AF germanium transistors - Uses in DIY?

Hi,
I have a lot of  AF Germanium transistors different number types.

The AF transistors are Germanium small-signal RF (Radio Frequency) transistors while the AC type (like the common AC128) are Germanium small-signal AF (Audio Frequency) transistors.

I would like to ask you DIYwize for the type of projects we do around here what could be the uses for the AF transistors?

I build guitar pedals and fuzz boxes, normally with the AC types,
could I also use the AF types also for those duties?
Are any limitation of those transistors that could not make them useful for Audio Frequency type projects?

Thanks

Try them in a Fuzz Face!

Tekay said:

Try them in a Fuzz Face!

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have you tried it?

any experiences with Af type transistors you could share?

thank you so much

Get a Peak DCA55 so you can test them and know the pinout and gain plus leakage (not neccesary but better than flying blind) And build any old fuzz pedal or otherwise that used Ge's. Brand or whatnot is not important. Most of those circuits will work with a very wide variety if you use trimmers to set the gain.

Wildfara said:

Get a Peak DCA55 so you can test them and know the pinout and gain plus leakage (not neccesary but better than flying blind) And build any old fuzz pedal or otherwise that used Ge's. Brand or whatnot is not important. Most of those circuits will work with a very wide variety if you use trimmers to set the gain.

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Hi wildfara. I have the Peak DCA75 and also the MK328 tester. Testing is no problem and I would build some units in the future for sure, but for now
I just wanted to learn some theory and knowledge on what might be the shortcomings of using them in Audio Frequency units and the type of units we do here and in guitar pedals forums.
What are the general differences of an AF transistor to an AC type, what are the shortcomings, the limitations, what could one expect or have in mind when using an AF type?

Thanks you so much

Build the circuit using sockets (I would anyway) And try them!

In general I would just bin them, but their different (smaller) Vbe might be interesting for guitar distortion efx.

JR

Since their gain is probably pretty low, you can form Darlingtons if their leakage is low enough.

JohnRoberts said:

In general I would just bin them, but their different (smaller) Vbe might be interesting for guitar distortion efx.

JR

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Thanks JR.

Any other specs I should take into account that could be limiting or interesting?

> I would just bin them

FYI: Ge parts are in HIGH demand for some odd purposes. Scrap barrels from old inventory is getting re-re-re-tested and sold for high prices.

> a lot of  AF Germanium

Just tune your guitar 30 Octaves higher.

Don't talk-test. Socket a FuzzFace and try them. Real-world answers much faster.

When new, the "RF" parts cost a dime more because they would give some gain at 1MHz. But the majority of these were sorted-out from crude Ge production batches with huge spread of parameters, from useless to pretty OK (like when I make cookies).

There may have been different specs on capacitance and leakage, but the spreads were large and good Ge design is not critical (even the FF makes some attempt to handle different parameters).

Just do it.

PRR said:

There may have been different specs on capacitance and leakage, but the spreads were large and good Ge design is not critical (even the FF makes some attempt to handle different parameters).

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Yes, I was reading that also.

Capacitance on AF types seem to be generally much lower than AC types

midwayfair said:

Since their gain is probably pretty low, you can form Darlingtons if their leakage is low enough.

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You coild also use the Ge’s that have hfe values too low for the Fuzz Face circuit for a Rangemaster. That circuit seems to do better with hfe values in the 50s to 70s. At least in my experience.

BT

rackmonkey said:

You coild also use the Ge’s that have hfe values too low for the Fuzz Face circuit for a Rangemaster. That circuit seems to do better with hfe values in the 50s to 70s. At least in my experience.

BT

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I was assuming these might be much lower, something around 20-40, which is really too low to do that much for one or two stages.

I do 50-80 for pretty much all my fuzzes.

I have several layouts/schematics on my site for variants of classics that are designed around slightly lower gains, like 50-60 if the op is interested, but there's no shortage of fuzzes in the world.