Power Supply for Tweety

“Granny”

High-Power Birdseed ...

Last modified: 31-Oct-2006

Tweety needs more power ...

Now I finished the amplifier part of Tweety it is time to finish Tweety's power supply. As shown on pictures of Tweety on the previous page, Tweety's amp contains a Hirschmann connector allowing to mix'n'match powersupplies and amps as long as they contain the same Hirschman connector and connections. Initially I connected some wires to "scratch" and a Hirschmann plug to feed tweety, and a while I played with the finisched powersupply only withou the power transformer itself (used an old 14Volts transformer (filaments) with a 12V step up transformer (for B+).

But there's nothing compared to your own power transformer from AE-Europe of-course. And because of the small footprint inside the box Will Blauw of AE-Europe made a special version of the transformer which was lower than the standard one for a nice price (thanks Wil).

Because Wil takes his time with hifi transformers, there's a long waiting list, and I had to have patience for several weeks. When I finally received my transformer and 10H choke it turned out that everything fitted exactly (not one spare mm ), and the rectifier circuit etc. had already broken in.

I decided that Tweety would receive it's food from Granny ..

the PowerSupply design

Granny's design is simple and effective. Because of floorspace available in the box I could not make use of tube rectifier circuits. I had to find and use small yet good components. I therefore made use of 4007 diodes for both the B+ and the filaments. Also I decided for space-sake to make use of Elco's in the B+ of Tweety. At a later stage I might redo the power supply and work with oil-caps or MKP in combination with a second choke.

For the filaments two 2200uF Elco's are used followed with a voltage regulator (78S12, the 2A type). After the voltage regulator two caps of 22uF are used, one inside the power supply cabinet and the last one is soldered on the first tube socket.

The ground lines of the amplifier power are directly connected to the 0V/Gnd lines of the filament power. For the tubes I used (ECC83 from JJ-Tesla) this is allowed, but a more elegant solution would be to lift the potential of the filament supply to 70Volts DC. This can be easily done by two resistors (and a cap) making a voltage devider giving the filaments an offset of about 70Volts. This will prolong the life of the upper tube in the SRPP stage. At this moment that tube operates with a plate voltage of 280 Volts and a cathode of 140 Volts. Using a filament supply of just 0-12 Volts is within specs but not the best solution.

Below you will find the power supply setup (please do not pay attention to the component numbering, it's broken)

The Result ..

The resulting power supply is more than capable of feeding Tweety. The transformer is slightly oversized and will therefore not get warm even if I decide to leave Tweety on for several days. This is very important since tweety's cabinet is closed without air ventilation but because it is made of Aluminium with cooling ribs I do not foresee any problems with that. The power supply box is fairly heavy and it will be a challenge to redesign such a powersupply such that it uses a tube rectifier and larger (MKP in oil) capacitors. It will be fun to try though.

Todo

Since there is always room for improvement, I'n thinking of the following:

• I feel challenged to try to fit a tube rectifier in, but probably this is going to be too difficult.
• Better power stabilization by using a couple of transisssstors or a tube (footprint ???)
• I could use a more flexible power interconnect cable between Tweety and Granny. Unfortunately I did not come accross cable both capable of safely transporting high-voltage and being flexible at the same time. O, it should be shielded too, since I consider the B+ to be an integral part of the signal path.
• Fine tuning of the B+ voltage with a pot, allowing to use the best sounding voltage.

© Maarten&Annemarie, March 2002, 2006