WAD 300B PSE build changes, improvements, direction

[jaguarxjr]

Good evening everybody,

Well its been about a year since my last post on here and the completion of my first 300B PSE. I did get it working (with some help from Richard - many thanks Richard).

I haven't really been able to use it as a) haven't got suitable speakers b) mono only until other side is built and c) output transformer gets quite warm after about 30 to 40 minutes use. d) not here to use it (normally power it up every 3-4 weeks to keep capacitors in good shape)

I generally work overseas so rarely get a chance to do anything like this type of build but am hoping over this coming w/e to get to buildling the other side (not that easy to get the time with a new baby as well!)

I learned a lot during the last build but as I am relatively new to thermionic construction techniques (have been reading both of Jone's publications) ideally would like to ask the members their ideas on ideal wiring layouts for this particular build.

Since the last time I have purchased some silver screened cable for the input end of things, some solid silver interconnect (1mm but unfortunately came un insulated am thinking I could get some teflon sleving?) silver solder and a variable temperature solder station.

So.....Does anybody have a pic of a 'best practice' internal wiring layout for this amp - what the original instructions don't really go in to is the inter connection/wiring best route.

Is the silver soldering worthwhile ideally reserve this for signal path only or use throughout construction? (will need to get some more if so)

Can't remember if the original hookup wire was teflon covered solid silver, think it was, but would silver coated copper make any difference to solid silver and what CSA should be used .5mm or bigger?

I don't really want to go into spending a lot of money on upgrade PIOs for the moment really just get he best build/practice and then rebuild the first amp in the same guise - unless somebody thinks something is essential.

For information this build is from the original kit purchased from WAD probably now more than ten years ago.

Can I also ask if anybody on the forum is using/has used these amps and what speakers they've used with them - should the O/P traffo get hot? (Currently using B&W 804 Nautilus)

Many thanks

Rgds,

Ray

[pre65]

I've no personal knowledge of this particular amp, but I've never had an output transformer get hot, or even warm.

[Ali Tait]

I used to have this kit many moons ago, and yes it does get a bit warm, but no more so than a lot of other valve amps.

Having said that, the speakers you are using don't present the best of loads AFAIK, so this would probably make the amps work a bit harder. I'd suggest a speaker that is easier to drive would give the amps an easier time, and probably yield better sound quality too IMHO.

As for the wiring, I'd just go for the standard "rats nest" style, as with valve amps I've found in my limited experience this gives the least hum and best sound, and if it doesn't, at least you've got enough slack on the wires to move them around until you do!

I did use mine with a pair of P5's at first, which I thought were great at the time, but I've moved on a fair way since then in the sound quality stakes by going more down the DIY route.

[Richard]

Yes agreed, a tidy rats nest is perhaps best. Wires running alongside each other or tightly loomed together look neat but often are less direct and will influence each other by inductance the most. To minimise this cross wires at 90 degreees, keep them apart, and take the most direct practical route. Most important is to keep small signal wires away from high signal and current wires. So keep input wiring away from output and mains ac wires. Some of the original wiring may have been silver plated copper but not solid silver afaik. I wouldn't worry too much about that though and would just construct both monoblocs to a good standard.

The amps run class A so are "flat out" all the time. Thus speakers won't influence how hot they run. (Well, in theory, speakers drawing a lot of current would cause the amps to run slightly cooler as the speakers would be dissipating some of the energy!) The pair of 300Bs are supplied HT via the primary winding. Current is 170mA so if the winding is around 100R they would produce about 3W heat and gradually warm up to a point of equilibrium depending on room temp. There will also be some radiated heat from the valves warming the TXs.

Those speakers may be a difficult load btw as although they are sensitive they dip impedance to 3 ohms. A friend has a pair of 803(?) I think, and my se valve amp will not drive them sounding weak and bass light whereas pp valve amp is better and MF ss is meaty! All about current supply so see how they go as a stereo pair!