This is my first post in homebrew, so be gentle with me.
I acquires an Ameritron 811 amp (not working) for a ridiculously small amount. After a simple repair, it worked well but the tubes were a bit soft. I ordered 572B tubes to replace the 811's originally supplied with the amp. When the new tubes arrived, I got to thinking (ALWAYS a dangerous thing) I couldn't help but notice that the 811 and the 811-H (800 watts with four 811 tubes) have the same power supply, so if were to increase output power, the power supply should be able to handle it. I've heard talk about mods to raise power and decided to give it a try.
I simply moved the "buck-boost" jumper to (a jumper inside the amp)110VAC.
PLATE VOLTAGE: This modification raised the measured idle plate voltage on my AL-811 from 1688 VDC to 1864 VDC. Which is well within the limits for 572B plate voltage(2700VDC). The measured filter caps voltage was 466 VDC (yeah, that's over the 450 volt rating). Plate voltage under load at 900W PEP into 50 ohms is
1600 VDC. While the idle plate voltage exceeds the rated 450 VDC of the stock capacitors, I have had no issues here....yet! There are other directly replaceable caps with higher voltage ratings such as 500VDC and 550VDC but I found them impossible to locate in stock. The stock caps do have a "surge" rating of 550VDC, but I guess I should replace them before a problem rears it's head.
PLATE CURRENT Plate current at 900W as measured by front panel meter is right at 750mA on voice peaks. Rated max plate current for 572B is 275mA x3 tubes or 825mA. Thus 750mA is within specs for this trio of tubes.
GRID CURRENT Grid current at 900W PEP on voice peaks is 120mA Max grid current for 3 572B tubes would be 150mA. Thus 120mA is within specs for these 572B's.
FILAMENT VOLTAGE This modification raised the 572B filament voltage from 6.3VAC to 6.9VAC. Close to the 6.6VAC max rating, but higher none the less. Do you think this higher filament voltage is something I should look into reducing, or are the extra 3 or 4, 10th of a volt negligible? And do you see any issues I'm missing here? I've had a few checks on the air and the amp seems to sound good, run clean, and give me more output than the original 300 watts. I haven't run it for any long periods of time.