Quote from: g1 on April 29, 2025, 03:02:13 PMAlso, the noise you experienced must be due to the dress of the wires.  Where you routed it through the back of the chassis must be a sensitive area.

Usng a metallic uninsulated jack bolted to chassis shorts a great part of NFB , increases gain big time and makes "natural" noise unbearable.


Solution is usin g a properly insulated jack, properly wired.

Both jacks shown are wrong for thatb use.
To boot they are *wired* wrong.
Also external speaker jack must disconnect internal speaker when used, amp can not drive two speakers at once.
Too busy now but tonight will upload proper jack and wiring.

He was lucky.
Ruffling military´s feathers the wrong way isn´t healthy anywhere in the World 

Thanks A LOT.
It is VERY kind of you.
Sadly I am way too far away, 5000mi-8000km away as the crow flies.
And it would become a VERY tired crow 



But again, thanks A LOT for your kindness.

Take care Friend.

It is safer this way.

I mean, *there are* Class A SS amps, with strong idle current all the time, some Audiophiles swear by them, but then they have HUGE heatsinks and are designed to run very hot all the time.
Not our regular Guitar/Bass amps.

Not kidding: all those transistors and massive heatsinks for a puny (for us) 30+30 W RMS amplifier:

Looks very good and Sams is a very good no nonsense Tech book Company.

Maybe there is a downloadable version somewhere?

I am too far away to order a paper copy.

Quote from: g1 on April 26, 2025, 11:20:31 AMThe 'original' zener was just a defective regular diode.  Someone very smart realized it could be controlled and utilized.  Like a lot of discoveries, I guess. 
Always analyze your mistakes. 

Hey, Penicillin came out of moldy bread 

First Vaccin (smallpox) came out of a rural Doctor noticing that girls milking cows caught a "light" version of Smallpox, including (small) scars, but never ever got the "real" one.

Observation and deduction is everything.

May remember wrong, but Zeners came out of WAY overdoped regular diodes.

IF it is the real early version such as used by Ike and Tina Turner, not the later Pantera era, back in the day "everybody copied the Twin Reverb idea" so Guitar and Bass preamps were the same (clean, no distortion), only the Guitar one added Reverb and Tremolo.

So if you find the old Guitar one, it will help you.

I have them somewhere, in some old hard disk, haven´t seen them for many years.

Quote from: franvelasco on April 10, 2025, 03:25:05 AMI have a Pathfinder 10 Bass and I'm thinking on getting the guitar one. I suspect the PB10 is the same circuit without the distortion channel, as it sounds great with a telecaster, but I don't really have a way to know because the schematic is impossible to find.

From what I've seen in the modded guitar version, removing C12 gives more clarity and the Bright switch in the bass version does something quite similar.

Anyone has a clue on what's going on? Maybe there's a way to make the LEDs work to add an overdrive channel?

Thanks!

Looking at schematics kindly posted by Tassieviking:

1) the black on white ones look reasonable, "should" work, but I can not trust the coloured Eagle/Kicad type one.

In any case, you can use the Guitar one with Bass (and a suitable speaker) by just not pushingb the Distortion button, now for the Bass one it is not practical, just use any distortion pedal up front.

Loved it, great idea 

Congratulations. 
Time well spent 

Quote from: g1 on March 16, 2025, 08:19:21 PM

Quote from: DPM309 on March 15, 2025, 11:57:50 AMThe schematic shows them as 2N5988 (PNP) and 2N5991 (NPN). The markings on the transistors are TIP42B (PNP) and TIP41B (NPN). The ones I purchased were TIP42B and TIP41B which are good replacements.

I responded to your post over at MEF forum, but will include it here for others who may be working on these amps.
The TIP41 and 42 have BCE pinout.  The original 2N5988 and 5991 have ECB pinout, so the TIP's will not work as replacements.
There are fake datasheets out there showing ON Semi 2N5988 with TO3P case and incorrect pinout, but those transistors do not exist.
The real 2N5988 and 5991 were TO-225 case with ECB pinout.

Edit:  received response that this amp had been working and came with TIP41 and TIP42 outputs.
So can only conclude there are more than one version and be sure to check where the traces of the output devices are going, as there seems to be only 1 version of schematic available, and it does not match the later version.

Guess you are right.

Back in the day Motorola salesmen were VERY active and lured many amp manufacturers to use their stuff.
One of them was Marshall and apparently Rickenbacker fell for it too.

This is a Marshall 100W SS amp made between 1975 and 1978.

This comes straight from the 1973 Motorola Power Amp design handbook.

It does not use generic transistors such as 2N3055, TIPs, etc. but specific models made only by Motorola, so end user is not tempted to switch later to cheaper suppliers.

Another dirty trick (as seen on the Rickenbacker amp) was to use non standard case sizes and pinout, so repairs HAD to be done with the original Motorola stuff.

Only Marshall "guitar" mods were to add a Presence control and a tapped autotransformer so user could have 4-8-16 ohm options, both features present in Tube amps and which Guitar players expected and were used to:



These were among the earliest Marshall SS amps, they had little to zero experience with them, so they went through with a respected suplier suggestions to play it safe.

Funny thing, I am quite certain Motorola sold them A TON of transistors, or they signed a contract to buy a ton per year for "X" years, so they ended up WAY overstocked.

So they used these anywhere, including a puny 12W amplifier: 5005/Lead 12 , where it is nonsense to use a pair Metallic TO3 10 Ampere 80V 150W transistors which eeasily power a 100W amp.
I bet they were SICK of having them for breakfast, lunch and dinner so they designed in inexpensive beginner amp to move them out fast.

I see no other explanation.

Original Pignose amp was a *cheesy* power  module, think a somewhat beefed up transistor radio power amp, bought premade at one of many Electronics suppliers.

Post original Pignose amp schematoc here and I will search and find a commercial si ila amplifier for comparison.

Pignose was 99% COOL visual design and idea, 1% Electronics.

And the right product at the right moment, there was nothi ng like it.

Today any 10W practice amp is better.

Welcome Tom 

You have just been answered, no need to repeat your question multiple times.
Do as I suggest and it should work.