| Author | Message | ||
     Mike (mike_h) Username: mike_h Registered: 06-2006 |
On a typical push pull amp, that has cathode to ground on the pwr tubes, pulling a pair of tubes, as long as they are the correct ones, is a good way to reduce headroom for the rock 'n' roll tone. Is this OK with MM amps? The schematic for a 65 watt amp compared to a 130 watt amp is about the same except for four tubes rather than two tubes and a different OT, so, I can't see why it wouldn't be OK. Of course there might be some concern with the correct match of the tube to OT. But, otherwise? Anyone do this? Any opinions? Thanks. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Each matched pair goes through a 10 ohm 1 watt resistor to ground. It's not a good idea to pull one of the pair out without re-biasing. And if you have the SS driver, It may overdrive the driver transistors. I've never tried it because I like mine the way they are. It would, if successfulwant to see twice the output load but the MM's will take a 100% mismatch without too much trouble. I still don't suggest it though. JMHO. | ||
| Mike (mike_h) Username: mike_h Registered: 06-2006 |
Well, I pulled two of the tubes to try it. It does reduce the headroom a bit. Plus, I can leave the amp on the high setting to enjoy the sweet juiced-up tubes. The voltage across the 3.9 ohm resistors is the same as with four tubes, plate voltage the same, etc. So, I guess I can consider this an option? Anyway, that's my experience with this. | ||
| Ingo Raven (ingo) Username: ingo Registered: 07-2007 |
I did the same with one of my amps (an 212HD-130 with 12AX7 driver), no problems so far. I first thought about replacing the 10 Ohms cathode resistor to 5 Ohms, but then thought it shouldn't matter much. When biasing, of course you must set it to 0.25 volts instead of 0.5 volts over the resistor. Or do I miss something? |