Randall Diavlo 100h Tube/Bias/Fuse Question?!

[judaslamb]

Hello All,

I had a previous post, and was worried I had broken some rules, but it seems a few other folks have had their post deleted as well...this post is far less in depth...

Basically, I have a 2 yr old Randall Diavlo 100h - gentle, average use. Started making slight crackle noises last practice about a month ago. Fired it up yesterday and it started again, and after a few power downs and restarts, I lost all signal. We noticed what we thought was a blown tube (#1 from left if you look at it from rear) - it was glowing blue and the filament wasn't glowing like the other 3...rest were fine.

After checking the pre-amp tubes and swapping with a spare 12ax7 and still no sound, I cracked it open to discover 2 blown fuses on the circuit board...

I do have a couple questions:

• Does ANYONE have any helpful hints, tutorials, guides, schematics, diagrams, etc., on this particular amp concerning re-biasing, and what it is supposed to be biased to?! I contacted Randall and they pretty much told me to get lost...or go find an authorized tech....I've never done this before, but it is definitely something I am looking forward to learning how to do.

• Does the issue sound like a blown tube could've caused the blown fuses within the circuit board?! (The main fuse is OK) - amp turns on, and there is FAINT audio coming from all 3 channels, but the channel volume and master volume is cranked...

I'm really hoping this is an easy fix - I have a matched set of JJ 6L6's en route, and will find some of the T500L250V fuses for the circuit board and replace.

Thanks again,
-Ben

 

[judaslamb]

Wanted to follow up - I was able to track down some (outrageously expensive...) fuses for the board - replaced them. Installed a matched set of the (outside) tubes, and held my breath as I fired it up....

All channels seemed to be working, and the volume was fine, no pops or crackling! YAY!

But I also wanted to see IF it was a faulty tube...installed the other 2 matched tubes to the inside...turned it on and it blew the main fuse...a 6.3amp 250v....so now I have to order a set of those, as they aren't regularly stocked anywhere around Waco....

 

[Dustyjams]

My rd100 literally just did the same thing, but i cant find any t500l250v fuses anywhere. I think the cause of the fuse blow was because i never burned my tubes in, causing them too drift and run too hot (2 tubes in the head started red plating frequently before fuses blew). I spent the extra money to get better tubes that are also burned in. I bought sovtek 6l6wxt+ matched quad, an upgrade from the ruby 6l6gcmstr, which arent a bad sounding tube, but i think the sovteks will last longer. I already have a sovtek 12ax7 in the 3rd channel preamp, which gave me a lot more headroom and punch. Also found the t500 fuses labeled as 0.5a fuses. Hope this helps out anyone else with a diavlo that cant find any useful info.