Need New Transistors For An Old Magnavox Receiver - Help

[Ozric]

I am trying to repair an old Magnavox (mid to late sixty’s) stereo receiver for a family member. It seems that some of the output transistors have gone bad. The transistors in question were made by Bendix and are labeled 68P1K – 6719W. Does anybody know where I can source a set of these ? Is there any other transistor still available that would be a good substitute ? This receiver is not the greatest thing world, but it has sentimental value to them as it belongs to their father. Any help with this would be much appreciated. Thanks.

 

[mbz]

It seems that some of the output transistors have gone bad.

You confirmed this by diode test? Or voltage measurement?

 

[Ozric]

The unit has one channel dead. I confirmed by switching them from one side to the other side, the problem moved with the transistors. One can only assume that one set is bad. I have no other means of testing them.

 

[cademan]

You should really get yourself a simple volt/ohm meter especially if you are going to be doing this sort of stuff for other people. Also, make sure that if you do get new transistors for the bum channel that there are no other transistors shorted like the drivers that sometimes get taken out by a shorted output transistor.

I think I might have one or two of those from stripped Magnavox units from the past.

 

[cademan]

Sorry, I don't have any spares. The one's I do have are in my working Magnavox amplifier from an old suit case record player. Of course this amp is not very powerful. It is only about 3 to 5 watt output per channel.

 

[petehall347]

am thinking they might be germanium . easily found out from diode testing the good ones .

 

[OMGCat!]

Are those T03 style or are they the smaller package that look like T03?
If they are the smaller ones I have some gm outputs from a parted amp that would likely work. I don't remember the PN but I can go look if the ones you need are the smaller package.

Also, definitely read up on transistor checking. It sounds like you've isolated the problem by moving them to the other channel but there are times where other bad components can damage your subs and then you're out even more parts.
Either way, learning will be helpful if you are going to pursue this type of work. I don't bother with a multi-meter and just use one of those cheapo testers from eBay. They do the job nicely.

 

[avionic]

smaller package that look like T03?

TO-66

 

[cademan]

These Bendix are TO-3's. I also have the smaller TO-66 styles in my stash.

 

[avionic]

Germanium.. Crosses to and ECG/NTE 121.

 

[avionic]

Germanium.. Crosses to and ECG/NTE 121.

From and old 1980 Sylvania ECG cross reference manual.

 

[gslikker]

If you do not have a schematic: your circuit MIGHT LOOK LIKE the one one left bottom corner of page 25 of following document.
You can try to draw the actual circuit yourself.
Depending on the total voltage on the amp, you may try to "guess" a generic replacement and ask around for such generic Germanium amplifier output transistors.
This book has a lot of Germanium transistor information.

http://n4trb.com/AmateurRadio/SemiconductorHistory/RCA_Transistors_and_Semiconductor_Diodes_1957.pdf

 

[OMGCat!]

You could also rebias for Si outputs as they are far easier/less expensive to get hold of these days. It's not super complicated, just takes a bit of math and/or trial and error.

 

[Pete B]

Are those two numbers PNP and NPN or do you have the specs for them?
I have some old TO3 Germaniums that might work.