I'll look tonight if I remember for the value of the feedback resistor omitted in the original schematic. A hint - it was considerably in excess of 10k - more like in the region of 330k.
What is the impedance of the transformer you used in your simulation? I used the One Electron UBT-1 in the actual amplifier, which has a 1.6k primary impedance (14.1:1 turns ratio). A higher impedance transformer will have a larger step-down ratio, lowering the loop gain and increasing THD, also reducing the available output power.
What is the impedance of the transformer you used in your simulation? I used the One Electron UBT-1 in the actual amplifier, which has a 1.6k primary impedance (14.1:1 turns ratio). A higher impedance transformer will have a larger step-down ratio, lowering the loop gain and increasing THD, also reducing the available output power.
Look at it this way, at least you're not in the ridiculous situation of burning more power in the tube filaments than you deliver to the load...
Edit - On another note, it's interesting that you cite 120k as a good value for the partial feedback resistor. I would have used a higher value so as to leave some gain for the global feedback loop. That extra gain also helps to straighten out the output transformer - this shows up in the square wave response. For an example, check out the "SiC Puppy" thread where I show the square wave response of that amplifier (also using UBT-1 transformers) before and after closing the global loop.
Edit - On another note, it's interesting that you cite 120k as a good value for the partial feedback resistor. I would have used a higher value so as to leave some gain for the global feedback loop. That extra gain also helps to straighten out the output transformer - this shows up in the square wave response. For an example, check out the "SiC Puppy" thread where I show the square wave response of that amplifier (also using UBT-1 transformers) before and after closing the global loop.
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Has anyone tried a lower voltage Schade Semisouth 085? Search turned up this thread. I don't know about using 300v. Rather not.
I want to keep it simple like the SIT-1 monos.
Don't mind using high power resistors for the current source.
10w sounds nice.
I was going to try to combine the Nemesis article and the Schade 50w schematic from BAF 2015, but I don't know if I can pull it off without frying the rare S.S. 085s.
If anyone has or can point me to a potentially similar schematic, like described, please share.
Thanks,
Vince
I want to keep it simple like the SIT-1 monos.
Don't mind using high power resistors for the current source.
10w sounds nice.
I was going to try to combine the Nemesis article and the Schade 50w schematic from BAF 2015, but I don't know if I can pull it off without frying the rare S.S. 085s.
If anyone has or can point me to a potentially similar schematic, like described, please share.
Thanks,
Vince
Could you try the concept with some other current production transistor before using the SS?
Has anyone tried a lower voltage Schade Semisouth 085? Search turned up this thread. I don't know about using 300v. Rather not.
I want to keep it simple like the SIT-1 monos.
Don't mind using high power resistors for the current source.
10w sounds nice.
I was going to try to combine the Nemesis article and the Schade 50w schematic from BAF 2015, but I don't know if I can pull it off without frying the rare S.S. 085s.
If anyone has or can point me to a potentially similar schematic, like described, please share.
Thanks,
Vince
Thanks for the reply.
I have both SS R100 (Enhancement) and SS R085 (Depletion). Of course have a sleeve of IRFP240s and other IRF mosfets.
Was just thinking of scaling down the BAF 2015 50w Schade to 10w or so, and using SS R100. Maybe just use a mosfets on the current side to save on R100s. I think recommend max dissipation on SS is 35-40w?
My problem is scaling it down and applying proper feedback. I should watch the presentation again.
Vince
I have both SS R100 (Enhancement) and SS R085 (Depletion). Of course have a sleeve of IRFP240s and other IRF mosfets.
Was just thinking of scaling down the BAF 2015 50w Schade to 10w or so, and using SS R100. Maybe just use a mosfets on the current side to save on R100s. I think recommend max dissipation on SS is 35-40w?
My problem is scaling it down and applying proper feedback. I should watch the presentation again.
Vince
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