: Transistors and substitutions  ( 805 )

Motorola Minion

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Transistors and substitutions
« : April 30, 2021, 03:39:30 PM »
By 1968, solid state equipment manufacturers "transitioned" from using Germanium to Silicon devices. As a result, DeOxit, new caps and an occasional resistor are on hand for any solid state repair of non-IC stuff.

This silicon was found even in most common equipment by the 70s, making repairs on older and cheaper solid state stuff (Silvertone, Airline, etc) dicey at best. I learned the hard way by recapping some easy-appearing ones and barely improving the crappy sound. Lastly, it was not worth replacing all of them if not one or two defective transistors.

But some older Germanium transistors still perform such as the RCA-made devices Zenith and Magnavox also used, making a recap generally a slam-dunk.

I think most of us here favor tubes and will dive with confidence into any repair on tube equipment ;D

But having said that, I welcome your opinions and experiences on this matter.
Tubes - Magical - Tubes

Dave

Bill

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Transistors and substitutions
« #1 : May 01, 2021, 08:05:37 AM »
As for me, I have avoided SS stuff like the plague.  Not sure why, maybe because I'm still trying to learn tube stuff.  I think what really scares me is the PC boards and all those tiny little solder joints.  Maybe someday!

Bill

TJ

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Transistors and substitutions
« #2 : May 02, 2021, 10:50:07 AM »
The 1964 Astrosonic that I recently redid sounds great, all germanium, and needed a full recap. 

The 1969 Zenith Z906, all silicon, full recap, likes to blow the output transistors...  Everything checks out correctly, I'm guessing there is a short somewhere that is over biassing the transistors. I've given up on it. 

My two mid '70s receivers that I have both had transistor issues, the Pioneer SX-750 has a 2-in-1 transistor that notoriously likes to fail, and there is no easy replacement. I was able to find a working pull on ebay. The Kenwood Kr-7600 had a bad filter cap and a bad bridge rectifier.  Both receivers got a full recap and sound great. 

For me, the tube equipment is much easier to fix, straight forward, easier to find parts for.  I dread older solid state equipment that is listed as not working as theres always the chance of a bad, unobtainable transistor...
My Consoles:
1962 Motorola SK112CW-FM, All original tubes
1958 Magnavox Continental - DIY Concert Grand!
1957 Magnavox Brittany - Amp 148 Magic!

Bill

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Transistors and substitutions
« #3 : May 02, 2021, 04:05:48 PM »
That's good news on your Astrosonic Trevor.  We all like to hear success stories and one of these days I will write about what I have been up too and how it all came out.   

Bill

Motorola Minion

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Transistors and substitutions
« #4 : May 02, 2021, 06:35:01 PM »
I agree that SS can be a royal PITA when looking for transistors.

Whenever a Magnavox has transistor issues, its not too hard to figure out. The circuits are very conventional and of course, not complicated like direct-coupled stages of Japanese high end units.

My Dynaco ST-120, QS-300 and SCA-80 are not simple but they are easy to work on and not very fussy about replacement parts.
Tubes - Magical - Tubes

Dave

firedome

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Transistors and substitutions
« #5 : May 03, 2021, 01:37:36 PM »
While I've always prefered tubes I'm learning to like more and more SS stuff, plus it's far more available now. Scott for one I believe skipped the Germanium stage altogether and went directly to Silicon from what I've read. My '68-ish Scott 382 is Silicon based and still sounds great with no restoration. With my stiff hands and fingers and terrible eyesight these days I don't work on much of anything anymore anyhow! I have been impressed by some Maggie SS stuff as well!
Happy Motoring! from Roger in NY

Motorola Minion

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Transistors and substitutions
« #6 : May 03, 2021, 03:03:24 PM »
The next SS unit to be tackled is that 67 Fisher Custom Electra E-492-CF http://www.fisherconsoles.com/custom%20electra%20e492.html

It was a free CL find about 5 years ago and, with have no fear of powering-up SS equipment as found, it was dead and I stopped there. I kept it around because the cabinet is "Country French", not excessively styled cabinet and has doors.

The 21R chassis in it is all-in-one and I sure hope the transistors are good. I have a spare 31R chassis and lots of experience with Dual 1009 record changers.
Tubes - Magical - Tubes

Dave

Bill

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Transistors and substitutions
« #7 : May 04, 2021, 09:20:43 AM »
There was a Fisher console stereo that I spotted in an Estate sale website last week.  I went to the Fisher site and tried to find the cabinet that was pictured in the estate sale.  No luck!  It had the SS receiver look to it and the changer was either Miracord or Dual.  I have trouble telling those two apart in a poor photo.  The cabinet was beautiful, and by its looks I would say this was an upper end model.  I should have went but instead I worked on a few projects at home. 

Bill


hermitcrab

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Transistors and substitutions
« #8 : May 16, 2021, 12:38:40 PM »
I think the maggie astrosonic would get my vote as one of the easiest sets to learn about solid state on.... nothing is tight or crowded together , the circuit is pretty basic , the design lets you power the set up on the bench ...and you can still get germaniums although pricey.... and they do sound great when working as they should.   
Elton

TC Chris

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Transistors and substitutions
« #9 : May 17, 2021, 02:26:41 PM »
What's the best source for obsolete transistors? 

I've been spending weekends in "no internet" locations and only catch up when I visit people with wi-fi. This is an interesting thread. One of these days I'll try to rescue my boss's Astrosonic. The big gripe seems to be the pots and that's the problem with hers.

Chris Campbell

firedome

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« #10 : July 11, 2021, 09:42:11 AM »
I recently found an Astrosonic R231-10 receiver my uncle had sitting on his workbench. I'm wondering if I'll be able to find output transistors if it needs them.
Happy Motoring! from Roger in NY

Motorola Minion

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Transistors and substitutions
« #11 : July 11, 2021, 10:05:03 AM »
What's the best source for obsolete transistors? 

I've been spending weekends in "no internet" locations and only catch up when I visit people with wi-fi. This is an interesting thread. One of these days I'll try to rescue my boss's Astrosonic. The big gripe seems to be the pots and that's the problem with hers.

Chris Campbell

The NTE (Nu-Tone electronics used to be ECG) of replacements are generic and with transistors, so I can get anything really. Telefunken-made transistors in a SABA tv Im working on has an equivalent from NTE but I did a reverse-cross and found a Zenith transistor also in the same basic configuration NPN and TO -220 package.

Shang066 has a video where he is working on an SS amp chassis from a Packard-Bell RPC-56 (?) that is a near copy of all US manufacturer's circuits. This is mainly due to transistor specs that define design, as a minimum. The Germanium transistors' failure mode is well-documented in this video.

Im not sure when every manufacturer went to silicon but that is the best replacement, provided the bias and load resistors are re-evaluated as Shango did.https://www.youtube.com/watch?v=HeBRG8GIuAY
Tubes - Magical - Tubes

Dave

firedome

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Transistors and substitutions
« #12 : July 14, 2021, 01:22:11 PM »
I wasn't aware that a Germanium xstr could be replaced by Silicon, would that be the case with a
Maggie R231-10 SS chassis?
Happy Motoring! from Roger in NY