Working with some Russian GEs in a Rangemaster

[ChuckZilla]

Hello all.

Let me first say that I am very new to this hobby, but have a lot of interest in learning about making pedals. I have invested some money in electronics stock. This is my first post on the forum, and I am sure thankful to be a part of it.

I bought many Russian GE transistors, because as far as I can tell, they are the only GE transistors that you can still find that are affordable. (~50 cents a pop.)
As I am a beginner, I wanted to first build the rangemaster as it is pretty uncomplicated (so I thought.) I followed the schematic resistor values, but instead of an OC44 I thew in a GT108v. It does not work. I can not get any sound out of the effect. The GT108Vs have an internal resistor shunt between the emitter and the base, so I think this must be due to biasing, I hope. From what I understand, if you don't bias it right, it could kill the input signal.

I built two circuits to make sure I'm not messing up. I tried biasing the 3K9 ohm resistor (Blindly, without use of a DMM by adjusting the wiper and checking every ~2 turns.) It still didn't work. I believe the other resistors (68K and 470K) are more important to adjust while biasing, but I only had a trimmer good for the 3K9 position. (5K trimmer) I have ordered a bunch of trimmers to add to my electronics stash, but they aren't here yet.

I've got a bunch of questions, but will start out with just a couple.

Does this sound like a Biasing problem? (I.E. I'm not getting ANY sound of the effect.)
Can you bias a transistor without an AC input? Will you get a voltage at the collector without AC input?
What resistor values have you used in an RM clone with GT108V trannies?

-Chuck

[LucifersTrip]

welcome...

I think you're making this a bit more complicated than it has to be. you're jumping ahead and guessing...

You will need a DMM to properly adjust the Rangemaster. Here are the instructions:
http://www.geofex.com/Article_Folders/Rangemaster/atboost.pdf

and here's the debug thread if you have problems:
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

In the other thread you said you bought GT308V's (B is V in Russian).

I built a Rangemaster with pretty much those same transistors:


No one can really tell you what resistor values you need because you haven't given the exact gain and leakage...
Even then, calculations or simulations have to be made...It is easier to breadboard and DMM

good luck

[Pyr0]

If your not getting any sound out you more then likely have a basic wiring problem, or maybe you have the pinout of the transistor wrong.
For GT308, the emitter is marked with a dot on the case, then next to it in the middle is the collector, and finally the base.

[pinkjimiphoton]

If your not getting any sound out you more then likely have a basic wiring problem, or maybe you have the pinout of the transistor wrong.
For GT308, the emitter is marked with a dot on the case, then next to it in the middle is the collector, and finally the base.

+1

also, the base on some of these is connected to the casing, can make the tranny short out. it's hard to find the pinouts on some of the russian trannys!

[davent]

Would the gain of the Russian trannies (being sure the pinout is known and wired up correctly) be insufficient for the Rangemaster to work properly? I have an order of GT308's where the gains all measured ~30 or less. Steve at Small Bear has an article on wiring up a pair of low gain ge's as a Darlington to get a more useful gain out of the devices.

https://www.smallbearelec.com/HowTos/GeDarlingtons/GeDarlingtonPairs.htm

dave

[Colonel Angus]

@ Jimi - ever hear of a russian tranny surprise?

Thanks for the ragemaster link on Geofex, I'm going to build another one now that I have some idea of how to bias the circuit.

[Pyr0]

While this is topical, I might as well post my adapted vero layout for my Rangemaster with "Beano Boost" switchable input caps, on-board pot and bias trim -  someone might find it handy.



caps C1, C2 and C3 are in series and I used a SPDT to switch the input between them

I tried a lot of different values before I settled on these ones.
C1 - 6.8nF, C2 - 33nF & C3 - 39nF  will give 4.93nF for classic, 17.875nF for mid boost  and 33nF for a low boost.

Another combination I liked was 6.8, 22 & 47 giving us 4.67, 15 and 47.

You might want to experiment with your own values.
The benefit of using serial capacitors is no pop when switching between them.

I also found that using various transistors with a gain between 75 and 110, I was always able to bias it correctly just using the trim and the stock 68k for R2.
The last one I built I used a 2N404, Hfe=92, Leakage=72uA and it sounded sweet.

Plug it in, crank up the boost and away you go, just like Rory

http://youtu.be/hGLzkFYghq4

[davent]

I've been playing around with a Rangemaster on the breadboard and found a Joe Gagan tone control, rather then switching between caps, works really well to accomodate different guitars and find great tones.

[ChuckZilla]

Thanks for the responses guys. I'm still working to get this little guy working. Can't lie, its making me feel kinda stupid as its the simplest possible circuit. I don't know why it isn't working,  but I'll be sure to let you guys know when I know.

@pyro and pinkjimi:I have connected all of the trannie leads correctly, and this was not the problem. Even as is, the bias on the collector is like 7.4 DC volts. (this is with a fresh 9v battery.) This should still give me sound, but nothing is coming out.

@davent: i dont think the gain is too low. it read ~80 in my cheepo DMM.

To answer my own question number two, I don't think you actually need an AC input to bias the transistor. I believe you are biasing the DC voltage at the collector. (I tried using a function generator set to an output of about .6 AC volts. It would appear that the DC voltage is trumping any AC current at the collector)

[Toney]

Just confirming the pinout for you - should be this:



The audio probe is a great tool and a simple circuit such as this is kind of ideal in learning how to use it. It s just a cap and a lead, couldn't be simpler.
How about a photo of what you have so far?

[ChuckZilla]

Correction, that is -7 DC volts at the collector, so bias apears good... 

@Toney, Confirmed, pinout is correct. I'll find a camera and post a pic. but my board is kind of crowded, so, ill see what I can get

[ChuckZilla]

Here are some pics. They are terribly low quality as my camera is not good. They are also hard to see. I went into paint to try and edit it.



This is was soldered on the perf board that has vertical lines of copper down the board instead of ringlets at each perf. I indicated the copper highways by orange.
Here is the one in paint, you should probably look at it. I hope this is sufficient. 

[Toney]

Your input cap is 5pF and your output is 10pF?

Think that might be your issue.

[ChuckZilla]

Oh snap. And you think someone with a masters in chemistry would know better. 

I knew you guys would get me through this... haha, thanks.

[ChuckZilla]

Just to follow up, I replaced the stupidly (not ignorantly) selected capacitors. The pedal works very well now. I also used the default values for resistors.

The bias came out to be exactly -7 volts DC. To my ears, this effect sounds beautiful.

It seems that this effect adds around 60 decibels of volume when turned on and turned up all the way. It's pretty rad, and I'm happy. Next feat is to build a fuzz face.

Also, the transistor used for this effect was of value 81 Hfe. I measured this value with my cheep-o DMM, and did not check the transistor for leak.

[Tony Forestiere]

Sound clips? 

[ChuckZilla]

@ Tony

I don't have a good means to record music with my current PC setup.  I'll get back to you on that in the future!

Cheers

[Toney]

Thats great ChuckZilla.
Such a good feeling getting a result after battling a circuit