Hey all, I've seen a little info around but I am not sure what to trust - I have a Maverick Bass amp with the 7591 tubes. Is there such thing as a 7591 to 6550 conversion kit? Can you even do that conversion in this amp, or are the values too different? I am looking to get as much clean bass headroom as possible out of the Mav. thanks yall!
Guild Maverick Bass - Power Tube Options
- Thread starter dcookNH
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Prince of Darkness
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My main concern about substituting 6550s would be that the heaters draw twice the current of the 7591s. It really depends on how much current the power supply transformer is specified to provide to the heaters as to whether this would be practical. The pinout of the two valves is also different, though it shouldn't be too difficult to rewire the sockets 
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It seems like you're trying to make the Maverick into something it wasn't designed to be. Given the changes you've already made cosmetically, I'd probably just custom make that fits in the cab.
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yeah you are prob right. I may just tweak the cap settings for the Tone switch to get some usable tones and call it a day. The brightest setting kills 90% of the volume, and the lowest shakes the house
I have a couple of Guild amps with tone switches and I find them to be pretty universally awful. I bypassed the one in my Thunderstar, but I also use it for guitar.
Bias (and corresponding drive requirements) for the 6550 are considerably different than the 7591 and would require considerably more changes than just rewiring the sockets.
6V6GT and EL34/6CA7 are closer in drive/bias requirements, but have different max plate voltages and heater demands. It's not that simple.
6V6GT and EL34/6CA7 are closer in drive/bias requirements, but have different max plate voltages and heater demands. It's not that simple.
yeah imma leave it as is.
matsickma
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If you want a Guild amp with 6550 finals you need a late 60's Quantum Bass head. It has to be the "big" head that says Thunderbass with the metal sticker that says Quantum. This is a larger head cab than a standard Thunderbass amp. The head is made of two parts. The front panel is screwed into the front of the cab. Inside the power section is physically separated from the preamp and controls.
The 6550 in that amp are biased very high. Default may know the voltages. I can only say that is the loudest amp head I ever heard! Granted I no longer have access to a friends 200 Watt Marshall head but my 18 year old memory of that Marshall head compared to my semi recent memory (i.e., within last 5 years) tells me the 6550 Quantum was the louder of the two. If you plan to use it for guitar you better get a Power Soak or modern equivalent!
The 6550 in that amp are biased very high. Default may know the voltages. I can only say that is the loudest amp head I ever heard! Granted I no longer have access to a friends 200 Watt Marshall head but my 18 year old memory of that Marshall head compared to my semi recent memory (i.e., within last 5 years) tells me the 6550 Quantum was the louder of the two. If you plan to use it for guitar you better get a Power Soak or modern equivalent!