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Oddwatt Push Pull Tube Amplifier Projects
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Author:  eshazen [ 08 Mar 2018, 08:33 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

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.

Author:  montesquieu [ 11 Mar 2018, 16:53 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

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.

Author:  Geek [ 11 Mar 2018, 21:23 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

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!

Author:  montesquieu [ 12 Mar 2018, 04:26 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

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.

Author:  montesquieu [ 12 Mar 2018, 05:39 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Or if anyone has measured the output impedance ?

Author:  gofar99 [ 12 Mar 2018, 09:08 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

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

Author:  montesquieu [ 12 Mar 2018, 09:19 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

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.

Author:  gofar99 [ 12 Mar 2018, 15:11 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

At 8 ohms

Good listening
Bruce

Author:  montesquieu [ 13 Mar 2018, 12:25 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Do you have any actual measurements? A figure for output impedance?

Author:  gofar99 [ 13 Mar 2018, 21:45 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, In the earlier post I said I had not measured it.

Good listening
Bruce

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