The BFlex is the second member of the B-Series and is based on the Ampeg Portaflex, which stands for a more "modern" bass tone.
This is achieved by a Portaflex-typical preamp circuit but also a very effective Baxandall tone stack, which has been optimized for the BFlex.
Compared to the HoneyB the BFlex uses adjustable fixed bias instead of cathode bias, allowing the tubes to be set to an optimal operating point depending on the builder’s taste.
No experiments are made in the area of the ​​power supply and transformers, the well-known transformers used in the 18-watt platform are also performing flawlessly in this kit.

The original idea was to operate the power amp in ultra-linear mode, but this combination did not bring any further tone improvements, however it had a negative effect on the achievable output power. Hence this idea was rejected and the tubes are connected in the classic pentode arrangement, which offers a maximum output power of around 15 watts. If you still want to try ultra-linear operation it is no problem, since the output transformer offers ultra-linear taps also.

The construction is quite clear, although a significantly larger amount of components are needed compared to the HoneyB. Care is necessary to correctly implement shielded wires to eliminate external interference and it is also important to ensure proper grounding. If above points are taken care of nothing stands in the way of a successful reproduction.


Schematic as PDF (2 pages, DIN A 4)

Layout as PDF (1 page DIN A 3)


The amp kit and accessories for the the BFlex are available in TT-Online-Shop

Warning !

Care is necessary during construction! The voltages used in this amp are potentially fatal. This amp is NOT a beginner's project!
A successful build requires that you can read (and understand!) a schematic diagram, you know how to use various measuring devices, and you have some experience working with voltages over 60V.