advice on substitute transistors.

[Fredrik 1977]

hi all!
sitting here with a receiver and apparantly one output has some gremlins living in it.
sometimes it works some times its full DC and sometimes just very noisy

the amp has 2N3055 NPN silicon, and AU103 PNP Germanium.
strange choise indeed!

one VALVO AU103 is pulled at the moment and tested bad. but sometimes it tests good

so the question would be. what to replace it with?

3055 and 103 is nowhere near eachother when looking at the datasheets.

 

[eiraved]

It looks like NTE127 can be used in place the AU103.

 

[OMGCat!]

I wonder if it's got the tin whiskers inside causing shorts.

There are some videos on using Russian germanium transistors as subs since they are far less expensive than what's available these days through normal channels. You could also rebias for silicon.

 

[Fredrik 1977]

I will probably get something available (Read silicon)
The schematic is in this post.

http://audiokarma.org/forums/index.php?threads/kirksaeter-rtx-400-in-need-of-tlc.811602/

 

[Tom B]

What type and model amplifier is this?
I know that Electro Voice had used 2N3055's in some of the amps/receivers, and they used some PNP Germanium T03 outputs in others, but never saw them using both. Both were usually high current but lower voltage devices. I may be able to tell you where you can get some 2N3055 and PNP Germanium outputs if you can tell me the make/model and approx power out (even if its just the watts consumed on the nameplate)

 

[Fredrik 1977]

Its a Kirksaeter rtx-400 receiver.

3055 are still sold but i dont think these are bad. But something is going on inside those AU103

 

[Goldie99]

Hi Frederik - you can still get NOS AU103 if you want to try changing them (not eBay). Will pm you details later.

 

[Fredrik 1977]

I wonder if it's got the tin whiskers inside causing shorts

I will open it and have a look

 

[gslikker]

sure it is AU103 not AL103??? AL103 seems more logical

 

[Fredrik 1977]

They are AU103. And it doesnt make sens to me either. Maybe some 60's era SS guru can explain why its designed this way?

 

[gslikker]

Just a matter of cost, I think. I have seen it before in DIY examples, too.
The AU103 is low watt, high voltage and fast, AL103 or AD149 were much more common in amps.

 

[Goldie99]

There's a bit more here - but from what I can see, cost & possibly reliability seem the most likely - https://www.vintage-radio.net/forum/showthread.php?t=109590

 

[Fredrik 1977]

3055 and au103 aint exacly a matching pair.

But ok i see what you guys mean.

 

[gslikker]

A real total class B schematic..from 1965..Maybe just use a silicon PNP transistor and maybe also forget about the BA127 diode. The BA127 is 1 amp only, btw.

 

[OMGCat!]

A real class B schematic.....it seems rather vulnerable. Maybe just use a silicon PNP transistor and forget about the BA127 diode.

That's what I was thinking as well. Seems like it's a straightforward class B design except the diode to drop the bias on the Ge device. There probably weren't suitable Si devices available at the time for a price that worked or they had a warehouse full of the old Ge stuff and needed to get them out the door.

Put it together with an Si device with the diode removed and run it on a scope, if the wave form looks good then you're good to go.

 

[gslikker]

I just see some datasheet the 10W is at 25 degrees free air, maybe I have some better datasheet somewhere in a philips/siemens pdf....since on the same page an AD149 is listed as 3.5 watts while it is more.
If a silicon PNP does not do the job, I found a NOS AU103 already....
funny, the 2n3055 old hometaxial was 1 MHz ft but the Germanium one is much faster.

Note if you can read German language: at this forum info http://www.military-tubes.com/forum/forum/mix_entry.php?id=152624 the poster states having his germanium one replaced by silicon also.

 

[Fredrik 1977]

thanks all for the input!

so if i try this replacing with silicon what specs am i looking for the specs of AU103 or the 3055, A PNP 3055 so to speak?

 

[gslikker]

thanks all for the input!

so if i try this replacing with silicon what specs am i looking for the specs of AU103 or the 3055, A PNP 3055 so to speak?

complement of 2n3055 is MJ2955 and widely available (Mouser has Central Semiconductor ones, cheaper than ON ).
I would leave the old 2N3055's in.

 

[Fredrik 1977]

ok i´ll try those out and report back will check the pinout pre-order.
btw the BA127 Diode isnt in the circuit in the receiver. as in never mounted

 

[Fredrik 1977]

ok i got those MJ2955 now, but before i start i´d like to verify the pinout they are the same right, just so i dont go blowing up the speakers