some fresh gut shots of an original interfax harmonic percolator

[Gus]

Looked up 2N3565 shows a hfe 150 to 600
The LT Spice model of the 2N5089 often sims correct to a build.
https://datasheetspdf.com/pdf-file/74107/FairchildSemiconductor/2N3565/1

I believe I corrected a bad trace of the dual NPN that was posted It does not look like it would work as shown

The HP is two cascaded gain stages that are powered in series the "center" point controls the interaction between the stages by the cap ESR and value, so you can play with value, type and even add a series resistor to the cap for more interaction.
For a dual NPN silicon you will need to adjust the C to B resistor for each stages DC biasing you can lower the AC gain in the stages with a resistor and coupling cap in parallel with the C to B DC bias/gain resistor

My post was related to digi2t's post

[Rob Strand]

Schematic looks wrong I would move the 20K at the first emitter to between the first transistor collector and the 47uf cap (remove the existing connection) move the 1uf? coupling cap to the 1st collector to 2nd base
Is the output volume wired like in the picture  or is that a mistake as well. It will work as shown but in an odd way.

I believe I corrected a bad trace of the dual NPN that was posted It does not look like it would work as shown

I was going to agree with you but I thought I would check the trace myself.

I think the connections on digi2t's version of the schematic are correct!
The 20k goes connect to ground and the 1k + cap are parallel with the 20k.

What's not possible to judge is the orientation of the lower transistor because the transistor pins are in-line
and the casings have no markings.

I see two possibilities:

1) 2 x NPN.  In this case the schematic  (ie. digi2ts) is correct as shown.

2) PNP + NPN.   So in this case we would have to interpret the circuit as shown but the lower
      transistor is PNP with CE flipped from the NPN.
     The PNP transistor is connected with the emitter to the big cap and the emitter of the NPN.
     The collector goes to the 20k + 1k + cap.
     The twist in this view is the 220k connects across the Base and Emitter of the PNP.
     We would do that if the PNP has high leakage.   In this case the PNP would have to
      be germanium.  It's quite possible one batch (or era) of transistors had high leakage PNP
      and the BC resistor had to be flipped to a BE resistor for it to bias.

So there's two consistent views but there's no further evidence to choose between them.
We would need to do some measurements of the parts or voltages.
(The thick gold pins is making it hard to go with case 2.)

One thing that makes me suspicious this is a clone and not a real unit is there is a making
2005 205x or something on the bottom side of the PCB.    I don't have my old pics with me
to check if some of the other boards had text makings underneath.

That made me think of this schematic, which was around in 2005 to 2007,

https://www.fredric.co.uk/misc/barge-concepts-incorrect-harmonic-percolator-bp-1-bp1-schematic.jpg


Well, it's not so clear since here's a similar unit, which looks vintage,

http://www.effectsdatabase.com/model/interfax/harmonicpercolator#

[Gus]

Rob

I guess you are correct about the schematic in reply 9.

I think you would not want a emitter follower to a gain stage setup for a HP like circuit

So I did some searching some links
https://web.archive.org/web/20111115192138/http://www.bargeconcepts.com/bp/largeschem.bmp
http://www.fredric.co.uk/blog/140-Barge-Concepts-%27Harmonic-Percolator%27-schematic
https://reverb.com/item/4990790-barge-concepts-bp-1-interfax-harmonic-percolator-clone
https://www.diystompboxes.com/smfforum/index.php?topic=55115.0

[Rob Strand]

I think you would not want a emitter follower to a gain stage setup for a HP like circuit

Yes, it doesn't seem right for a HP.

So I did some searching some links
https://web.archive.org/web/20111115192138/http://www.bargeconcepts.com/bp/largeschem.bmp
http://www.fredric.co.uk/blog/140-Barge-Concepts-%27Harmonic-Percolator%27-schematic
https://reverb.com/item/4990790-barge-concepts-bp-1-interfax-harmonic-percolator-clone
https://www.diystompboxes.com/smfforum/index.php?topic=55115.0

I actually remember that era and those circuits floating around.

There was also a few videos, with Steve Albini.   This was one which doesn't sound too convincing to me as far as the Barge pedal goes.   There were some other videos.

https://www.youtube.com/watch?v=XzNXKrMynW4

The weird thing is the Barge pedal in that demo seems to have a bit more gain than you would expect if the first stage was a buffer.