A variety of 2203 questions

Chubbs

Chubbs

Well-known member
1: Recently tried out a plate fed tonestack (thanks GLPG), and checked my phase inverter voltages both with and without the plate fed tone stack. Comparing to the metro chart most all my voltages were high. After this, I pulled v3 and swapped it to little effect, then swapped back to my PTP board and saw no change. This was with 120v in, a PV of 472, and a bias of 28-32ma. Not sure if I should fix this or let it be.

Pin| Metro My Amp
1 218 293
2 28 100
3 42 170
4 3.15 3
5 3.15 3
6 214 298
7 28 118
8 42 170
9 3.15 2.9

2: Are there any worthwhile power section mods for the 2203? I remember hearing something about Cameron doing that but haven't found much on the subject. I had a beat set of el34's that drifted themselves up to a PV of 520 and the amp sounded great, not sure if that can be recreated without changing the transformer.
 
Going to have to have a schem to understand why your voltages are so far off but my initial guesses is DC over voltage of ceramic capacitors somewhere or a ground issue. Could also be you’re just slamming the PI harder.

Power supply mod wise it’s usually to rebalance the preamp voltages after adding a stage somewhere. However there is a tradeoff with stability and stage isolation you make with getting greedy with too low of B+ dropping resistors. Nothing is for free.

To get to 520V you’d need a 560V PT to account for droop from all of the quiescent currents and heater supply pulling down B+ from 560 to 520.

470 is healthy for an idle B+. My PT is at 440V in its latest revision hence why I plan to pull both transformers for aftermarket versions. At some point mods can just demand more than stock transformers are made for and there’s nothing you can do component wise to get back the right feel with low voltages everywhere. I don’t think you’re anywhere close to that yet but it’s worth noting for the more serious tweakers.

In summary check your grounds, and check for ceramic capacitor dc over voltage/punch-through.
 
The voltage that seems really off is your cathode voltage. It shouldn't be anywhere near 170v. Check the values. Is the cathode resistor 470R and is the tail resistor 10k? Is the PI grounded thru a 4k7-5k resistance (either the Presence pot itself or a 4k7 dangling off of it). Since your plate voltages are so high it looks like very little current flowing thru them. And it looks like something at the cathode end could be the cause.
 
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