I have owned this amplifier for several months now. Although it sounds great right out of the box there are things that can be done to greatly improve it's sound. First....junk the Chinese 12AU7s that it comes with. They are not actually 12AU7s anyway. If you measure them they have an output closer to a 12AX7 than a 12AU7. I put in several different 12AU7s before realizing this and lost about half of the volume. A pair of Tele 12AX7s worked wonders. Next.... almost all the "known brand" caps in the unit are fakes. Some of the names on them are even spelled incorrectly! Replace the .22 coupling caps with Vitamin Q PIOs or Russian K-40s. The replace all of the output caps (2uf) which are ridiculously small for their value with equal value, but good quality caps. I used Russian K42s. It was a really tight squeeze, but it can be done. The difference in sound is immediate! I then pulled all of the EL34s and replaced them with Gold Lion Reissue KT66s. With their tapered base they will plug in directly even though the Ming Da has the beauty rings around the sockets that prevent most other tubes from being used. I also purchased some inexpensive octal socket savers that space the tubes up about an inch which will allow you to even run 6550s or KT88s in it if you like. The filament current is almost the same for all the tubes so there is no problem doing it.
Bias is set by measuring from pin 8 to the ground bus on each final tube. Ming Da suggests .33-.35 volts for the EL34s. The KT 66s or KT88s would require more...something in the area or .5-.6 volts. You will be shocked at the improvement that changing the finals and caps makes.
I have the complete schematic of the unit if anyone needs it. Apparently it's a closely guarded secret from Pacific, but Meixing was kind enough to send it to me. Anyone needing it can email me and I'll be happy to send it to them.
Enjoy your amp....Once modded it's a killer!
Bias is set by measuring from pin 8 to the ground bus on each final tube. Ming Da suggests .33-.35 volts for the EL34s. The KT 66s or KT88s would require more...something in the area or .5-.6 volts. You will be shocked at the improvement that changing the finals and caps makes.
I have the complete schematic of the unit if anyone needs it. Apparently it's a closely guarded secret from Pacific, but Meixing was kind enough to send it to me. Anyone needing it can email me and I'll be happy to send it to them.
Enjoy your amp....Once modded it's a killer!