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Poll: What's your KT150 bias set to per tube (ma?)

To: Owners with purpose-built KT150 based tube amps and the ability to measure bias for each output tube.

What are you biasing your KT150s to in your amps (45ma, 50ma, 55ma, 60ma, or more) per tube ?

Background:
Today I discovered I had been conservatively running bias a bit too low for my mono tube amps. Was a little thin. Went up +10ma per tube and wow. Hit the tube magic window with increased lower midrange presence and overtones coming in nicely, smooth detail. No loss of soundstage. Still within manufacturer spec for my amps. While I realize it can be circuit dependent for different amp designs, just curious what others have found to be a sweet spot for your KT150s in your amps? Feel free to post the name/brand of your amp and the bias setting if you are able to share. Please disregard if your amps are auto-bias or LED bias only. Thanks in advance for your replies.
decooney
russ69's avatar
russ69
3,579 posts
 
Amps are of different designs, stay within manufacturers specification. Sometimes a tad lower if tube life is suffering. 
decooney OP
2,358 posts
 
In my case I could go even higher on bias +5-10ma more, and remain in spec. First time I experimented with wider adjustment sweeps since amps were new. Seems I originally underestimated KT150s ability to sound more lush and "tubey". It is possible, and discovered it a bit later with my amps after months of burn-in of all tubes, upgraded coupling caps, and more. Felt kinda stupid once I found the proper bias setting window many months months later, like "ah, there it is!", thus realizing KT150s can do it too if I simply adjusted bias to the sweet spot, duh...

Now I have no desire to go back to KT88s, KT77s, or EL34s (or back to my former parallel strapped triode based amps) any more. Was not expecting this realization to actually happen with my particular KT150 mono amps, and it just did. Ultra conservative low-biasing is no longer an option, the higher bias is well worth it now :)
oldhvymec
5,101 posts
 
I learned that the hotter I bias the BETTER the lower listening levels are.

If I bias to hot then the upper listening levels suffer. It has to do with performance vs SQ. So if there is a party coming up and your going to be turning it up a bit, its best to bias down a bit. If your doing a lot of late night low level listening, bias hotter.. They just sound better, cleaner and sharper. IF your using them for bass, TOO, it’s kind of a happy medium to bias in the middle so to speak..

If you could limit the bass duty on the valves, I think you’d really be surprised. Valves really don’t transition as well as SS from say 40hz and then 5Khz then back to 100 hz.. Remove that duty, 300 hz and down.. Valve amps REALLY preform much better.

That is where EL34, 6550 and even KT88 do a whole lot better too, NOT doing bass. If you can cut from 80-100hz and down, its night and day especially EL34.. They just come alive, when you LOSE the bass duty.

I like 6L6 if a valve amp is going to do full range. I think it’s the best of ALL the valves even KT66s (VERY close) They can take the punishment too especially the mil spec 6L6. 6V6 is really good too, if you get enough going at one time.. Lovely valves..

I would like to have about 4-6 sets of quad RCAs 55-65 vintage.
Coke bottles 4, sets of quads would be fine.. Macs (MC30,40,240s) and Cary both just loved RCAs BPs.

Regards
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