Before I do final wiring and tests, is there anything I should be wary of regarding the use of KT120's in my SSE.
I plan on running around 430vdc on B+ and am using a 560 ohm cathode resistor (value chosen from George's KT88 simulations).
My power trafo can provide the necessary amperage for the extra heater current.
I will be using tube rectification and a choke in the PSU.
Thanks,
Charlie
I plan on running around 430vdc on B+ and am using a 560 ohm cathode resistor (value chosen from George's KT88 simulations).
My power trafo can provide the necessary amperage for the extra heater current.
I will be using tube rectification and a choke in the PSU.
Thanks,
Charlie
Let us know if it pulls any more cathode current than a KT88 can pull at that voltage and bias configuration.
If memory serves me correct, there is a thread somewhere on the KT120 in the SSE, and there was some chatter about it in the 6146 SSE thread. That thread went all over the place before finally petering out.
KT120 and KT150 would probably be best served by considerably higher current than the typical SSE is built for, or even better, higher anode voltages than the typical SSE is built for, so the current can be kept reasonable.
Win W5JAG
If memory serves me correct, there is a thread somewhere on the KT120 in the SSE, and there was some chatter about it in the 6146 SSE thread. That thread went all over the place before finally petering out.
KT120 and KT150 would probably be best served by considerably higher current than the typical SSE is built for, or even better, higher anode voltages than the typical SSE is built for, so the current can be kept reasonable.
Win W5JAG
Last edited:
How can I calculate the potential cathode current and bias voltage?
I am using the lowest idle current setting shown for the KT88 at 450v = 73mA.
Most importantly, do I risk damaging anything using KT120's in a SSE setup with George's KT88 specs:
KT88B+= 450 Load z=5000Vp= 436 Vk=41Rk=560 Ik=73 idle diss.=29
I did read that the KT120 needs about 25% more negative cathode voltage.
Of course, I may not hit 450vdc on B+ so if I only get 420, I'll be running the kt120 with very little current.
Maybe I should get some kt88's and get things working with those first???
Charlie
I am using the lowest idle current setting shown for the KT88 at 450v = 73mA.
Most importantly, do I risk damaging anything using KT120's in a SSE setup with George's KT88 specs:
KT88B+= 450 Load z=5000Vp= 436 Vk=41Rk=560 Ik=73 idle diss.=29
I did read that the KT120 needs about 25% more negative cathode voltage.
Of course, I may not hit 450vdc on B+ so if I only get 420, I'll be running the kt120 with very little current.
Maybe I should get some kt88's and get things working with those first???
Charlie
I don't own any KT-120's so I am only speculating. And since I already own literally thousands of tubes that I am struggling to find uses for, I'm probably not going to own any, anytime soon. But, since you have verified your transformer can handle the heater current, I doubt it will hurt anything.
Probably, one of two things will happen: it will sit there like a KT88, drawing similar current. I think it likely that this is what will happen. If this is what happens, this may or may not be a benefit. They will last longer because they are not being pushed very hard, but you are not using the power capability of the tube and they may not sound as good as a KT88, because they are not being worked hard enough. Going from memory, when you look at Tubelab's models, most tubes wok best when being run at, or even over, their dissipation specification, and at higher anode voltages.
Or, KT120 will draw more current than a KT88 under similar conditions. If it draws more current, your power transformer and choke needs to be able to handle the extra current on the B+ side, and your cathode resistors may need to be upgraded to 10 watts to handle the increased power dissipation through them, and your output transformers need to be able to handle the increased current through their primary without saturating. Increasing the cathode resistance would push the current back down, but then cathode voltage could increase in excess of the specification for your cathode bypass capacitors, so you would have to take a look at that.
As Tubelab has said, when you go outside of what the designer intended, you have to be prepared to experiment. Some experiments work, some don't. Some don't work in a catastrophic manner.
There are pictures of SSE's, as best I recall, with KT150's sitting in them, so I really doubt that anything bad will happen, and your risk is close to nil. I was just curious about the tubes, hence my comment to let us know if KT120 pulls any more cathode current than a KT88 does when plugged into a socket set up for KT88. I don't think any of the other SSE builders have commented on that, one way or the other.
Win W5JAG
Probably, one of two things will happen: it will sit there like a KT88, drawing similar current. I think it likely that this is what will happen. If this is what happens, this may or may not be a benefit. They will last longer because they are not being pushed very hard, but you are not using the power capability of the tube and they may not sound as good as a KT88, because they are not being worked hard enough. Going from memory, when you look at Tubelab's models, most tubes wok best when being run at, or even over, their dissipation specification, and at higher anode voltages.
Or, KT120 will draw more current than a KT88 under similar conditions. If it draws more current, your power transformer and choke needs to be able to handle the extra current on the B+ side, and your cathode resistors may need to be upgraded to 10 watts to handle the increased power dissipation through them, and your output transformers need to be able to handle the increased current through their primary without saturating. Increasing the cathode resistance would push the current back down, but then cathode voltage could increase in excess of the specification for your cathode bypass capacitors, so you would have to take a look at that.
As Tubelab has said, when you go outside of what the designer intended, you have to be prepared to experiment. Some experiments work, some don't. Some don't work in a catastrophic manner.
There are pictures of SSE's, as best I recall, with KT150's sitting in them, so I really doubt that anything bad will happen, and your risk is close to nil. I was just curious about the tubes, hence my comment to let us know if KT120 pulls any more cathode current than a KT88 does when plugged into a socket set up for KT88. I don't think any of the other SSE builders have commented on that, one way or the other.
Win W5JAG
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.