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phrarod 4th September 2009 02:47 PM

Can I use this output transformers with a 5965?
I have a pair of AN output transformers C-core HiB that are designed for ECC82, 5687, E182CC, 6SN7, 6463 tubes. Would these load a 5965 correctly or do I need other output trans for optimal performance?

BudP 5th September 2009 02:30 AM

Likely will be a bit light on bass. Inductance needed for -3db at 20 Hz, for the 5965 is 27 Henry, with -0.5 db some 2.76 times that. The other tubes need around 15 Henry for - 3db. If your transformer is from Lundahl, they generally post the useful inductance out in the middle of the permeability range. A 1volt 120Hz test will provide you with the lowest operational inductance of the device, but you need to know the permeability curve of the core material to guess at what will be available. Typical inductance will be about 10 times what the 1volt 120 Hz reading shows, from an inductance bridge.


phrarod 5th September 2009 02:44 AM

Thanks Bud. I am having bass issues.

That all makes sense. I've been searching for a output trans that would work. I've contact Lindahl and Silk. Silk can build a 12K:600 ohm (1 :0.22) OT but he insists on potting it and I've been told potting can create problems.

BudP 5th September 2009 02:53 AM

Not potting will create even more problems, like corona death in under 12k hours of use, as opposed to 300 K hours with vacuum potting. I will not let a high voltage signal or power transformer out of our plant without vacuum potting. Plus, we only build to CE 6500 safety standards. All of this so you don't end up with a fire or shock hazard.


Poindexter 5th September 2009 03:27 AM

5965 has same rp as 6SN7, 12AU7 (ECC82 etc.), with ~twice the gm. What am I missing here, Bud? I always look at load/rp.



phrarod 5th September 2009 03:58 AM

I didn't know you made transformers. Would you be willing to discuss making a pair? If so please PM me.

BudP 5th September 2009 05:01 AM

Hey Poinz,

Long time no see.... I suspect I am missing far more than you are, but, here is the data I have. Doesn't mean I understand it with the same clarity that you, or any amp designer must, but it is the data I would design from, out of Frank's archives.

Plate resistance 7250 ohms
Transconductance 6500 ohms
3427 Z ohms without pri DCR 27.87 Henry for -3 db @ 20 Hz

Plate resistance 3000 ohms
Transconductance 5400 ohms
1928 Z ohms without pri DCR 15.35 Henry for -3 db @ 20 Hz

Plate resistance 7750 ohms
Transconductance 2600 ohms
1946 Z ohms without pri DCR 15.50 Henry for -3 db @ 20 Hz


BudP 5th September 2009 05:43 AM


You have mail.


phrarod 5th September 2009 05:44 AM

Reading it now...:)

Poindexter 6th September 2009 01:55 AM

Bud, it appears to me that you are loading the 6SN7 and 5965, which have almost identical rp, very differently. Why is this? Am I reading your numbers incorrectly?



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