Custom-built Williamson-style 300B Push-Pull Tube Monoblocks

This is a pair of custom-made, push-pull 300B Williamson-style monoblocks.  They combine the power (15wpc @ < .5% THD) and bandwidth (30Hz-30kHz) of a classic triode Williamson amplifier with the magical mid-range and transparency of the famous 300B output tube.  I have to admit that it takes a pretty darn good amp to tear me away from my KT66 Williamsons, but these amps have managed to do it.

A while back I heard an excellent podcast with custom amp designer Justin Weber, who compared the 300B to a "tease" (he used a racier term than that), offering incredible sound but not enough power for most systems.  "If I could just have a little more, a LITTLE more..." he kept repeating.  Very funny but also very true!  Power isn't the only issue.  The 300B is so transparent that the driver stage becomes critical.  Finding the right combination of low distortion and adequate drive voltage is critical, and a lot of commercial 300B amps fail on both counts.  One answer is expensive interstage transformers, another is using silicon gadgetry to maximize the driver output.  These amps use neither.  In fact, the super-linear 6SN7 Williamson front end is a natural match for the super-linear 300B.

These amps feature heavy-duty, custom PCBs that afford reliability, an optimized signal path and easy repairs (should they ever be needed).  The sturdy Belton sockets are offset from the board to practically eliminate any heat transer, a common problem with tube PCBs.  The 300B filaments are powered by simple DC supplies that, combined with the noise cancellation of push-pull, guarantee ultra-silent operation.  The main power transformers are custom-made by Heyboer of Michigan and run cool and quiet.  The output transformers are classic UTC LS-57s that deliver clean, sweet sound.  The amps employ 10dB of negative feedback to further reduce noise, extend the frequency response and provide excellent speaker control.

The amps are self-biasing, making tube-swapping a cinch.  A built-in front panel meter allows for easy balancing of the output tubes (very important in a Williamson amp).  Test points are also included for checking the bias and letting you know when it's time to replace the 300Bs.  The UTC LS-57s must be wired internally for 4, 8 or 16 ohms, but this output impedance can be changed by the user in a matter of minutes using the kit and instructions included with the amps.  This is a very simple operation with no soldering required!  Any high-current 5-volt rectifier tube can be used, including 5AR4/GZ34, 5V4/GZ32, GZ37, 5U4, 5R4 and 274B.  The 5AR4/GZ34 offers the lowest voltage drop and thus the most power, but any of the others will work with minimal power loss.  These amps are "ultra-tuneable" and a wide variety of flavors can achieved by swapping out any of the tubes.

I use these amps with my ProAc Response 2's with excellent results, and they will drive any reasonably-efficient speaker in a modestly-sized room.  Speakers with an efficiency rating of 90dB or greater will of course work better than less efficient speakers.  If you have any questions about whether or not these amps would be a good match for your system, feel free to ask me.  They have been fully tested and broken in, so you'll know right away if you like them or not.  If they turn out not to have enough power or are otherwise not suitable, you can return them within 14 days in the original packaging.  I have no interest in selling someone an amp that doesn't work for them!

The price includes free UPS ground shipping in the continental US.  The amps ship with a manual, all schematics and a kit for changing the output impedance.  Also included are a matched quad of Psvane HI-Fi 300Bs, four NOS GE 6SN7GTBs and two Genalex 5AR4s.  The Psvane Hi-Fi 300Bs are very good for the money, and in push-pull configuration with a bit of negative feedback they perform extremely well.  But of course there are a lot of options in terms of 300Bs, not to mention the other tubes.  If you prefer to provide your own tubes I'll take $700 off the price.

I fully guarantee these amps for one year, and am happy to provide service for as long as you own the amp.  Shipping is not cheap, because I tend to over-pack my amps, but I'm happy to discuss the return cost with you.