The BorderPatrol S20EXD Parallel Single-Ended Amplifier offers 18 Class A Watts per channel from two pair of Western Electric 300Bs.
The dual mono S20EXD employs interstage transformer coupling, essentially marrying the 2x NOS Sylvania 6DR7 double triode input tubes directly to the 300B output tubes. TheS20EXD comes with a pair of tube rectified external power supplies (PSU), one for each channel, and the whole affair is point-to-point wiring throughout. What’s not found in the S20EXD is negative feedback which, at least in my experience, can lead to be improved measured performance but can also lead to lousy music performance. Hmm, tough choice.
Each PSU contains:
1x Mullard GZ37/CV378 full wave rectifier in the 300B high voltage supply
1x EZ80 full wave rectifier in the input driver stage high voltage supply
1x EZ80 full wave rectifier in the 300B negative bias supply.
From BorderPatrol:
Each PSU contains three independent tube rectified, choke input filter high voltage supplies to independently feed the 300B’s, the input/driver tubes and the negative bias supply, together with filament supplies for the 300B’s and small signal tubes. The use of choke input filtering is a critical difference and is unique to BorderPatrol power amplifiers.
The ins and out on the S20EXD reside behind the tubes and transformers mounted to the top plate and include 4 and 8 Ohm speaker outputs and a pair of single-ended RCA inputs. The review unit came with the optional volume control.
I’ve seen and heard the BorderPatrol S20EXD at hifi shows past as this pic from Capital Audiofest 2023 attests, here paired with the Living Voice R80 OBX with outboard crossover units. More on these shortly…
I look forward to lighting up the Barn.
BorderPatrol S20EXD Parallel Single-Ended Amplifier
Price: starts at $22,500 without 300B tubes | optional volume control +$500
Recommended Power Tubes:
Western Electric 300B tubes: $3100/matched quad
Genelex PX-300B: $775/matched quad
Emission Labs 300B (solid plate): $1600/two matched pairs
Takatsuki 300B: Market price (typically $1600-2000/pair)
Company Website: BorderPatrol
