5687 SLCF
I found here http://www.pearl-hifi.com/06_Lit_Archive/07_Misc_Downloads/Public_UL_Cascode_RIAA.pdf a SLCF with the 5687 tube and a FET.
File was too big to upload
I found here http://www.pearl-hifi.com/06_Lit_Archive/07_Misc_Downloads/Public_UL_Cascode_RIAA.pdf a SLCF with the 5687 tube and a FET.
File was too big to upload
Not really an SLCF at all, since the CCS sits inside the bias loop of the upper triode, instead of being on the cathode of the lower triode, and the output is taken from the upper triode rather than the lower one. It looks more like an SRPP or mu-follower circuit.
Alex
yes, same current
tube current is set from the current source with fet so no changes there (a little below 15mA) but you have to set the heater current source to the higher heater current for the 6h30
tube current is set from the current source with fet so no changes there (a little below 15mA) but you have to set the heater current source to the higher heater current for the 6h30
better sound?
i didnt do alot of measurements, i changed the middle tube for 6h30 and the other 88´s running quite hard so i cant increase current, but i earned a much more open and faster sound-so i kept the 6h30 in place and went never back.
i didnt do alot of measurements, i changed the middle tube for 6h30 and the other 88´s running quite hard so i cant increase current, but i earned a much more open and faster sound-so i kept the 6h30 in place and went never back.
Same plan here, altough i plan to use pl83 in triode for lower (css) tube current of 30mA seems nice
At the very bottom, I plan to use a high hfe transistor with a red led reference,i`ll draw up a schematic next year when i get home
Why not run the PL83 as a pentode with its grid tied to earth and its screen fed by a simple transistor regulator. I did something like this with my ECL80 version of the FVP5, works a treat and minimal extra components. The draw on the screen is so small that the transistor is operating very stably and so introducing minimal distortion.
Shoog
Shoog
Good idea, do you think it makes much difference? I mean not only ri of the ccs but the whole outputstage
Its really difficult to predict. Every component has an effect on the sound so I think if we have made the decision that tubes sound better than FETs which sound better than Transistors, why use an inferior component when we can achieve stellar performance from a valve. Effectively a pentode is a CCS of high enough ri for our purposes.
The advantage I found was that I could set the total stage current by having an adjustment on the transistor voltage (by a simple adjustable resistor network from B+ to ground), and as if by magic everything else just self adjusts into place to accommodate that current - since the pentode current is independent of its plate voltage.
Shoog
The advantage I found was that I could set the total stage current by having an adjustment on the transistor voltage (by a simple adjustable resistor network from B+ to ground), and as if by magic everything else just self adjusts into place to accommodate that current - since the pentode current is independent of its plate voltage.
Shoog
I would consider running the first stage as a differential pair, but the second stage requires individual CCS for each half otherwise the purpose of keeping each CF triode in constant current constant voltage mode is lost. Therefore if you were to use a pentode as the bottom element they would have to be one for each side. This is how the circuit is configured in the original with one triode and one FET forming the CCS on each side.
Shoog
Shoog
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Because there is 120V at the cathode of the cathode follower, as mentioned by morgan jones, high voltage resistors have low gain and are non-linear.
Allen wright used a jfet+triode cascode, i plan to use a high hfe transistor+triode cascode while shoog suggest to use plain pentode ccs (also descibed in `valve amplifiers`)
Direct heated triodes have low gm, 1,8mA/V for this one, not very suitable for cascode i`m afraid..