Up to you lot, but myself I would not use this servo open loop inverting type op/amp on an o/p stage using an closed mag loop toroid o/p tranny or with a large E/I core with a very high inductance ....there´s a nice juicy looking very low frequency pole ready to create trouble. The time constants may be long but as DC is approached with a closed magnetic circuit, strange things can happen. Anyone simulated it ?
Only my views but I would tend to keep things simpler.
Bench Baron
Some old rev limiters were not so friendly.
Depending on how long the rpm was at the limit . . .
broken connecting rods
valve springs that did not return the valve quick enough (sticky substance where the rod went through a hole; or aweakened spring).
Pistons stuck to cylinder
etc.
Those were un-intentional rev limiters.
Depending on how long the rpm was at the limit . . .
broken connecting rods
valve springs that did not return the valve quick enough (sticky substance where the rod went through a hole; or aweakened spring).
Pistons stuck to cylinder
etc.
Those were un-intentional rev limiters.
And some tubes don't perform well biased at their rating limits either.
My testing with the newer production KT120 and KT150 tubes in a fixed bias single ended UL amp has seen these newer Tungsol tubes starting to red plate at the bias point the OP is using, some as low as 80ma/500V. None of them made it to 90ma/500V, while the earlier production of the KT120, with the smaller offset getter, biases to 115ma/500V with no signs of distress. The difference being they changed the size/location of the getter, from being a smaller one offset from the hottest part of the plate to a large one directly over the seam of the plate at some point in production, as verified by a Tungsol representative who responded in the comments of this video.
Clearly to me these tubes are designed to be used in a push/pull AB amp used at a lower idle bias point than this 90ma+ at 500V range, which by their ratings shouldn't be an issue, but it is.
My testing with the newer production KT120 and KT150 tubes in a fixed bias single ended UL amp has seen these newer Tungsol tubes starting to red plate at the bias point the OP is using, some as low as 80ma/500V. None of them made it to 90ma/500V, while the earlier production of the KT120, with the smaller offset getter, biases to 115ma/500V with no signs of distress. The difference being they changed the size/location of the getter, from being a smaller one offset from the hottest part of the plate to a large one directly over the seam of the plate at some point in production, as verified by a Tungsol representative who responded in the comments of this video.
Clearly to me these tubes are designed to be used in a push/pull AB amp used at a lower idle bias point than this 90ma+ at 500V range, which by their ratings shouldn't be an issue, but it is.
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This is a con or near like racketeering .......trying to fool us with a rated-down spec (worse paying original price) and ending up with a derated performance or grotty materials. This trashes the idea of running in true class A as I do. If the anode drowns in orangness, then watch out that bias resistor value to avoid runaway, which will effect the previous stage.
Some years ago I found exactly the same issue with clear glass 6550 with pellet getters, there was no way I would accept orange anodes at 28W power at 450V. I claimed they were reglassed 6L6´s and at the protest I was given a box of the B version 6550 which on my rig performed even better and consistent than the latter C version.
As video mentions standards have fallen after the two world class events, Covid and Ukraine with all that fishy embargo thingy.
There is only one solution, buy from reputable vendors, JJ etc. and insist on a soak test.
no con artist, Bench Baron.
Some years ago I found exactly the same issue with clear glass 6550 with pellet getters, there was no way I would accept orange anodes at 28W power at 450V. I claimed they were reglassed 6L6´s and at the protest I was given a box of the B version 6550 which on my rig performed even better and consistent than the latter C version.
As video mentions standards have fallen after the two world class events, Covid and Ukraine with all that fishy embargo thingy.
There is only one solution, buy from reputable vendors, JJ etc. and insist on a soak test.
no con artist, Bench Baron.
My KT150’s with 90mA cathode current (even with 100mA @ 600 VDC) are not showing any signs of stress. I can only see the tube’s heater glowing, nothing else.
I probably have the “older” versions of the tubes. It’s definitely something to keep in your mind when buying new tubes.
Regards, Gerrit
I probably have the “older” versions of the tubes. It’s definitely something to keep in your mind when buying new tubes.
Regards, Gerrit