Harmonic Percolator - make one!

[pinkjimiphoton]

hey phend,
i'm in new england...

what parts ya need? pm me. i can hook ya up.
hell, if you're close enough to hartford ct, we can even hook up and burn one if ya wanna

[Phend]

Hey Jimi, thanks for the offer, got all the pots (new england pronunciation for parts) in a bag plus some different tranies. I'm up nord in Vt. My burning days have gone by. But have a toke on my behalf. Peace.  Hopefully I will have this assembled soon. Nothing like taking an easy build and making it truly unique and challenging.

[pinkjimiphoton]

hahahah all good, neyba, i know ya cain't get theyah from heayah.

enjoy your build!

[Phend]

Reference:
See Pictures Pictures post #29694

[digi2t]

Having cheated death one more time, I decided "@#$% it!", and treated myself to a Chuck Collins / Theremaniacs unit. Early model (pre silkscreening), from a vendor in Japan. Sounds pretty much like the one in Albini's video, and into an already overdriven amp, does become an instrument unto it's own. The voltages in the schemo below are higher than what I was expecting to find, which would tend to lean towards the transistors being of pretty low gains. I didn't feel like pulling them to find out.

[Mark Hammer]

So does it justify 21 pages of posts?

[digi2t]

The 1.4 pages per component is rather excessive. Imagine what such dedication to the Hi Fli would yield? Heck, the phaser diodes alone would account for over 300 pages.

[Rob Strand]

So does it justify 21 pages of posts?

Perhaps it does.  There's a hell of a lot of "percolator" schematics out there and on top of that many variations from people's builds to get it working.  It looks like the Collins schematic and the Giblet schematic are in good agreement.  So thanks to digi2t, we can at least say after 16 years we have some verification of the Giblet schematic.


EDIT:
I got a crude estimate for Q2's gain at 71 (seems low).  If you measure the voltage *across* b and c of Q1 and Q2 it *might* be possible to get a better estimate for Q2's gain and also a estimate for Q1's gain.   Q1 is right on saturation so you need to make sure the meter + probe is on the *base* of Q1 (but the collector of Q2).

[Mark Hammer]

I've built a few for buddies since the original post, using the Giblet schematic.  Holds up well all these years later.  A somewhat unique character.

[pinkjimiphoton]

dino!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!   

[Ben N]

Having cheated death one more time...

Is this what they call burying (you should excuse the verb) the lede?
You ok, Friend?

[Mark Hammer]

Having cheated death one more time...

Is this what they call burying (you should excuse the verb) the lede?
You ok, Friend?

Those Greeks are capital-S stubborn.  And some people dislike hospital food SO much they will recover quickly, just to avoid it.

[digi2t]

dino!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!   

jimi!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!   

So does it justify 21 pages of posts?

Perhaps it does.  There's a hell of a lot of "percolator" schematics out there and on top of that many variations from people's builds to get it working.  It looks like the Collins schematic and the Giblet schematic are in good agreement.  So thanks to digi2t, we can at least say after 16 years we have some verification of the Giblet schematic.


EDIT:
I got a crude estimate for Q2's gain at 71 (seems low).  If you measure the voltage *across* b and c of Q1 and Q2 it *might* be possible to get a better estimate for Q2's gain and also a estimate for Q1's gain.   Q1 is right on saturation so you need to make sure the meter + probe is on the *base* of Q1 (but the collector of Q2).

With a battery voltage of 9.42v, no input and controls at max, I read Q1 B/C = 40.3mV, and Q2 B/C 4.07v.

Having cheated death one more time...

Is this what they call burying (you should excuse the verb) the lede?
You ok, Friend?

Those Greeks are capital-S stubborn.  And some people dislike hospital food SO much they will recover quickly, just to avoid it.

@Ben - Doing better day by day. Nice to be back.

As Mark accurately points out, my initial recovery was directly proportional to my dislike of the hospital food. This ad sums up, in a nutshell, where I stand on hospital food...

[Mark Hammer]

Mango chutney and burnt hair.  That had me both smiling and revulsed at once.

[Rob Strand]

With a battery voltage of 9.42v, no input and controls at max, I read Q1 B/C = 40.3mV, and Q2 B/C 4.07v.

Well it turns out the Q1 gain can't be estimated reliably since the germanium transistor leakage swamps all the numbers.  Even gestimating the leakage doesn't produce a sensible result!  (IIRC the leakage problem on the percolator has come up in some of the old threads.)

For Q2, your B/C voltage is way way higher than the schematic.   The schematic has VCB = 5.19 - 4.69 = 0.5V.   

The Q2 base emitter voltages on the schematic look consistent.  If we add your Q2 BC voltage of 4.07V to the 4.69V base voltage on the schematic we would expect a Q2 collector voltage of 4.07 + 4.69 = 8.76V  which is way higher than the 5.19V on the schematic.

In short something has gone wrong with the 4.07V BC voltage measurement or the voltages on the schematic.

Forgot to mention:  if you calculate the current in R3 using the Q2 collector voltage and the current through R4 using the Q1 collector voltage the currents are within 10%.  That means the voltages on the schematic are likely to be more correct.

For a circuit like this you might find you get more consistent measurements with the pots set to minimum, since it will let less noise in.   Lots of buzz can upset the DC measurements.    Sometimes the multimeter leads inject noise into the circuit and screw-up the DC measurements - I've alligator-clipped 100nF to 1uF poly caps across the multimeter leads to shunt out noise.

[digi2t]

With a battery voltage of 9.42v, no input and controls at max, I read Q1 B/C = 40.3mV, and Q2 B/C 4.07v.

Well it turns out the Q1 gain can't be estimated reliably since the germanium transistor leakage swamps all the numbers.  Even gestimating the leakage doesn't produce a sensible result!  (IIRC the leakage problem on the percolator has come up in some of the old threads.)

For Q2, your B/C voltage is way way higher than the schematic.   The schematic has VCB = 5.19 - 4.69 = 0.5V.   

The Q2 base emitter voltages on the schematic look consistent.  If we add your Q2 BC voltage of 4.07V to the 4.69V base voltage on the schematic we would expect a Q2 collector voltage of 4.07 + 4.69 = 8.76V  which is way higher than the 5.19V on the schematic.

In short something has gone wrong with the 4.07V BC voltage measurement or the voltages on the schematic.

Forgot to mention:  if you calculate the current in R3 using the Q2 collector voltage and the current through R4 using the Q1 collector voltage the currents are within 10%.  That means the voltages on the schematic are likely to be more correct.

For a circuit like this you might find you get more consistent measurements with the pots set to minimum, since it will let less noise in.   Lots of buzz can upset the DC measurements.    Sometimes the multimeter leads inject noise into the circuit and screw-up the DC measurements - I've alligator-clipped 100nF to 1uF poly caps across the multimeter leads to shunt out noise.

OK, tried again...

9.42v at the battery, controls at zero, and a 0.1uF cap across the leads;
Q1 - 34.0mV
Q2 - 0.400v

[Rob Strand]

OK, tried again...

9.42v at the battery, controls at zero, and a 0.1uF cap across the leads;
Q1 - 34.0mV
Q2 - 0.400v

I've put all the calculations below so you can see what I did and see limitations:
- Unknown leakage for Q1
- Lower *in-circuit* current mean lower in-circuit hFEs than would
  be produced by a hFE tester.

hFE estimates using directly measured Vcb voltages + schematic voltages.

Q1 (Ge)

   Vcb1 = 34.0mV   ;Vcb unsigned (take 1 was 40.0mV)
   IB1 =   34.0mV / 220k = 0.183uA
   IC1 ~ IR4 = 4.09/91k = 44.9uA   ;from schematic voltages

=>   hFE1 = 44.9uA / 0.183uA = 245

Actual hFE significantly lower due to leakage.
Estimating the collector leakage at say ICEO = 100uA doesn't help
since it's already larger than IC1.  However we can estimtate
the base leakage.

If ICBO = 2uA then the total base current is,

   IB1_total = 0.183uA + 2uA = 2.18uA
   hFE1 = 44.9uA / 2.18uA = 20.6

If ICBO = 1uA, fairly low but for the calculation maybe OK since
we aren't factoring in IEBO,

   IB1_total = 0.183uA + 1uA = 1.18uA
   hFE1 = 44.9uA  / 1.18uA = 38

The problem is IB1_total is totally dominated by the guessed base leakage ICBO.

The conclusions we can make are:
- the collector leakage needs to be relatively low
- the transistor gain is likely to be quite low
  say 30 to 50.

Note also the low collector current means the in-circuit gain,
as estimated above, is going to be lower than the gain measured
in a hFE tester (even when leakage is removed, like in RG's tester).


Q2 (Si)
   Vcb2 = 0.400V
   IB2 = 0.4V / 750k = 0.533uA
   IC2 ~ IR3 = (9.48V - 5.19V)/91k = 47.1uA ;from schematic voltages
=>   hFE2 = 88

Not an unreasonable value for the low collector current.
If the hFE measured in a hFE tester with say a 1mA test current
we might measure hFE2 = 150.

Note also IC1 is about the same as IC2 which gives some credibility to
the schematic voltages and collector currents.

[zbt]

base on this potentiometer

If you want a lookalike clone -  start with the enclosure. The sliders have to just fit the flat bit of panel. Original slider look might have the cool factor, but it will be difficult to protect the slide potentiometer track free of dust down on the floor so most builds are in the standard stompbox enclosures with rotary pots.

These look the part...
https://www.taydaelectronics.com/potentiometer-variable-resistors/slide-potentiometers/ra300bf-b50k-ohm-linear-taper-slide-potentiometer-dust-seal.html

... but just to frustrate the heck out of us, they only have linear types while the log ones don't appear to have dust gaskets. Probably don't come with screws - usually M2.

the board would be around 73mm x 52mm, I guess

[digi2t]

base on this potentiometer

If you want a lookalike clone -  start with the enclosure. The sliders have to just fit the flat bit of panel. Original slider look might have the cool factor, but it will be difficult to protect the slide potentiometer track free of dust down on the floor so most builds are in the standard stompbox enclosures with rotary pots.

These look the part...
https://www.taydaelectronics.com/potentiometer-variable-resistors/slide-potentiometers/ra300bf-b50k-ohm-linear-taper-slide-potentiometer-dust-seal.html

... but just to frustrate the heck out of us, they only have linear types while the log ones don't appear to have dust gaskets. Probably don't come with screws - usually M2.

the board would be around 73mm x 52mm, I guess

30mm Alpha slide pots, with straight metal lever. They're marked "Alpha". The Tayda ones match exactly.

Measured from my unit, PCB is 73.5mm X 52mm.

[zbt]

30mm Alpha slide pots, with straight metal lever. They're marked "Alpha". The Tayda ones match exactly.

Measured from my unit, PCB is 73.5mm X 52mm.

Thank You Sir, may i know what is the distance between the potentiometers?