Sick WD88

[Shian7]

Hi All,

My loverly WD88 seems to be sick !!!

I've recently changed the KT88's and now I seem to have a bit of a heater problem!
When powered up nothing happens for a while, then after a few seconds all the valve heaters start glowing as usual followed shortly afterward by the LED glowing green ! This is not how things should be.

What should happen is the LED glows red until the heaters warm up and then it should glow yellow, this normally takes about 20 seconds or so.

Now there's no red but after about the usual 20ish sec's the LED goes straight to it's green state. Green indicates a heater voltage problem according to the destructions.

I was always a bit unsure about weather or not the LED was glowing green or yellow in use before, but now I'm very sure it was yellow. When it glows green it's very very obvious!

I don't have time to do any testing today but in the morning I'll get it out on't table and have a good ol' measure around its innards!

Just wondered if anyone else has had any 'problems' like this? ..... Oh!, I should add that it still works but I'm not happy using it for any length of time until I get to the bottom of it all!

Cheers,
Mike.

[soulminer]

Originally Posted by Shian7

after a few seconds all the valve heaters start glowing as usual <snip>..... Oh!, I should add that it still works...

Get rid of the LED!

[Shian7]

Thanks for that Lee.... most helpful! :p

Best wishes,
Mike.

[pre65]

Hi-do the building instructions specify exactly what each colour is supposed to indicate ?

If so,can you not check with a DMM what happens to the voltage as it warms up and see if it is within limits.

Also,contact Peter about the modified diodes,they may be relevant.


Philip

[Shian7]

Hi Philip,

LED states mean the following (roughly )

1. RED - Warming up (this states has vanished!)

2. YELLOW - All systems go (this state has vanished)

3. GREEN - Heater voltages gone to pot. Stop and make checks! (this is the only state I get now!)

I'm fliting between PC and cooker ATM.....I'll do more 'testin' when time permits !

[systemx]

Hi Mike.
Do the following.
(1) Get rid of the LED, they are more trouble than they are worth.
(2) check all the voltages, If all is o.k fine, if not then take it from there.
(3) If you want to keep the LED (why?) and all else is o.k then I would suspect a dry joint at the LED end of the wiring, under the heat shrink.

Terry.

[John Caswell]

Hi all,
I know that I am being naive and stupid, but, if it worked OK before you changed the valves and now it doesn't, does that not point to the fact that something may be wrong with the new valves?
I suggest that before you "get rid of the LED as they are more trouble than they are worth" measure the voltages around the KT88s especially the cathode volts as this is what changes the LED colour and gives you an indication that the output stages are working as they should. For the uninitiated it is actually two LEDs in the same package one green and one red and when all is OK with both glowing equally then yellow is the result. Additive colour mixing from the Primary Colours :
Red, Green, & Blue
Red & Green = Yellow
Red & Blue = Magenta
Green & Blue = Cyan
Red & Green & Blue = White
Non of the primaries = Black

John - Dr John

[Richard]

.....or put the old valves back in to see......

[Shian7]

I'll try all of the above.
I'd like to keep the LED as I find it useful - after all, the colours mean something!
It was working fine with the new valves for a week or so, so I think they're OK, but I'll certainly pop the old ones back in to check.

Cheers,
Mike.

[Richard]

For the uninitiated it is actually two LEDs in the same package

It would be helpful if we all had the circuit

Fortunately some kind soul emailed it to me.

The 2 LED package has 3 legs;

One to earth,
Another to an output valve heater,
and the last to the output valve cathode.

When the amp is switched on one LED will receive voltage from the heater connection and glow red.

As the valve warms it will conduct and a voltage will appear at the cathode. This will be applied to the other, green, LED and the two will show as yellow.

Why you should need this I don't know; if the heaters glow orange they are working. If they glow orange and sound comes out then the valves are conducting.

Whether the LED or a connection is faulty, and what the threshold voltages are we don't know. Possibly simply a different brand of valve has caused this. Checking the voltages around the new valves would seem to be the starting point.

Rich