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Oddwatt Push Pull Tube Amplifier Projects
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Author:  Diyengineer [ 30 Jun 2018, 21:10 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hello,

I noticed Edcor makes the CXPP25-8K in 23% & 40% screen taps. I just want to confirm which one to get.

Thanks

Author:  JanG [ 01 Jul 2018, 04:32 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Bruce,

What is the effect you wanted to achieve with the 2 resistors and 1 cap marked in blue on your most recent schematic? Since I did the upgrade I notice a slight hardening of the midrange. Upgrading the psu brought a welcome tightening of the sound and better articulation. It is now identical to the psu in my Oddwatts, no problem there. So my question is, could the change in the midrange be the result of these (slightly) altered resistor and capacitor values?

Jan

Author:  JanG [ 01 Jul 2018, 15:11 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Diyengineer

The answer is on page 146.

Author:  gofar99 [ 01 Jul 2018, 21:27 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Jan, Huh? I am not sure what parts you are referring to. Please mark up a schematic and post it so I can tell what you are asking about. I use blue mostly to show a change from an earlier version. It can be for many reasons, lower distortion, better S/N, better power filtering. Sometimes, based on the wide variation of diy builds especially concerning the tube brands and types as well as other components changes may not be better in all cases. I can only talk about stuff I have actually tried. I like to hear back when something doesn't work so that I can warn others to not do whatever it was. Thus far (fortunately) none of the changes to Oddwatts in design over the past 10 years has caused something to fail (tube amp failures are often exciting and costly) but have in some cases altered the sound a bit. I find that changes in the sound are common when the coupling cap brands and types are different as well as changing tube types (like KT77 in place of EL34) and sizes (like KT77 vs KT88). That is something that can not be eliminated. In some ways it makes the diy process fun as tube and cap rolling can be rewarding.

Just as information... right now my personal choice for driving my main speakers (Martin Logan ESLs) is Oddblocks running new production Mullard EL34s with the 15 inch subs (in 200+ L enclosures) on another pair of Oddblocks using JJ KT77s. A close second for the mains is a pair of KT120 Oddblocks. Considering the heat generated and power used I went back to the smaller ones about 6 months ago. All present amps are set for about 15 wrms each with the crossover (electronic 24 db/oct) at 55 HZ. I'm using a Forewatt in passive mode most of the time when the input signals are sufficient. When not sufficient it uses JJ ECC802S tubes. All coupling capacitors in all components are Audyn TrueCopperCaps. I have worked a long time to get it to sound to my liking. Others might prefer something else. IMO it is quite stunning. It (like all systems) will never create the effect of being at a concert....but it certainly presents a believable rendition of one. Pianos, female vocals and stringed instruments (like acoustic guitars, harps and banjos) are to die for. 8-)

Good listening
Bruce

Author:  JanG [ 02 Jul 2018, 05:01 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Bruce,
I was referring to the main circuit you posted on 15 June with three component changes (12sl7's pin 3) marked in blue: 470uF (was 220uF), 1100R (was 1200R), 100R (was 120R). Could the change in midrange character I experience be the result of these changes?

Thanks for the update on your system. I started with KT77s, which are great at the price, but then I ordered original Svetlana winged C el34s (from 1999, before the issues on the right to use the Svetlana brand name and before the onset of the decline in production values that followed). These are just great: extremely detailed, good bass, extended soundstage, but as a result very revealing of even minor changes in the sound. Very interesting to have your view on new production Mullard el34.

My coupling caps were Jantzen Superior Z, very detailed but a bit bright and lacking in the bass department I thought. Now I'm using Musicaps (still running in), which are a favorite brand of mine.

Author:  gofar99 [ 02 Jul 2018, 13:33 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, Possibly the bigger cap might do that. The resistors put the two tube sections closer together in gain and improved the linearity a smidgen. It really was rather excellent before. The mismatch when evident was more the result of differences in the two tube sections. I have on occasion been tempted to get triodes with matched sections, but it always seemed unnecessary. The resistors also reduced the NFB by a very small amount. That ought not be audible as the effect is way above band. It already is quite small and the amps 99.99% of the time will run fine without any. It is there to insure stability with really odd loads in the presence of EMI.

The new Mullards seem fairly nice. A well rounded presentation IMO. Nothing bad. Perhaps not the best on top end...but then my ESLs are really fast and don't need any help there. Funny thing is the JJ KT77s seem both faster on the top end and seem to have a better bottom end. Not bad in the mids, but the Mullards are nicer there. It may be due to the different construction of the tubes. One is a beam tetrode the other a true pentode.

Good listening
Bruce

Author:  Diyengineer [ 05 Jul 2018, 17:50 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi,
Referring to the 47uF cap feeding the LR8 on the latest schematic , would there be any negative effect using a 50uF 500V? As I have several of those already.

Thank you

Author:  Trackhappy [ 05 Jul 2018, 18:17 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

50uF will be fine. Electrolytics have a 10-20% tolerance anyway depending on brand.

Author:  JanG [ 06 Jul 2018, 02:35 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Bruce,

My question "I was referring to the main circuit you posted on 15 June with three component changes (12sl7's pin 3) marked in blue: 470uF (was 220uF), 1100R (was 1200R), 100R (was 120R). Could the change in midrange character I experience be the result of these changes?"

Your answer "Possibly the bigger cap might do that".

Your diagnosis was spot on. Putting the smaller cap back made the slight midrange hardness disappear. Thanks.

Jan

Author:  gofar99 [ 06 Jul 2018, 09:01 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, :D

Good listening
Bruce

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