Vintage Wah Specs

[willienillie]

So, a friend of mine has a Thomas Organ-era Crybaby (with the "stack of dimes" inductor) that I consider to be the benchmark of vintage wah tone.  I guess it's really nothing special, but it just sounds as classic as can be, does Hendrix, SRV, etc. perfectly.  It's my favorite wah that I've played, and has been the main inspiration for my own DIY wahs.

I've worked on it a couple times before, including rehousing it last year into a modern Dunlop shell, as the original was plum worn out.  Well it came back recently for a new switch, battery snap, and an added DC jack.  And THIS time, dammit, I took measurements.  I originally wasn't going to remove anything from the PCB, but I changed my mind and took out the transistors and sweep cap to measure.  No problem, I put everything back exactly how it was!

But anyway, I wanted to share what I got, for the record, and in case anybody else might find these numbers useful.

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My only method of measuring hFE is my RG "FF Select" tester, so consider that.  My tester's two resistors are exact, but I didn't have a battery that read 9.00V in circuit, so I used one that read a little high, another that read a little low, adjusted those readings accordingly, and averaged the results.  Best I can do.

Q1 - 393   Q2 - 251

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The sweep cap measures 10.72nF, the input cap 10.35nF.  I didn't measure the .22 caps.  The "bypass(?)" cap is a 3.9uF, I think tantalum (black bullet shape), I didn't measure that either, but I know from my own experimants that small variations there are inaudible.

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The resistors are all carbon comp and mostly read high.  The "68K" input resistor measured 75.2K.  The "470K" that connects to Q2b measured 503K.

Q1 emitter resistor: 528Ω
Q1 base resistor: 1704Ω
Q1 collector resistor: 23.97K

Q2 emitter resistor: 1234Ω
Q2 collector resistor: 10.17K

DC resistance across the inductor, with the 33K connected in parallel, was 38Ω.

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Voltages!

With my regulated supply reading 9.10VDC in circuit.

Q1c: 3.98V
Q1b: 0.678V
Q1e: 0.105V

Q2c: 8.75V
Q2b: 3.26V
Q2e: 2.812V

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Again, hopefully somebody finds this info useful.  I definitely would have, had it been available when I started my own wah projects.

wacka-wacka

[Rob Strand]

I have a feeling some measurements were posted 15 to 20 years ago on the forum but they are probably lost.

Nonetheless it's good to have as many samples as possible.

[willienillie]

I have a feeling some measurements were posted 15 to 20 years ago on the forum but they are probably lost.

If so, I wish I would have seen them, it would've saved me some time.  But it's been a learning experience for me anyway I guess.

A few months ago I posted hFE recommendations of 415 and 260 in someone else's wah thread.  Those were the numbers I had arrived at by ear, through trial and error.  At the time, my "RG tester" had a base resistor that was a bit higher than it was supposed to be, and gave me higher readings than it does now.  So really, I had almost nailed my buddy's transistor gains without any measurements.  But it took a LOT of experimenting.

And I guess there is no such thing as an absolute hFE anyway, as it varies with voltage and current.  So maybe the voltage and resistance measurements above are better indicators of actual conditions.  But for starters, consider those "ballpark" numbers.

it's good to have as many samples as possible

For sure.  And by no means do I intend to imply that this is the only classic sounding wah out there, just one very nice example.  I've played several TDK inductor wahs that were pretty much just as good, and I'm sure they had some different component values.

[Rob Strand]

I know I collaborated with someone on the group and traced a very early Thomas unit.   I can't remember the if gains or voltages were measured. 

Dan N measured 10 x 5117 transistors in this thread,
https://www.diystompboxes.com/smfforum/index.php?topic=18668.msg110248#msg110248

"I just tested 10 for hfe and they averaged around 325. The highest was 496 and the low was 258.  ECB pinout. "

I maybe have some collated info on the 5117.

When I get my new PC up and running I'll have a look through my stuff.   At the moment it's not easy to get to.

[Chugs]

Great info, thanks.

What transistor type does the Wah have? 5117?

[Audiotrove]

Not to hijack this thread, but since we're on the topic of vintage wah information, can anybody help me out with this?

I believe this a CTS pot, but maybe a replacement. I'm not sure what this is exactly. Can anybody tell me what the numbers on this wah potentiometer mean?

The codes read 295S0114 9537 ROC CTS

If the 9537 is the date code, this is obviously a replacement. This is in a Thomas Organ Vox V846 Sepulveda with a TDK 5103 inductor, which appears to date from 1976.

I'm also looking for suggestions on what to replace this with. Thank you.

[willienillie]

What transistor type does the Wah have? 5117?

The Thomas Organ "5117" transistors were Sprague 2N2925s.  They were usually seen in the TO-98 package, but in the later Thomas years became TO-92, but the same transistors.  FWIW, the early Dunlop Crybabys were made with leftover Thomas parts, including "5117" transistors.  Also FWIW, the Dunlops were always called GCB-95, even before they added the input buffer circuit.  I have some 2N2925s from Sprague, GE, and Solid State brands, with gains from about 100 to about 430 (from memory).

[willienillie]

Not to hijack this thread, but since we're on the topic of vintage wah information, can anybody help me out with this?

I believe this a CTS pot, but maybe a replacement. I'm not sure what this is exactly. Can anybody tell me what the numbers on this wah potentiometer mean?

The codes read 295S0114 9537 ROC CTS

If the 9537 is the date code, this is obviously a replacement. This is in a Thomas Organ Vox V846 Sepulveda with a TDK 5103 inductor, which appears to date from 1976.

I'm also looking for suggestions on what to replace this with. Thank you.

Yes it's definitely a replacement.  I remember these being called "ROC Pots" back in the 90s, which maybe sounded cool, but ROC stands for Republic of China, aka Taiwan.  CTS pots are still made there.  The current 100K HotPotz II with the square body is an excellent replacement, it has a nice taper and should last a good while.

[Rob Strand]

FWIW, I had a quick look through my unsorted notes on backup:
- Could not find voltages.   There were voltages but the pedal had a problem, so they are rubbish.
- Schematic mentioned gain of 490.  Seems high.

You will have to wait until I get my sorted notes back on line

[Eb7+9]

... hopefully somebody finds this info useful

what about coil inductance and associated DC resistance ??

[willienillie]

what about coil inductance and associated DC resistance ??

I listed the resistance, albeit with the 33K still in parallel.  I have no means to measure inductance, and I wouldn't risk removing that from his board even if I did.  It seems common knowledge that they were normally 500mH or close to that.  FWIW my early Dunlop also has that stack-o-dimes inductor, but reads about 6 ohms higher resistance, in circuit.  But transistor gains were the main point, since there's little info to be found online about that, and it really makes a difference between "working" and "sounding great."

[Rob Strand]

FWIW, the "other" forum has a thread where 5117's were measured gains at 416 so the 490 on my schematic is probably correct.

The unit I traced back in 2003 had an "03" stack of dimes which measured 45 ohms.

[willienillie]

"03" stack of dimes which measured 45 ohms.

Same as my '83 Dunlop