I love simple one triode spuds for less than 3k use a pl84 el86 a too abundant tube in the especially I like it a lot it has a rp of 600r and overdriven heaters are a blessing in disguise I love the warmth of the tone the look of the tube the improved operation when overheating these dirt cheap tubes it really helps us spud guess sometimes we try lots of things to make the tone better sometimes we put to much plate voltage drive tubes harder put quality components and I that but it's necessary and essential to drop all we know and play around with things imperfect be inspired by Sakuma San not just to chase specs and audiophile design and other people's opinions but to have faith in our ears are subconscious mind our body and build something magnificent even if the tube will burn up in a week the memory will always be present I would love to advise you to try a trioded pl84 overheated or a ecc85 ecc81 overheated it will all work if lining servers you most of the time I scavenge for opt in many places and use many things as opt it might not be perfect in the blind man's eye one blinded by many nonsense told by ignorent audiophiles and diyers but one must be open to the truth to his truth Sakuma uses mismatch transformers many say Sakuma is the best tube amp artist of our time don't they I love calling me and us all not just the diyers but the consumer product creators of this feald of art tube amplification instrument artist's for this is a art and not a dieing one but one of rising for there is a more than ten percent increase yearly in the cash flow of our art our high end now a billion dollar a year total is spent on tube amp more of which are becoming dht triodes it's only getting better and its only the beginning sorry for some bed righting my display and touch screen are broken so some things slipped I right solidly English being originally from South Africa but it has declined a bit considering I can't use it often not being in English speaking countries
Those grid leaks seem unnessary; the input transformer secondaries are surely much lower in resistance.
Jan
Jan
I had a conversation about those grid leaks with Jack Eliano when I bought some interstage transformers and had the same doubts. He definitely wanted the secondaries to be loaded but to determine the value experimentally using a pot then replace it with that resistor value. He said vary the pot while monitoring the THD, when you have the lowest THD use that value.
I don't see how that parallel resistor could affect to THD, but for sure it may affect to frequency response of the input transformer.
Does this come out to a 1:25 input SUT? (newby at calculating this ratio). Who sells an input transformer with such a large SUT ratio? Maybe a moving coil phono step up?
The STU-001 input transformers were manufactured by Tamura. Sakuma used them very often in his designs. I was able to find some pairs of Gardners (British) with the same characteristics and better bandwidth of 20-20000Hz. They are signal transformers (perhaps designed as step-ups for turntable cartridges or microphones), so I think it is not possible to run current through them, even a few mA.
https://jandkaudiodesign.blogspot.com/2017/09/tamura-stu-001-input-transformer.html