Valvecaster troubles

[Xander8280]

Built a valve caster, a few changes to the original schematic. I have a pot at the grid of V1 for a pad/pre gain control. I'm only getting audible guitar sound with a booster pedal in front of it. very staticy and crackly when I do get sound. Basically silent, no hum. Very gated static output if any output.


I've checked everything. Running 9v with a AU7.

going crazy

My lack of a input cap?

I have it set up like a typical tube preamp just different voltages.

[Xander8280]

My plate resistors are 100k and I'm getting about 9v on my plate pins....
Read that the voltage should be around 3v?

Possible cold solder joint?

[xtian]

Wow. Cool.

http://www.beavisaudio.com/projects/ValveCaster/

How does the heater run on 9v?

Anyway, simple project. Either a bad tube or an error in wiring, don't you think? Post photos and I'll help you look.

[M Fowler]

This is a starved plate design and I don't think work well at all but I'm not a good pedal builder.

Go larger with transformer to get 200v and then it will sound good.

One local tag guy built one we tested out but he is using 18v.

[tele_player]

How does the heater run on 9v?

The heater voltage is low, but should generate heat if there it's sufficient current available at 9v.

Robert

[dorrisant]

I agree with Mark... Matsumi or whoever designed it did it as a proof of concept. I used a toroid transformer from Amveco to put about 200v on the plates for better function and tone. It should work without the boost as it is though.

I have a handful of 6BF7s that I would like to try this way. If you look at the datasheet you can see that a handfull equals quite a few of them. Anyway...

Did you mount the components on the sockets? Pictures?

Tony

[Stevem]

How the hell does a 9 volt stomp box supply have enough current to fire up the heater in that au7 and yet power the tube also?

[martin manning]

12A_7 12V heater running on 9V only draws about 130mA.

[Stevem]

But the start up current surge on DC is huge!

[matt h]

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[martin manning]

But the start up current surge on DC is huge!

Maybe 2x the steady-state current? Not a big deal IMO.

[Xander8280]

How did you wire the input pot?

Anyway, with such low voltage it's quite possible the grid will start drawing current, in which case having that cap on the input is important. If you replaced that grid leak with a pot, depending on how it's wired, that can screw with your bias, acting as a grid-leak-bias resistor.

That's where I'd start looking.

This is great thanks!

Also the fact that my point to point rats' nest is too embarrassing to post of photo of means I should clean things up.

[matt h]

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[Xander8280]

I don't know what your background is, so apologies if this comes across as condescending... but I view electronics building a lot like cooking and follow my mother's advice: first time making a dish? FOLLOW THE RECIPE. It's one thing to mod something that already works, than it is to change something before it launches and try to troubleshoot after the fact.

My background isn't vast, I'm just a student. I get excited and push things a bit. That analogy is perfect and I need to stick to that.

[vibratoking]

This isn't the first starved plate design. The often lauded Butler/Chandler Tube Drive is a starved plate at like 25V or so. Many guitarists are in love with it. Whether you think it sounds good is a different story, but Eric Johnson was able to boost it into epic proportions. I have one and it is very good at what it does.