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PostPosted: 31 Jul 2016, 11:22 
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Joined: 07 Dec 2015, 14:21
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I forgot to add that the wiring diagram they send can be misleading. They mark the white wire as "common" even though it completely depends on the application. In this example you are taking part of the output and injecting it back into the input, you need the two to be 180 degrees out of phase in order to cancel, the white wire is the one you needed not the yellow, so you now just make the yellow the common by connecting it to ground. If the amp had one more inverting gain stage you could have injected in there and using the yellow wire would have been 180 degrees out of phase. So it's application dependent. It would be more accurate for them to mark the phasing on the the wiring diagram with a dot.


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PostPosted: 31 Jul 2016, 12:10 
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Not grounding the speaker wire was the main problem, I believe. If I had done that I could have then dealt with the phasing problem. Having 2 problems was what made finding a solution harder. I am a happy camper now. It did sound great without feedback but at least now I know I have built it as designed. The building is the fun part for me as well as listening to music. Thanks everyone for the help.


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PostPosted: 31 Jul 2016, 13:02 
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Well pat yourself on the back amigo! You now have I believe your first push pull tube amplifier. Don't tell Maynard how much you like it ;)

I ground my output back to the input. I don't like to use the "star ground", it's a recipe for disaster. Just look at each current loop and keep the loop as short as possible.


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PostPosted: 31 Jul 2016, 13:49 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, That will do it. I beg to differ on the star ground as I easily can exceed 90dbv S/N with it (even in phono preamps). I put the star where the inputs and outputs enter the chassis. I use a large diameter copper wire between the connectors and attach all the other grounds to it. The problem is folks don't implement it correctly. It only takes one incorrect wire to mess things up. However YMMV.

Enjoy the music.....

Good listening
Bruce

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PostPosted: 31 Jul 2016, 14:26 
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Yes Bruce your grounding works because you know what you are doing. As you mention I have seen people do it wrong by following a "recipe" so to say.

Basically I have a laugh when I see terrible ground loops leading to audible hum and they say "but I star grounded everything"

Ahhh good times :)


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PostPosted: 03 Aug 2016, 07:44 
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Joined: 18 Aug 2015, 07:38
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I replaced the K42Y-2 PIO caps with the Cornell DME polyester caps again to see if there is any difference in the sound. I like the DME caps much better. I have ordered some Orange Drops to try but I may not use them and just leave the DME caps in. My 6P15P-EV tubes are sounding much better as well. On my Decware SET in took a few hours on these same tubes for the soundstage to really open up. All I can say is the amplifier sounds great using these crummy parts. The great sound I hear can be attributed to the design and not exotic parts. I have over a dozen amplifiers I have built and I know what sounds good. Sure it may sound better, "different", with better coupling caps or tubes but it now compares with my better SET's in sound. There are differences of course but when you reach a certain level in amplifiers the differences could come down to personal preference and the speakers you are using. Believe me my horn speakers will show a fault with an amplifier especially when you crank it up.

I hope others that have built this same amplifier will give these 6P15P-EV a shot. They are on Ebay from Russia at giveaway prices. I would love to hear what others think of these tubes in this amp. One will need to put a jumper from pin 3 to 6 to connect the suppressor grid to the cathode. Doing this should not make a difference using EL84's since this is done internally in them. My tubes gave no problem biasing them being matched close enough. They are Russian Military tubes so the quality should be very good. They are very impressive when you get them in your hand.

I hope even Bruce gives them a try.


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PostPosted: 03 Aug 2016, 13:30 
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Hi, I ordered a bunch. As you say cheap so I'll give them a try.

BTW I didn't like the K42s, The K40Y9s are much better. Also you can try FT-3 Teflons. Huge in size but nice sound. Audyn True CopperCaps are great but both big and expensive.

Good listening
Bruce

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PostPosted: 03 Aug 2016, 17:01 
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I am looking forward to your impressions of the 6P15P-EV tubes. I am sure you will test them with more than just your ears. I would like to know if it would be beneficial for me to try the EL84's. Right now I am well satisfied with the way it sounds.


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PostPosted: 03 Aug 2016, 20:30 
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Hi, Yes I plan to put some through all the tests I usually do plus listening tests. It will be interesting to see the response and distortion compared to the JJs and EH tubes I normally use in these amps. BTW the new production Mullards have about 50% more distortion at low levels vs the other two brands. Still low at about 1.3-1.5 % at 1 watt. But curious. The increase was mostly 2nd order and adds a warmth to the sound a bit.

Good listening
Bruce

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PostPosted: 04 Aug 2016, 06:40 
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I first became aware of these tubes from my Decware Zen project. Here is what Steve Deckert has to say about the 6P15P-EV tube. Be sure to put a few hours on them before doing any serious listening. I do believe they improve with some hours.

"you'll find the 6P15P-EV's to be unparalleled in speed and detail. The reason for this is because the 6P15P-EV is actually a video tube as opposed to an audio tube. This gives it much wider bandwidth than a normal audio tube and that results in great SPEED.

We think these small bottle tubes are some of the best sounding and best quality available today"

I did a short A/B comparison of this PP amp against my 300B amplifier based on the following build. The 300B amp was much more expensive to build. I used One-Electron OPT's and Genelex Gold Lion 300B tubes. I also added some extra capacitance on the regulated DC heater circuits. I had a touch of hum still present on my horn speakers before adding more capacitance.

http://diyaudioprojects.com/Tubes/300B-SET-Amplifier/

This PP amp has more similarities to the SET than differences. My short comparison was done with vocals and orchestral music and I would be hard pressed to tell that much difference. There are subtle differences but nothing substantial. I also have a ElectraPrint Audio 45 amp I built with some of the cleanest sounding vocals I will compare this PP amp to at a later date. For now I am just going to enjoy the music.


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