Gunter Steinhart Bolero amplifiers - fully restored and upgraded.

300W Class A valve Mono block's

I purchased the two vintage Gunter Steinhart Bolero mono blocks from a collector in Cape town during December 2015, they were electrically working but many years at the cost had takin it toll on the mechanical parts.
These amplifiers were manufactured in the early 1990's in South Africa by Steinhart Audio, they are equipped with eight Sovtek 6Pi45C valves each and are rated at 300W / 8 ohm.



What's in the name?

At the time we planed the job I wanted to distinguish the rebuilt units from the original so I added an R (for refurbished) into the brass nameplate, this spelled BORLERO instead of BOLERO (it seemed like a good idea at the time), in the future units we will change this to BOLERO R as it falls easier on the eye and does not look like a type-o.

The two mono block's were electrically tested in my workshop and I found them working well except for the power-up delay (pre-heating) circuits that seems to have been modified "butchered" in the past or this may just be a bit of "MacGyver" work on the part of Steinhart Audio. 

I re-designed the circuits using similar components to the original parts, etched the PCB and installed and tested it.

The power-up timer circuit is similar to the original using a NE555 timer in a one-shot configuration.

The new Power-up PCB installed and tested, I added an internal LED so I can see what is happening during the very long two minute delay. It is like watching paint dry..... but  it is Sovtek's recommended pre-heating time.

Photographs showing the rust damage to the metal parts and output transformers, the metal parts were all stripped using an industrial paint stripper liquid for the removal of epoxy powder coating, then sanded with an orbital sander and finally polished with a wire brush. The transformers were removed, sand-blasted with AB grade glass beads and re-varnished with an air drying transformer varnish from WILEC. 

Stripped Metal work ready for professional bright chrome at African Electro-plating.

http://www.africanelectro.co.za/

Newly bright chromed metal work ready for assembly.

Our 4 axis 6 tool machine from HEIZ CNC-Technik (S720T), normally this machine is used for advanced rapid prototyping was used to manufacture various parts including the new brass nameplates.

Machining new nameplates from solid brass bar. I created the CNC program with Solid Works and Deskproto.

I developed the legend Silkscreen in our dark room for printing on the newly chromed faceplates, I used 120T screens and a UV Photo-imageable emulation from AZOCOL and ULANO. The Artworks was designed in DraftSight and printed on transparency for UV exposure. 

Baking the silkscreened parts at 100'C to permanently fix the self etch Safire opaque white ink to the chrome. (This ink is similar to the ink used by stove manufacturers)

Final Assembly of the units ready for the listening room.


The total project ended up costing US$3'225,00 including the purchase of the amplifiers and two new valves.

They sound and look fantastic!


I enjoyed this project and have been asked by a friend to rebuild his Boleros, I have started and will post photographs once completed.

Michael :)

Picture of our workshop in full swing - make me smile.