Power Supply Transformer question

[Howlin' Mad Mac]

I came up with this crazy idea to build a clone of an Altec 1566 mic pre (hi z input/output only) into a pedal to add a clean tube gain stage between my guitar & amp kind of like a second channel. I'm using the schematic available here:

http://www.tangible-technology.com/tubes/1566/1566.html

Looking at the power supply schematic the PT has a 110v sec/22v CT sec. To build this as cost effectively as possible would it be possible to use a 110v pri/24v CT sec transformer & a 110v pri/12v sec wired backwards across the 1st 12v tap on the 1st transformer to give me the equivalent of a 110v sec & a 12v sec (from the 1st transformer) for the heaters? Yes? No? Why?

[loudthud]

Link to schematic isn't working but.....

Your idea for the transformer sounds exactly like what Hoffman suggests. He powers a tube stompbox from a 12V wall wort and uses a small transformer to step-up for the B+.

http://www.el34world.com/projects/im...lSchematic.gif

[Russ]

This is related to Loudthud's post, but I'm planning on using the same Hoffman PT for a 1 stage tube booster/pre pedal build.

http://www.el34world.com/projects/im...lSchematic.gif

In the above Hoffman's schematic he taps off the 12vac to make a 12VDC supply to run the filaments & the LED. My pedal is kinda tight on space so I'm wondering if I can eliminate the 12VDC rectifier/capacitor/regulator components and just go with elevated 12VAC for the filaments and the LED as in the attached schematic. Basically I'd be running the LED & the filaments off of 12vac with pin 9 elevated. Any thoughts on if this will work and/or if it might be to noisy?

Thanks,
Russ

[loudthud]

Hoffman's preamp has substantial gain and that might be the reason for the DC heater supply. It's hard to predict the amount of noise in advance when you try to squeeze things into a tiny space. The DC heater supply might have been an attempt to fix the hum after the first pedal was built. The elevating of pin 9 is a good idea, but it mostly reduces the line frequency (60Hz in the US) component. It won't get rid of 120Hz buzz. You certainly can try AC heaters and hope for the best.

A word of warning: The small transformers in wall warts and the one used to make B+ have very poor voltage regulation. A 12V 1A wall wart might put out 15V or more at low current. So you may need to add a small resistor in series with the heater to reduce the voltage to the tube. Also, you might come up a little short on the B+.

[loudthud]

Weber VST now sells a transformer, WPDLPT, that is claimed to produce 260VAC from 12VAC. Not much different from using an off the shelf filament transformer with a universal primary.