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PostPosted: 26 Jul 2018, 14:58 
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Hi Everyone....the 6NO30 is by Amperite not as I indicated in the earlier post

Good listening
Bruce

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PostPosted: 27 Jul 2018, 16:16 
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Hi Everyone, overnight something very strange happened. The tubes grew up. :D Actually I did a batch of tube rolling. I didn't change the current or voltage, just the tubes (I have several sets obviously). I tried JJ KT77s in all amps to get a base line then started swapping. The JJ 77s were nice, but a bit on the bright side IMO. Next came new production Mullard EL34s in the amps on the ESLs. Warmer, but seemed to lack detail. They didn't matter in the subs (subs are set for 45 HZ crossover BTW). Then tried JJ KT88s with the ESLs. More robust and good details, on the warm side when compared to the 77s. Then I put JJ KT88s in all amps. Better bottom end as expected. Next went whole hog and stuck some Tungsol KT120s in the amps driving the ESLs. Nice, solid and clearly the tubes of choice. Left the 88s in the woofers. Remember all the tubes are just loafing in forced class A U/L at a mere 62ma and 460 volts. Tube life ought to be decades. The sound is really nice. I had heard from other folks that big tubes with thick glass tended to sound better in some amps than tall thin ones. At least in this case they do. I don't know what factor actually matters as the tubes are run well below ratings too. Power consumption is nearly the same as only the heater power is more. BTW the amps both use SMPS for that. It was a feature in the old ones from 2008 and seemed logical to use in the new ones.

Good listening
Bruce
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PostPosted: 28 Jul 2018, 09:02 
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Finally done with my OddBlocks (KT88s & 5751s). Replaced the faulty power tube but Antique Electronics Supply refused to replace it for free. I understand that I bought the tubes 9 months ago. But, I did not use them until now. At the least they could have given me some discount. I’ll never buy anything from them again. Thus, I purchased a couple of KT88s from Tube Depot, who was able to match them to the original ones.

They sound great. Good bass & clarity, except for some low background/white noise which you do not hear when playing music. Again, maybe it’s just me. You hear it near the high-efficiency speakers (96dbw).
We will see what happens after the break-in period.
And, oh boy, they do get hot!!
The addition of the subwoofer outputs is great when playing hard rock. When playing classical, classical string instruments or light music, the sub is not needed.

I use a ground bus connected to frame ground both at the AC connector/filter and at the RCA input. I was wondering if I should remove one of the frame grounds.

Thanks to all for the support.

Danny


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PostPosted: 28 Jul 2018, 21:16 
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Hi, Nice chassis and builds. I would leave the grounds, an extra measure of hum prevention and unlikely to cause any other issues. The his is probably the 5751. What brand did you use some are noisier than others. Another possibility is that it may be bleeding over from the heater circuit. In some of my high gain applications using SRPPs I have found that a capacitor of about 50uf (electrolytic is fine) going from the heater circuit to the signal ground is helpful. It is unpredictable which side to attach it to though. Try each and use the best if it helps.

Yes the amps do run hot. This is a consequence of the fully class A design. The tube dissipate the most power at idle.

Good listening
Bruce

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PostPosted: 28 Jul 2018, 23:24 
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Bruce,

Thanks.
I use Sovtek 5751s. Which driver tubes do you recommend that are quiet?


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PostPosted: 29 Jul 2018, 13:48 
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Hi, My ones of choice are NOS Phillips, ex military JAN ones. They initially seem "softer" but really everything is there but IMO they are quieter. You can use 12AX7/ECC83/ECC803 etc. They have a bit more gain and tend to seem noisier IMO. The ECC803S might be a good alternative. Thy the heater cap and see if it helps. Let me know if it does as I normally don't use that in power amps and it may be a useful tip to other diyers with high sensitivity speakers.

Good listening
Bruce

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PostPosted: 29 Jul 2018, 13:55 
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More tube rolling in my amps. I have all KT120s now running at low power (62ma/460V) in all 4 amps and they sound great. The big bottles win hands down. I would suggest that anyone with these amps might give the KT120s a try, especially if you are running in the lower power mode. If you do watch out for the heater power as the 120s use more than the others. Get matched pairs as the range in gain for KT120s is quite wide and some random pairs might not balance. Running the KT88s at the lower power also sounds good, but the big guys are better.

This BTW is not what I would have expected. I would have thought the anode to anode load of 8K would be too much for the KT120s and both power output and response would suffer. They actually will deliver a few more watts than the KT77s/EL34s would. Not likely enough to be audible though.

Good listening
Bruce

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PostPosted: 29 Jul 2018, 18:15 
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Bruce, yes a while ago I tried a 47uF cap on either side of the driver’s heater and ground. But, it did not make any difference.


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PostPosted: 01 Aug 2018, 06:08 
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Hi Bruce,

With the KT120’s, you rolled those into the smaller odd blocks with the single LM317HV, correct?

Did you do anything to the heater string to handle the extra load?

Thanks


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PostPosted: 01 Aug 2018, 15:59 
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Diyengineer wrote:
Hi Bruce,

With the KT120’s, you rolled those into the smaller odd blocks with the single LM317HV, correct?

Did you do anything to the heater string to handle the extra load?

Thanks


Ditto on this question-
I'd like to try KT120's in my mid size (el 34,kt77,kt88) mono blocks as well, but I figured the transformers (at least) would not agree....


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