WAD 300B PSE - a kit - no probs!

[andrew ivimey]

weird, I thought I'd posted this and now I can't find it so here it is again.

A couple of weeks ago I bid and won a WAD300bPSE. It meant hard earned being withdrawn from the bank but with the interest rates as they are, can't a boy have a little fun?

As far as I can make out the first owner hadn’t done a very good job and was not a happy chap. He sold it on eBay about six months ago and the chap I bought it off had spent the last few months enjoying it and then growing ever more dissatisfied. Whether it was right or not it had to go!

There was too much hummmmmm anyway. So the previous owner stripped it down, labelled and bagged the components and sold it as a kit.
Thus I acquired it. And had no time to do anything substantial until this morning.

It is strange building a kit. If the WAD instructions are any good or not, I am not sure, but the first monoblock I made up more or less using the instructions. I found it wearying and stressful as just copying the diagrams I lost the sense of the circuit and so had to spend loads of time ‘checking’ before switch on. It worked, so on with the second monoblock. I suppose making up the first helped orient me but this time I followed the circuit diagram and felt more cheerful and confident.

The previous owner had made up some beautiful little bridge rectifiers with hexfreds but I thought this tweak could come later. I like AC heating and so it was AC for me.

With the second monoblock finished and tried it was time to put them both on together… through Fostex (to listen for the hum) and …. No hum at all after a quick twiddle of the humbucker pots.

It works!

And it sounds luscious and lovely, powerful and capable of lots of dynamics and subtlety. It has only been on a couple of hours so I can change my mind later.

Black Gates on the cathodes Jensens couplers and big mundorff on the B+, there are no other hupgrades, so a few obvious ones come to mind, like non-inductive wirewounds. The 6AU6 surprised me with its ability and the rects. are only cheapie russian 5U4gs. I have a million ecc82 equivalents but we’ll see and the 300bs are the ubiquitous EHGGs.

So far, so very good indeed.

half an hour later - there is a hint of hum on one channel; now it gets challenging.

[Ali Tait]

Nice Mr I,it's not a bad kit is it?.I miss mine in some ways.

[Tony Moore]

Hi Andrew,

You're not going mad, yes you did post it! But where did you post it at?

[andrew ivimey]

Ah! thanks Tony - but yes...where? Oh well no time for that.

What can really drive me bonkers is that hummmmmm. One monoblock is silent, one is unacceptable.(The 'scope may haveto come out.) I have about eight things to try, all to do with the power supply, as the circuit looks right and, in my experience, a right bird's nest does not of itself make for hummmmmm.

The amp that hums is the one I built following the instructions too!

onwards!

[paul(555)]

Andrew,

Have you made any progress with this problem?

I'm interested as I have similar problem with a pair which I built from an unfinished kit a while ago. I very carfully followed the instructions, not having the skill or knowledge to do otherwise, and both amps hum. Otherwise they work perfectly having been tested by a freind with the necessary equipment.

Fortunately I use relatively inefficent speakers, PRO9TL, so whilst the hum is irritating they are still very listenabe. I'm therefore not inclined to spend hours chasing this problem at the moment but would be very happy to be guided in the right direction.

Regards,
Paul.

[andrew ivimey]

I went DC on all the heaters. That helped but still unaccpetable with my speakers (and it is inelegant to have such dc on the output.) One amp was nearly okay but the other one was showing wrong voltages around HT. I think there is something wrong with one of teh transformers.

And what did they sound like?

Mediocre.

So, I've scrapped them. The chassis will do for a really nice single 300b SE amp, and then it doesn't have to be 300b.

No, it was a great waste of time and money! I don't always get it right.

[pre65]

A lesser man would have taken it apart and sold it on e-bay as a kit !