The Amp Garage

Hi guys I'm building a Princeton Reverb head but with a long tail PI and a PPIMV, housed in a 19" rack case. As the amp will be 15 watts and because I'm also trying to add a little computer fan (to keep the case cool) which uses a little DC converter tapped from the 6.3V heater wires, I need to cons...

the concorde is also supposed to be closer to an express than what the k60 was. the express has much lower voltages and uses 18k2 between the screens and phase inverter. Perhaps they just though that 22k worked the best with this particular circuit. The question now is what the k60 HD uses I know t...

Tried removing the negative feedback but no change there. Tried swapping the primary leads on the output transformer - still the same problem, with EL34's I cant get more than 15ma with tubes maximum biased and with 5881's I can get in the 30's but as soon as I get the volume past 7 it jacks up almo...

Thanks Martin, have tried so many different combinations and still stuck. Have twisted the wires of the PPIMV very tightly and tried to ensure they are nowhere near anything else until the hit the 820ohm resistors going to the power tubes. I get the following measurements: With EL34's and a 250ka PP...

Ok so I will try to redo the leads on the PPIMV to see if there is a way to ensure there is no interference. As for the still crazy biasing, I just cannot ascertain what else to do. The biasing just will not get to a stable 30-35ma no matter what I seem to do. Also the fact that the bias milliamps g...

Thanks Martin

Would the PPIMV lead dress cause the actual amp itself (ie not the sound from the speaker) to make this squealing/squeeking noise?

Thanks Mark I've changed every tube in the amp and replaced all the electrolytics for good measure. I've still got the same problem no matter what I do. My only other suspicion is the transformers themselves? There seems to be a strange squealing noise coming from the xformer itself (although I cann...

Ok now this amp is really driving me nuts!!! I've changed caps in the bias supply and still I cannot seem to lower the amount less than 42ma. Plate minus cathode voltage is 484v. If I measure pin 5 without the tubes, at the lowest point I can get it is a stable -55v. Cant seem to reduce it to -40v. ...

Thanks Martin, its crazy unstable at -40v and the trimmer won't do much to change this

Hi guys, as for the "Knopfler mod" for this build, with 5881's I seem to be getting all sorts of crazy bias readings. I cant seem to lower the bias enough and would presume with a 5881 it would need a bias milliamp reading in the low 30's. I'm guessing I'd need to change out the bias resistors to gr...

Great thanks Martin

Hi guys I'm sorry Im still a newbie but am hoping you could confirm if I'm correct with how to calculate resistor values in parallel using the ohms law formula. I want to make a modified PPIMV. The traditional Lar Mar uses a 250k dual gang pot with 2M2 resistors for each gang. I understand this is s...

Ah I understand - so the schematic with Colossal's switcher has those two caps in the right configuration anyway!

I'm also wondering about the mod to reduce the flabby bass - so called 0.1uf cap after the gradual/fast switch being reduced to 0.01uf etc. Whilst I accept it may be beneficial at high gain settings, does it compromise the tone at lower settings I wonder? I am debating whether it adds a benefit to ...

I'm also wondering about the mod to reduce the flabby bass - so called 0.1uf cap after the gradual/fast switch being reduced to 0.01uf etc. Whilst I accept it may be beneficial at high gain settings, does it compromise the tone at lower settings I wonder? I am debating whether it adds a benefit to ...