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 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Sat 05, 2019 3:38 am 
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fifties wrote:
tubeAMP wrote:
the cheat about tubes is that many are dual purpose. cant say that about early transistors at least not until OP amp. transistors have a single purpose so there may be many more of them than tubes :wink:

That's not really accurate; they may have been designed for a specific purpose, but can also work just as well in other applications. Many small signal Transistors can be used in high speed switching circuits, as one example.

Agreed, ya don't kno ifin ya don't try something different.

I installed a TO-66 auto radio audio transistor in a GE P805A as output, worked same as the orig. I enlarged the base and emitter land openings, then soldered collector(case) directly lug of audio output transformer. I did try rebias it for additional current draw, but it was difficult to tell difference in 80mw vs probably 125mw. To really make a improvement, it would have needed a more robust audio transformer and a lot more battery power. I decided a LM386 audio module was far more practical.

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 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Sat 05, 2019 3:47 am 
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I meant to say that there can be more than one tube in a single envelope like a diode/triode where a transistor there will always be only one triode. there are no diode/triode transistors that I know of :?


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 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Sat 05, 2019 5:00 am 
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tubeAMP wrote:
I meant to say that there can be more than one tube in a single envelope

The same can be said for some Transistors. In the case of the converter function in an AM radio as one example, both mixer and oscillator functions can be performed by but one Transistor, the same as a lone tube does.

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 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Sat 05, 2019 2:08 pm 
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for instance a four tube plus power rectifier would actually be six tubes using dual tubes. there are no dual transistors so there would be six transistors using the same circuit one transistor as diode


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 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Sat 05, 2019 8:39 pm 
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Actually using a Transistor in place of a Diode for the detector didn't really come into play until the cost of Transistors (obviously) became cheaper than Diodes. The standard six Transistor Superhet used one for the converter/osc, two for IF amps, one for the audio driver, and two for a push-pull output. A diode would have additionally been employed as the detector.

I will grant you that the tube doing dual functions as detector and first audio couldn't be matched by any single Transistor; two solid state devices were needed for those functions.

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 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Sun 06, 2019 3:20 pm 
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all true :|


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 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Wed 09, 2019 1:28 am 
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Location: Sacramento, CA
Deadshort wrote:
Thanks so much guys! I went ahead and took a chance with the 2n3906. Works and sounds great now.

My hats off to ya'll...you just rescued another one!

I'm guessing the originals were germanium. When you installed the 2N3906's did you do any other circuit modifications?


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 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Sun 13, 2019 3:36 am 
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I've been wondering the same thing Bob !

Sounds like he used the good germanium original paired with the silicon 2N3906 replacement...

John


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 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Sun 13, 2019 10:27 pm 
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xrhonda91 wrote:
I've been wondering the same thing Bob !

Sounds like he used the good germanium original paired with the silicon 2N3906 replacement...

John

If it does have both Ge & Si transistors installed and steps were not taken ballance current, radio is most likely operating on the Ge transistor only. That sounds bad enough but actually one operating transistor sounds better than a pair in PP that are badly out of balance. The .15 - .2v B-E differential required for Ge is not enough to operate a Si transistor.

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