6g2 blocking distortion at high volume

[audiosalvage]

Hey all, I've got a princeton build here that gets all farty and buzzy after 3:00 on the volume knob. You can actually hear the double tremolo beat at this point too. I've got the 470R 5 watt grid stoppers and 1.5K screen resistors in place. Speakers all good, tubes good. What else can I do? or is this normal?

[maxkracht]

Grid stopper before the phase inverter helps. I think somewhere in the 220k-500k range is standard.

[Stevem]

Try changing the two .1 uf caps on the output of the splitter to .05 or even .022 if you still have enough low end for your needs.

This may allow you to get up to 5 on the volume knob, the only question then is will you have enough low end when your playing below 3 on the volume setting due to these types of amps only having the tone control which is nothing more then a treble cut.

[audiosalvage]

I have a 470k stopper on phase inverter pin7, helps a little. I changed post PI caps to .047, did nothing, in fact made it worse.

[audiosalvage]

It's like a fuzz pedal after 8 on dial

[maxkracht]

Pictures might help.

[audiosalvage]

Here are my voltages, a gut shot and the layout i followed.

[audiosalvage]

Here are my voltages, a gut shot and the layout i followed.

[maxkracht]

I'm not seeing any voltages and a clearer picture or two would help. Need to make out the colored lines on the resistors at least. V2 looks like you mounted it backward to your layout. You can run the wires to the opposite halves of the tube for shorter runs, lower noise, and less chance of oscillation. Pins on a 12a*7 are (PGCHHPGCH:123456789) It doesn't matter which half you use for which purpose. This probably isn't your problem, but it likely is a problem. Also, how hot do you have it biased?

[audiosalvage]

With a plate voltage at 320v I biased at 70% but if you turn up the trem intensity, the bias current dives down. Is this just a normal thing? I suppose I should turn the sockets 180 degrees, I realized it later. Here is a better pic of voltages.

[maxkracht]

I meant a clearer picture of your actual amp in case you have a wiring error or an incorrect component value.

The tremolo is supposed to vary the bias, but you need to set the bias with the tremolo off. Turn off the tremolo switch or short the grid of the term oscillator to ground while setting bias. Cooler bias will result in better tremolo. Others might have different opinions, but I usually set amps with that kind of tremolo around 50-60%.

You do not need to flip the preamp tube. Each preamp tube has two identical triodes, you just need to swap the wires around for each half of the tube. Plate to plate, grid to grid, cathode to cathode. Look up a 12ax7 datasheet, it will make sense.

[audiosalvage]

ok, I physically flipped the two 12ax7s and rewired. here are better pics. I do recall when testing for the first time using 1/2 watt 470R 6v6 stoppers and not noticing the fuzz. Then I read that you need 3 to 5 watters in there. Does this make sense, or was it just my lack of sleep

[maxkracht]

Lower wattage screen grid resistors wouldn't change the sound, they would just get hot rather quickly. Grid stoppers are the 1k5 ohm resistors connected to the control grid(pin 5). You don't need a high wattage resistor for those but it shouldn't hurt anything. Is the tone knob wired correctly? Not sure if there is a problem or if the picture is playing tricks on me.

[audiosalvage]

I rechecked the tone control. I am beginning to think that I am expecting too much from this circuit. I am testing this out with an attenuator at full on volume with a full shred pickup. With no attenuator, I get very loud and clean tones past the halfway point. I know it's an old fender design and I'm looking for smooth marshall grind out of it. I'd like to try the zener trick to equal out the Cathodyne balance

[maxkracht]

For more marshally sounds, your're going to need to cut some bass. I would start with .68uf as the first cathode bypass cap and something like .0047 as the first coupling cap. Both of those could be made switchable fairly easily so you can keep the lows for clean settings. You aren't going to turn it into a plexi without turning it into a plexi, but you can get closer...