This amplifier , beautifully built by Cape Town EE John Gilmore is based on the famous Dynaco ST70 . John designed the top plate as per the Dynaco ST70 layout . Output transformers are the Dynaco A-470 (as in ST70). Tests performed show these offer incredible performance , -1dB @ 20hz to 0dB @ 30khz frequency response . Power transformers are upgraded double stack made for ST70 , offering much more power than the original . The amp tests for an incredibly low (for valve amplifiers) 0.4% at full power output . Distortion will then be much lower at reasonable listening levels . THD vs frequency tests virtually flat from 20hz to 30khz .
SDS labs psu board under the hood is a huge improvement on standard ST70 PSU setup , offering better smoothing and more capacitance . https://store.triodestore.com/st70capupgrade.html .
ECF82 board for ST70 , allows the use of large range of tubes compared the the unobtainium original 7199 board. This board also allows individual output tube biasing , as opposed to original board which only allows adjusting both tubes at once with no balance option .