Changing tube in randall rg75g3

[RandallFan79]

I'm having some trouble achieving this - I take the screws out of the back cover but the cover won't budge. Is there something else I need to do before removing the cover?

[WRGKMC]

You probably have to remove the head from the cab. I'm guessing its done the same way as most combos where the head is held in from the top. You usually have screws on the top (4) that need to be removed and possibly the strap screws too, but save those for last because its much less likely they hold the chassis. Not sure of the screws go all the way through the chassis and have nuts on bottom 4 corners on the inside. You'll have to look. Some have nuts built into the chassis and just unscrew. Be sure you don't loose them. Some may fall out withdrawing the chassis especially those steel clip type.

 

 

 

My Big question however is. What makes you think the head has tubes????? Its a solid state head that uses Mosfets that sound like tubes. Some SS heads use a Preamp tube for some coloration and drive but I don't see anything on the net or in their advertisements that mentions that. If it was a tube amp, they would be out in the open where you can get to them. Only in some Rare cased so they mount any tubes inside the chassis like the Marshall Valvestate heads. These tubes operate on low voltage so very little heat is generated.

 

 

Tube richness combined with the solid performance of a MOSFET power amp!

75 watts come courtesy of the Valve-Dynamic power section, which combines the warmth, feel, and character of power tubes with the durability of a MOSFET power amp. A 12" Celestion G12P-80 speaker provides crisp, cutting tone. The clean channel has a boost option, while the gain channel lets you choose between classic and modern voicings. Dual 3-band EQs, spring reverb, an effects loop with level controls, and a line out round out the features of this powerful, expressive combo amp. Includes 4-button footswitch.

 

My other worry is what are you unscrewing from the back? I'm worried you may be trying to unscrew might be the power transformer looking for tubes. that surely should not be tampered with. Then the last question is why are you messing with it. There are no user replaceable parts in the thing and you need to be a tech to fix just about everything in there. If you're thinking you can mess with it to make it sound better, stop. The only thing you can try is a different speaker or in the case the pots get dirty you can clean them. If you're real good with a soldering iron, you may be able to replace an input jack, but that's it. All the components are PC mount and all you're going to do by going in there is risk damaging the head. Even with guys like be who have been electronic techs for 45+ years, have to be very careful dissembling some amps because they keep adding cheap plastic parts that can fracture easily.

 

My best advice is leave it alone. If something's not working right then take it to a pro. If you screw up messing around inside then you'll be forced to take it to them anyway. Difference is the cost might be allot higher with the damage you cause.