Any experiences with "tone bones" in TWreck Expres

[Tube_S_Cream]

Companies like Tube Amp Doctor etc. provide an adapter socket to use an EL84 instead of EL34 or 6L6. There a two different types of adapters availlable: Class A Triode Mode and Class A Pentode Mode. The output power shall be reduced to 8 Watts (Triode) or 18 Watts in Pentode mode.
No further modifiations or biasing is needet, so it is always possible to use the "tone bones" at home or studio and the big EL34s on stage.

Will they also work (and sound good) in a TWreck-Express Clone?

[ODwan]

I don't really know about the ToneBones. I guess that they use some kinda zener network to get the voltages right.
What I plan to do in the next two weeks is building adapters from octal to noval so I can plug EL84 into my Express Clone. My biasnetwork is set up so that it can provide voltages from 0 to -50. I also will integrate a pentode/triode switch. Maybe that would be interesting to you?

Timo

[Tube_S_Cream]

Yes, that sounds really interesting... by the way ... ich komme auch 70 km westlich von Hannover

[ODwan]

Hui, dann sind wir ja fast Nachbarn! Woher bist Du genau?
Ich bin aus Eime, ca. 40km südlich von Big H an der B3.

Timo

[Darkbluemurder]

I tried the tone bone adaptors in my Bandmaster and my JTM 45. They do not make the amps noticeably less loud although the sound is very good. Have not yet tried it in an Express type amp since I do not yet have such an amp.

BTW I am in Frankfurt.

[stoo]

Couldn't you go from El34s to 6V6s and accomplish much the same thing?
That's what I've done with my old Traynor YBA1. Sounds good!
stew

[Tube_S_Cream]

Couldn't you go from El34s to 6V6s and accomplish much the same thing?
That's what I've done with my old Traynor YBA1. Sounds good!
stew

Will the 6V6 work with a B+ of 420V?

Im am just thinking about doing a sacrilege to use a discrete built MOSFET High Voltage regulator to adjust the B+ and B1 voltage over a wide range.
With such a unit it is also possible to provide a soft current limitation to emulate the characteristic of a valve rectifier.
Some work to do for my SPICE-Tool. When it works fine, i'll post it here.

A nice hint: A free simulation tool with schematic capturing is downloadable at the homepage of www.linear.com (Linear Technology).
It is named Switcher-CAD or LTSpice and offers nearly the full functionality of it's big brother PSPICE.
I really like it to simulate equalizer networks, power-supplies etc. and it is easy to handle.

@ODWan... Ich komme aus Porta Westfalica

[stoo]

The 6V6 from JJ Tesla will handle those voltages no problem!
Check out power scaling here..http://www.londonpower.com/kits/psk.htm
Stew

[ODwan]

he 6V6 from JJ Tesla will handle those voltages no problem!

+1 on this but most other 6v6s also will. 6V6 tubes are notoriously underestimated because of the design center system in most datasheets. Check out Jim Kelley's amps where they take 460V on the plates.

A nice hint: A free simulation tool with schematic capturing is downloadable at the homepage of www.linear.com (Linear Technology).
It is named Switcher-CAD or LTSpice and offers nearly the full functionality of it's big brother PSPICE.
I really like it to simulate equalizer networks, power-supplies etc. and it is easy to handle.

I use LTSpice a lot, too! Great tool yet I need to learn how to use it better. As it happens I am curious about powerscaling, too. Have all TUT issues and read them. As soon as TUT4 comes out I will order it. As it stands now I just can't really get my head about it especially the link between B+ and B- scaling. Has someone some enlightening comments? (@Tube S Cream: Or a LTSpice file? Feel free to mail me timojuenemannATwebDOTde)

Timo

[UR12]

As it stands now I just can't really get my head about it especially the link between B+ and B- scaling. Has someone some enlightening comments? (@Tube S Cream: Or a LTSpice file? Feel free to mail me timojuenemannATwebDOTde)

Timo

Odwan

What would you like to know regarding power scaling? I have a 18watt amp that I added my own version of Power scalling to. It works great.! I have only Scaled a self biasied amp(cathode biased) because it doesn't require the bias scaling. Basically you have to scale the bias circuit in a fixed bias amp because if you just scale the B+ the bias would stay constant and you need the bias voltage to track along with the reduced voltage to the power tubes. There are a few ways people have implemented scaling. You can scale the whole amp (I like this best) or you can just scale the Power tubes or you can scale the power tubes and PI. If you just do the power tubes then the preamp will overdrive the power tubes creating some nasty distortion so some people have added a "Drive Compensation" control which is nothing more that a PPIMV.

I am seriously considering adding power scaling to my liverpool as it is a cathode biased amp and doesn't require the extra circutry to Scale the bias.

[ODwan]

Odwan

What would you like to know regarding power scaling? I have a 18watt amp that I added my own version of Power scalling to. It works great.! I have only Scaled a self biasied amp(cathode biased) because it doesn't require the bias scaling. Basically you have to scale the bias circuit in a fixed bias amp because if you just scale the B+ the bias would stay constant and you need the bias voltage to track along with the reduced voltage to the power tubes. There are a few ways people have implemented scaling. You can scale the whole amp (I like this best) or you can just scale the Power tubes or you can scale the power tubes and PI. If you just do the power tubes then the preamp will overdrive the power tubes creating some nasty distortion so some people have added a "Drive Compensation" control which is nothing more that a PPIMV.

I am seriously considering adding power scaling to my liverpool as it is a cathode biased amp and doesn't require the extra circutry to Scale the bias.

Scaling my Liverpool Clone would be great also, but if you just lower B+ wouldn't that bias it a lot colder? Even with cathode bias?

Timo

[stoo]

If you order the P.Scaling kit from LondonPower you also get a bias supply that senses the B+ and adjusts the bias on each output tube accordingly. The kit also has test points and bias adjustments for each o/p tube individually.
stew

[UR12]

Scaling my Liverpool Clone would be great also, but if you just lower B+ wouldn't that bias it a lot colder? Even with cathode bias?

Timo

Well no, not for a cathode biased amp. The bias is directly porportional to the voltage drop across the cathode resistor. As you lower the b+ the current through the power tubes decreases and you have less of a voltage drop across the cathode resistor lowering the bias voltage. By keeping the cathode positive in respect to the grid this effectivly makes the grid more negative than the cathode supplying bias to the tube(s).

You can order a Power scaling kit from london power to do a cathode biased amp or a fixed biased amp. The fixed bias kit comes with the necessary parts to scale the bias supply and it isn't needed for the self biaed amp so the cathode bias version is a cheaper kit.

The power scaling works realy well and it actually saves your tubes life, unlike a power soak or airbrake that is harder on your tubes and OT. You can set the controls on your amp to get the sound you want and then turn the PS control down to lower the output of your amp. You will get the same tone at a lower volume until you reach a point where your amp isn't putting out enough power to move the speakers enough. At this point you will notice a change in tone. This also happens with speaker attenuators too so it's no better or worse at bedroom levels than any other attenuator.

[ODwan]

Thank you for your insights, Dana! Had I put a bit more thought to it I could have figured that cathode biased powerscaling thing out by myself. After all I think I know how cathode bias works.
I don't think I will buy a kit from London Power cause it will be about 300$ for me incl. taxes and shipping. And the parts are seem to be readily available here in Krautland. And: doing it yourself has that educational side effects!
Whatever, I will post my findings here!

Timo

[UR12]

Thank you for your insights, Dana! Had I put a bit more thought to it I could have figured that cathode biased powerscaling thing out by myself. After all I think I know how cathode bias works.
I don't think I will buy a kit from London Power cause it will be about 300$ for me incl. taxes and shipping. And the parts are seem to be readily available here in Krautland. And: doing it yourself has that educational side effects!
Whatever, I will post my findings here!

Timo

Wow $300 for the Kit. I assume if you have the TUT books then you have the schematic. I have actually scavaged some Power Mosfets from old computer power supplys. Even if the power supplys don't work, the chances are that the Mosfet is good. (I have done 4 or 5 and never found a bad one yet). Just check the part number and check the mfg ratings and the best part is they are free.

I will say that the mosfet gets REALLY hot so a good heatsink is in order. Also if you Mount the mosfet to the chassis and run wires from it to the rest of the circuit make sure you mount the zener right on the pins of the mosfet or you may end up with a little squeal sound when you turn the control. I made a PCB for mine and it works out great. Let us know how it goes with your build and if you need any help just let us know.

Best of luck on your build!