Help!! Silent WAD 300B PSE

[Guy Pettigrew]

One of my WAD 300B PSE monoblocks has gone silent.

It was OK yesterday. Today there is nothing coming out of it. No hiss, no hum.

The valves are getting hot, so power is clearly not the problem.

Anyone got any ideas, please?

Thanks.

Guy

[John Caswell]

Hi Guy
Yes it could be a power problem - however first thing to do is swap valves from the good amp, 5U4 first then 6AU6, ECC82, then the 2-300Bs. If that doesn't sort out the problem it does sound like an HT fault so check whether you have HT on all the valves and also the correct cathode volts on all the valves, that should help pinpoint it down. If still stuck, post here, and we will see what we can sort out.

John

[Guy Pettigrew]

Hi Dr John

Thanks for the fast reply.

Valves all swapped, still no sound.

Tomorrow morning I'll get into the amp, check the voltages you've suggested, and report back.

No music tonight, though. Misery!

Guy

Ps. This will be done tomorrow and not today because evenings are not my thing. Mornings suit me better!

[Richard]

Originally Posted by Guy Pettigrew

One of my WAD 300B PSE monoblocks has gone silent.

It was OK yesterday. Today there is nothing coming out of it. No hiss, no hum.

The valves are getting hot, so power is clearly not the problem.

Anyone got any ideas, please?

Thanks.

Guy

Gadzooks! No hiss, no hum? On a 300bpse? It must be terminal
Here's a quick check, even though the heaters are lit, compare the temp of the 300Bs in the good and bad blocs.
The heater looks hot but only gives off 6W. The HT gives off another 32W. So it will be obvious to the touch if the HT is on or not.
If the HT is on but there is no hiss suspect a OPTX connection is off. That could be primary or secondary or even a break in the speaker leads. To eliminate the speaker leads swap the blocs complete across channels.

[Guy Pettigrew]

Originally Posted by Richard

Gadzooks! No hiss, no hum? On a 300bpse? It must be terminal

Ha ha! No such thing as terminal with these amps. Everything can be repaired. Apart from their wonderful sound, this is the main reason I love the WAD/WD stuff. I built it, so I can repair it.

Good tip about the temperature. I'll give it a go and report back. Pointing an infrared thermometer at a valve is well within my evening capabilities!

Already swapped the 'speakers, so the problem isn't there.

Guy

[Guy Pettigrew]

Ah well.

On the good amp the 300Bs measure 95 and 110 centigrade. On the duff amp they measure 110 and 114 centigrade.

Assuming the measurements are very inaccurate, they're all the same.

It's just a point and press infra red thermometer. Who knows what it's measuring when it's pointed at a 300B?!

Guy

[Richard]

Yes sorry about the pun couldn't resist it, you are so right, man made it, man can fix it, I say to myself at these oh bugger moments
Check the speaker leads and connectors as well in case you just swapped the speaker boxes.
100c sounds about right, smell of burning flesh and sound of cussing replaces hissing!
So is it completely quiet, nothing at all with ear to tweeter? If so it must be a primary or sec OPTX lead off inside or heaven forbid a TX fault.
If there is a little hiss that would be from the op stage so it might then be just a signal fault earlier on, at the input connection for instance.

[Guy Pettigrew]

Absolutely nothing from the tweeter.

There's a light hum, accompanied by a very quiet and very odd "boinging" noise from the mid and bass units about once every 2 seconds.

Even if it's the output transformer which has gone, I'm sure it can still be fixed. I'm not an optimist, I'm much more cheerful than that!

Guy

[Richard]

Boing is good, possibly just a bit of motorboating, anything is good
A last check before diving inside checking voltages and for fried and exploded bits would be to stick one probe in the rca input and the other on the outer rca shell looking for 100k to check the input signal connection is still there.

[Guy Pettigrew]

OK, will do.

Early breakfast tomorrow, then lots of probing voltages and whatever anyone else suggests.

I have no idea about electronics, but I'm a good technician. In other words, I've no idea what I'm doing, but I'm good at following instructions!

Guy