Ampeg B-25 1968-1972

The Ampeg B-25 is a 55W all-tube bass amp head released by Ampeg in 1968 and produced until the late 1970s. By 1968, Ampeg was firmly planted as a world class amp builder, having had massive success with their Portaflex "flip top" amplifier series, headlined by the B-15N which was the preferred amp of nearly every Motown act of the 60s. The B-25 was something of a "spiritual successor" to the B-15N, at least in terms of the circuit topology. While the B-15N featured a 6SL7-based preamp mated to a 2x6L6 30W power amp, the B-25 used the nowadays more familiar 12AX7 tube in its preamp but rare 7027A power tubes for a rated output of 55W, the same power amp design used in the V2 and VT-40 guitar amps of the era. While the preamp tubes are different between the B-25 and B-15N, the preamp design is almost the exact same, including identical tone stacks and a very small modification to the "Ultra Lo" switch. For all intents and purposes, the B-25 is the B-15N's big brother. The vastly increased headroom makes the B-25 a bit less gritty than the B-15N, but both feature a very similar warm, punchy sound that is unmistakably Ampeg. This particular B-25 was built sometime between 1968 and 1972, and we aren't any more certain about its age than that. Condition is good, with some scratches on the control plate, some small tears in the tolex, non-original power switches, and some pitting and rust on the metal parts. Amp is fully functional and sounds great. It's one of the loudest amps I've ever heard at 55W. Designed for a 16 ohm speaker load, the amp has a strange hard-wired 4-pin XLR speaker cable as well as a 1/4" Extension Speaker jack. Using just the extension speaker jack switches the amp to the 8 ohm transformer tap, while the 4-pin XLR (pinout unknown) would be for use with a 16 ohm cabinet, like the original Ampeg 2x15 cabinets of the era. To our knowledge, the amp is unmodified, with an original 2 prong power cable.