[Chris Cusick]

OK - Thanks for the ideas - I'll aim for 6. There are 5 tubes in this one - it has a push / pull output. It's more of a challenge to wire things up in parallel than series - as long as there is enough room, I plan to get 6 x single D cell battery holders and wire those up in a 'ladder'. I have a goodly supply of D's that I grabbed from my local Menards store when they were on sale. The B supply will probably be 10 x 9V batteries snapped together, just because that's so easy to do.