Increasing the resistor at the grid moves the low frequency roll off due to that RC downward.
How much this matters depends on whether this RC is the dominant one in your system.
If there are other RC roll offs set at higher frequencies, you may not notice much.
Last edited:
On the scheme, are R29 and R34 (both 100k) responsable from high freq. Rolllof? In that case 100k seems high
The negative bias supply is fed to the grid through those resistors, they also load the preceding stage.
Aha... Sorry for all the questions ;-)
Someone else here also said i should replace R23 and R35 for matched same value resistors to balance the phase inverter, but looking further at the schematic this seems wrong since R35 is tied to ground where R23 is not
Someone else here also said i should replace R23 and R35 for matched same value resistors to balance the phase inverter, but looking further at the schematic this seems wrong since R35 is tied to ground where R23 is not
Not really. The 470k resistor ties the grid to GND. The capacitor blocks DC and low-frequency signals. Together, the resistor and the capacitor form a RC high pass filter, you shouldn't remove them. I'd just replace the volume pot with a resistor going from input to GND (47k or 100k or similar should work well).
Not sure how this would affect HF response.famousmockingbird said:
'Normal' grid leaks are often 470k-1M. Much above 1M and you are getting into the territory of using grid current to provide grid bias.
Does anyone know how to mod this amp from UL to triode?
I've heard people talking how much better it sounds but I cant find how to mod it.
I've heard people talking how much better it sounds but I cant find how to mod it.
Just connect the 200 Ohm screen resistors to their same tube plates instead of to the transformer primary taps.
Take them of the pcb, and solder them on the tubesocket between pin 4 and 6 like normal . Leave the place on the pcb where they were empty?
Last edited:
Yes, just make sure that the "transformer end" of each resistor goes to the SAME tube's plate.
You may need to adjust the bias current, so check it afterward.
Please be careful around high voltages, check with a meter to verify it is safe to work on first.
Tube amp circuits are relatively simple compared to most semiconductor amps.
Last edited:
What do you mean "transformed end to same tube's plate"?
If i take out the resistors and solder them straight on the pin4/6 of the socket
If i take out the resistors and solder them straight on the pin4/6 of the socket
Well, isnt that easy. When i take out the resistors and put them straight between pin 4-6 there is no audio anymore
Yes, 3 and 4 seem to be the correct pins. Pin 6 is not connected to anything internally.
- Status
- Not open for further replies.