6L6GC in Marshall

[NannerPuddin]

I have a Marshall 50 watt head from 1969.  It has 6550's in it.  I want to try some 6L6's does any know what I need to change for this to work?

Thanks,

NP

[sluckey]

You'll probably need to change the bias. You may have enough range of adjustment already, otherwise you may need to change a resistor value in the bias circuit. Worst case, if your B+ is too high, you may need another PT.

[bigdaddy]

Measure the B+......if it's OK for 6L6GC then you're good to go as long as they bias up. It's more about the OT, is it 2k or 4K or what??????? Was the 6550 from the factory, I don't think so, it probably came with EL-34s if it's an American amp. Does it have the voltage switch?

I think those amps sounded best with EL-34s. The Mullard reissues would probably sound great in there.

Years back a lot of players went with the 6550 tubes and away from the celestion speakers like the greenback because they were playing certain types of music in larger venues. To me that amp is best with EL-34s and a 4-12 cab with the 30 watt Celestion as they called them 120 watt bass cabs....LOL. For instance even Hendrix preferred 6550 and higher voltage PTs because he was playing in stadiums and larger venues and terrible sound systems. The Allmans went with open back cabs and K-120 JBLs with their 100 watters. The sound of the what I feel is the true Marshall sound has been lost over the years. Listen to Live Cream for instance, that's the true Marshall sound to me. Same for Santana at Woodstock with his small box 50 watt head and 8x10 cab with an SG and P-90s, that was his best sound/tone ever IMO.