# RangeFinder Questions



## Travis (May 7, 2021)

Hi everyone, I wanna build this Range Booster but I not sure about the transistor.

One OC75 with 75-100 hfe will be a good option?


Also I don´t know wich mode is on the eight positions of the RangeFinder.



Thanks for help


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## Travis (May 7, 2021)

I didn´t find enough information about the eight positions


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## benny_profane (May 7, 2021)

What are you asking? The range finder has a rotary switch that allows you to select the input capacitor to the circuit. This input capacitor is part of a high-pass filter (i.e., a filter that cuts low frequencies). The threshold is adjusted with the capacitor value. A larger capacitor allows more low end in; a smaller capacitor cuts more low end.

The stock value in a rangemaster is 5nF (or 4n7).

Don't worry about the part number of the transistor. There are plenty of Ge transistors that will give you good results. A PNP Ge with a gain (hFE) range of 65–100 with less than ~300uA leakage is fine.


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## Travis (May 7, 2021)

Ok, so if I buy the oc75 with 65-100 hfe it's okey?

Thanks for explain me the 8 positions, wich ones are similar yo Rangemaster 1 or 2?


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## benny_profane (May 7, 2021)

If you can find one, sure. You'll pay a premium for that particular part number and there are no guarantees regarding leakage. I would suggest finding another device to save some money unless you're very set on it.

Position 2 (4n7) is the 'stock' position. Keep in mind that it's a rotary switch, so you may have to test it to see which position is actually being connected.


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## fig (May 7, 2021)

Here is the selection part of the schematic. It shows the switch positions and the associated capacitance.

Hope that helps!


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## Travis (May 7, 2021)

benny_profane said:


> If you can find one, sure. You'll pay a premium for that particular part number and there are no guarantees regarding leakage. I would suggest finding another device to save some money unless you're very set on it.
> 
> Position 2 (4n7) is the 'stock' position. Keep in mind that it's a rotary switch, so you may have to test it to see which position is actually being connected.


This store sells them with the hfe that you decide.









						Retroamplis
					

Retroamplis es una empresa de distrubución de componentes electrónicos para la fabricación artesanal de pedales, amplificadores y efectos de guitarra bajo eléctrico. Disponemos de condensadores, resistencias, integrados, potenciómetros, trimmers de ajuste, cajas de aluminio hammond y eddystone...




					www.retroamplis.com
				




#6 Thanks for the picture


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## Big Monk (May 7, 2021)

Travis said:


> Hi everyone, I wanna build this Range Booster but I not sure about the transistor.
> 
> One OC75 with 75-100 hfe will be a good option?
> 
> ...



You’ll probably have to tweak the bias arrangement of the stock circuit to accommodate the leakage of the OC75.

Having ordered OC75 from Retroamplis I can vouch for the quality but keep in mind that their prices are in Euros so be prepared to pay $13-$14 each.

Try Small Bear for a RM specific device. Then you know it’s tested for that circuit.


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## Travis (May 7, 2021)

Big Monk said:


> You’ll probably have to tweak the bias arrangement of the stock circuit to accommodate the leakage of the OC75.
> 
> Having ordered OC75 from Retroamplis I can vouch for the quality but keep in. I do that thier prices are in Euros so be prepared to pay $13-$14 each.
> 
> Try Small Bear for a RM specific device. Then you know it’s tested for that circuit.


I'm from spain that's why I'm looking retroamplis, I think I Will buy It with hfe 75-100.

Some recomendation for biasing? Thanks.


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## Big Monk (May 7, 2021)

Travis said:


> I'm from spain that's why I'm looking retroamplis, I think I Will buy It with hfe 75-100.
> 
> Some recomendation for biasing? Thanks.



Tweak Rb1 (nominal 68k) and Re1 (nominal 3.9k) until you hit 7 vDC. Keep in mind though that OC75 leakage will give you fits under changing temps.


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## fredeharley5 (May 24, 2022)

I was looking at building the LPB-1 Booster as my next pedal as it seems very simplistic and I thought it might be fun to really drive that valvecaster I built with a booster. Looking through my stock of parts though, I have a few NPN general-purpose transistors but I don't have the 2N5088 that the schematic calls for. 
Has anyone here ever built it with a different transistor or maybe have some thoughts on the design as it pertains to the electrical characteristics of the transistor chosen? I notice that the 2n5088 has an absurd max hfe of 900 vs the theoretical max of 300 for a 2n2222. In short, any ideas or things I should be investigating to figure out what I could maybe replace it with? Or maybe I should just breadboard it and start throwing transistors in until it sounds good... Let's see


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## Diynot (May 24, 2022)

@fredeharley5 I modded a stock lpb-1 and socketed the transistor. I tried 3904/bc108/5088 all with similar results. I think I landed on the bc108, but def socket the tranny and try a bunch. Just mind your pinout


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## HamishR (May 26, 2022)

An OC75 with hfe around 75-100 is good for a Rangemaster style boost AS LONG AS IT DOESN'T LEAK TOO MUCH. There is more to it than just hfe. FWIW I have had fantastic results with relatively cheap Russian Ge transistors. There really isn't any magic guaranteed by the brand or model number. An OC75 isn't a magic transistor. It's what was available when the original boosts were built. It wasn't chosen for tone, it was chosen because that's what was in the shop at the time. When I first built a treble booster the "magic, must-have" transistor was an OC44. Now it seems to have changed to OC75 - maybe the OC44s have all been used up. Germanium transistors are known for being incredibly inconsistent.

Sorry, not trying to be a Mr Poo-poo! But there is a lot of hype being spread by people who want to get maximum $$ for their old transistors. My advice if you want a great sounding treble booster with a Ge transistor is to buy a bunch of Russian MP20s (PNP) or MP38s (NPN). The MP20s I have been using lately have been fantastic.


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## Big Monk (May 26, 2022)

OC75s have a good amount of leakage. I’ve had maybe 40 in my possession at one time or another, and only 5 or so tested as having less than 150 microamps. 

Not a good choice for a Rangemaster.


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