Tony

I just did that this weekend and I recommend it. You can build a voltage doubler on Bob's LM4500 board itself. Insert one rectifier diode into the PSU ground hole, cathode pointing up, and leaving enough room below the body to make a connection to ground. Insert another rectifier diode into the + hole, cathode pointing down. Twist and solder the free ends together; solder the + end of a radial 1000uF electro to this junction, and connect the other end to the heater supply. Voila! An RF bead at the heater end of the lead is nice if available.

I used 1N4004, 2200uF, and LM317 because I had them, but next time I will use 1N5819 (lower Vf), 1000uF as I think it's enough, and an LDO regulator. The doubler delivers 2 x 6.3 x 1.414 = 17.8V, less 2 x Vf + half the ripple current, which was about 100ma. At the 317 output the ripple was a couple of mA, and the LM4500 has another 57dB of ripple rejection anyway. I used R2=220R and R10 = 2k2 | 6k8 to get the voltage down to where the LM317 had enough headroom to regulate properly. This was about 10.8 volts in the end but with the low-vF diodes and an LDO regulator I think you could get another volt or so out of it. I tried 4700uF, which made zero difference, which makes me think 2200uF was already more than enough.

If this is a TL II or III (not a Stereo) you should also do the following:

- short-circuit the 470K resistor and remove the two decoupling capacitors leading to the grid of V5

- take the compsite audio input to the LM4500 board from the cold side of the 1uF capacitor leading to the volume control.

In other words use the cathode-follower V5 as the input buffer to the decoder. This means that the mono output is now composite, so suitable for an outboard decoder, but not suitable for listening in mono, but nobody does that any more, and if you want mono the mono from Bob's board is just as good, in fact it is the same thing as what used to come out of the cathode follower - you can add a mono switch to Bob's board. IMO you also will need Bob's filter board which has yet to appear, but till then it's quite listenable as long as the 38kHz doesn't fry your tweeters.

I'm not posting this to the group as this is business for me ;-) Bob has it all.

Regards

Esmond Pitt
Dada Electronics Australia