Metropoulos Forum

Hey again!! I need some direction on this. What have you guys done to up the overdrive in your amps??
Does the change from .022 to .1 on the phase inverter make a difference?
Hey Gnugear, where are you??
Thanks, Rick

I would start with adding the GT 12AX7M's, they are quiet with high gain. You can also try switching the purple negative feedback wire to the other taps (4,8 or 16 Ohm). It makes a difference. Also try changing the feedback resistor. I think it's changing from a 100K to a 47K or vice-versa. It's connected to the purple wire.

100k will give you more gain on the feedback, but the 47k will give more smothness and thighter bass respond.

You could change your plate resistors to 220k instead of the regular 100ks for more gain.

Also changing the 47pf cap on top of the phase inverter section to a 100pf will give you a little more compression and smothness in the hight mids very nice....

Changing the .022s for some .1s will not give you more drive really(George?..), but it will warm up the output section buy letting less highs go through.

Actually upping any of the coupling caps from .022 to .1uF will let more bass through, not cut highs per se, but you may encounter mushy bass problems at that point if you do increase your gain; maybe not the right direction at this point.
You can certainly get more power amp gain with the feedback loop; I like the 100K/four ohm output tap combination, which is the least feedback you typically see in a Marshall-type amp. Again, watch your bass, it can get mushy if you're not careful.
Are you running 270K's or 470K's as mixer resistors where the channels join together? 270K's will let a little more drive through, but it seems like I remember reading about some effect doing this has on the way the channels bleed into each other.
What bypass caps are you running on the first and second preamp tubes?
If you don't have the classic .68uF across V2A's cathode resistor you could get a bit more upper mid and high end zip there.

Where are the Plate Resistors located on a PTP Board?

just below V1/V2 on top of the board, you should have bleu wires connected to them "the plates" (top left of the board when chassis is upsidedown, preamp controls facing you)

so is there a total of only 2. I see the 2 on V1 but V2 confuses me.

Yes two 100K resistors with two bleu wires (if you fallow proper color codes...) that go from them (a upsidedown V shape) and connected to the plates (V1a pin1 and V1bpin6)

Try some 220k there you will get harsher type of sound more gain also

Thanks, one day, i'll know what i'm talking about. Everyone here has been of great help. I have no problem with gain on my 76' with Metro Board, my voltage is low, about 355 Volts. The amp saturates early,I get killer overdrive.