Pentode/Triode Mod on Mark III blue stripe.

[Schmoog]

heh. yeah I tried with it disconnected and it didn't work. gotta follow the mark IV diagram if you want to switch that bit so DPDT on-on 15A switch.

though like restless rocks said, you can get a tech to do it. I brought mine the schems and said do this. he did it for like 50 bucks plus parts.

and make sure you drain the caps before doing anything like this......

 

[psychodave]

heh. yeah I tried with it disconnected and it didn't work. gotta follow the mark IV diagram if you want to switch that bit so DPDT on-on 15A switch.

though like restless rocks said, you can get a tech to do it. I brought mine the schems and said do this. he did it for like 50 bucks plus parts.

and make sure you drain the caps before doing anything like this......

Cool.

I will post my findings. Thanks for everyones help!!! 8)

 

[edward]

Unless I'm missing something, this seems like a very easy mod to someone accustomed to soldering. So long as the amp has been off for at least a day (or more??) this is a safe mod ...but like anything, be careful and methodical. Interesting tip about the fuse, though. Any thoughts as to whether that worth adding to this simple circuit??

Edward

 

[Restless Rocks]

Sorry again, what I meant was temporarily substitute your main power fuse (over by the AC power cord) with a 1 amp fuse. This will give you alot more protection in the event you have not wired properly. Once you feel that your DPDT switch is working properly then return the 3amp sloblo fuse and enjoy.

 

[Boogiebabies]

The screen grid and resistor are still connected to pin 4. Usually, in a pentode the screen grid goes from pin 4 to 6. In a triode Boogie it goes from the screen supply to the screen grid resistor, then to pin 4 and 3. The Pentode has the screen grid resistor going to pin 4 only. Switching the connection between the screen grid and pin three would give you a pentode-triode switch. when disconnecting the pin 3 and 4 circuit, the connection needs to be shut off.
No one said the screens need to be shut off.

 

[edward]

Thanks to all you guys, Restless, Schmoog, BoogieB, for you continual contributons and refinements here!!

Hey Psychodave,
When you get it all sorted out, could your impressions? And also post pics and the wiring diagram of how you wired up your switch? That would be absolutely great if you could! And on the switch options, a simple center-off switch wouldn't help you ...you would have to find a switch with a minumum of a 4-pole switch ...a rotary switch with 4 or more poles comes immediately to mind.

BTW, is it ok to switch bewteen pentode and triode with the amp on? Or does one have to switch to standby (sorry, never owned such and amp that is thus switchable). TIA!

Edward