Sx3,
I've been battling software, trying to get a circuit board layout squared away for people who want to build Alephs (see that thread for the gory details--assuming that you have enough morbid curiosity). And, to make matters worse, I can't remember the spell to utter to make it all come together. Anyway, the point being that I'm tired, so this may not make sense. If not, say so, and I'll make another run at it later.
Step 1--Information. Go to
www.triodeelectronics.com and find the tube data section. Download the sheets for the 6BQ5 (there are at least 4 or 5 page images).
Step 2--On page 2 (?) you'll find a couple of tables of numbers for class A, class AB, class B, etc. For this amp, it's safe to assume class AB, but we'll get back to this in a moment.
Step 3--Look for the plate load. It'll be on the order of 4-8k ohms. It will vary somewhat depending on the rail voltage, the bias, etc.
Step 4--Go to
www.hammondmfg.com (or any other transformer site that makes you happy) and look for a 10 to 20W transformer that presents a plate load close to what the data sheet said.
Step 5--If you don't find one that's exact, it's okay. The tube may want 5.5k, for instance, but your best choice of transformer presents a 5k plate load. Don't worry about it. You'll suffer a slight loss of efficiency, but not enough to lose sleep over.
Step 6--Sip some eggnog and congratulate yourself on a job well done.
Sources (retail) for transformers. I don't know about Australia, but I'm sure that American retailers will be happy to ship to you. My advice would be to wait a week or two until Christmas is over so that UPS/FedEx/USPS have a chance to catch their collective breaths. Note that these will be fairly small transformers--the size of your fist or less. Shipping shouldn't be that bad. Christine, if your travels take you as far as AZ, you can save postage. Try Antique Electronics
www.tubesandmore.com for transformers and tubes. (Christine, I think you'll find that their tube prices are better than Percy, although they don't carry as many high-end parts. The last I looked Percy doesn't sell transformers at all.) They're good people.
Grey
P.S.: Sorry, forgot about the 12AX7 circuit. (The "12's" i.e. 12AX7, 12AT7, and 12AU7 are all small signal tubes, and good ones at that.) That's a preamp, not a power amp. Won't drive speakers. Might be a good choice for a front end for this amp should it not have enough gain to suit you.