Marshall 1987x died ... questions

[rickc007]

Was playing my Marshall 50w 1987x ... with attenuator on, both volumes at about half way. Typically play it like this

All of a sudden the volume just faded to no sound, in about 2 seconds. Now nothing

I have all lights and the tubes are glowing

Was wondering if this is a known failure that would produce this

Or where to look .... I was an EE, but it's been a while since I've dug into anything

[neikeel]

Commonest problem is tube failure, ie one of the outputs dies, takes the HT fuse with it.

Your tubes will still glow due to the heaters and the mains fuse did not pop so the standby light will still come on.

Usual process is to get a new HT fuse (slo blow correct rating for where you live (US vs UK) and pinch a pair of tubes from an amp that you have played through recently.
If it works some new tubes and a rebias should do the trick.
Of course it could be a preamp tube but they rarely die like that (same substitution method to test is).

If that does not work post back.

[neikeel]

Edit - double post.

[rickc007]

Commonest problem is tube failure, ie one of the outputs dies, takes the HT fuse with it.

Your tubes will still glow due to the heaters and the mains fuse did not pop so the standby light will still come on.

Usual process is to get a new HT fuse (slo blow correct rating for where you live (US vs UK) and pinch a pair of tubes from an amp that you have played through recently.
If it works some new tubes and a rebias should do the trick.
Of course it could be a preamp tube but they rarely die like that (same substitution method to test is).

If that does not work post back.

Spot On ... thanks
HT fuse is gone

Off to the Tube Store

[robert]

Hi Neil,

the correct rating (500mA slo blo) of the HT- fuse has nothing to do with the country you live

Is it possible that you've confused the HT fuse with the mains fuse (1A slo blo)

Regards

Robert

[neikeel]

Yes Robert you are quite correct it is mains that varies!

At least it was the right diagnosis!