Justblairs Audio and Electronic's Pages

This project was completed by Brendon in January 2004.  Brendon built a pair of monolock valve amplifiers using 211B+ Valves in its output stage.  This provides 20 watts of power to the speakers.

This project page gives photographs and descriptions to the main features of the amplifier build.  It was origionally published on Brendan’s web site hosted on Geocities.  Brendon has generously allowed the article to be re-published here in order to preserve it beyond the closure of Geocities free hostings.

Overview:                                                              Completion Date: January 27th, 2004

All aluminum chassis made from 3mm thick stock.

All components are isolated from the chassis with these rubber washers and rubber grommets to protect the wires.

Rubber feet for the chassis. No special spikes around here!

Hybrid full wave rectifier design. 1N4007 & 6AU4GTA TV damper diodes. I really enjoy the slow voltage rise of these tubes at power on.

Rear of unit. I've made allowance for an extra IEC main power plug. Really a thing of the past but VERY handy for power other sources (like the other monobloc)

I've purposely left plenty of space for future modifications. Possible extra LC stage to go on the HV B+

You can see the Lundahl 1660 (40ma) interstage transformer. Originally I had tested the cheap Allied Elec IT with bridging capacitor with good results. I went with the Lundahl because it had more high frequency response. But for those on the cheap, the Allied IT does the job.

Separate transformers for each monobloc. The big donut is for the 211 B+ supply. The smaller donut supplies all the filaments and 6c45pi B+.
Yes the 211 tubes glow nicely. They also give off a lot of heat. Much like a 100 watt light bulb.