... many people think the BTO was designed for Bachman Turner Overdrive, but in reality the name stands for Big Time Operator ... I made well over a hundred of these, way more than one band could need ...
Gar Gillies, phone conversation 6/97
... around the time of the Guess Who everybody in Winnipeg was using Garnet amps ...
Randy Bachman, CFOX Radio Interview Vancouver 8/98
I'm the lucky owner of a couple of early Garnet amps designed by Gar Gillies' ... a first edition BTO (with an upside down control panel from the one seen in Aspen Pittman's books) and an early version Session Man ... both running on EL34's and carrying outstanding output trannys ... The BTO has a transformer phase driver circuit, quite a unique design in many ways- personally I like the tone and feel of the dry signal path, I never use the effects except sometimes for the vibrato which is the bias-modulating kind, similar to late 50's Fender and 60's Traynor amps ... the SessionMan was given to me by NJAMusic Store in Vancouver after being considered not worth fixing ... after a few snips to decouple the faulty Reverb and Distortion circuits this thing began producing the most awesome Plexi tone outside of a 60's Marshalls ... when paired with older Celestions both these amps produce undeniable tone ...
... since on-screen rasterization of computer images occurs at 72 dpi, high rez pics will appear huge and will take a long time to download ... a 72dpi FastView version of the schematics is provided for reference, followed by a 300dpi printable version (you may need to convert these before printing) ...
Apart from their superlative tone and power handling Garnet amplifiers suffer from a slight under-design in one place in the amp ... turns out that the filter cap in the bias section is prone to blowing because of poor capacitor quality and close to rated-limit applications ... usually this makes a big mess in the amp, blows the power tubes and potentially damages the output tranny ...
Gar Gillies has been buying back his amps to moddify them for many years now ... the first thing he does after congratulating you on your purchase of a old Garnet amp is he offers to buy it from you so he can upgrade it ... the man goes beyond dedication !! I've spoken to him on a couple of occasions to request schematics for my amps and once asked him why he didn't include variable bias in his circuits. His response was that the amps really didn't need it, and he was adamant (understandably) that the circuits shouldn't be modded in any way though I mentioned that with different tubes bias might need to be adjustted skightly for tone and here he disagreed ... after I realized how contrary he was to the idea of variable bias I dropped the issue with him ...
... still, I present a simple circuit variation for anyone who feels they might bennefit from having variable bias in their Garnet amp ... the bias circuit shown below is the one that Gar seems to favor for many of his early amps ... the bias cap shown without value in the schematic should be rated at 75volts and valued around 25uf to 50uF ... a 25Kohm pot and series connected 25Kohm resistor pair replaces the bottom resistor in the original AC divider circuit; make sure the pot is turned to its max value before turning the amp on for biasing ... tranny shunt is the best way to measure bias and side-to-side matching ... but be very careful- read up on the technique first, you're handling two sides of a tranny leg floating around 400-450vdc with both hands - in particular, do not let any part of your body touch metal during this test, and make sure the Ameter is fuse protected (usually is in DMMs - fuse is inside) in case one side accidentally hits metal or a considerably different voltage node ...
this picture gets a 10 for composition ...
photo source unknown ...