DSL100 5 dead tubes

[fweijers]

Today I switched on my JCM2000 DSL100 but no sound!
Looking inside (removed back cover) I found that all preamp tubes were dead (not glowing) plus V1 of the power tubes.

So tubes 1-5 are dead, 6 7 and 8 are glowing.

Anyone ideas?
The power tubes were recently replaced, the pre amp tubes were replaced one year ago. The amp is being used 8 hours per week.

 

[Buggs.Crosby]

check your HT fuse

 

[fweijers]

The fuse looked ok ...
I will test it of course, but what would be the next check if it is not the HT-fuse?

 

[Buggs.Crosby]

don't know what i was thinking when i posted the HT fuse
but i bet F1 on the tube board blew

 

[jcmjmp]

don't know what i was thinking when i posted the HT fuse
but i bet F1 on the tube board blew

You mean the rear board? If it were that, the LEDs would not light up.

 

[Buggs.Crosby]

yes tube board.....F1 going to the heaters
unless i followed something wrong F! will take out all 4 pre's and v5

now here is what i don't know and where theory comes into play.....why are v1 and v2 heaters rectified?

 

[jcmjmp]

yes tube board.....F1 going to the heaters
unless i followed something wrong F! will take out all 4 pre's and v5

now here is what i don't know and where theory comes into play.....why are v1 and v2 heaters rectified?

Ah! Ok - I get it now.

 

[Procter2812]

now here is what i don't know and where theory comes into play.....why are v1 and v2 heaters rectified?

Probs because they are gain stages, and DC powered heaters are much less noisy than AC powered heaters

 

[fweijers]

Ok I finally got 5 minutes to open up the amp ... to my surprise all fuses are ok

There are no burned areas as far as I could see ... so I'm a bit confused (funny: con-fused )

Anyone a bright idea for me to check?

 

[jcmjmp]

If you're not familiar with electronics and high voltage safety, I would strongly suggest that you bring the amp to a qualified tech. Its probably something simple.

 

[Buggs.Crosby]

i agree with JCM.....do have have any background with electronics?

 

[Buggs.Crosby]

and how do you know they are all O.K....looks mean nothing

 

[Vraull]

The fuse on v5 is for the heaters in V1-V5.
I had the same problem, all the pre-tubes and V5 not lighting up.
The fuse was blown, but it still looked intact. Check the fuse with a meter.

 

[Buggs.Crosby]

it is F1....but if you have no clue around the inner workings i would stay clear

 

[jcmjmp]

Buggs & Vraull are correct - Visual inspection of a fuse is worthless. Everything must be checked with a meter.

The fuses are F1/F2/F3/F4 on the tube board. F1 protects the preamp tubes, the PI and V5.

 

[TwinACStacks]

Yep Visual isn't accurate. Use a Meter set to continuity on each end.

TWIN

 

[Lane Sparber]

...with the fuse REMOVED from the circuit.

+1 on the BE CAREFUL THESE AMPS CAN KILL YOU thing.

-Lane

 

[fweijers]

sorry guys, I wasn't clear on this.
Yes, I checked the fuses with a meter. All good.

PS I have a degree (engineer) in electronics, but I have not much experience in repairing a DSL100. But thanks for your warnings anyway. It is always good to be carefull with tube amps!

 

[fweijers]

PS I'm looking into this thread now: they say check solderings etc.
Another DSL Marshall problem..
Think that will be my next step.

 

[Buggs.Crosby]

from what i can see it is not possible for all fuses to be good but v1 thru 5 going down unless it was the PT....but b7-8 should not be heating up either