@atmasphere While I agree with you that a tester that cannot properly test a KT150- shows the limits of the tester, ( BTW, yours- nor any Hickok- I am aware of can test these tubes--and your KT88 spec is no good for them) it also points to the fact that they need more voltage than 400 volts to come to spec, IMHO.
Tube amp question
I am a novice tube amp owner. I have had my Black Ice Audio Fusion F22 for not quite a year. I want to understand plate voltage and how it impacts tubes or vice versa. I want to roll the tubes to the KT150's which Black Ice has said can be used without issue. The plate voltage of the amp is 500v. In other posts, someone said that KT150's require a minimum of 600v at the plate. Since Black Ice says their amp can use them, does this rating depend on the circuit? I have some basic understanding of electronic circuits and I googled plate voltage but I'm still not clear on what it is exactly. Can someone knowledgeable with tube amps help me understand this? Thanks!
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So @daveyf are you saying the 500v plate voltage is not enough to realize the full potential of the tube? If that's the case then why does Black Ice indicate they will work? I'm not taking sides with anyone, just trying to learn. May the debate continue! |
If you use the KT150, I would bias it to 80ma. Based on the amp power specs for the EL34 and 6550, the bias settings of the tubes and 500V at the plate, the amp operates in Class A/B and the output transformer is about 6500 ohms in Ultralinear. The manual also shows the ammeter's upper limit as 80ma. The EL34 operates at about 5 watts Class A, and A/B to its rated power. The 6550 runs about 12 watts Class A. The KT150 at 80 ma with a 6500 ohm xfmr at 500V will operate in Class A for 20 watts and max out in Class A/B at about 75 watts. The bias point is a little less than 60% of the tube dissipation which is on the cool side but within the sweet spot envelope for Class A/B. The tube should work fine. But... save your money. The KT120 operates identically biased at 80ma and runs 70% dissipation, which is the upper limit for Class A/B operation. |
If I may, three different scenarios to share. The first two are friend’s amps I helped them with when they were ready to make tube changes. The last mono block amp(s) mentioned are mine. 1. The Jolida amp my friend Alan had KT150s in it, worked fine, sounded neutral, lacked the velvety rich sound. Swapped to PSVANE KT88s. More engaging now. My friend loves it, everything he was looking for from the sound in this circuit. 2. The Black Ice F22 my friend Richard has came new with lower grade EL34s. He swapped in new production Genelex Gold Lyon KT77s. He truly enjoys the change and sound after there was 50-70hrs on the 77s. He listens to it daily now. I don’t think he’ll ever try KT150s after hearing this setup. 3. My own tube mono block amps have massive transformers, came stock with KT150s, sound very linear, super clear, neutral, amazing sound stage and detail. The designer recommends running them as low as 40ma and high as 60ma. I run them at 50ma per tube. Sometimes I’ve felt it was lacking velvet tube sound, kinda missed KT88s. Can’t run 88s in my amps, too high of plate voltage. Split the difference with KT120s, a more lush tone. After the KT120s had 100hrs on them, I have no desire to put the KT150s back in immediately. KT120s were as close as I could get back to 88 sound. Been enjoying them past three months. Your F22: fwiw, I’ve heard your F22 amp and it can sound really nice moving from EL34s to KT77 or KT88s. Hey, KT150s are expensive. FYI, my four KT150s are sitting nicely tucked away in their boxes. Bigger is not always better, IMO. You can also try extra nice KT77s or KT88s s in the F22 if you want to stay closer to a rich full sound without being overly neutral. Trying to save you from skipping a good in-between option to consider. Some of my other friends rotate from 150s back to 88s, 77s - often. |
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