Transistor/Tube equivalent

[stokes]

I am trying an experiment,I want to build a tube wah-wah sort of thing.I like the sound of a "cracked wah" so I want to use an extra 9pin socket in one of my amps for this.Trouble is I know nothing about transistors and looking at the schem for a Vox wah it seems I could use a 12au7 in place of the 2 transistors in the circuit.Can anybody point me to a schematic,if there is one, for a tube wah,or tell me what values plate/cathode resistors would get me in the ballpark to approximate the transistors?Thanks

[bob p]

If you google for "tube wah", the first hit will take you to R.G.'s writeup.

[stokes]

Thanks Bob,thats what I was looking for.The first time I googled tube wah-wah and didnt get R.G.'s item,or anything of any use,leaving off that last"wah" did it.

[Enzo]

And keep in mind that tubes and transistors are only functionally eqivalent in that each can provide amplification. Beyond that there is no cross reference. That would be like which guitar is equivalent to a snare drum.

You can make a tube curcuit that does what a transistor circuit does, but there won't be a circuit you can just plug a tube in and change some values.

[stokes]

Thanks Enzo,I guess my big concern is the high voltage and where its going.I have a copy of R.G.'s actual tube wah circuit to work with,I am sure you guys will hear back from me if and when I get this thing started.Any body know of any other tube wah circuits out there?I see there is one listed in the "Homebrew/Effects" section here at Ampage,but I cant connect to it for some reason.

[Rob Mercure]

Hey Stokes,

There are lotsa tube designs optimized for low voltages that may provide some circuit benefit - in particular those "space charge" tubes designed for a 12VDC automotive "B" supply - there were scads of these manufactured during the late 1950s and early 1960s and they're still pretty cheap and available. There was even a nine pin miniature dual "triode" (if it's possible to call a four element tube with space charge acceleration electrode a "triode"). I've built a two stage "fuzz box" type circuit with these but moved on cuz they require lotsa heater and space charge electrode current - and get quite hot - and I was primarily interested in portable battery operated devices - but no reason not to use these if you don't mind being tied to an AC power supply and the 12K5 (and it's variants) is a 400 mW output tetrode which you can use to drive a tone stack or speaker (with a 600 ohm matching tranny).

Then there are lotsa directly heated cathode tubes designed for pre-transistor portable radio service usually using a 30-90 VDC "B" source. Many of these will work very well on 30 VDC - or less for signal use - and I'm currently cobbling up a 36 VDC "Herzog" type using a couple of 1W5s triode connected with a 3Q4 or 3V4 output (with individual "A" batteries for each tube's heater to simplify biasing).

And, if you can find 'em (I've got three <grin>) the 8056 Nuvistor is optimized for a 24 VDC supply - and unconfirmed web reports state that they work well on 12 VDC (the same reports state that the venerable 6J5 will work well with only 12 VDC on the plate as long as you've running the heater at 6.3 V or hotter!). Seems like there are other low voltage Nuvistors and that many other tubes - such as the also venerable 6AU6 if I remember correctly (4 AM here in the hills) - also work well.

Please note that the 12 V auto radio tubes get pretty hot and require lotsa ventilation while the 1 and 3 volt battery radio tubes draw infinitesimile currents - the 1W5 has a 40 mW heater so you can safely solder the tube down beside a transistor!

So, hopefully this give you some options for mixing hollow and solid sand without worrying about too much potential difference.

Rob

[Amp Kat]

Certainly you'll have to toy with the gain to get the wah effect you want and I'm thinking the 5119 germanium was about 200hfe which dont' ask me what that is in tube language. Another big part is the Fasel 150mh inductor you'll need and they are all quite different. There are a few that wind their own so that may be an option but finding an old Italian is like pulling hair and there are some Thomas Organs you can but on ebay for a resonable deal and get the fasal out of it which there are two types or shapes. One is potted and the other is gooped. The new fasals in the Dunlop's and other generics just don't sound as good IMO and are quite thin sounding. Much to be said of getting them to sound smooth without sucking all your tone. I played a real Clyde Mcoy that had the picture on the bottom and it sounded awesome but it ate up some volume too.

[TD_Madden]

Spence makes good inductors....I ordered one fom him and like it quite a bit.

[stokes]

Spence makes good inductors....I ordered one fom him and like it quite a bit.

Do you have a link for Spence?Thanks.

[Enzo]

And have we determined that the regular little inductor from a pedal is what the tube circuit would need? Would it have voltage ratings to suit?

[dai h.]

Any body know of any other tube wah circuits out there?

there was a commercial one--a "Kern tube wah":

http://www.google.com/search?q=kern+tube+wah

perhaps someone tried a homebrew but I don't remember. Might try searching Aron's site though:

http://www.diystompboxes.com/smfforum/index.php

[TD_Madden]

Spence's homepage

http://www.shedpickups.co.uk/asp/default.asp