Any info about this amp? A friend of mine's got one of these, made in USA, and it hasn't any Celestion speaker but an Ampeg Special Designed one (or something like that) that sounds quite like a Celestion, but I think it's not the original one because it's supposed to be Celestion equiiped (there's a plastic label that afirms that). It seems it's a newer version of the SS-70, but I think it has the same circuitry (I've seen a guts pic and looks the same)

Hi! Well, I decided to use low voltage tubes in a fenderish style preamp with my all-mosfet power amp. I chose a couple of ECC189, they run really well with about 90V DC. In fact, I used dual 45V DC taken from a couple of zeners (power amp uses dual 50V supply), with 1000uF caps filtering for both lines. It's basically a 3 stage Fender preamp, with a cathode follower after first stage, and before tonestack. Every cathode goes to a resistor to -45V DC, and tonestack and volume and master pots are referred to 0V. I placed a small resistor and a 470uF cap as LPF for first tube (that's first stage and cathode follower) B+ (that's about 44VDC), but didn't make this LPF in negative supply after 2nd tube (2nd and 3rd stage). The fact is when I turn vol pot (right after tonestack, before 3rd stage) a bit of hum appears, so, it must got to do with first stage. I already changed from filament AC to DC supply, 6V regulated. Probably I'll place some small inductors in the tubes supply for better filtering. How does it sounds? Pretty cool!

Any more ideas or comments?

thanks!

Well, the fact is when I played for some time, when it heats up, the preamp starts to sound like unbiassed, it has no problem with the PA, I plugged the bass directly to the PA and sounded ok. I also installed a couple of cooler fans pointing directly to the OT transistors, but I'm going to disconnect them and see what happens. Any ideas, any similar trouble like this?

thanks!

Hi! I want to fix a problem in a friend's Vox AD 50, it seems that oscillates with distorted amplifier emulations at max gain, master volume and PA gain pot... also sound gets noisy after a few minutes of hard playing. Can I do anything to solve this? Maybe changing output IC? A power amp schematic would help me a lot!

MODS? Pretty easy... just replace 12AX7 for a high quality NOS 12AU7 and 2200 uF caps for 4700... tone improvement! Really awesome!

A friend of mine's got one of these, I had to swap output transistors for the right ones (had bipolars instead of Darlingtongs), Tip142 and Tip147, the fact is when a strong signal is applied, volume shuts down. I thought it was a channel switching problem like the one I had with a Roc Pro 1000, but I plug the guitar directly to the PA (using a stompbox to increase volume) and happened the same. Could be a output transistors problem?

Any suggestions will be grateful!

I'm looking for this schematic... tubes and power mosfets seems to be an excellent combination!

Suddenly, channel switching started to switch on its own, and this happens usually when I play at mid output or more, with guitar strumming... could be a faulty capacitor, or switching Jfets went bad? Any help will be grateful.