Basics with transistors: Can I stack in series to combine Hfe?

[gcme93]

Question is pretty much in the title, I'm looking to build a Trotsky Overdrive, but would like to use a fancy Germanium Transistor.

They're hard to get hold of here in the UK so I was going to go for this pair: http://www.doctortweek.co.uk/shop/article_231/Transistor-AC176-NPN-Germanium-(Pair).html?sessid=VVLhzAG4lbjDXa0K5sptBSU0owu6qClenfLNShYu6Hmx2ghlp2HCmaFIkAz1TvoJ&shop_param=cid%3D38%26aid%3D231%26

They have an Hfe of between 50 - 180, and I've heard Trotsky needs at least 200 to get some good overdrive going?

Can I just stack up the pair? I'm thinking this would multiply the gain, not add them 

Thanks a lot in advance

[defaced]

Sounds like you are describing a Darlington Pair.  http://en.wikipedia.org/wiki/Darlington_transistor

[gcme93]

I thought I'd heard about that combo and a special name for it!

Okay, I understand all that, very straight forward - and probably should have been more obvious in the first place.

I think honestly, I'm just going to have to go silicon with a 2N3904, because it's not worth the effort to get a germanium work around. It would double the size of the circuit anyway :/

Thanks for your help!

[defaced]

You're welcome.  Best of luck with your build. 

[gcme93]

Hi again all,

Just a last question on this topic, as Im a little gutted to miss out on some germanium fun.

The Trotsky overdrive schematic calls for a KT312 (its Russian) which has this data sheet:

http://www.5v.ru/ds/trnz/kt312.htm

The data sheet is also Russian but my cunning skills tell me the only column beginning with an 'h' is the Hfe ranges. Do I assume that Beavis audio uses the B spec ones that have higher Hfe, because otherwise I don't see much of a difference between that and the Ac176. The build guide certainly doesn't specify the B spec and suggests a 'low gain NPN transistor'.

Thanks a lot for any comments

George

[Thecomedian]

Try looking for data sheet at datasheetarchives or something that has listings of PDFs of all the transistors in a "series". Those will be in english. It's basically bare white sheets with numbers and model IDs, and no pictures or anything.

From what I have seen looking at MP25's, The original is very low gain, the A is double, and the B is double to triple the gain of the A. So, it likely works the same for the ones you're looking at. Check to be sure.

The data archive should be a pretty much blank white looking affair that has PDF files to download from S1 and S2 servers.

[gcme93]

Really don't think theres much point in checking out the best russian part: the only thing I can get hold of here is the AC1... series but I took your advice and did some spec checking: http://pdf1.alldatasheet.com/datasheet-pdf/view/131448/ETC1/AC141.html

It seems that the two best alternatives are the AC187 (hfe 100-500, might be a little high) and the AC176 (hfe 50-250, a bit more like it).  I guess I'll just get both because they're cheap enough and what's the point in DIY if you don't try a few alternatives right? If the AC187 roars, I might find another application for it (I'm only after a smooth overdrive, not a chainsaw)

Thanks a lot for the advice!