Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  
previous: STEVE When adding a pentode/triode switch... -- 5/30/1997 11:31 PM View Thread


6/2/1997 12:48 AM
Dave Harris
I think the original screen grid resistors are 470R not 470K so it may be OK to keep these in series with the grids when you switch to triode mode instead of using 100Rs. Any comments on this ?  
You can use a DPDT switch to have 470R in pentode and 100R in triode and not have them in series. Could be tricky to describe but here goes. I will just describe the switching of one tube. The other tube is obviously the same using the other pole of the switch.  
W=switch wiper, P=switch pentode contact, T=switch triode contact.  
Disconnect the 470R from the screen grid and connect the disconnected end of the 470R to switch-P.  
Connect the screen grid to switch-W.  
Connect the 100R to plate. Connect the other end of the 100R to switch-T.  
Repeat for the other tube. Make sure you don’t get one tube in pentode and one in triode. That could be fun ! It looks OK to me but sketch it out to make sure. Let us know how it sounds.  
Good luck  

john Martin You can use up to 1K on the scree... -- 6/3/1997 1:42 PM