "no user serviceable parts inside," and to keep people out, GE used weird 3-slot screw heads that are like inside-out Philips head screws... shallower in the middle than at the edges. I haven't seen them before. Anyone know what they're called? It's not the "tri-wing" listed on Wiki: http://en.wikipedia.org/wiki/List_of_screw_drives .

Thanks,
Rodney


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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Fri 15, 2013 3:00 am 
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Transistor radios are a different breed.

Not much in the way of paper caps, but you will find many small electrolytics which are likely bad or failing.

Be careful with PC boards and old germanium transistors as they don't handle heat from soldering very well. Use a controlled temperature soldering iron and put heat sinks on transistor leads before soldering them.

I've seen those screws before, but I can't remember what they are called. Maybe someone else remembers?

-Steve

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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Fri 15, 2013 6:25 am 
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palegreenthumb wrote:
I picked up a GE C3300A clock radio, which is a transistor radio from 1965. It works, no hum. Does it need to be recapped?

Only if you want to peak it's performance. In time, however, it's 48 Y.O. components will start showing their age.

palegreenthumb wrote:
to keep people out, GE used weird 3-slot screw heads that are like inside-out Philips head screws... shallower in the middle than at the edges. I haven't seen them before. Anyone know what they're called? It's not the "tri-wing" listed on Wiki: http://en.wikipedia.org/wiki/List_of_screw_drives .

Thanks,
Rodney

You may be able to turn them out using needle-nose pliers, pressing against two opposite sides of the edges, to get them loose. WD 40 would probably help quite a bit, in addition.

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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Fri 15, 2013 6:35 am 
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Actually, I think that radio is a little newer than '65, more like late '60's-early '70's.

In many cases, there are lower voltages involved with transistor radios; thus, there is not as much danger of something blowing up if a cap fails. Paper capacitors were not being used much, if at all, by the time this radio was made and you will actually find more electrolytic capacitors in a solid state radio than you will in a tube set.

Some AC operated transistor radios used a step-down transformer; thus, all stages of the radio operate on low voltage. The only dangerous voltage present in such a radio is the 120VAC input. Other models use a transformerless "hot" chassis design with an audio output stage that requires a high voltage that's obtained directly from the rectified 120 VAC power line voltage and dropping resistors and/or a voltage regulator to provide the lower voltages needed for the other stages of the circuit. In this type of circuit, the main filter cap will be rated at around 150V. Some of these used a multi-section cardboard tubular electrolytic filter cap and these go bad and cause the same symptom (loud hum) just like in a tube set. When working on one of these, the same precautions should be taken as what would be used when working on a piece of "hot" chassis tube equipment.

I've had to recap many transistor radios; but, the bad caps caused performance issues and no serious parts destruction. If the radio works OK, I'd probably keep using it until it fails.

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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Fri 15, 2013 4:01 pm 
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Recently I went over an older Graymark-512 radio ('67). Out of the electrical caps the smaller (10uF and so) coupling capacitors were all bad, while the bigger two filter capacitors (100uF, 200uF) were fine.
I built the 99c ESR meter some time ago, most useful equipment for fixing solid state radios, TVs, test equipment.

Peter


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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Sat 16, 2013 4:57 am 
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orbanp wrote:
I built the 99c ESR meter some time ago, most useful equipment for fixing solid state radios, TVs, test equipment.

Can you start a thread and post the schematic for it?

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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Sat 16, 2013 10:12 am 
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The screw may be a Tri-Groove or 3-Notched Spanner (or something else!):

http://www.kayguay.com.tw/products/screws/security/security.html

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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Sat 16, 2013 1:37 pm 
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fifties wrote:
orbanp wrote:
I built the 99c ESR meter some time ago, most useful equipment for fixing solid state radios, TVs, test equipment.

Can you start a thread and post the schematic for it?


Hi fifties,

I posted a link to it in this thread: http://www.antiqueradios.com/forums/viewtopic.php?f=4&t=204036&hilit=99c

Peter


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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Sat 16, 2013 5:56 pm 
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If you have a transistor radio that is a battery-killer, it is leaky electrolytics.
If it is your storm-radio, leave the batteries out until you recap it or need it.

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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Sat 16, 2013 10:59 pm 
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pehamel wrote:
If you have a transistor radio that is a battery-killer, it is leaky electrolytics.
If it is your storm-radio, leave the batteries out until you recap it or need it.
Funny you mentioned this.
I just picked up a windup AM/FM/Radio/Flashlight which won't play for more than a minute or two after
spinning the crank for several minutes. -- I'd bet those diddly-ding-dang caps or the internal battery is at fault.

I'll open it up later this weekend and see what the verdict is.

~ Mitch ~


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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Sun 17, 2013 12:51 am 
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Your radio was manufactured in 1972. It was apart of GE's "Youth Electronics Division" which was marketed towards children. This was a way for GE to make even more money by making Mom and Dad GE buyers get the next generation involved...(hmmm, kinda like big tobacco?).

Because of the target users (little kids), child-proof measures were taken. You have security head screws preventing unauthorized access from tiny curious hands and standard screwdrivers. What you should do is go to Harbor Freight and buy their 22 or 32 "security bit set" which would have about any weird security bit you need.

"C3300" was a generic model given to the Youth line of clock radios as they all have the same basic chassis and were used from roughly 1969 to 1973. I have the C3300 version that is a Leopard inside a circus train car from 1970. The clock face is the leopard behind the bars of its cage. Be thankful you don't have this model, there are no screw heads--there are glued in plastic slugs that cover standard philip head screws. It is impossible to service without doing some damage.

I would not waste your time to recap this set unless it has issues or you plan on using it heavily. Inside there actually is a small step-down transformer to provide low voltage to the circuit board unlike the "adult versions" that used a surge resistor to drop incoming line voltage to feed the circuits and make a "hot" chassis transistor set.

These models electronics were made overseas and used Nichicon capacitors, Nichicon has been and still is a world leader in electrolytic capacitors, they rarely have issues even after decades. The clock uses American made components which includes a GE/Telechron movement utilizing an "S" rotor.


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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Sun 17, 2013 4:20 am 
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PBPP wrote:
pehamel wrote:
If you have a transistor radio that is a battery-killer, it is leaky electrolytics.
If it is your storm-radio, leave the batteries out until you recap it or need it.
Funny you mentioned this.
I just picked up a windup AM/FM/Radio/Flashlight which won't play for more than a minute or two after
spinning the crank for several minutes. -- I'd bet those diddly-ding-dang caps or the internal battery is at fault.

I'll open it up later this weekend and see what the verdict is.

~ Mitch ~


...internal battery. Crank is a generator that charges a little NiMH or similar battery, something on the order of 300 mAH. They're cheap little Chinese things, and chances are that battery has crapped out...those batteries are popular in those little RC helicopters...

...now, back to topic...


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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Sun 17, 2013 3:18 pm 
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Joined: Jan Tue 15, 2013 4:47 am
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Location: Buffalo, NY
PBPP wrote:
pehamel wrote:
I just picked up a windup AM/FM/Radio/Flashlight which won't play for more than a minute or two after
spinning the crank for several minutes. -- I'd bet those diddly-ding-dang caps or the internal battery is at fault.

I'll open it up later this weekend and see what the verdict is.

~ Mitch ~


My bet would be the NI-cad Mitch.....I don't think these wind-ups have been around long enough for bad caps, at least commercially.

Paul


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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Sun 17, 2013 10:57 pm 
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orbanp wrote:
fifties wrote:
orbanp wrote:
I built the 99c ESR meter some time ago, most useful equipment for fixing solid state radios, TVs, test equipment.

Can you start a thread and post the schematic for it?


Hi fifties,

I posted a link to it in this thread: http://www.antiqueradios.com/forums/viewtopic.php?f=4&t=204036&hilit=99c

Peter

Thx, Peter! It appears though that one would need a 'scope to use it with.

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 Post subject: Re: Recap transistor radios?
PostPosted: Feb Mon 18, 2013 2:29 am 
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thebeav wrote:
PBPP wrote:
pehamel wrote:
I just picked up a windup AM/FM/Radio/Flashlight which won't play for more than a minute or two after
spinning the crank for several minutes. -- I'd bet those diddly-ding-dang caps or the internal battery is at fault.

I'll open it up later this weekend and see what the verdict is.

~ Mitch ~


My bet would be the NI-cad Mitch.....I don't think these wind-ups have been around long enough for bad caps, at least commercially.

Paul


I have no specific information, but I had always presumed they were supercaps, and cheap supercaps go bad in very short order.

Brett


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