VOX (JEN) Tone Bender - circa 1966 - 197(?)  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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modman
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Post by modman »

LucifersTrip wrote:
sinner wrote:Nice, I see nothing (cheep shit screen I have here).

It's low gain transistor 10-40hfe... and NPN indeed
according to this, it's a power transistor....which is doubtful
http://transistor-spravochnik.ru/descri ... n5580/5047

I built the ge version a while back with this schematic:

[ Image ]

It's a smooth, thin & very trebly (look at in/out caps!) fuzz with very good sustain. If you don't like the mushy-ness or darkness that you can get with some ge FF's, this is for you!

At the time, I had no idea what Q2C voltage was supposed to be, so I have an external pot. I believe Solidhex noted that it should be a bit higher than a Fuzz Face...but how high? Were there voltage measurements from an original in any threads here....
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02.JPG
Vox Tonebender SFT transistors 02
Vox Tonebender SFT transistors 02
Vox Tonebender SFT transistors 01
Vox Tonebender SFT transistors 01
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modman
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Post by modman »

More 60s Vox SFT transistor Tone Bender guts
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60s Vox Tone Bender SFT
60s Vox Tone Bender SFT
60s Vox Tone Bender SFT
60s Vox Tone Bender SFT
60s Vox Tone Bender SFT
60s Vox Tone Bender SFT
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Post by modman »

And here's a third one with still other caps
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60s Vox Tone Bender SFT 03/03
60s Vox Tone Bender SFT 03/03
60s Vox Tone Bender SFT 03/02
60s Vox Tone Bender SFT 03/02
60s Vox Tone Bender SFT 03/01
60s Vox Tone Bender SFT 03/01
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sinner
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Post by sinner »

Yep. They comes in all sorts of different flavours cap-wise

I got it covered and documented here

The ones ain't know shit about are the ones with silicon transistors. You know, the same board's layout but with silicons. Not the later ones with clipping diodes

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Post by ringworm »

Regarding the silicon transistors, does someone know 'The Captain', to ask him? If the silicon gut-shot is indeed his... http://stompboxes.co.uk/forum/viewtopic ... =10#p12741
I definitely think one is 2N5550 but I can't read the other.

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Post by sinner »

I have RE to many DAM and EFE pedals to be brave enough to ask him ;)

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Post by ringworm »

I'm sure he appreciates your attention to detail :wink:

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Post by polifemo »

Got one of these at home right now.

6.1v on Q2's collector.

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Post by polifemo »

Here are some pics

Image

Image

Image

Image

Great sounding unit!

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The Rotagilla
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Post by The Rotagilla »

Question for you guys. RG Keen’s schematic shows a 47k resistor in parallel with the 500k volume pot which (and correct me if I’m wrong) drops the value of the volume pot to 42.96k. Fuzz Central’s schematic omits the 47k resistor and shows a 50k volume pot. My question is this…is there any particular need for the 47k resistor?

Thanks!
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Post by ljn »

Using the 47k resistor in parallel with the 500k volume pot cuts bass. If you use a 50k pot for volume, it isn't necessary.

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Post by The Rotagilla »

ljn wrote:Using the 47k resistor in parallel with the 500k volume pot cuts bass. If you use a 50k pot for volume, it isn't necessary.
That's what I thought, just wanted to check. Thanks!
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Post by ljn »

Glad to help. Just remember that in these fuzz circuits, a smaller value on the volume control will always cut bass.

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Post by The Rotagilla »

Also wondering about the resistor that goes from lug one to ground on the fuzz pot. I've seen schematics with a value of 820r and 8k2, has anyone verified that an 8k2 was ever used or is it a color band reading error?
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Post by ljn »

Every schematic and gutshot I've seen of this circuit has a 820 between lug 1 of the attack control and ground. If you tried a 8k2, it would be so distorted that it would barely pass signal (if at all ).

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Post by LaloFP »

Hi!

So.. is there any news about the Si transistors? Gains?

Some mension 2n5550 or 2n5551 for one, but dont know about the other.

Thanks!

:horsey:

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Post by modman »

Here's what I could grab from a recent Reverb listing:
Vox Tone Bender 1967 04 tracing.jpeg

Transistor is as yet unseen RCA SK3004 (radiomuseum spec sheet):


7F = July 1967?
7F = July 1967?
Still a few for sale on Ebay (and he's gots da baax!)
8D = April 1968?
8D = April 1968?
RCA SK3004 box.png
Here are the rest of the gutshots from the Reverb auction:


Vox Tone Bender 1967 01.jpeg
Vox Tone Bender 1967 02.jpeg
Vox Tone Bender 1967 03.jpeg
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Post by mozz »

Probably was repaired sometime in the past. The RCA SK3004 is a cross to the factory transistor (and hundreds of others). I have some here, they are really crappy transistor leakage wise.

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Post by modman »

mozz wrote: 23 Jan 2022, 20:04 Probably was repaired sometime in the past. The RCA SK3004 is a cross to the factory transistor (and hundreds of others). I have some here, they are really crappy transistor leakage wise.
Just posted those because they were such clear and beautiful gut shots... Red dot on the original transistor is paint, on the SK3004 it's marker. And period correct transistors are still available it seems. Now I'm even beginning to doubt the originality of that nice row of carbon comps... other gut shots of this pedals always show stranger assortments of resistors.
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Post by nightraven »

modman wrote: 23 Jan 2022, 23:58
mozz wrote: 23 Jan 2022, 20:04 Probably was repaired sometime in the past. The RCA SK3004 is a cross to the factory transistor (and hundreds of others). I have some here, they are really crappy transistor leakage wise.
Just posted those because they were such clear and beautiful gut shots... Red dot on the original transistor is paint, on the SK3004 it's marker. And period correct transistors are still available it seems. Now I'm even beginning to doubt the originality of that nice row of carbon comps... other gut shots of this pedals always show stranger assortments of resistors.
The carbon comps look fine to me. This model was in production for several years, and so it's not unusual for the parts selection to change over time.

My grey Vox has the same set of resistors. Mine does, however, have a tropical fish input cap, instead of the Arco cap, but that's also normal because my Vox is ever so slightly younger than the one in your pics. (Don't mind the blue electrolytic -- I had to replace the dead Ducati with that one myself!) The shielded wiring is different between the two pedals as well, but both types have been seen used in other examples, so that's not suspicious either. It's just the RCA transistor that I haven't seen before. Would those have been available in Italy?

Image
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