TW Express clone with a Post PI Master Vol...

[John_P_WI]

Ampdoc,

Thanks for the update to your quest. I find this a very interesting and unique approach. BTW, on your test rig that you ran for 4 weeks, do you recall the plate voltage?

Thanks in advance,

John

[surfsup]

What were the voltages on the power tube filaments? I saw this somewhere else:

Filament life goes down with a power of the applied voltage. I can't remember the actual exponent. I do know that for light bulbs, it is the 13'th power of the applied voltage (!) which is why "long life" bulbs are simply designed for 130V instead of 120 like other bulbs - they're the same technology, just running within their nominal voltage even at high line voltage. For the lower temperatures involved with heaters, it may well be a lower exponent, but it's worse than the fourth power.

This means that tube life drops dramatically for every bit of voltage over nominal - and increases dramatically (as long as hard life in a rock-n-roll band doesn't take its toll otherwise!) for every bit of decrease from nominal toward -10%. For preamp tubes, running them at -5% to -10% can cause a dramatic increase in life, and perhaps more importantly a much higher stability in characteristics over the longer life. Gain is a bit lower, but there is usually more than enough in the amp. For power tubes, you really need the heat to make enough emission so you don't get poisoned cathodes and/or stripping, but you sure don't want to overheat them either, so dead nominal is where you'd like to run them for best life.

[ampdoc1]

John,

The amp I recently tested is a K&M Ruby,..a lower powered Express copy. The plates in this run about 420VDC unloaaded, probably in the high 380-400 running. The first amp I built with the funky pot, was built in the hulk of a TwimAmp 5F8A. which has about 390 VDC at the plates.

Surfsup,

There are several well respected tube gurus who have debunked the poisoned cathldes/srippiing myth, maintaining this is a problem only in transmitting tubes. I don't know the ultimate answer, but after 30 days of 24/7 running my output tubes with ~2.5VDC on the heaters, they didn't show any signs of power loss or other problems.

[ampdoc1]

I knew I had this info, and ran across it today while looking for something else. See the last paragraph on page 3, Heater Standby Switching.

a'doc1

[John_P_WI]

Thanks Ampdoc! Good stuff.

John

[hans-jörg]

Hi,
I tried this out this weekend and must say -I pushed the heater current down to around 2 Volts - its still not bed room! But such a nice tone. No lost at all, than I swiched back to 6,3 V and forgot that I´m on Volume around mid - my wife wanted to pack my bags and throw them out of the window. So there should be rearly a loss of volume changing the heater current from 6,3 to almost under 2 Volt.
Good idea, I only dont know how to handle. But time comes ...
What I done was a high speed diode which tooks 3V and than, step by step, 1 Ohm, and 1ohm and 1 ohm .. on the end: the diode plus 4 ohm =2 VAC

Hans-Jörg

[John_P_WI]

Hans,

Did you scale the voltage to all of the tube heaters or just the power tubes?

Thanks,

John

[My-Co]

Ken had over 50 plus Master circuits, If he wanted to use one he would have done so. IF you use a master you may have missed all together.
just my 2 cents.

[hans-jörg]

Hans,

Did you scale the voltage to all of the tube heaters or just the power tubes?

Thanks,

John

Hi,
I scaled only the power amp tubes down.

Hans-Jörg

[dr. who]

Couldn't you add another tube ala dumblator, but have a fixed send and use the return as the master? That way a MV circuit wouldn't suck tone.

[leadfootdriver]

What about an express with a cathode follower and a pre PI master volume?

[Reeltarded]

Any master changes the sound away from what it is supposed to be, to average.. a good average, maybe, but still.

The outstanding thing the Express does is start clipping everywhere at the same time. It's not about the pre and PI, it's the output moreso than any other amp I have ever heard.

[dorrisant]

I don't know the ultimate answer, but after 30 days of 24/7 running my output tubes with ~2.5VDC on the heaters, they didn't show any signs of power loss or other problems.

Any new info?.. How are the tubes doing?

[Diablo1]

Those fluxtone speakers look like a nice idea, but I think there are too many roadblocks to success. Price being at the top of the list. Losing the ability to use the 'real' speaker of choice, instead of a clone, being next.

The clone speakers that fluxtone is building use the original oem parts that control the frequency response - the cone, voice coil and spider. He's adjusting the magnetic flux in the voice coil gap which controls the efficiency of the speaker.

[leadfootdriver]

Do they sell a stacked pot that's push/pull, so you can defeat the MV?