Anyone had any success with making a Rangemaster using an AC128 ?? just that I happen to have 4 lying about and wondered if they would work in that situation providing that there within the correct gain parameters and not too leaky.

Quote... wondered if they would work in that situation providing that there within the correct gain parameters and not too leaky.

Sure - if they have the right gain and are not too leaky, they ought to work. They may be noisy, but there's only one way to find that out.

Thanks RG but isn't it true to say that most Ge transistors are noisy ? and that following the technology of the rangemaster and using metal film resistors should help somewhat with regard too reducing the noise, I had a Rangemaster in the late 60's and early 70's and yes it sure could be noisy.

Quoteisn't it true to say that most Ge transistors are noisy ?

Yep. Germanium was humanity's starter semiconductor material.

Germanium transistors were made by methods that now seem unbelievably crude, essentially garage-shop methods. That was before humans found out about noise from surface contamination and glass passivation (I'm not even sure there is a good equivalent to glass passivation in germanium) to avoid it, clean rooms, and all the junk we now use to make silicon - and all the junk that makes a new silicon fab cost over $10 billion before you turn out your first wafer. Sigh... those were the days...

Anyway, germanium processing was our learner material, and processing got better as we went along. The earlier a germanium device was made, the more likely it is that it's leaky, noisy, low gain, and generally barely useful. The problem with AC128's is that they were a medium-early device as originally made, but there are some places making them now - or at least recently. Whether the ones you have are recent or old, and whether recent new ones were made with care or just slopped together is something that can only be told by whopping them into a circuit.

Quotefollowing the technology of the rangemaster and using metal film resistors should help somewhat with regard too reducing the noise,

It will keep the resistor part of the noise down, but it can't cover up a noisy transistor. Metal films just don't make it worse.

Thanks again RG for the info,  I haven't had these AC128's that long perhaps about 2 years or so, they were purchased from Maplin before they ran out of stock so in truth I haven't a clue as to there overall value, I also wondered if going the Si road and perhaps using the Piggyback method would result in a quieter unit but I have concerns as to whether this method would produce results in keeping with what one hopes to achieve with Ge.

Yeah - like I said, try it out! It is also possible that one of them is pure gold for the application.

oBVIOUSLY DON'T FORGET TO SOCKET THE Q