The Original WAD 300B Push-Pull (like Greg's)

[Dave_The_Vinyl_Junkie]

A little while ago I managed to snap up a complete Quad II set of about '57-'58 vintage - almost mint condition, sold by a friend of a friend of a friend - you know the sort of thing.

I've been listening to them this evening in place of the T16's, and was very struck by how wonderfully sweet, warm and enveloping the sound was. It's made me realise that whilst the T16's can throw a heck of a soundstage, they can sometimes sound a bit etched and hard in the treble and mid. So thoughts have been turning toward trying alternative circuits. Some friends with solid state rigs are suggesting that I ought to be using amps with output power in the hundreds, but I'm not so sure.

I have attended 2 Eggfests, and both times have been able to listen to Greg's 300B push-pull, which if memory serves correctly is a clone of an old WAD design and not their latest p/p? Also, is this a zero feedback design, and what's the output power? They'll be driving 88dB speakers with a fairly flat impedance curve (link in my sig takes you to a graph showing that and the phase angle). Both times I have been very impressed with what I've heard, I thought it sounded absolutely wonderful, and I'm now giving serious consideration to building one of my own.

There are one or two hurdles to overcome - my experience so far is with two kits - the Rozenblit T16 and Grounded grid, with the WAD 2A3PSE before that. This will be the first scratch build that I will have attempted. Also, just to be difficult, I want to build it as two monoblocks - presumably this is possible? The reason is that I tend to site the amps close to the speakers and run long pre-power interconnects - I found that this configuration seemed to benefit the T16's.

I'd been thinking about using these guys for the chassis - hopefully they'll be able to make something suitable as I have neither the expertise nor the equipment for metal-working! http://www.bluebellaudio.com/ . I'd wondered about going vintage for the output transformers (old Stereo 20?) - though presumably they have to conform to a certain spec. I suppose the circuit diagram and component specs would be useful as well.

It may be a while before I take this on due to time constraints, but I'd certainly be grateful for any input/caveats from the good people on this BBS, particularly Greg and others who've already built the circuit. It would be greatly appreciated.

Many thanks all!!

Dave,

It is a completely different design to the last WAD 300B PP amplifiers.

It does not use Phase Splitting valves, but has Interstage Transformers instead. Have a look in the gallery for some photos of Greg's clone. Feedback was switchable on the original amplifier, everyone switches it out or diconnects it which gives a sensitivity of 280mV and a quoted output of 28W at full whack. I use mine with 88dB/w/m 'speakers at a distance of 3 metres or so and a passive preamp.

The amplifiers were 'monoblockable' using the 16 Ohm taps to give 60 Watts per channel.

I have some scanned HFW and other related articles you might like to look at, PM me your e-mail address.

OR you could be patient and wait for that tease Peter to tell us more about the WD version of this amplifier! See this thread!

[Paul Barker]

Or bight NealG's hand off you wally!

Indeed!
I thought that Graeme had decided, but apparently not.

Dave, see these two threads for possible solutions:
http://www.world-designs.co.uk/forum...ead.php?t=1023
http://www.world-designs.co.uk/forum...ead.php?t=1315

And I see you're back on the NAS for a while...

Here's another link for your signature:
http://www.hi-fiworld.co.uk/hfw/olde...tml/quad2.html

[Greg.]

Hi Dave,

I concur. Do a deal with Neal. His is nicely tweaked already, and if you later want to develop what you have into mono-blocks, you'll have most of the building bricks to start with.

I can supply alot of material to you regarding this amp including build specs for the clone and various useful articles, instructions etc if you wish.

Although WAD claimed 28 watts per channel this is not the full picture, particularly if like me you reduce the 300B dissipation to give them an easier life. Neal (he's a mathematician and I'm not) calculated my amp produces about 11 watts per channel in class A. Plenty for most needs into my 90dB KLS3's although a bit of a struggle trying to fill the Eggfest hall with loud Bach organ music!......incidentally for those who heard that in June, no damage done and that rather harsh treble was down to the CDP which I'd not used with the amp before.

Best wishes,

Greg

[KennyK]

I must confess was (still am) very tempted by Neal's one.

But I'd feel like I was 'cheating' if I bought a completed kit, if you see what I mean. regardless of whether I could achieve the same sonic results on my own, I feel that physically building the amp is as important as listening to it, not only that it gives the novices like myself a chance to understand the amps and circuits more fully - and the more experienced a chance to discuss, impart knowledge and perhaps make new discoveries themselves as discussions unfold. its a kind of passing the baton as it were.

I'd certainly be interested in seeing some of the articles if that's at all possible.