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Tung Sol 7581-A in the ZMA (Read 222 times)
DAKO
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Tung Sol 7581-A in the ZMA
06/08/20 at 15:12:04
 
Hi all,
  I just ordered a new quad of KT66's from Decware and an awaiting their arrival. In the meantime, I was reading through some of the posts regarding the 7581A's and am was very curious to try a set since it seemed everything I read was positive. I ordered a quad from TubeDepot.com and they are arriving soon. My question is, has there ever been a conclusion on the bias setting? I am seeing various values in the posts I've been reading but never a final conclusion. I am really looking forward to listening to these tubes as this is my first time tube rolling with this amp. Looking for some guidance/a place to start.

Thanks
Dave
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Archie
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Re: Tung Sol 7581-A in the ZMA
Reply #1 - 06/08/20 at 16:26:32
 
Dave,

I'm using the Tung Sol 7581As now and I'm biasing at 64mA.  I tend to bias towards the high side of tubes but try to stay below 70mA for heat reasons.  I think if you bias high you will shorten tube life some.  I got my 7851As for less than $100/quad so I'm not too worried if they go a little sooner.

Here is a bias calculator that I've used:  https://www.tedweber.com/webervst/tubes1/calcbias.htm

You may have to use a similar class tube since all aren't on the list.  I seem to remember Jeff measuring his ZMA plate voltage somewhere in the 480V range.  If you search his old posts you might find it.

Let us know how you like the 7581As as compared with the KT66s, My favorite are the 7027As followed closely by the 7581As.
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DAKO
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Re: Tung Sol 7581-A in the ZMA
Reply #2 - 06/10/20 at 17:15:30
 
Thanks Archie.

I received the tubes and set the bias at 58ma for short listening session. I am very impressed at the difference in the sound stage that these project as compared to the KT66's. I think the highs are a little cleaner as well. I think the KT66's do better in the bass department, but not by much. My overall impression so far is that I really like the tubes and may keep them in for a while. My KT66's were on the downhill side of life and may be the big difference I am hearing. The KT66's I ordered from Steve should be here any day and I will put them in and compare them. I am also going to play around the with bias for the 7581A's and see if anything changes. I am in no way abandoning the KT66's as they sound good as well. This will be a long term comparison and not sure which way I will be going in the end.

I can say this, this is my first foray into tube rolling and I am thoroughly enjoying the experience. Not sure if that is a good or bad thing.

Thanks
Dave
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Archie
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Re: Tung Sol 7581-A in the ZMA
Reply #3 - 06/10/20 at 17:46:41
 
Dave,

The mids and highs of the 7581As, 7027As and the 6P3S-E coin based all seem to exceed the KT66s in my experience.  They all sound "sweeter" to me.  I don't mind the KT66s but they somehow don't last long when I put them it.  The 6P3S-Es are a very inexpensive tube and prior to finding the 7581As and 7027As, they were my favorite.  I personally don't find a lack of bass.
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NormD
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Re: Tung Sol 7581-A in the ZMA
Reply #4 - 06/14/20 at 22:40:42
 
I just took out my TAD 7027's in put TAD KT66's in my 25th Anniversary ZMA and I much prefer the KT66's.   Cleaner, better sound stage. Here we go again...
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Archie
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Re: Tung Sol 7581-A in the ZMA
Reply #5 - 06/14/20 at 23:36:01
 
That's interesting.  Was it you, Norm, who was encouraging me to try the TADs?  I've only used the Tung Sol 7027As.
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DAKO
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Re: Tung Sol 7581-A in the ZMA
Reply #6 - 06/25/20 at 18:11:54
 
Update- Received the new KT66's and did a 2 hour listening session. I have to admit that as of now, I think I prefer the 7581A's. The sound is darn close though. I am going to give the KT66's a few more hours and see what I think. I am in no way thinking of abandoning the 66's as these were what has been in this amp since I got it and it has sounded sweet from day one. At this point I am probably at the point of just swapping the tubes back and forth depending on what kind of mood I am in.  I don't think I will prefer one tube over the other.
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