|
Somewhere down the line I'm going to build an uprated Champ with a 7591 tube just because I have an "orphan" single 7591 tube and a vintage output transformer that won't work as well with anything else. A 7591 wants to see a 3k load which is less than half of what works for a 6V6. 300 volts on the plates, 300 volts on the screens, 11 watts output according to the data sheet although actual output would be less. With max ratings of 550 plate and 440 screen just add more voltage for more output.
Consider that we'd end up with a 10 watt "Champ". It's going to be clean at the "5 watt" level. That's how to build a "5 watt" amp with respectable cleans although no "respectable" manufacturer would call it a "5 watt amp", not when they could sell it as a 10 watt amp! It's primarily a matter of upgrading the power supply to support the superior (ratings wise compared to a 6V6) tube.
Why not swap to an EL34? Vintage amps used 6V6s, 6AQ5s, 6BQ5s and the like because that's what was most commonly used in the output stages of radios and phonographs. Thumbing through the data sheet: 265 volts plate, 250 volts screen grid, 2000 ohm load, 11 watts output. Oh, my. See how low the voltages are in relation to the output? And the max ratings are 800 volts plate, 450 volts screen. We won't go anywhere near 800 volts on the supply because it makes our lives difficult when we shop for capacitors. We need to pay attention to the fact that an EL34 is greedy when it comes to power consumption, we'll allow 100ma with a 20% safety margin (120 ma) on the high voltage and we must consider the 1.5 amp filament requirement. It's not a straight plug and play in a vintage Champ. However, if we started with a bare chassis and some adequate iron we could easily end up with a little amp that would give a tweed Deluxe a thrashing. Is it a "5 watt" amp? Nope. Would it play cleaner than a stock Champ at the "5 watt" level?
|