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KT150 pp amp operating points please
KT150 pp amp operating points please
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Old 10th October 2018, 08:18 AM   #51
Vortex is offline Vortex  Hungary
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Send a message via ICQ to Vortex KT150 pp amp operating points please
Hi all,

Google brought me here (great, I'm member anyway).. I read this whole thread, insteresting talk so far.. great comments. I thought I might ask you about my plans..

Among the considerations everybody else might have too like efficiency, output power, stability, etc. I would tune my choice of amp design into following direction:

- triode mode (distortion characteristics vs pentode mode) ?
- ~200W into nom. 8 Ohm (yeah, lot..)
- speaker driver "Re" is at 5.4 Ohm, this is the impedance minimum (manufacturer states nominal 8 Ohm) so medium-low impedance driving capability should be safe too when more currents rush into the load
- reliability and long term usability is a prio over heavy output power (it will be powerful enough anyway).. driving the tubes safely below factory limits
- I'd rather opt for a balanced Class A window when listening at home at low volumes than instantly going into AB.

Maybe you can provide me some hints out of your experience, a recommended design (we'll resize accordingly) .. or just in general, any innovative idea of how to compensate small tube differences (manufacturing spread) within 1 tube block and how to deal with tube wearing, failing tube (protection of the others and the amp itself), etc. ?

I think of some kind of monitoring / diagnostics / auto biasing solution, I'm going to embed an Arduino based microcontroller which can be used to take care of all such functions and wear, running hours count, warnings, whatever. It will display some basic info on a small OLED screen anyway and also take care of heating monitoring, controlling the power-on relays, infrared remote etc.

Why I'm asking all this here: the topic was interesting and originally I was shooting for KT150s but the reliability of them is a question for me now. Or isn't it anymore ? Are they safe to buy today ? Money is not unlimited but I'm building for the long run so then I would accept some extra 1-time cost now. I'm still open to more reliable tube types like JJ KT88s and use +1 more (per side). The topology is parallel pushpull anyway so then 2 or 3 tubes per wave side.. doesn't matter imho that much (vs. single-tube SE). No problem for me to use 3xKT88s (per side) instead of 2xKT150s when matched and small imbalances can be compensated safely without compromising sound quality.
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Last edited by Vortex; 10th October 2018 at 08:21 AM.
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Old 10th October 2018, 08:27 AM   #52
jazbo8 is offline jazbo8
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KT150 pp amp operating points please
I suggest that you go over Patrick Turner's site for some insight on triode vs. pentode output. 200W parallel triode output is doable but asking a lot. If you want reliability, then clearly KT88 has a superior and longer track record than the KT150.
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Old 10th October 2018, 08:57 AM   #53
waltube is offline waltube  Italy
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At this moment there are four pairs fo monos with 4 x KT150 running since 1 year and no fail on them
2 pairs normally workin around 4 hrs/day driving a pair of B&W 800 in bi-wiring

It seems that the last batch are better than the older.

Walter
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Old 10th October 2018, 09:08 AM   #54
Vortex is offline Vortex  Hungary
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Send a message via ICQ to Vortex KT150 pp amp operating points please
Quote:
Originally Posted by jazbo8 View Post
I suggest that you go over Patrick Turner's site for some insight on triode vs. pentode output. 200W parallel triode output is doable but asking a lot. If you want reliability, then clearly KT88 has a superior and longer track record than the KT150.
Great, thank you !
Edit: uh, Patrick Turner's site is whoaaa. Amazing.

@ Walter: same.
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Last edited by Vortex; 10th October 2018 at 09:10 AM.
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