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As my first foray into SET I purchased a Dennis Had Inspire KT150 amp. What I dont understand is why/how it does not require any biasing when the input and rectifier tubes are changed.
The amp provides 12 watts output with the KT-150 output, 6H30 input, and 5AR4 rectifier tubes provided.
I switched to a Telefunken E88CC/6922 input tube paired with a Philips 5R4GYS rectifier.
Dennis said the amp can also use the following tube combination:
5 watts per channel - 6V6 output tubes and 5Y3 rectifier tube
7 watts per channel - 6L6, KT66, 5881 output and 5U4 rectifier
10 watts output - KT88, EL34, 6550, KT99, and KT120 output and 5U4/274B rectifier
12 watts output - KT-88, KT-120, KT-150 and 5AR4 rectifier
Follow Ups:
Many thanks for all the reply's. Here's a photo of the wiring.
PHOTO
This must be a single-ended pentode (SEP) amplifier. There's no way you can get, for example, 5 watts out of a single-ended 6V6 with triode connection. It may use an ultra linear connection, though, which is sometimes referred to as "partial triode."
It probably also uses some feedback to reduce distortion and especially output impedance. I'm not saying there's anything wrong with any of that BTW.
It is a single ended pentode.
This was an amp that he could not sell in the 1990s and was offered as a schematic from his DIY business. Solid state rectifier and fixed bias. The problem I found with the original circuit is that he did not raise the voltage on the heater for the SRPP input/driver and it toasted a nice pair of Tung-Sol 6SL7s. It is still a little bit different in that Dennis did not like to use the traditional 10 ohm measurement resistor and wanted you to insert a current meter directly into the circuit. It was my first "nice" build. Chassis was mine.
Nice looking amp and I imagine it sounds great.
Dennis said the amp can also use the following tube combination:
5 watts per channel - 6V6 output tubes and 5Y3 rectifier tube
7 watts per channel - 6L6, KT66, 5881 output and 5U4 rectifier
10 watts output - KT88, EL34, 6550, KT99, and KT120 output and 5U4/274B rectifier
12 watts output - KT-88, KT-120, KT-150 and 5AR4 rectifier
The map is self biasing with the recommended tube complements. You do not have to make adjustments. Stick with the above and enjoy!
I have the same amp (actually the first KT150 Dennis built) and have played with all sorts of input and rectifier tubes. I have never need to adjust the bias on anything. The Telefunken E88CC from Upscale is an excellent choice.
I will tell you that I replaced the 5R4GYS rectifier I installed with a Sophia mesh plate 247b to GREAT improvement. It might not have quite as much power (about 10 watts I think) but the sound is totally seductive.
So much for rectifiers having no sonic impact. ;-)
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