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tube amp power vs power tube composition?

#22
skier 913 said:
If an amp with 6l6's says it can take EL34's, does that mean that it can also take 6550's ?
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This would be a dangerous assumption.

There are amps that can take different tube types. They are usually clearly marked as to what is compatible.

You really need to balance the tube to the circuit or the circuit to the tube type.

If you're hoping to boost the output of a 6L6 amp to 6550 levels the answer is basically no. Unless that amp is designed to supply higher voltages and current at 6550 levels.

Others can explain this better.

A good example might be replacing the 6V6 GTA in a VibroChamp with a Fender STR type 6L6GC. Been there. Done that. You "Might" find a tiny bit of headroom. If you're expecting ~30% more power It ain't happening. You're limited to the stock 6V6 circuit and voltages. Yes they are pin compatible. So it can be done. But there's essentially zero benefit.

It's a combination of tube and circuit.

Compatible or not your asking the circuit to do something it wasn't designed to do. If your lucky a fuse blows.
 
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#24
skier 913 said:
If an amp with 6l6's says it can take EL34's, does that mean that it can also take 6550's ?
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Sometimes, but the 6550 draws 100mA more heater current per tube which may be an issue, how the screen is connected and the screen circuit could be an issue, and the 6560 needs a lower impedance drive/bias circuit plus the grid bias voltage will be different.

I wouldn't recommend it.
 
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#25
ajkula66 said:
This.

And circuit design - in any field - is serious science.

I know people who run 6550s as well as KT88s in their 1959 Marshall Super Lead amps. Never made sense to me since I really couldn't tell the difference, but then again my hearing is damaged so...:cool:
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Many years ago I did many mods from Aspen Pitmans Tube Amp book. One was this for lack of a better term 6L6 to EL34 quasi universal tube base rewiring mod.

The subject was a rather nice clean 68 drip edge non reverb Bandmaster. It did not create the raging Marshall wannabe I was hoping for. Even after setting the bias it sounded like a 68 drip edge Bandmaster. Those were a lower gain non master volume amp and it should have sounded different. But it sounded essentially the same.

The circuit matters.

My old 2204(?) 50 watt JCM 800 head came with factory installed 6550's. Everyone said EL34's were the bomb. This was a high gain master volume amp. EL34's seemed a bit mushy in comparison and the 6550's went back in for their combination of headroom and grit and grind. I was looking for classic rock aggression and they did NWOBM type tones better. The amp sounded the same. JCM 800's are all about the preamp gain in a sense. It responded a bit differently but the "tone" was the same.

On the other hand having a 50 watt JTM head with EL34's and no master volume I can say that I'd probably not want 6550's in there. It doesn't need to be cleaner and louder.

I'm not an expert here by any stretch. But to get the most out of a tube type you need to match up the transformer(s) and power supply.
 

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