50 to 100w amp mod ?

[JQUILL6]

Apologies in advance if this has been discuss ad nausea. I've a 50w carslbro 50w (4x12ax7 + 2 EL34) works fine and sounds great with bass or guitar. A cheap amp so I don't mind modding it for fun. Is it possible to 1. Increase the amp wattage to 100w to be used as a bass amp, and 2. Install a 4 ohm tap (currently runs at 8 and 16ohms only ). I've a hunch I'll need new transformers etc and it's probably not worth pursuing . Again I'm in no way an expert .

[pompeiisneaks]

Yes to support the extra tubes you'd need a new power transformer and a new output transformer, usually between 85 and 150 bucks depending on the quality you buy per transformer (meaning 170 to 300 total). To get different output transformer taps, also you'd need to specify that on the new output transformer, the more taps, the higher the cost. So basically it's almost a new amp, and the other parts cost a lot less than the transformers. At that point it makes more sense to try building an amp from scratch that fits your needs, but due to the complexity and danger of tube amps, I doubt that sounds like a good starting point. Instead it's good to try modding the current amp to maybe change components to make it sound more like another amp instead of this one, etc.

But it's your call ultimately.

~Phil

[JQUILL6]

Thanks Phil

Pretty much what I reckoned, but is it worth experimenting with different tubes , 6L6s, KT77s etc. Will they give me more clean headroom for bass applications.

[pompeiisneaks]

Even different tubes can end up needing different transformers. I'm not an expert at knowing which works best where, but the expected impedance of the output transformer is quite often a bit different between all types of power tubes. Also some draw a lot more current than others and would need more ampacity in the power transformer to run them, etc.

So basically it's not impossible, but would require doing the right math for the tubes you're wanting.

Someone here probably knows that tube X or Y works great anywhere that two EL34's did. I know you can use 6L6GC's with the same type of setup, but you need to bias them quite differently (they also draw less power than EL34's if I recall but don't quote me on that). Hopefully that helps. Basically there's likely to be a required change to at least one of the transformers to add new power tubes in. Power maybe, OT almost definitely.

~Phil

[xtian]

Don't forget that the relationship between output power and sound pressure levels is logarithmic, not linear. In order to double the SPL of a 1-watt amp, you need 10-watts output power, and to double that again, you need 100 watts. So, increasing from 50 to 100 watts is not that big of an improvement, especially from a bass-player's perspective--they typically want 300 watts or more for a good, solid thump.