My Rm100 Tube Dillemma

[Patrick]

Well it came with Ruby el34BStrs .
One Fuse was blown (tub2) so I replaced tub2 and 3 with GTEL34Ms . After Following GTS own install directions on the box(lackluster at best ) and eurotubes videos on Biasing (Bang On) I finally got to the part where i get to press play (switching the standby).

Tube 2 Fail.

Replaced fuse

Tube 3 and 4 Fail.

Replaced Fuses

Removed Tube 2 and 3

Redid Test

No Problems

...................

GT Suck(SO FAR)

....................

But!!!!!!! Existing Tubes 1 and 4 were checked for bias after removing the GT Tubes and both (Rubys)were biased to 45-46 mV. This is way higher than the manual states. So could this be the cause o fthe GT Tubes Failure?

 

[KillTone]

Sorry to hear of your tube problems - frustrating.

The bias was too hot but I do not think it was high enough to cook those GTs that quickly.

What rating are the fuses you put in for the tubes? It is OK to use a higher rated fuse than the stock - I believe up to 400.

Also, it takes a little longer but just to be safe turn the bias pots all the way down before you put new tubes in and then make the adjustments. This will prevent cooking them if the setting is too high at start up.

Good luck!

 

[Patrick]

Sorry to hear of your tube problems - frustrating.

The bias was too hot but I do not think it was high enough to cook those GTs that quickly.

What rating are the fuses you put in for the tubes? It is OK to use a higher rated fuse than the stock - I believe up to 400.

Also, it takes a little longer but just to be safe turn the bias pots all the way down before you put new tubes in and then make the adjustments. This will prevent cooking them if the setting is too high at start up.

Good luck!

Killtone, Cheers for mentioning the Fuse rating, I asked that in the first thread i made, so do you know whether 400mA, 315mA or 250mA is the best choice for fuses with the RM100?

As for the GTEL34Ms, I think my own precautions came into play with this lot (bar the high bias for tub1 and 4) as i lowered the bias adjsutment for tub2 and 3 to as low as it can go before Installing them. I also sprayed the Valve seats with Contact cleaner(While Off of course) as per eurotubes recommendation, handled the tubes with newspaper (cause i didnt have any good gloves) and they literally went from package to amp...... so I dont know what the dealio is. I also gave it probably 15 minutes at least before standby was switched to play!

Kind regards
Patrick

 

[KillTone]

Sounds like you took all of the right precautions - way more than most take I am sure. You can probably only conclude that it was bad tubes then - unless you have some more complicated problems related to the current going to the tubes. One of our electronics experts needs to chime in on that though.

Regarding the fuse ratings: I put 400ma fuses in my RM100 and have not had a problem in 2 years of gigging with it. They were suggested to me by a Randall employee at the time.