Trying to turn a rangemaster kit into a full range (UGH)



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Trying to turn a rangemaster kit into a full range (UGH)

Postby MechaGodzilla » Wed Jun 05, 2019 12:25 pm

trying to add a range control to the front of this kit, to turn into a red rooster-type booster

I'm using a 1T308Б (pnp), which is itself posing some issues for me (i know the pinout of the transistor but not exactly how it's supposed to go on the board) but at the minute I can't get any sound out of it.

the board is hooked up to a battery snap and jacks for testing but the battery got hot really quick and there was no sound. does that sound like a short somewhere?

i burned my finger pretty bad (first time that's happened lol) trying to get this to work which gives me plenty of time to work out how to do it right. y'know, like i should have done before today :facepalm:
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Re: Trying to turn a rangemaster kit into a full range (UGH)

Postby crochambeau » Wed Jun 05, 2019 1:05 pm

Yeah, sounds like you have a short across the power rails somewhere.

Don't overlook the possibility of a shorted transistor (in addition to the usual suspects).
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Re: Trying to turn a rangemaster kit into a full range (UGH)

Postby MechaGodzilla » Wed Jun 05, 2019 1:31 pm

crochambeau wrote:Don't overlook the possibility of a shorted transistor (in addition to the usual suspects).

i have left the legs real long and insulated them so that seems unlikely. more like i have installed it backwards or something.

crochambeau wrote:Yeah, sounds like you have a short across the power rails somewhere.

any tips for solving this? anywhere that's likely to be the issue (diodes/polarised caps or something)? actually, there's a protection diode in there that may or may not be the right way around :facepalm: really flummoxed myself with this one.
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Re: Trying to turn a rangemaster kit into a full range (UGH)

Postby crochambeau » Wed Jun 05, 2019 4:20 pm

MechaGodzilla wrote:
crochambeau wrote:Don't overlook the possibility of a shorted transistor (in addition to the usual suspects).

i have left the legs real long and insulated them so that seems unlikely. more like i have installed it backwards or something.


I mean to say that the transistor itself can fail and be a short circuit, I've seen it happen.

MechaGodzilla wrote:
crochambeau wrote:Yeah, sounds like you have a short across the power rails somewhere.

any tips for solving this? anywhere that's likely to be the issue (diodes/polarised caps or something)? actually, there's a protection diode in there that may or may not be the right way around :facepalm: really flummoxed myself with this one.


You have a continuity mode on a DMM or voltmeter of some sort, correct? Measure between the rails and see what resistance the power supply is working into. There are few enough parts on that kit that you can probably just do the "remove parts until your short goes away" method and lose a bunch of time.

If that protection diode is a "shunt to ground" (parallel to the circuit) the wrong way around that's a contender for your problem, if it's a "pass" diode (series with the circuit) it's probably not your problem.

If it is the diode in backwards, the continuity test above will only display a short in one direction..
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Re: Trying to turn a rangemaster kit into a full range (UGH)

Postby eatyourguitar » Fri Jun 07, 2019 6:33 pm

a transistor with the base pulled high will be ON all the time. you can damage the transistor or not damage the transistor but still have the heat problems if you exceed VCBO, VCEO, or reverse VCBO reverse VCEO of that sample. not all germanium transistors are created equal. not all germanium transistors age well. not all NOS parts are stored properly. sometimes the PCB or the instructions are incorrect. this has happened to me before. the only thing confirmed right now is that your circuit is consuming an unusually large amount of current. the battery does not normally heat that much. we can say that it is probably 100mA or more. you should first test the transistor to make sure ICE (leakage) is <0.1mA at 9VDC with the base open. you can attach a 100R resistor to either the collector or the emitter. then get the voltage drop across the resistor and then across the CE. from this you can see right away if it is shorted closed, a bit leaky or not leaky. ohms law is how you convert a known voltage drop over a known resistor into a current measurement. kirchhoff's current law says that the current through the resistor is equal to the current through the transistor (while the base is open). then you can use ohms law again to calculate the resistance of the transistor with the base open and 9VDC applied. you don't really need to do this but it is educational in many ways. to get the ON current you would attach a 10K resistor to the base and apply 5VDC. this is similar to the first test again using 9VDC applied to CE. this is what the datasheet calls ICEmax at IB = 1mA. sometimes there is a range of values on an XY plot to show how they are proportional. if your transistor is shorted then you may have it for a diode but you would need a curve tracer to confirm that you have a working diode from a broken or just leaky transistor. if it happens twice then the wiring or the PCB or some component is not right. post here and we will give you more tests depending on what happens next.
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