NEW SCHEMATIC - Class A PNP Germanium Boost - Thoughts?

[Gus]

I do not see the schematic
What you could do is drop a Ge in the beginner project/ NPN boost.

The beginner project "design" will bias up even a Ge with no parts change, there is a small change because of the different Vbe but it still works.  A forum member has built one IIIRC I forget who it was that posted they used a NPN Ge in the boost.  You could use a PNP with some changes.

The input string is low enough in value to have good control of the DC operating points and the input is bootstrapped for a good input resistance.

[supertulli]

Hello Darren! Hi everybody watching!

It's been awhile since i've touched a bread board, (and threaded something here  ), but have in the last month fiddled with the Rangemaster circuit, trying to make the better use of very low leakage/low Hfe Ge transistors i got from eastern Europe. I'm trying to diverge a little, by experimenting with different applications for those little components... and stumbled upon this old thread! Do you have your beefed up schematic still? Would it be possible to get a glimpse at it? I'm wondering how it would differ from the Rangemaster, and willing to give it a try and compare.

Hoping this doesn't fall into the void

Pedro

[darron]

Hello Darren! Hi everybody watching!

It's been awhile since i've touched a bread board, (and threaded something here  ), but have in the last month fiddled with the Rangemaster circuit, trying to make the better use of very low leakage/low Hfe Ge transistors i got from eastern Europe. I'm trying to diverge a little, by experimenting with different applications for those little components... and stumbled upon this old thread! Do you have your beefed up schematic still? Would it be possible to get a glimpse at it? I'm wondering how it would differ from the Rangemaster, and willing to give it a try and compare.

Hoping this doesn't fall into the void

Pedro

hey mate!

happy to share the schematic:




here's a positive ground version. i imagined i running off battery only, so no power filtering or diode to protect a filter cap.



Here's a few notes:

Output cap could be anything from 100n upwards.

The inductor in series with the power filtering can be replaced with a 47ohm resistor.
The inductor coming off the bias can just be removed/bypassed/jumped.
The 2K7 sets the gain for it to be a little dirty. Increase this value to 3K3 or higher to clean it up a bit.
Try to get a really nice trimpot for the bias. I use a multi-turn one.

EDIT: the range switch is an ON-OFF-ON three-way toggle of course

[rankot]

Why inductors? Just some RF filtering or some other reason? Can I use 4.7mH, cause those 6.8mH are unobtanium here where I live?

[darron]

Why inductors? Just some RF filtering or some other reason? Can I use 4.7mH, cause those 6.8mH are unobtanium here where I live?

WELL.... for the power filtering actually it's almost only there for the DC resistance. which in this case those inductors are about 40 ohms -ish. my local shop sells these in a small axial package, not much bigger than a resistor or so I figure i'll put something cooler in for the same job. Since it's PNP with the negative ground, it's really critical to have a resistor to combo with the 220uf to really set a solid and stable low-pass filter. otherwise, ANY instability on the ground ends up coming up on the signal. with the standard positive ground, this wouldn't really be a problem.

do this too if you ever build a positive ground fuzz face. they normally suggest a "big f'in capacitor" like 470uf upwards. but with that 47ohm resistor in series, it MASSIVELY magnifies the filtering power of that capacitor. try to imagine if you wanted to roll off some high-end from the signal with a capacitor to ground. you can't calculate the roll-off frequency without knowing the impedance of the signal, and if the power supply is coming in close to ideal zero resistance from the supply... just saying this is often overlooked.

for the bias one, you could throw in the 4.7 in for fun. not SURE how much effect it really has. but since germanium is always noisy, and negative ground PNP is just are a recipe for problems already, then i wanted to know i tried to eliminate all noise addition points. BTW though, i haven't had any problems from building hundreds of these for customers regarding power supply issues, noise, or daisy chaining. for those who are anti-PNP-negative-ground... this system works fine! much better than using a voltage inverter chip like max1044 or 7660S etc.

[rankot]

The closest match in my local store is 10mH, 30 Ohm inductor (radial one, drum type). What do you think about that?

[darron]

The closest match in my local store is 10mH, 30 Ohm inductor (radial one, drum type). What do you think about that?

sure

[supertulli]

Thank you!

Very nice touch with the inductors. have a few salvaged from electronic junk. Will try the approach next build.

[monkeyz]

Can't see any of the schematics, any chance of reposting them?

Best regards!