Rangemaster - Modern germanium transitor equivalents?

[J M Fahey]

Fine with me.

[Steve Conner]

Yes, I agree too...

I have one question though. What do you mean by "the EF86 sound"? Surely it is very easy to emulate it with tubes, by using an EF86

It would be interesting to see whether the grit comes from non-linear Miller capacitance. That could be simulated by putting a large diode (1N4001) from base to collector of a silicon transistor.

[kleuck]

Because a Germanium transistor used as in the RM makes the same kind of harmonics ratio than a hard-driven preamp pentode like the FE86.
And i wanted to say "if you want to get rid of the EF86 microphony by using some other tubes, it's not an easy task to emulate its sound"
If you heard at my sound sample, you know that even with a Ge transistor, it's not easy to emulate the true RM/Beano sound.
If you design a modern circuit, with less issues (impedance, stability), it doesn't sound the same.
Perhaps is it in close relation with the exact transistor though, i do not have OC44 yet, so i tried only OC75, AC128, SFT323 yet.
Pentodes have a low Miller effect Miller Capacitance

[Steve Conner]

OK, well the way to fix that is to use only NOS Mullard EF86s on rubber shock mounts. Works for me.

I know EF86s have low Miller capacitance, and that's what makes them sound bright. I'm suggesting that germanium transistors have a bad frequency response because they have extremely high Miller capacitance. If that capacitance were non-linear with voltage, that would be a source of distortion. I'm saying that is maybe the "grit" you're looking for, and it could be simulated by taking a device with a large, non-linear capacitance and putting it from base to collector of a modern transistor.

Since large diodes leak a lot, it would also give authentic vintage bias drift with temperature.

The low input impedance is an important part of the sound, as with the Fuzz Face. But any low gain transistor will have that low input impedance.

[J M Fahey]

If you want a *large* and *voltage modulated" collector to base capacitance, look no further than a BB104 or some from that family.
It might provide true grit even on an Op Amp.
Ooops !! I did it again. Sorry.
You can me if that pleases the Gods.

[Steve Conner]

Wow, it goes up to something like 30pF, I think that would be overkill.

The OC44 has a Ft of 6-15MHz, so that kind of kills my hypothesis.

[tubeswell]

Yay! I scored a NOS Mullard OC44 for NZ$25 - more fool me I s'pose.

http://images.trademe.co.nz/photoser.../163002806.jpg

[Alex R]

Phillips Miniwatt NOS EF86 are low-microphonics too ime, and cheaper than Mullards. (@ Steve)

[tubeswell]

Double yay! My (very expensive) Mullard OC44 arrived in the post today (and I feel like a tin-arse). How do I test it in my multi meter? - I have a Digitech N287 meter with a socket with 'E' 'B' 'C' and 'E' holes for NPN and for PNP, but which lead is which on the transistor? There is a red dot on one side (and a yellow dot on the top)

[J M Fahey]

Well, you can hook it to a 300V, 15A Lab PSU in certain way, and if it doesn't produce a mushroom shaped cloud then ......
ok ok, just kidding .....
seen from below leads form a triangle: E B C with the red dot being the collector.
Plug it into your multimeter and you should hav a rough idea of its gain (Beta) which should be around 30-40.
*This* test is non-destructive.
The yellow dot on top should give an idea of the gain, but don't remember the original coding.
Good luck.
Remember reading the approppriate issue of Beano magazine helps a lot.

[tubeswell]

seen from below leads form a triangle: E B C with the red dot being the collector.
Plug it into your multimeter and you should hav a rough idea of its gain (Beta) which should be around 30-40.

The yellow dot on top should give an idea of the gain, but don't remember the original coding.

Thanks. The leads are in a line on the bottom. So the one closest to the red dot is the collector, and the next one must be the base?, and the furthest one must be the emitter? But do I read it in the PNP side or the NPN side? (Never mind I tested it - it reads at '41' on the hFE)

Remember reading the approppriate issue of Beano magazine helps a lot.

Is that a mag for South American electronics enthusiasts? (Haven't seen it over here) ;-)

[tubeswell]

So to re-cap, I have my OC44 and it measures 41 Hfe on my meter.

R.J. has some Rangemaster circuit tuning and improvement suggestions, (including 2M2 switching noise snubbers, and a couple of tuning pots for the bias, and a 25kA boost level pot where you have a transistor with a lower Hfe) which I think I have captured in the attached schematic. (Are those 2M2 resistors in the right place R.J.? TIA)

[R.G.]

Nota Bene
The germanium vs silicon issues in the Rangemaster seem to stem from the near-cutoff behavior of early germaniums. Back when I messed with this, getting the collector into near-cutoff was important to get a good sound to my ear at least. That's what all that stuff about getting -7V on the collector was.

I think that like many early effect circuits, this one happens to use an undocumented side effect of the crude semiconductors. In this case, it's the near-cutoff behavior of hfe change. It's a much softer distortion than more modern devices. I've built this with germanium devices of more modern manufacture, and that doesn't sound the same to me, either. In my mind, early germanium and crude processing is what gives the exploited side effect. I'm pretty sure I could whip up something with opamps to do a similar transfer function with a little time. It is likely not that it's germanium, but that the transistors get squirrel-y near cutoff.

It's a theory anyway. I did the Rangemaster stuff almost 11 years ago. Even the revival is becoming archaic. 8-)

[kleuck]

You must adapt the bias to the transistor you are actually using, it's an issue i encountered with my modernized RM, OC75 sounds best at 6 volts where OC44 are fine with 7, etc etc
I obviously ended up with trim.

[tubeswell]

Thanks gentlemen. So are those 2M2 in the schematic I posted in the right place or...? (TIA)