To Simul-Class or not, that is the question.

[fusionbear]

Hello all,

I have been away from this forum for a while. I just got a 1988 Mesa MKIII Blue stripe and I already performed the "+" mods on it. C30 to 1000pf, C27 to 20pf. But, I noticed at another forum the proof that the OT primary just has extra wires coming out of it, but they are not tapped. That seems to be the case on mine. The voltages are 490-491+ on all four primary wires on pin three of all four tubes. Anyway, I have three questions.

1. The MKIII schematic calls for double the filtering on the Simul-Class Models. From 110uf to 220uf on the first stage!!!!! Mine has that. Why is that much necessary on the Simul-Class models? I can't see any reason why, what am I missing?

2. Should I ditch the whole Simul-Class wiring and just use four 6L6's in standard wiring? The new Mesa John Petrucci model has done this.

3. I hate onboard spring reverb. Anything bad if I just pull out the Driver tube and disconnect the tank? I can't see any issue other than a slightly less draw on the PT.

Thanks all of you!!!!

[Stevem]

Do not pull the driver tube which will kick up the heater voltage on all the other tubes, just kill the B+ to the driver transformer if you feel you need to do anything or full unplug the tank and or just leave the darn reverb control pot at zero!

[Guy77]

Do not pull the driver tube which will kick up the heater voltage on all the other tubes, just kill the B+ to the driver transformer if you feel you need to do anything or full unplug the tank and or just leave the darn reverb control pot at zero!

Yes this is definitely the way to go. If only the tank is unplugged and the tube is pulled the reverb transformer will still be getting power (B+)and it will want to see a load.Since there is no tank it will damage itself by not seeing a load.


BTW is it a 2x6L6 or 4X6L6 amp?

Cheers
Guy

[fusionbear]

It is a four tube model. Currently 2-6L6's and 2-E:34's

Question on the Reverb: I there are two Caps that Isolate the B+ from ground when the tube is pulled out, how can it cause damage? What am I missing. I am still learning everyday. Thanks again gents!

[fusionbear]

Do not pull the driver tube which will kick up the heater voltage on all the other tubes, just kill the B+ to the driver transformer if you feel you need to do anything or full unplug the tank and or just leave the darn reverb control pot at zero!

It has 5 pre's and 4 power tubes. Pulling 1 pre-amp tube can't make that much difference, can it?

[Guy77]

It is a four tube model. Currently 2-6L6's and 2-E:34's

Question on the Reverb: I there are two Caps that Isolate the B+ from ground when the tube is pulled out, how can it cause damage? What am I missing. I am still learning everyday. Thanks again gents!

I know that on all fender type amps like the deluxe reverb, you can reference the weber 6A20 layouts here https://www.tedweber.com/media/kits/6a20x2_layout.jpg
the reverb transformer (red wire, bottom right of layout) connects directly to the B+ line. Maybe your amp is not connected this way but if it was
it would be good to disconnect this from the transformer if tank is pulled.

Cheers
Guy

[martin manning]

Don't just disconnect the tank. That leaves the reverb transformer’s secondary open. If you must do something, just pull the driver tube. Reducing the filament current draw by 300 mA won't make any practical difference, and there is no harm in leaving the supply voltage on the reverb transformer primary if no current can flow.

[fusionbear]

Just to be safe, I unsoldered the b+ connection for the reverb transformer.

Still on the fence if I should leave the amp wired for simul-class or wire the two outer tubes to Pentode and use the existing switch as a 60/100 watt selector. Pros? Cons? Love to hear your thoughts. Or just stop messing with it and just play the thing......lol...


Thanks!