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Transistors (ugly ones) for more research


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1/3/2005 1:54 AM
Glenn
Transistors (ugly ones) for more research
Hey guys/gurus!  
 
I'd like to do some more research on the tube vs. SS debate, and needed some pointers. Could you guys name some transistors (model/manf) that would/could/should/have been used in guitar amplifiers that are either:  
1) nice & ugly or typify the transistor 'sound'  
2) ones that actually sound decent/passable  
3) some plain ole butt-ugly, nasally, honky, no-bottom at all, could dish out the power but should never have been used transistors? TIA!  
I should be able to post my results after I build a few test amps from these transistors.  
Glenn  
 
P.S. Any pointers on bldg a transistor amp (I haven't a clue, LOL). There are some schems floating around the 'net, so any schems that could accomodate the most types in a rather neutral way would be super-hip.
 
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1/3/2005 10:16 AM
Wild Bill

Glenn, I don't think it works that way!  
 
I could stand to be corrected but IMHO the physics of transistors and their circuitry is such that you don't get tonal variations like with brands of tubes. You can get more or less noise and different transistors have different voltage/gain/current ratings, of course. IC's are more complicated but the only thing I've ever known about tone variations is the famous JRC4558D used in the original tube screamer, where the old chips distorted in a more pleasing manner than those of modern manufacture.  
 
Transistors are just too linear! They amplify clean until they hit their limit and then get fuzzy very abruptly. There's almost no slope to the degree of distortion.  
 
You could get some differences between bipolar types and power FETS, I suppose. The circuitry involved is different so you've got more skull sweat ahead of you - you won't be able to just swap transistors as easily as you can swap a tube.  
 
You might have an interesting experiment underway but when you're all done - tubes will still rule! :)  
 
---Wild Bill
 
1/3/2005 10:34 AM
Glenn

Thanks for the rapid reply, and tubes will still rule the roost until something else comes along...  
 
I wasn't fishing for subtle nuances, just a greenhorn looking for (hopefully) a couple examples of really 'nice' and some really 'bad' sounding transistors (in any cct. at any operating point) that are more/less common to MI amps. I don't know scratch about transistors and the possibilities are endless, so I was hoping I could get steered into a more fruitful direction. I guess, for 'bad' transistors I mean ones that have low headroom and have a nasty dist. at that (i.e. break-up quick & hienously; forum consensus aside LOL). TIA!  
 
R. Glenn
 
1/3/2005 4:07 PM
Enzo

From a repair tech point of view, I can tell you that transistor circuits often as not don't care what you stick in there. They are VEEEEEERY forgiving of substitutions. It almost never matters. In higher gain circuits or low signal level circuits, I wuill usually opt for a low noise part, but other than the noise factor, they all sound alike.  
 
The small TO92 USA types are EBC across the front, while the Jap parts are ECB. I chose the nationality based on the leg pattern I want. Then there are the voltage and current specs.  
 
Those are for the preamp stuff. If you want to build a SS power amp, at this point I would seriously consider a chip. The little TDA2040 works fine for small amps, and the TDA7293 puts out quite a few clean watts if you want big. Those are used in Marshall AVT series amps and SPirit Power Stations among other places.
 
1/3/2005 6:44 PM
Glenn

Thanks Enzo!  
 
I'll look into the transistors you've mentioned. Thanks a lot. :)  
 
Glenn
 
1/3/2005 10:00 PM
Enzo

Those were ICs. For US xstrs for small signal use, you can't really go wrong with general purpose types 2N3904/3906 or 2N4401/4403. Low noise types might suggest 2N4124/2N5088/MPS8097 and 2N4126/2N5087.  
 
Jap numbers try 2SC945/2SC1815 and 2SA733/2SA1015
 
1/3/2005 10:34 PM
Steve A.

Enzo said:  
 
From a repair tech point of view, I can tell you that transistor circuits often as not don't care what you stick in there. They are VEEEEEERY forgiving of substitutions.  
 
    That may be true for guitar amps but for tuned radio circuits the gain can be very critical. When I worked in the parts dept of Pacific Stereo 30+ years ago, the various vendors would typically put colored dots on the transistors used in front ends, etc., to indicate the gain factor (or other parameter). So it wasn't good enough to put in a 2SC945- they wanted you to match the color dots as well! (I do think that the ace techs could recalibrate the circuit to work with whatever parts they had at hand.)  
 
    But the transistors in the power amp section were much less critical- if you changed them all out you could pretty much use any decent variety. (Or so the service techs told me... I was just the parts guy!)  
 
--Thanks!  
 
Steve "Transistor Steve" Ahola
 

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