WAD300BPP - extraordinary amplifier

[andrew ivimey]

It occurs to me that the 300mv input is a little tricky.

Why not rewire for 5687 as input valve instead of the otherwise totally superb6072; gain goes down nicely and welly goes up - much better Ra or I'm a monkey's uncle!

Superb amplifier, though!

yours, Johnnie come lately

Oh you actually have the nerve to enjoy the amplifier, how very dare you :p

[Andrew]

Did you buy one, Andrew?

[Richard]

You could try ECC82(17) 6072(44) ECC81(60) 5751(70) and ECC83(100) in there first Jonnie without rewiring. I didn't find drive an issue and prefer it without a bypass cap which raises Ra in fact, but lowers distortion and sensitivity, and the whole amp then measures superbly to boot, have fun

Rich

[Greg.]

Hi Andrew,

OK, you've discovered something. Excellent but please stop talking in riddles. If you have something to offer on development of the WAD 300B PP, I'm seriously interested (as several others are) but without doubt we want it in plain simplistic directional English. Some of us (certainly I am) are thick. A clear directional explaination would be very good for all of us. As much as I try to reach up to understand the interlect of your postings, with no offence intended, generally I struggle to make sense of what you post albeit I know it is all in there one way or another. On this occasion I simply ask you to explain simply what you have done that in your view makes the amp perform better.
Otherwise, I'll need to tie you down at Owston and not release you until I understand what you are going on about..........that might mean you miss out on your supper. Shame

Best wishes,

Greg

[richardcooper2k]

do you think he likes cryptic crosswords ?

[Ianm2]

I can't see what's cryptic, he's simply saying lower gain and ra by using 5687 as the input.

I liked ecc81 and 5751 best as input and e182cc as driver, but may need a little attention measurement wise, its very full on.

[Max N]

Also probably worth mentioning that when we did the 300B shoot-out at Greg's, we were using the WAD 300B PP. And on that occasion, we all decided that the TJ mesh plates were the best 300B. So if you want to stick some new output valves in, the TJ's would be a safe bet I would say.

[andrew ivimey]

Hello Max, I'm afraid I have posted elsewhere and I am only running to catch up with what is already known. I have tried Ni-cad, resistor, resistor plus cap and gone back to Ni-cad, as I prefer the sound, not the gain.

With 300B cathodes I have tried going to 1.5K, then to those lovely green RS wirewounds (1.32k) and then to Mills 1.32K. - much much better.

Why, I wonder, are Mills none inductive?!?

No, lovely as 6072 is (a great valve) I naturally thought of others ....and Steve's explanation is right.

Also,

Since that 'shoot out' more 300B valves have come on the market so although we would all agree that for the money EHGGs are smashing but I know some of us have WE 300Bs of which I was very impressed and if only I could get some more 32Bs - WOW! but I only have three and the recommended equivalent is KR300BLX. I'd settle on these too, I admit.

I'd be happy with TJs too but I'm loaded up with 2A3s and can't afford to splash. BUT, it isn't the output valve's fault. We all agree that the gain of this partic. design is very high for modern inputs or using a Pre, so something has to be done. I haven't tried 5687 as input valve but it springs to mind as a good'un.

I like your harmonic theory Max, I wonder. I loved the sound of Amity (super fast, like SE but better - ducks!; it was just silly getting something to drive it. Amity mk2 was free of harmonic distortion to an amazingly high degree. Karna probably is the only solution!

What might I find with some square waves and the 'scope.... good or not so good???

The last time I mentioned using a scope on this BB I was nearly burned as a heretic because despite about 10volts of 70KHz oscillation the vociferous wisdom in reply to my finding was a variation on, 'I trust my ears!' Yeah right, ludicrous. It is difficult to be polite to such a comment.

So, Max old chum, what might I find?

[Max N]

Well, its a long time since I did it and I can't find my notes, so I probably should just say nothing until I get a chance to measure them again. Maybe someone else can chip in? From memory, they do not measure particularly well - but the amp sounds great none the less. I think the problem was that they rang quite badly.
Now Kevin at K&K (Lundahl dealer) is firmly of the opinion that a ringing transformer within reason is not a problem at all and certainly sticking a zobel across the secondaries to kill the ringing can sound worse.
Whatever, the measured performance of the SE:PP interstages was one reason why I lashed up the circuit I took to Owston, to see if PP:PP interstages sounded better.
In the end, the only thing that matters is the sound - and this amp is universally liked. Maybe best not to try the squarewave and scope lest you end up less happy with the amp - irrational but then this is always a subjective game isn't it?