fetzer based marsha valve tube

Night0wl · February 23, 2006, 05:35:33 AM

Hi all,

Is it possible to substitute the cap and resistor values at the beginning of the Marsha Valve Tube circuit (ie; the 2k7 pin 3 to a 1k5 and 0.68uF pin 3 to 22uF elec) to be similar to the fetzer circuit? I noticed the schematic seems similar to the fetzer and I don't have the 2k7 and 0.68 value resistor and capacitor but I do have the 1k5 and 22uF.

If it is possible, would I have to change the rest of the values throughout the circuit aswell?

Thanks,
Shane

vanhansen · February 23, 2006, 08:11:59 AM

Sure. That's not a problem. The Marsha Valve came to be from the Fetzer Valve actually. Fetzer = Fender, Marsha = Marshall.

By putting in 1.5k/22uf off the source and moving the 1M resistor after the 68k input resistor, that would make it a Fetzer Valve. Or you can leave 1M where it is.

Have fun with it and experiment.

Night0wl · February 23, 2006, 03:01:10 PM

Cool! would that also mean changing the other resistor values in the circuit?

I am trying this schematic, replacing the 2k7 and .68u components. By doing that would I also have to change the 100p, 470k and 10k components aswell or doesn't it matter?

I tried breadboarding it last night, copying this layout and all I got was a strong 'hum' sound that got stronger when the trimpot was turned. All I did different was change the 2k7 to 1k5 and .68uF to 2.2uF and left out the 100p but everything else was the same. Atleast I got the valve to light up!

Any ideas??

Thanks,
Shane

vanhansen · February 23, 2006, 03:15:14 PM

You shouldn't have to change anything else. That's good the tube lights up. Being that you got hum we know there's something coming out. Now it's finding out if anything is going in. Audio probe time. Also check and double-check the pin connections. What kind of power supply are you using, 12V?

Mihkel · February 23, 2006, 03:49:53 PM

You say you breadboarded it? Did you make sure to get all the "stripes" correct, as if you were building it on vero? If you find anything wrong with the layout, let me know!

Night0wl · February 23, 2006, 07:14:56 PM

Yes I am using 12v power supply.

I am pretty sure I had the layout right on the breadboard. I dismantled it (using the dining table is a hassle!) and I will try puttng it together again today and see how it goes.

Cheers,
Shane

Night0wl · February 24, 2006, 04:35:40 AM

OK....I rebuilt the marsha valve tube again (breadboard) and I got a very faint distorted signal that sounded like an octaver! I triple checked all connections, wiring and everything to make sure it was all correct with the schematic. Then I compared it to the vero layout and everything checked out fine. I still get the loud 'hum' aswell as a very weak 'octaver' guitar signal. Are the valve socket pin connections correct in the vero layout? I am not sure where else to look.

Thanks,
Shane

Mihkel · February 24, 2006, 05:25:14 AM

Hmm...

Pin 1 goes to the 100k resistor, 0.022 and 100pf caps.
Pin 2 goes to the 68k resistor on the input.
Pin 3 goes to 2k7 and 0.68.
Pin6 goes to 0.022 and 100k.
Pin7 goes to 0.022 and 470k
Pin 8 goes to 10k

... looks alright to me..

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fetzer based marsha valve tube