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6W6GT SE or SET or PP...any recommended plan to learn from ?
http://www.diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3577
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Author:  Isophon [ 28 Nov 2011, 23:55 ]
Post subject:  6W6GT SE or SET or PP...any recommended plan to learn from ?

Hi guys,

I have read somewhere that the 6W6 is a real sleeper tube...so I just bought 4 of them on e-bay.

Does anyone from this forum ever tackle this tube...apparently when triode strapped it sounds just like a 45 so I figure hey..lets give it a try I just happen to have a few small Edcor OPT on the shelve.

If someone has any idea as to how to properly bias this tube it would be awesome, this is how I intend to connect it but I can be totally wrong :eek:

Any help with either SE, SE triode strapped or PP would be awesome.
Attachment:
SET_6N1P_6W6GT.JPG

Thanks in advance,
Isophon

Author:  Suncalc [ 29 Nov 2011, 01:09 ]
Post subject:  Re: 6W6GT SE or SET or PP...any recommended plan to learn fr

Give me 24 hours and I'll get you a triode stage load line design optimized for overall performance.

Author:  Isophon [ 29 Nov 2011, 02:48 ]
Post subject:  Re: 6W6GT SE or SET or PP...any recommended plan to learn fr

Suncalc wrote:
Give me 24 hours and I'll get you a triode stage load line design optimized for overall performance.


Awesome Matt !!

Isophon.

Author:  HT Performance [ 29 Nov 2011, 06:13 ]
Post subject:  Re: 6W6GT SE or SET or PP...any recommended plan to learn fr

I like that IRF840 based filter type. I wonder how good can it perform.

Cheers,
Miguel

Author:  Geek [ 29 Nov 2011, 07:50 ]
Post subject:  Re: 6W6GT SE or SET or PP...any recommended plan to learn fr

HT Performance wrote:
I like that IRF840 based filter type. I wonder how good can it perform.

Not for very long with that big cap on the source.

Isophon, you might want to drop that value significantly - it's not even needed there and puts huge charging currents through the MOSFET.

Cheers!

Author:  Isophon [ 29 Nov 2011, 12:04 ]
Post subject:  Re: 6W6GT SE or SET or PP...any recommended plan to learn fr

*** I wonder how good can it perform. ***

It works nicely, before the B+ ripple filter I normally have about 25-30mV of ripple, after the ripple it's down to about 3-5mV so it's dead quiet. This part is taken from Peter Millett's 'Engineer Amplifier so this guy know what he's talking about. See here : http://www.pmillett.com/dcpp.htm

You can fine tune the output voltage by tweaking the 10K resistor.

Rgds,
Eric

Author:  Isophon [ 29 Nov 2011, 12:30 ]
Post subject:  Re: 6W6GT SE or SET or PP...any recommended plan to learn fr

Geek wrote:
HT Performance wrote:
I like that IRF840 based filter type. I wonder how good can it perform.

Not for very long with that big cap on the source.

Isophon, you might want to drop that value significantly - it's not even needed there and puts huge charging currents through the MOSFET.

So, should I be reducing the value from 220uF (the one connected to the source of the MOSFET) to about 47uF ?

Total current through the MOSFET should be around 100mA max. I wonder if the ripple will increase with a 47uF...

Thanks for the help.
Isophon

Author:  tombethe [ 29 Nov 2011, 13:42 ]
Post subject:  Re: 6W6GT SE or SET or PP...any recommended plan to learn fr

In my experience, Mos-Fet filters can perform very well. I have used them with some headphone amp circuits (also the Szekeres)
and with EL84 tube amps. They act like a "capacitance multiplier" (http://www.tcaas.btinternet.co.uk/jlhcapmult.htm
and adjustable regulators http://www.fortunecity.com/rivendell/xentar/1179/theory/seamptheory/SEAmplifiertheory.html (scroll down).

Depending on the design, they provide high currents or high filtering.

Author:  Suncalc [ 29 Nov 2011, 21:58 ]
Post subject:  Re: 6W6GT SE or SET or PP...any recommended plan to learn fr

Ok, I'm not sure exactly what you mean by a "sleeper" tube. The 6W6 is one of the family of lower power beam power tubes for use in support of television deflection service and small audio amplifiers. It is in the same class as the 6V6 (and all it's variants), 6Y6, and 6K6.

While I do believe that the 45v bias point shown in your schematic is probably good if using this as a guitar amplifier, it is far too high a bias voltage for effective SE operation of this tube for decent fidelity. Since the 6W6 cannot support UL operation due to screen limitations, I'll start with a triode strapped design. In this operating mode, the sweet spot for loading the tube is around 3kΩ. So I did three load line designs for the power stage since you didn't mention what impedance were the Edcors you had on the shelf.

Here is the schematic for this design with the pertinent performance characteristics for 2.5kΩ, 3kΩ, and 3.5kΩ loads.
Attachment:
pic764.jpg
You're probably best off with the 2.5kΩ design, but any should be acceptable. Edcor has ten watt GXSE transformers in 2.5kΩ and 3.5kΩ and XSE transformers at 3kΩ. This design needs 20v p-p to drive it so I would use a standard 12AU7 bypassed cathode preamp stage to drive the tube. Something like this. Then if you wanted more gain you could just swap preamp tubes. The whole circuit would look like this.
Attachment:
pic765.jpg

This is a nice simple design that you should be able to put together in an afternoon. If you need help with a PS design let us know.

I hope this helps.

Author:  Geek [ 30 Nov 2011, 04:10 ]
Post subject:  Re: 6W6GT SE or SET or PP...any recommended plan to learn fr

Isophon wrote:
So, should I be reducing the value from 220uF (the one connected to the source of the MOSFET) to about 47uF ?

Total current through the MOSFET should be around 100mA max. I wonder if the ripple will increase with a 47uF...


Yes, and Pete will most likely agree ;)
(we think a lot alike on forums)

I would use 4.7uF to 47uF, not critical. It's more to keep audio floating on the power rail out of mischief (it's a power filter, not a regulator)

The power filter here will be the cap * gm of the transistor.... 22uF * ~4500 = a tad under 100,000uF equivalent filtation. Lowering the last cap to 47uF will do nothing to the ripple, but will go a long way at reducing transistor dissipation on AC charging peaks and turn-on surge.

Cheers!

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