Triangle Big Muff Weak Tranny Advice

Paul Corusoe · February 13, 2007, 05:40:19 PM

I recently bought a Fulltone Soul Bender on ebay that had a cap blown in half. I read the numbers went to an electronics store bought it and soldered it in and it works great now. I get a lot of satisfaction knowing that I fixed, it's like that pedal is really mine. So I figure I can maybe fix my old Big Muff. I have asked one prominent guy to repair it and he said it sounds like a weak transistor but the guy that does these for him is away for a couple of months. I want to fix it my self. How do I test which one is weak? If I take a picture of the board with the components showing will some of you help me learn how to test a transistor? It has the fairchild 2N5133 transistors in it. I have read by googling that # that smallbear has a very similar part in looks and tone but they must be sorted for the right ones. I want to know how but I don't know how to know how other than ask.
Thanks,
Max
(real name)

zachomega · February 13, 2007, 06:07:50 PM

Try measuring the voltages in the circuit on the emitter, base, and collector of each transistor. Lots of guys on here know those things well enough to help pinpoint troubles.

-Zach Omega

Quote from: Paul Corusoe on February 13, 2007, 05:40:19 PM
I recently bought a Fulltone Soul Bender on ebay that had a cap blown in half. I read the numbers went to an electronics store bought it and soldered it in and it works great now. I get a lot of satisfaction knowing that I fixed, it's like that pedal is really mine. So I figure I can maybe fix my old Big Muff. I have asked one prominent guy to repair it and he said it sounds like a weak transistor but the guy that does these for him is away for a couple of months. I want to fix it my self. How do I test which one is weak? If I take a picture of the board with the components showing will some of you help me learn how to test a transistor? It has the fairchild 2N5133 transistors in it. I have read by googling that # that smallbear has a very similar part in looks and tone but they must be sorted for the right ones. I want to know how but I don't know how to know how other than ask.
Thanks,
Max
(real name)

Paul Corusoe · February 13, 2007, 06:20:04 PM

This is what I've done,
I plugged a 1/4 guitar plug into the input.
I put the negative to groung on my meter.
I touch each leg of the transistors and get a number.
How do I know which is b,c,and e?

Paul Corusoe · February 13, 2007, 06:21:25 PM

the battery is getting hot

brett · February 13, 2007, 06:25:51 PM

Hi
try making an "audio probe". It consists of only one cap, and is easy to make. Use the search function to find out more. (IIRC there's a diagram at geofex.com too).
Use the probe to check the base and collector of ech transistor in the two gain stages (the ones with the pairs of feedback diodes). The signal at the drain should be MUCH louder than at the base (it'll sound 3 or 4 times as loud). If it's not, it's a bad transistor.
Also.
The first transistor is a buffer, and the base should sound the same as the emitter.
The last transistor has low gain, and the drain will sound slightly louder than the base.
cheers

brett · February 13, 2007, 06:29:45 PM

the battery is getting hot

That might be a dead capacitor in the power supply. It's an electrolytic can (22uF to 100uF).

Or a short anywhere from the supply to ground. These can be tricky to find.
cheers

Meanderthal · February 13, 2007, 06:39:30 PM

If it turns out to be a bad tranny(I doubt it), don't worry about matching gain or anything like that. The BMP circuit is very happy with all kinds of transistors; The smallbear ones will work just fine, and need not be sorted.

Yes, it might be a bad power supply filter cap(if it has one), but whatever it is the battery getting hot tells me it's a short from pos. to ground. (I agree with brett)

Paul Corusoe · February 13, 2007, 06:48:19 PM

I made a mistake, I had the guts laying on my desk and the on/off switch terminals was touching the output jack.
I am going to buy the parts for the audio probe tomorrow and I'll ask for guidance.
So I'm reading and there is always a flat side and a round side and if the round side is facing me the collector leg is on the left, the base leg in the middle and the emitter is on the right.( trying to show you I'm not lazy) Thanks for the help thus far' Im trying.

R.G. · February 13, 2007, 06:51:23 PM

In general, to resuscitate an old EH pedal, make yourself up a list and replace every single electrolytic cap. Just do it. Make notes or take pictures as you go so you get the polarity right when you put new ones in.

Then remelt every single solder joint, touching it with a whiff of fresh rosin core solder. Just do it.

After those, we can help more. A few pics of the transistor cases would help us nail down the pin connection.

Meanderthal · February 13, 2007, 07:22:09 PM

QuoteSo I'm reading and there is always a flat side and a round side and if the round side is facing me the collector leg is on the left, the base leg in the middle and the emitter is on the right.

The 2N5133 is... hard to describe so easily, it's a bit 'off center'.

Don't know where I got this from, but-

R.G. just gave ya some rock solid advice.

R.G. · February 13, 2007, 07:41:29 PM

Izzat a top or a bottom view???

Meanderthal · February 13, 2007, 07:45:50 PM

I'm pretty sure that's the top. I could go dig mine up and confirm that if needed...

Paul Corusoe · February 13, 2007, 07:47:29 PM

I want to get this right so I'm looking at replacing 5 ceramic film caps(round and flatish) and 8 radial electrolytic(barrel shapped with connectors on both sides). What about the barrel shaped things with the stripes(resistors)? The radial caps read Ebar Son 3 MFD 15V are these available? I'll work on pics. Thanks

Meanderthal · February 13, 2007, 08:00:04 PM

I felt it was needed to confirm the pinout. That IS a top view, and the first one I grabbed has hfe 457, so I wouldn't exactly call it low gain. Just fine for BMP.

Don't worry about the resistors (yet), and leave the ceramic caps alone also. It's the aluminum electrolytic caps that need replaced. They don't age well. It's the first thing I do with old stuff.

Paul Corusoe · February 13, 2007, 08:03:40 PM

http://i145.photobucket.com/albums/r240/collinsford/bigmuff003.jpg

http://i145.photobucket.com/albums/r240/collinsford/bigmuff002.jpg

http://i145.photobucket.com/albums/r240/collinsford/bigmuff001.jpg

Meanderthal · February 13, 2007, 08:34:06 PM

Nice!

Ok, if ya don't have desoldering braid, get some.

You're going to have a hard time finding 3uf electros... 4.7uf should work. There should be other electrolytic cap values too, maybe 1 uf, or .1uf(I'd replace those with film, if it has those.) Be sure of the cap values first! Can't read the values of those in the pics...

Paul Corusoe · February 13, 2007, 08:52:26 PM

so is a uf the same as a mfd? I'll be looking for 4.7 uf 15v yes?

Meanderthal · February 13, 2007, 08:59:48 PM

Yes, 15v, more than 15v is fine too. uf = MFD. 2.2uf would also work fine. Might even be better.

Paul Corusoe · February 13, 2007, 09:14:58 PM

I want to fix it, but in your opinion does doing this harm it's value? What I mean is should I bust my hump trying to find the exact same parts? Is there a place that folks shop for old electronic parts? I DO realize it's worth a lot less not working and sputtery. I don't want to sell it, just curious.

Meanderthal · February 13, 2007, 09:34:57 PM

Any 3 uf aluminum NOS caps would be so old I personally wouldn't buy them. Chances are very good they wouldn't work. I'd stick as close to the specs of what is on the pcb(the reason I didn't recommend more commonly used cap values), but I would avoid old electrolytics if ya want it to work.

Actually, I find those cap values rather interesting. That is NOT the values you see on triangle muff schematics floating around...

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Triangle Big Muff Weak Tranny Advice