VOX Beatle 500 mH Inductor

[CJ]

the Vox Beatle amp has some 500 milli Henry torroid  inductors in it,

 

[CJ]

we can get a close approximation of the turns by using the PRR method of winding a phantom secondary around the core and taking measurements,

it looks like this coil has about 415 turns around it,

by computing the turn length and using the DCR specs of the wire chart, we can figure out what size wire it is,

this stuff looks like #39

 

[CJ]

here is a cut sheet with the Dims and a few other electrical characteristics,

why all the interest?  it just so happens that the first Wah Wah pedal was a direct result of using a pot instead of a 4 dollar switch to control the mid range boost on the Vox beatle amp . By turning the mid knob fast, a wah wah sound was heard. so they attached a string to a pot and the rest is history.

me was thinkin that since the Crybaby pedal uses a 500 mH inductor, that is inductor here might have been used in the first wah wah pedals. some folks like the sound of the older wah pedals. since the inductor shapes part of the sound, we might be able to mod a current pedal with a vintage inductor.

 

[CJ]

there are some after market inductors made for the crybaby by a few people. Fasel, Fulltone, Halo, and a few others. Most are pot cores modeled after the TDK inductors,  i believe that some of the Fasel inductors are torroid cores.
none have the 19.5 ohm DCR spec. There is a gap in the knowledge  as to the specs of the really old pedals from JEN in Italy, and the Thomas Organ pedals, so hopefully this 67 Beatle amp has shed some light on the subject.

 

[CJ]

we have some freq plots graphed out for 40 Hz, 100 Hz, 1000 Hz and 2000 Hz that we will post in a few hours.

it will be fun to wire this into a pedal and see what happens.

 

[CJ]

here is a frequency vs voltage graph, the inductor saturates at a fairly low voltage at low freqs as the flux goes up, which may be the reason why they sound different than the bigger pot core,

 

[Gus]

CJ

Joe knows about whas. You might want to contact him.

https://www.youtube.com/user/joegagan

 

[CJ]

thanks Gus!  that guy is king of the wah wah pedal fo sho.

 

[kpearsall]

Just a note for archival purposes. That Inductor doesn't look correct for the original wah. I'm not an expert on the sound differences of inductors or anything but I recently went through quite a few original Clyde wahs and the one and only prototype wah (which are actually slightly different!) and they all were made with the same inductor, which is a stack of dimes type, with a bolt through the center. If you want the exact inductor, don't worry about the vintage amps. Start looking around for old and broken Thomas Organs. Vox was so unsure that the wah would even be a good seller, they didn't really invest in new custom parts. It was invented and subsequently produced with the same parts they had sitting on the shelf.

 

[CJ]

had a chance to check out a Thomas Organ wah wah, so we ran an inductor test and also ran the same test on a newer Dunlop GCB-95 to see what gives,

in this pic the Thomas Organ TDK inductor is top, Dunlop on the bottom>

 

[CJ]

here is the inductance vs voltage  test, the newer Dunlop has a higher DCR probably because there are more turns of small wire on a lower perm core,

the Thomas Organ TDK looks very much like the inductor we pulled from the VOX Beatle amp as tested above, DCR is also very close,

 

[CJ]

we pulled the original transistors for the Thomas Organ circuit and did a gain chart.

p/n is 5117,

 

[CJ]

pc board

 

[CJ]

in circuit ohms check

 

[CJ]

this project is finished, we ran a freq plot with different pot settings, this model has a log 100 K which is kind of on and off, a linear pot would probably sound better,

 

[CJ]

and a voltage chart ,