# 72’ pignose



## dlazzarini (Jul 14, 2020)

Not pedal related but maybe somebody has a little insight on these. I was given an early 70’s pignose that isn’t working. I found an old 1ohm wire wound resistor that looks burnt down to the wire coils in the middle. I pulled it out and still get a reading of 1 ohm with the meter although I’m not sure what happens to it under any load. Does anybody have any experience with repairing these. I have the schematic. It looks fairly straight forward. Is there a way to test the little transformers?  Any help is appreciated


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## Gordo (Jul 14, 2020)

Nothing add here except I was curious to see what a 72 foot Pignose looked like


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## Chuck D. Bones (Jul 14, 2020)

That is a vintage piece of hardware!  I did some work for Howard Chat, the owner of Pignose, back around 1978.  I'm very familiar with the circuit.  I have 3 of 'em. Post the schematic here so I don't have to go digging around for my copy.  Those low-value WW resistors can appear burnt even when they're new.  No more soldering or unsoldering please until we do some testing.  What are you using to power it?


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## Nostradoomus (Jul 14, 2020)

Get yer Terry Kath on!


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## dlazzarini (Jul 14, 2020)

Chuck D. Bones said:


> That is a vintage piece of hardware!  I did some work for Howard Chat, the owner of Pignose, back around 1978.  I'm very familiar with the circuit.  I have 3 of 'em. Post the schematic here so I don't have to go digging around for my copy.  Those low-value WW resistors can appear burnt even when they're new.  No more soldering or unsoldering please until we do some testing.  What are you using to power it?


This is the schematic that matches this pignose and a pic of that resistor (1E). This pignose wasn’t taken care of very well. It’s missing the stock speaker. Somebody put a radio shack realistic speaker in its place. It’s in pretty shabby condition. The 9v snaps that connect to both of the AA battery holders are all broken off. I jury rigged them to get temp battery power to test if it was working. I hear an almost inaudible little pop when the front pot is turned on but no volume or sound


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## Chuck D. Bones (Jul 14, 2020)

It would take a lotta current to burn that resistor.  Good chance one or both of the output transistors are fried.  I doubt the output transformer could take that much current either, but ya never know...  Try measuring the resistance from -9V (meter negative lead) to either side of the output transformer primary (meter positive lead).  If that's good, then we can move onto testing the transistors.  If the transformer is fried, all is not lost, I'm sure we can find a usable replacement.  How far are you willing to go with restoring this amp?

Here's the background story of that amp and my involvement.

Howard Chat owned a company called Cases Inc.  They built shipping containers that were used to ship amps, speakers, instruments, etc. by touring bands, in addition to more mundane uses.  Howard ended up buying the Pignose company.  The electronics inside the original Pignose amps were from an intercom.*  Some smart guy figured out that they sounded great as mini guitar amps.  Howard was having the amps manufactured in Taiwan.  One day, his supplier told him that they could no longer obtain the germanium transistors.  The provided an alternate amplifier design that used an IC power amp and a few R's & C's.  Needless to say, it lacked the tonal character of the old design and basically sounded like shit.  A friend of mine who worked at Cases Inc. contacted me and asked me to go see if I could help Howard out.  I was into tube amps at the time so I realized right away that most of the tonal qualities resided in those tiny transformers.  I told Howard, "you gotta keep those transformers."  I replaced all four germanium transistors with silicon, using some hefty 2N6124s for the output.  I also replaced the thermistor with a 1N4148 and tweaked the bias resistors.  Problem solved.  I got something like $50, two amps and a Pignose windbreaker for a few hours of work.  Howard told me, "don't replace the transistors in those amps, they work just fine as-is."  And so they do. 

* I have a story about making a mini-Champ from an old tube intercom I bought at a garage sale, that's a story for another day.


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## Gordo (Jul 14, 2020)

Fascinating.  I was never really a pignose fan but then again I could never sound like Kath or Zappa.


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## Nostradoomus (Jul 14, 2020)

I don’t know if Terry Kath actually used them or was just invested/involved in the company somehow. His most righteous sounds came from an old Bogen PA amp and his hacked up Tele...well and his hands.


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## Chuck D. Bones (Jul 14, 2020)

Yeah, it was Terry.  A good musician can make any instrument or equipment sound good.

So I pulled out one of my old Pignose amps and fired it up.  Sounded good for about a minute, then fizzled out.  The output transistors went into thermal runaway.  I'm using the power supply that came with it, but the voltage is too high.  Should be 9V, it's more like 12 and change.  I'll have to do something to stabilize the biasing.  Mine is dead stock, model 7-100.  The first two transistors are BC558B, silicon.  The output transistors are clamped to the heatsink and I can't read 'em at the moment.


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## dlazzarini (Jul 15, 2020)

Chuck D. Bones said:


> It would take a lotta current to burn that resistor.  Good chance one or both of the output transistors are fried.  I doubt the output transformer could take that much current either, but ya never know...  Try measuring the resistance from -9V (meter negative lead) to either side of the output transformer primary (meter positive lead).  If that's good, then we can move onto testing the transistors.  If the transformer is fried, all is not lost, I'm sure we can find a usable replacement.  How far are you willing to go with restoring this amp?
> 
> Here's the background story of that amp and my involvement.
> 
> ...


That’s a really awesome story Chuck. So cool.  About the amp, I’d love to get it working if possible. I know nothing about transformers. Haven’t gone down that road yet. What wires would I be using to test. I don’t have it in front of me at the moment so I’m not even aware of how many wires the transformers even have.


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## Chuck D. Bones (Jul 15, 2020)

How are you at reading a schematic?


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## dlazzarini (Jul 15, 2020)

Chuck D. Bones said:


> How are you at reading a schematic?


I’m getting better. I can usually find my way


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## Chuck D. Bones (Jul 15, 2020)

The two devices with curly lines in them are the two transformers.  The curly lines represent the windings and the two straight lines represent the core, the thing that contains the magnetic field.  A transformer is simply two or more inductors that share a common core.  The transformer on the left is the driver transformer, it drives the bases of the two push-pull output transistors.  The transformer on the right is the output transformer.  It takes the signal from the output transistors and couples it to the speaker.  The one we're interested in right now is the output transformer.  It's the larger of the two and in my Pignose, the windings are wrapped in blue tape.  If you look at it from the bottom of the board, there are three pins on one side and four on the other.  The three pins are connected to the primary winding, where the signal goes into the transformer from the transistors.  The four pins are connected to the secondary, where the signal comes out and drives the speaker.  The wire in the windings is pretty fine, and there 's a lot of it, so it will have a measurable resistance. On mine, the primary measures about 3 Ohms end-to-end.  Measure it with power off.  I can hear a faint click in the speaker when I connect the DMM.


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## dlazzarini (Jul 15, 2020)

T


Chuck D. Bones said:


> The two devices with curly lines in them are the two transformers.  The curly lines represent the windings and the two straight lines represent the core, the thing that contains the magnetic field.  A transformer is simply two or more inductors that share a common core.  The transformer on the left is the driver transformer, it drives the bases of the two push-pull output transistors.  The transformer on the right is the output transformer.  It takes the signal from the output transistors and couples it to the speaker.  The one we're interested in right now is the output transformer.  It's the larger of the two and in my Pignose, the windings are wrapped in blue tape.  If you look at it from the bottom of the board, there are three pins on one side and four on the other.  The three pins are connected to the primary winding, where the signal goes into the transformer from the transistors.  The four pins are connected to the secondary, where the signal comes out and drives the speaker.  The wire in the windings is pretty fine, and there 's a lot of it, so it will have a measurable resistance. On mine, the primary measures about 3 Ohms end-to-end.  Measure it with power off.  I can hear a faint click in the speaker when I connect the DMM.


Thanks Chuck for taking the time to give me very clear instructions. I’ll get some measurements as soon as I get some free time at home and report my findings to you.


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## Chuck D. Bones (Jul 15, 2020)

In the meantime, I'll see if I can get the bias dialed in on mine.


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## dlazzarini (Jul 15, 2020)

Chuck D. Bones said:


> In the meantime, I'll see if I can get the bias dialed in on mine.


Primary side of output transformer is measuring about 3.4 ohms


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## Chuck D. Bones (Jul 15, 2020)

The transformer is probably good then.  

Were you using batteries or a power pack to power yours?  I suspect both of our amps have the same problem.  Have not had a chance to tweak the bias on mine yet, but here's what I have in mind:
Replace the 1Ω resistor with 10Ω 1W.  Put a 100uF (or larger) cap in parallel with the 10Ω resistor.  That cap can be 6V or even less, it will have <1V across it.  One mine, the ground end of that resistor is closest to the edge of the board.  These boards are *positive ground*, so the positive end of the cap goes to ground. The bias will be much more stable.


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## dlazzarini (Jul 15, 2020)

Chuck D. Bones said:


> The transformer is probably good then.
> 
> Were you using batteries or a power pack to power yours?  I suspect both of our amps have the same problem.  Have not had a chance to tweak the bias on mine yet, but here's what I have in mind:
> Replace the 1Ω resistor with 10Ω 1W.  Put a 100uF (or larger) cap in parallel with the 10Ω resistor.  That cap can be 6V or even less, it will have <1V across it.  One mine, the ground end of that resistor is closest to the edge of the board.  These boards are *positive ground*, so the positive end of the cap goes to ground. The bias will be much more stable.


Thanks Chuck I’ll give this a whirl when I obtain the proper wattage resistor. All I have are 1/8’s and 1/4’s. Imagine that. To answer your question about power. The guy that gave it to me told me it didn’t work but I went ahead and tried it with batteries. The AA battery holders had 9v battery snaps plugged into the top of them but they were corroded and broken so I just rigged up a little temp setup to use the batteries.


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## Chuck D. Bones (Jul 15, 2020)

Ha ha ha, I don't have a 10Ω 1W wirewound resistor either. Getting one from a friend tomorrow.

Battery power is better than the Pignose power pack I have because with batteries, you won't get too much voltage.  I'll probably end up replacing the thermistor with a diode so that the bias doesn't change if the battery or power pack voltage changes.

So is that Radio Shack speaker in yours any good?  I forgot how heavy these things are.  Most of the weight is in the speaker magnet.


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## Nostradoomus (Jul 15, 2020)

Man I had one of those (the new ones) and it just would not play cleanly at all. Even with my guitar volume down there was this irritating distortion under everything. Returned it pretty quick!


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## Chuck D. Bones (Jul 17, 2020)

I didn't get the resistor as planned, I've set the Pignose aside for a few days 'til the resistor gets here.  Plenty of other pedal and home projects to keep me occupied.


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## Bobbyd67 (Jul 17, 2020)

Chuck D. Bones said:


> I didn't get the resistor as planned, I've set the Pignose aside for a few days 'til the resistor gets here.  Plenty of other pedal and home projects to keep me occupied.


Couldn't you use 4 40 ohms (or 47r which is probably more common) 1/4 W resistors to make a 10 ohms 1 W resistor ? Or is it too dangerous on a amp circuit?


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## dlazzarini (Jul 17, 2020)

Chuck D. Bones said:


> I didn't get the resistor as planned, I've set the Pignose aside for a few days 'til the resistor gets here.  Plenty of other pedal and home projects to keep me occupied.


I just placed an order with Mouser including that resistor. Should have it early next week


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## Chuck D. Bones (Jul 19, 2020)

Bobbyd67 said:


> Couldn't you use 4 40 ohms (or 47r which is probably more common) 1/4 W resistors to make a 10 ohms 1 W resistor ? Or is it too dangerous on a amp circuit?


Could, it's just a matter of space.  I have some 10Ω 5W "sandstone" resistors, but no way one of those will fit.


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## dlazzarini (Jul 26, 2020)

Chuck D. Bones said:


> Could, it's just a matter of space.  I have some 10Ω 5W "sandstone" resistors, but no way one of those will fit.


Hey Chuck I replaced that 1ohm resistor on that pignose and it fired right up. I did also order a 10 ohm resistor to try out that capacitor thingy you were talking about. What was the end goal of that


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## Chuck D. Bones (Jul 26, 2020)

I finally got my wirewound resistors.  I replaced the 1Ω resistor with a 12Ω and a 100μF in parallel.  I replaced the 680Ω resistor and thermistor with a 1N4004.  The Pignose works, and it gets plenty loud, but above a certain volume there is a fair amount of crossover distortion.  I'm thinking the 12Ω is too large, so next I'll try something around 3Ω.  1Ω is too low with a 12V power supply.  If you're using batteries, the 1Ω is probably best.

To answer your question, the goal of increasing the 1Ω resistor was to stabilize the bias.  It's very stable, but the consequence is too much crossover distortion.  I need to find some middle ground.


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## dlazzarini (Jul 26, 2020)

Chuck D. Bones said:


> I finally got my wirewound resistors.  I replaced the 1Ω resistor with a 12Ω and a 100μF in parallel.  I replaced the 680Ω resistor and thermistor with a 1N4004.  The Pignose works, and it gets plenty loud, but above a certain volume there is a fair amount of crossover distortion.  I'm thinking the 12Ω is too large, so next I'll try something around 3Ω.  1Ω is too low with a 12V power supply.  If you're using batteries, the 1Ω is probably best.
> 
> To answer your question, the goal of increasing the 1Ω resistor was to stabilize the bias.  It's very stable, but the consequence is too much crossover distortion.  I need to find some middle ground.


I see. I don’t really know what they’re supposed to sound like but it does start distorting once I get the volume up around half way or so


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