Purity Audio Design
PSE300B Ultra
18 watt Parallel 300B Mono Bloc Amplifiers

The PSE300B mono bloc amplifiers are the result of several years of design work and redefines the capabilities of 300B amplifiers. The PSE300B Ultra is a premier example of 300B amplification that only Purity Audio Design can bring to you. Using two 300B output triodes for each channel in a parallel configuration, we are able to provide up to 18 watts of that glorious 300B sound. The preconceived conception of weak bass and less than stellar dynamics has been put to rest with the PSE300B Ultra mono blocs due to our custom design amorphous core output transformers.

The PSE300B features a Pure Class A parallel single ended output stage which is the purest and one of the most sought after circuit topologies available. We use only Zero Feedback Designs throughout all of our Single Ended Amplifiers. A separate choke filtered power supply and polypropylene filter banks bring the PSE300B to a level not yet realized in the industry. The internal components in both the power supply and analog circuit were selected after years of listening to find just the right recipe to bring the Purity PSE300B Ultra up to par.


When designing tube amplifiers,  you have to make a few choices before the design can start. There are only two school of thoughts..... design for highest output power or design for highest sonic quality. Like any Purity Audio Design product, we build for the absolute best sonic quality.

When designing around the 300B tube in the output stage, an output of no more than 9 watts [per tube] provides the lowest in regard to 2nd harmonics which results in a presentation that shows the most potential the 300B has to offer. Maintaining these guidelines allows the 300B tube to remain in it's comfort zone providing the most realistic tone and soundstage.

Our custom designed Amorphous C-Core output transformers are truly a one of a kind design and a key factor in why the PSE300B shines above the rest.  Their unique design greatly reduces the negative impacts of what common transformers with multiple output taps normally bring to the table. The output transformers have been custom designed for Purity Audio Design by Dave Slagle.  See below for details on our output transformers.

The final leg of the output stage of any amplifier is the speaker binding post.  Used in the PSE300B Ultra are a new patented design binding post utilizing "Magnetic Conduction Technology" by Magnetic Innovations LLC.


The input is fed into a single 6SN7 medium mu triode which drives the output stage. Each of the two output triodes are individually self-biased, with only the plates tied together in a  parallel configuration, which is nearly equivalent to having one high powered triode.

 Provided are both single ended and transformer coupled balanced inputs. The entire circuit, from the power supply to the output stage is 100% hardwired.


The power supply is an often overlooked importance in audio design. The quality and design of the power supply is critical for a top class component. Purity Audio Design spends as much time developing power supplies as the circuits they are driving. After all, one is no good without the other.

A high current transformer is used for the main B+ voltage requirements as well as feeding the regulated DC supply for the 6SN7 filaments. A separate high current toroidal transformer is used to feed the regulated filament supplies for each 300B. Each 300B tube as well as the 6SN7 driver tubes received its own, highly regulated DC supply. Separate DC filament supplies provide total isolation between the input and output stages.  The use of LCR filter networks with very large polypropylene capacitors and heat sinked high power resistors provide an unparalleled ripple reduction and low noise operation.

Mains input voltage is set at the factory and is available for  115V/230V 50-60 Hz operation.

The chassis is constructed entirely of 1/8" thick aircraft quality black anodized aluminum and then hand assembled in our New York facility. The transformer covers are custom made of 1/8' thick walled 6061 aluminum and finished in a flat black powder coat.

Vacuum Tubes: Each PSE300B comes equipped with the following tubes:

4 pieces - Sophia Electric Princess 300B
2 pieces - Sophia Electric Grade A 6SN7
2 pieces - 5U4 Rectifier

Frequency response: 10Hz-40kHz
Input Impedance: 100k Ohm single ended
Input Sensitivity: 250mV for full output
Maximum Output: 18 watts into 4, 8 or 16 ohm loads
Tubes 1 x 6SN7, 1 x 5U4G, 2 x 300B per chassis
Weight: 42 lbs each
Size: 12" W x 15" D x 11" H (each chassis)
Fuse: 2A Slow Blow (120V Supply)
Power Consumption: 135watts

Suggested Retail Price: CONTACT US

Please allow approximately 60 days for the assembly of the PSE300B Ultra mono bloc amplifiers.

Please see our Product Comparison Chart to help you in making the proper decision for your system goals.

Due to the complexity of the PSE300B Ultra amplifiers, all pieces are built to order.



First of its kind output transformer

Purity Audio Design is always working to bring you cutting edge technology and performance with every product carrying our name. Our new PSE300B Ultra mono bloc amplifiers are no exception. For such a high performance product, our goals were simple; 1) Amorphous Core 2) Optimized for multiple loads and 3) Ultra wide bandwidth

Output transformers with multiple taps such as your typical 4, 8 and 16 ohm outputs typically have a different frequency response for each tap and usually only optimized for one particular load and even that is a rarity with off the shelf designs. The best solution is to wind a single tap for the best bandwidth. Obviously this is not a viable solution for a commercial offering with so many different speakers in today's market.

To solve the deficiencies common with most output transformers, Purity Audio Design approached Dave Slagle of Intact Audio to design an output transformer that provided top performance regardless of speaker load and at the same time was end user friendly.

Looking at the graph below, you will notice that the transformers designed for Purity Audio Design for use in the PSE300B Ultra mono bloc amplifiers are -1dB at greater than 40kHz with minimal variations in performance from each the 4, 8 and 16 ohm taps. The graph also shows the measurement of each transformer used in a pair of Ultra amplifiers which can be considered a matched pair. Another rarity in today's market. When we look at the low end performance at 160mA and at 20W (@50Hz) signal, the inductance still remains linear and provides a 1dB point at 10Hz or slightly below when driven by the parallel 300B tubes. This is how Purity Audio Design puts to rest any claims of amorphous core output transformers having weak bass.

Below shows the amorphous core output transformers used in the PSE300B Ultra amplifiers.

This transformer design allows the end user to choose the proper tap for his/her loudspeakers and maintain optimal performance with minimal effort. The picture below shows how to wire your PSE300B Ultra for your required load. We provide the appropriate straps in both spade and banana termination to best accommodate the type of speaker cables used.