The BBB range
The BBB range started off on the original test chassis - an
old Dell server power supply - which used to be called Test Dog. It was
made into an 18W push pull amp - the pre-prototype Mistress. A pair of
oversized HiFi Ultralinear transformers were accidently purchased from
VVT on the Isle of Wight, and fitted. The results were astonishing.
When that circuit was moved over to a hand-beaten & drilled
bespoke chassis, the Test Dog became redundant.
The next circuit to move onto the chassis was a 10W single ended 6L6 amplifier, based on Piotr Stanisz's Black Dog Rebel 10. Unfortunately the output transformer I used was too small, and the over-sized power transformer did not have enough poke, voltage wise, so that got shelved for a bit. However, I did need to test a 6L6 based output stage, so a phase splitter and another output valve were added.
There were things about the new circuit that were problematic - the additional phase splitter stage threw a lot of voltage at the output valves, and the additional gain was making the amp feed back between valves. A load of switches were added to re-configure the various stages of the amp - a lot of the fixes were taken from the Soldano SLO schematic. The final amp had a total of something like eighteen switches, and still no stand-by. It was to used as a design tool to help customers decide which configuration to have the amp.
One thing the amp had an abundance of was balls - the oversized transformers gave it plenty more than it needed. Because of this, it got called Bertha. Big Balled Bertha was how it started, and the name has stuck. The amp was demo'd, among two other amps, to two studios, both of which went for Bertha.
The first BBB-30 Studio was built in July 2015, and delivered to CDS studios on the 25th of that month. It has a mere nine switches and an external bias control. The person who ordered the amp for the studio now owns the amp, and loves it.
Due to various constraints with borrowing the amp, a copy was made in June 2017, incorporating the ultralinear taps on the original output transformers. Due to interest in this model the first of a limited edition build of three signature BBB-30 amps was built in March 2018, incorporating the most requested features.Features of the BBB-30UL Studio
- "Modern" AC bypassing on the pre-amp stages, to keep the bottom end tight before overdrive
- Rigid single strand wiring infra-structure, in silicone sleeving
- External bias measurement and control
- Nichicon PW 8000hr HT filter caps
- Plenty of extra solder tags for tweeks and mods
- Relay switching between gain levels
- Footswitch or manual switching control
- "Deep" switch on Dirty channel
- Negative feedback (NFB) on / off switch for power control
- "Rebel" configuration for TMB tone controls
- Composite hardwood cabinet, using repurposed beech, finished in Osmo, by Joe Welden
- Easy access thumb screws for back panel
- Sovtek 12AX7 / 5881WXT valves
- 20% and 43% capacitor linked Ultralinear tap power control
- Two 4, 8 and 16Ω output jacks
- Fixed or cathode bias switch on output valves
- Single ended or push-pull operation
- 1/2 or full power switch defers distortion to the phase splitter or output valves
- Line out jack (can run without a speaker)
- Output protection dumps load to a power resistor.
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