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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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It is currently 08 May 2021, 21:16

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 Post subject: Now I remember
PostPosted: 06 Feb 2021, 13:08 
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Joined: 04 Jun 2008, 20:59
Posts: 4365
Location: Arizona, USA
Hi Everyone, the title says it all, but the text is a bit lengthy
Backing up a bit… I spent considerable time dialing in my huge Altec speakers. It involved careful measurements of the response and sound pressure levels for each of the drivers. Especially when nulls and peaks were seen. To put it into perspective the speaker cabinets because of their massive size have to be in the corners on opposite sides of the fireplace. There is nowhere else they can fit. The listening position also cannot change as it has to be opposite the fireplace. The distance between is also fixed. So with a calibrated microphone used both for close measurements and measurements at the listening position I adjusted the levels and crossover points between the drivers for best match. I bi-amp the speakers using matching identical power amps. The crossover is handled by a 24 db/octave, phase and level correct Behringer electronic crossover. The preamp is fully passive with resistive pairs switched by relays. Sources are vinyl, cd, blue ray and to measure response an I7 laptop. The laptop also shows the real time response from the calibrated microphone in 1/6th octave increments. One thing noticed in all this agreed with a calculation that a 2-3 db null would occur at the listening position at 80HZ. This was handled by a Behringer DEQ2496. The measurements and actual listening resulted in a 1950 HZ crossover from the Great Plains 416-8B woofer to the Radian 475PB. The Radian needed to be padded down 15 db to match the sensitivity of the 416. This was done so the power amps would be running in approximately the same output level. The amplifiers themselves are a quad of Oddblocks running KT120 tubes at low power in forced class A ultra linear mode. Power output is just under 20 watts RMS each. OK, wonderful so what? Once set up I decided to leave it alone for 6 months. The time has passed. Lots of good listening, really nice sound, soundstage and overall response. A robust sound as would be expected from the large enclosures. A person that did not have any other speakers would be really happy. As a diehard tinkerer and having lots of other speakers I could not leave well enough alone. I pulled out my Martin Logan ESLs and dialed them in with the 416s doing only sub-woofer duty. A crossover of 60HZ was used as the MLs start to drop off at about 45. Surprisingly, the level matching was really close between the two speakers. I left the room correction in place as well. Then I put on some music. I listened to several types and all sounded great, but not until I put on some harp music did I notice a really significant difference. The ESLs were quite a bit better at reproducing the plucked strings. Fast, clean response. The Radians are not slouches, but the ESLs are way better at this. So now for at least the next six months the ESLs rule the room.

Good listening

Some of my DIY Tube Amplifier Projects:

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