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Author Topic: power supply for a hybrid  (Read 4954 times)

awdman

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power supply for a hybrid
« on: April 21, 2009, 12:33:51 AM »
I am creating an amp using the TDA7293 and have completed the main stage. I need to know since tubes require high voltage and I am running 36 vdc to the main will I have to use 2 transformers? What is the best Tube preamp schematic to use with this chip? and should I do solid stare instead of tubes on the preamp?

Thanks,
Anthony

teemuk

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Re: power supply for a hybrid
« Reply #1 on: April 21, 2009, 09:55:41 AM »
The high voltage is not mandatory so you could use starved voltage (is the 36 Vdc a single rail voltage? It would mean you could actually run the tubes on 72Vdc (voltage difference between rails). For a "starved" voltage that already is a quite big figure.) Another option is a voltage multiplier, which should work perfectly with preamps that do not draw great amounts of current. In each case, the tubes will definitely need their own power supply and rectifier but you can save the expense of finding another power transformer. The filament voltage... now, that's your real problem....

awdman

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Re: power supply for a hybrid
« Reply #2 on: April 21, 2009, 04:28:47 PM »
I am using ±36Vdc, what is the defintion of "Starved" voltage.  As for the fillament I would just use about 5V correct?

Enzo

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Re: power supply for a hybrid
« Reply #3 on: April 21, 2009, 07:07:38 PM »
You can also use a voltage doubler/ tripler/multiplier circuit running off the same power transformer to generate a higher voltage for a tube.  Your common tube preamp stages only draw a milliamp or two.

If you use common tubes like 12AX7s in your preamp, each tube has two triodes in it.  The heater in each tube serves both triodes and can either be wired for 6V at .3A or 12v at .15 amp.  That is per tube.  How many tubes will you have?  If you have three tubes, then you can run their heaters in series wired for 12v each.  That makes 36v, and you could just power those heaters off your existing supply.  it wouldn;t be much of a strain to come up with a similar plan for two tubes or even just one.

phatt

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Re: power supply for a hybrid
« Reply #4 on: April 24, 2009, 12:10:11 AM »
To awdman,
Your idea of Valve pre Amp SState powerAmp has been done to death
Try it the other way round and you will achieve a lot better results.
Although you get some benifits from valve preamps it's nowhere near as good as a Valve power amp stage,,,,
---------THAT is where the magic happens NOT the preamp.-------
I am speaking because I've done this stuff both ways,,,,
Just my 2 cents worth.
Phil.