"Vibratone" Submini Tube Guitar Amplifier

[frequencycentral]

I designed and built this for stereovoid, who was one of my early Murder One customers (he has #3, the first one built in a 1590B). He asked me to build him something similar but with more features, so it's based on Murder One but using a 6112 submini dual triode for the preamp instead of a 6111, a little more gain, which makes up for the losses in the tonestack. There's a bypassable MOSFET boost, based on a varient I developed for Le Craquement Thermionique, but without the Mu amp part. There's also a tremolo section, based on the Vibracaster , but modded slightly for this application. The tonestack is Muffy based. There's a pre amp output taken from after the volume control, and a dummy load on a switched socket, so when there's no speaker plugged in the transformer secondary is bridged by a 18ohm 3 watt resistor (I forgot to add that part to the schematic).

It's really flexible! I wish I still had it to make soundclips, but but's gone to it's new owner. Great as a standalone practice amp, with built in effects - the boost is insane - instant massive compression and feedback at the highest setting! It's even more fun as a preamp into another amp, with a lot of control over the sound using the gain and volume in combination, the boost and trem just add to the fun.



Here's a direct link to a larger version of the schematic: http://dl.dropbox.com/u/967492/Vibratone.JPG





...not my neatest build, but it was a work in progress, took a bit of modding to get it all just right, hence the long wires - gave me a bit of wiggle room when modding different sections.

[Plan B]

Fack....right as I'm about ready to finish soldering up the Murder One...

Oh well--guess I'll eventually have a "modular" FC amp one day.

MO, Vibratone, Promiscuous Girlfriend...sounds like I'm gonna be busy for quite a good minute.

Edit: bah! Almost forgot the superfly too!  Better let the neighbors know they won't see me for a few weeks.

[Brymus]

NICE

[Toney]

 Yeah....awesome work Rick, I want one.
Are you still able to find 6112's? I have never been able to get any locally.

[frequencycentral]

Are you still able to find 6112's? I have never been able to get any locally.

I've got a small stock. They are always available on Ebay if you're willing to pay top prices, though they occasionally go for cheap.

[KazooMan]

Thanks for sharing the schematic!  We all appreciate it very much.

This looks like a challenging build, but it should be a lot of fun.

[Sidd]

Looks like a nice amp. How exactly did you arrange the dummy load on the output?

[frequencycentral]

How exactly did you arrange the dummy load on the output?

The load resistor is on a switched socket. This is a mono socket but with an extra tab, when there is no jack in the socket, the tip makes contact with the switched tab. The load resistor is wired between the switched tab and ground, so when there is no jack in the socket the O/T secondary sees an 18 ohm load. When there is a jack in the socket the load resistor is disconnected. I used 18 ohm because I had that value available in a 3 watt resistor, I guess 8 ohm would be more in keeping with the O/T's ratios, but I've used Murder Ones extensively with 16 ohm cabs, 18 seems close enough to me, it should work out fine.

[Ben N]

A suggestion: Rather than bypassing the mosfet stage altogether, how about switching between boost and buffer mode? (Jack Orman has some suggestions as to how one might accomplish that in the Mosfet Boost article.) That way you still have the high input impedance, and the amp wont brighten up when you kick the boost in.

[moosapotamus]

badass! 

[KazooMan]

Rick:

Is the enclosure a 1590B or a 1590BB?  From the pics it looks like the ratio of length to width is more like a BB.  Lots more room in the BB.

1590B  length/width = 4.39/2.34 = 1.87

1590BB length/width = 4.67/3.68 = 1.27

Thanks

[frequencycentral]

It's built into an:

Eddystone 120mm X 95mm X 30mm.
Manufacturer: Hammond
Manufacturers Part Number: 29830PSLA

[Hides-His-Eyes]

A suggestion: Rather than bypassing the mosfet stage altogether, how about switching between boost and buffer mode? (Jack Orman has some suggestions as to how one might accomplish that in the Mosfet Boost article.) That way you still have the high input impedance, and the amp wont brighten up when you kick the boost in.

I dunno, a bit of brightening is probably a good thing for a boost.

[KazooMan]

Thanks, Rick.  That would be equivalent to a 1590BB here on the other side of the pond.

[frequencycentral]

A suggestion: Rather than bypassing the mosfet stage altogether, how about switching between boost and buffer mode? (Jack Orman has some suggestions as to how one might accomplish that in the Mosfet Boost article.) That way you still have the high input impedance, and the amp wont brighten up when you kick the boost in.

I wanted the amp to have the option to be pure tube without the MOSFET in the signal path. If you did want the boost/buffer option though, changing the boost pot to a standard SHO arrangement would give you that, as the SHO appears to be at unity (or very close to) with the pot at minimum. As it stands now, my boost pot is higher than unity at minimum, and higher than an acid-crazed hippy at maximum.

badass! 

Thanks Charlie!

[Ben N]

Got it. Anyway, the whole thing looks great.

[Brymus]

and higher than an acid-crazed hippy at maximum.

Around here it would be higher than a tweaker helping you find the stuff he stole from you...
or higher than tweaker 2 hours after leaving the pawn shop...

[KazooMan]

Hey Rick.  I need some advice!

Well, I am well into building the Vibratone, thanks to Rick's generous sharing of the details on how he pulled parts of three of his builds into one project.

I have all the sub-assemblies I can make put together.  The Main board (based on the original Murder One with several mods), the Boost section, and the Tremolo section.    I am awaiting a box to mount it all in, and it's in the mail.

However, I have a small problem.  I followed the Murder One design using the 1 and 2 watt resistors in series with the tube heaters to get the desired voltages.  No joy here.  I have a rock solid 12 volt supply but my heater voltages are way off. Perhaps I am taking the measurements improperly.  I did purchase some voltage regulators and some relly great looking heat sinks from Mouser just in case, but they will take up more room and I would like to keep this as small as possible. 

Here's the Noob question.  Is it correct to measure the filament voltage by reading from the hot side to ground with NO load or input on the tube?  As I mentioned, I have a good 12 volt source.  The charge pump side of the build seems fine giving me about 80 volts at the end of the bank of caps. 

I got my 6112 from on ebay and my 5672 from Small Bear. 

[frequencycentral]

Cool that you've taken this project on!

6111: with an 18R / 2 watt resistor connected between +12v and pin 3, and pin 6 connected to ground, you should get ~6.3v at pin 3 irrespective of what the other pins of the tube are doing.

5672: with a 220R / 1 watt resistor connected between +12v and pin 3, and pin 5 connected to ground, you should get ~1.25v at pin 3 irrespective of what the other pins of the tube are doing.

Might be worth you checking the pinouts of both tubes, and also checking for shorts.

Also, check the recent posts in the Murder One thread re 5672 from Small Bear.

[KazooMan]

Thanks for the reply.  As far as the tubes go I do have the correct 5672.  Pinouts are correct and no shorts. 

I am glad to know that my understanding of a voltage divider is OK!  I think I figured out the problem.  My 12 volt supply is only 200 milliamp and apparently can't keep up with the board.  I was reading about half of what I should for each filament.  When I checked the 12 volt supply (DOH  ) I found it was pulled down to 6.7 volts.  It's adjustable so I can compensate to continue on with the build, but the real solution is probably a beefier power supply.  At least I haven't gone to the opposite extreme and burned up a tube.

The other option is to try the voltage regulators to see if the current draw is as high as the resistor approach.

I had tested the charge pump before installing the tubes so the draw from the filaments was not present when I got that good reading.