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Transistors for SS Vox

5/22/2003 3:06 AM
Tim Gagan
Transistors for SS Vox
Anybody know the modern equivalents for these transistors in a Vox Kensington?  
5/22/2003 3:48 AM
Dai Hirokawa

Looked like the same sort of code. Only saw one tho'. Maybe they know what the equiv.s are?
5/22/2003 7:03 AM

Those are house numbers. The first two digits indicated the type component. What the actual underlying part is I couldn't tell you, but unless you are restoring one to absolute original condition, you will be subbing parts anyway. Although if you know an old organ repairman, his Thomas Organ stock may include some of these numbers  
The 5044 is used in small signal circuits like the input channels and stuff. It is NPN silicon. I am thinking you have about a 20 volt rail here, so most any 40 volt xstr will work. I would use a 2N3904 or a 2N4401. Or I might use a low noise type - I forget what I stock in those types. NTE crosses it to their 123APm which is their most used general small xstr. At 600ma and 75 volts, it is maybe more than you need, but it would work too.  
The 5050 also crosses to NTE 123AP. NPN ssilicon. It looks to be used as a predriver, but I am looking at other models than yours - don't have your schemo. Here I might prefer the 2N4401 or maybe an MPSA06 for their slightly heftier specs than the 2N3904. The circuits I looked at ran the drive on a 27 volt supply. Yours is probably similar.  
Those two may be metal types, but the ordinary TO92 size plastic will be fine.  
The 5075 I saw used as a reverb driver. NPN silicon. The reverb was transformer driven a la Fender. The transistor drives the transformer. A bit more current therefore. NTE crosses it to their 192, which is a 1 amp 70 volt part, and it will dissipate almost a full watt. I would determine my sub based partly on the package of the existing xstr. TO39 cans will dissipate up to 5 watts easily if they have to, and I keep numerous ones in stock, but you probably don't, so NTE is as good as anyhting I suppose. I might even try a TO126 or TO220 before I went that route though. I am not an NTE fan.  
Lastly, the 5043 crosses in NTE to their 121. This is a Germanium power xstr and is PNP in a TO3 case. That would mean it was your output xstr. Does that sound like what you have? The cross is a 5 amp 60 volt device. I have no schemos using this part. The Nte, ECG, SK guys are about the only place to find germanium xstrs anymore and you may have to look around to find them in stock. I have not bought them in a decade. Old Fender Rhodes Piano amps had germanium, but we routinely converted them to silicon when they needed new xstrs. You could do that to your amp by a few component value changes. You got transformer drive output stage?  
That's the best I can do, hope it helps.
5/22/2003 3:53 PM
Tim Gagan

Thanks guys. That's some pretty good deducing, Enzo, about where in the circuit each of these transistors appear. The Kensington does have a transformer output stage, with the 5075 driving the transformer and the 5043's after the transformer, driving the speakers.  
The Kensington in my care is apparently making some horrendous noise; I haven't done any troubleshooting yet, but I wanted to get the jump on the transistor numbers in case any of them need to be replaced. Looks like you've given me plenty to go on, thanks!  
5/22/2003 7:31 PM
Did you read good the stuff At Geofex?
5/22/2003 9:22 PM
Tim Gagan

>Did you read good the stuff At Geofex?  
How would I find it?
5/26/2003 10:16 PM
I hope that was rhetorical... 8-)  
It's under "Bulletproofing your Thomas Vox Amplifier" look at, it's in the lower left hand corner.  
I replace all the plastic small signal devices in TV amps with 2N5088. They're quieter than the stock ones.  
If the amp has not been re-capped, get the owner's approval and re-cap it. If you don't, likely one will go bad a week after you send it home.  
I have some TO3 subs for the germanium outputs if you get in a bind, but read the section on converting to silicon. All you have to to is plop in PNP silicons and mod the biasing string. The article points you to it.  
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