Old hearing aid transistors

[MarkALeuchter]

I'm wondering if anybody has experience with the tiny Mullard OC-59 or Raytheon mini germanium transistors used in old hearing aids for fuzz or even rangemaster applications.  Such small devices strike me as ideal for tight builds, but I've never seen any discussion about them as viable Ge devices for these purposes.

[PRR]

In a 9V world, these 7V transistors are close to breakdown. Yes, you will bias them far below 9V but big (distorted, clipped) signals will still hit the rail. On modern stuff with a few hundred Ohms of resistance in the circuit, breakdown may not be instant-death; but these matchstick-head parts have a very-very low dissipation limit: 10mW (compare to 300-750mW on modern jellybeans). And repeated breakdown on non-passivated semiconductor tends to open surface-states which fill up with hiss. (Not a rigorous explanation....)

"Rausshzahl .. 10dB" is a noise figure, good for the time but any transistor today does better. Remember these parts were sold to DEAF people who had not heard the wind in the trees in years, and would not notice hiss well above theoretical.

And "tight builds"- I've never seen the transistors be a large part of a build. It's usually jacks, caps, pots. And a guitarist can't work a fuzz smaller than a toe?

And they are $5? (I remember paying $7 for the rejects from the hearing aid trade, back when $7 was real money, two tanks of gasoline.)

The hearing aid schematic needs only small mods to be a fuzz. An AA cell hardly need a power switch.

[antonis]

Could OP find 50mW resistors other than SMD for RF applications..?

[amptramp]

Heathkit had a fuzz that ran on one 1.5 volt battery, so I suppose you could make a fuzz from these old transistors.  Frankly, I am surprised we don't get a lot more low-voltage designs.  9V batteries are getting expensive now and with a fuzz, exceeding the dynamic range of the amplifier is how a fuzz works.

[duck_arse]

https://www.diystompboxes.com/smfforum/index.php?topic=102619.0

different to mine.

[Elektrojänis]

Hearing Aid Fuzz: When you really need to cut through to everyone!

[amptramp]

Let's go back even further.  There were complete three-stage pentode amplifiers made for hearing aids but also for some portable equipment like wire recorders.  Some of these used the Ampec PC-201 amplifier you could buy in 1954 for $22.50.  This article is about a wire recorder (suitable for a delay like a flanger or chorus if you make the recorder one continuous loop with a variable speed motor or variable position heads) that was built using one of these devices:

https://vintage-technics.ru/Eng-Mohawk_midgetape_44.htm

In the middle of this page, you will see a tube amplifier that used two CK512AX and one CK525AX tubes but other tubes were used as well.  Some tubes had 0.625 volt filaments at 30 mA so you could run two in series from a 1.25 volt NiMH cell.  A 22 volt B battery was used as well and this could be made from a stack of lithium coin cells.

[PRR]

Could OP find 50mW resistors other than SMD for RF applications..?

Why? It will play fine with 1/2W or 3W parts. Bulky, but he's not trying to stick it in his ear (I assume) or even in a very chunky eye-glasses frame or pocket-box (how they did HAs then).


However HA makers have been in a forefront of miniature parts since the beginning. (Even before vacuum tubes.)

[antonis]

Could OP find 50mW resistors other than SMD for RF applications..?

Why? It will play fine with 1/2W or 3W parts.

I was just kidding for original scheme resistor wattage..