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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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PostPosted: 08 Mar 2018, 08:33 
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Joined: 16 Feb 2016, 19:45
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I got the caps from Mouser, along with most of the other parts. I've just added a parts list to my web page. Of course, I can't promise it's 100% accurate!

My project page: http://ohm.bu.edu/~hazen/TubeAmp/

Direct link to parts list (CSV text): http://ohm.bu.edu/~hazen/TubeAmp/BOM_Octal.csv

No audible hum (to my 58-year old ears!) with AC heaters. Taking a bit of load off the power tranny does sound like a good idea. I ran mine for many months in the summer with it just running hot, no problems. I finally put a muffin fan in front of the transformer which made me feel better.

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PostPosted: 11 Mar 2018, 16:53 
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New to the forum and to this thread but curious about the Oddwatt KT120 push pull design. Has anyone measured the damping factor? Have always found that a significant consideration when running no or low NFB amps. Can't see any specs for this anywhere.


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PostPosted: 11 Mar 2018, 21:23 
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Hi, welcome!

Unlike solid state, DF is kind of a moot spec in tube amps - tube amps either work or they don't into a certain set of speakers.

DF also depends on the turns ratio used for a particular tube design. Example: The DF of a typical 300B amp is 1 to 3. Same for an 845. Take a pair of Tannoy Red and drive with both amps. Chances are the 845 will work and the 300B will barf ;)

As for a direct answer to your question, I'll leave that to the Master, Bruce :)

Cheers!

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PostPosted: 12 Mar 2018, 04:26 
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Ok a specific question then. This relates to 12in tannoy golds and hpds. My experience has been that they need the DF in a specific range - at least 15-20 at the low end, and no more than 40- 50.

In practice this means single ended tube amps (DF in single figures) have no bass control on these big cones/moderately complex crossover with notch filter/ported or vented designs tuned typically in the 30s hz ... this also applies to some PP amps eg 300b as you say and yes, at least one KT120 amp I tried. (Though more often EL84, EL34 and KT88 family in PP tend to work well).

At the other end too high as in many solid state amps with 100+ DFand while the control is there, the life can be sucked out of the music.

This comes from 20 years of Tannoy experience and trying out 50+ amps of all sorts with them. I’ve found DF to be a reasonable predictor of whether they will work well or not.

So not an academic question on these speakers! I’m also curious about whether the lack of a phase splitter/one fewer gain stage than typical and potentially unusual phase characteristics will have an impact too. Keen to get a view. Tannoys are peculiar beasts.

EDIT just to clarify, earlier Tannoys were 16 ohm but golds and hpds (and onwards) are 8 ohms so it’s DF at 8 ohms I’m interested in.


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PostPosted: 12 Mar 2018, 05:39 
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Or if anyone has measured the output impedance ?


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PostPosted: 12 Mar 2018, 09:08 
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Hi, I have not measured it, but the calculated values for all the Oddwatts fall in the 15 range. All BTW work well with Martin Logan ESLs that are a really difficult load for many tube amps. They look like huge capacitors and the impedance drops to about 1 ohm at 20KHZ. Strange peaks and dips around the crossovers as well. I used MLs as the main speakers for several years and the combination was really nice. I now use Updated Altec Lansing Magnificents. To date I have not heard of anyone having a problem with the amps driving their speakers.

Good listening
Bruce

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PostPosted: 12 Mar 2018, 09:19 
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gofar99 wrote:
Hi, I have not measured it, but the calculated values for all the Oddwatts fall in the 15 range. All BTW work well with Martin Logan ESLs that are a really difficult load for many tube amps. They look like huge capacitors and the impedance drops to about 1 ohm at 20KHZ. Strange peaks and dips around the crossovers as well. I used MLs as the main speakers for several years and the combination was really nice. I now use Updated Altec Lansing Magnificents. To date I have not heard of anyone having a problem with the amps driving their speakers.

Good listening
Bruce



Is that 15 damping factor at 8 ohm? Or 15 ohm output impedance? (Surely not the latter :) )

A measurement would certainly give confidence.

Tannoy measured impedance don't dip unduly but it's back EMF that is the concern.


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PostPosted: 12 Mar 2018, 15:11 
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At 8 ohms

Good listening
Bruce

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PostPosted: 13 Mar 2018, 12:25 
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Do you have any actual measurements? A figure for output impedance?


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PostPosted: 13 Mar 2018, 21:45 
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Hi, In the earlier post I said I had not measured it.

Good listening
Bruce

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