BHK Preamp tube rolling

You can give Brent Jesse a call in the meantime, I’ve had good luck with him in the past with 12AU7’s for my Concert Fidelity Pre (Siemens and RCA 5814) have also bought from Andy, he gives great advice as well a great tubes!

https://www.audiotubes.com/

Best,
-JP

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Telefunken 12au7 Tubedepot great people

Get em while you can and don’t gripe about a
near unobtanium nos tube

Best wishes all

With the Tele one really wants the ECC802S. The very special one at 3x the cost if you can find a matched pair. Current price is ~$1000+/pair

I obtained a very nice set 2nd hand but originally from Brent Jessee. Date codes match to the same month July ‘65 Ulm Germany.

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Way to go Brett…well worth it!!

I put the 6DJ8 tubes in my DS Pre a few months ago and cannot take them out… Too GOOD!!!

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Hi folks, I’ve recently picked up the BHK Pre to go with the BHK 300 mono’s and DSD in my setup. I wanted to try out a pair of WE6SN7 tube that I picked up. I got the adapter to used this tube, but before firing it up, I like to check what should the Voltage and Amperage jumper be set to run 6SN7 tubes on the BHK Pre.

Thanks.

Be extremely wary of using these. I used a 6SN7 compatible in an adapter and you could smell overheating components. There’s a thread where this is not recommended possibly by BHK himself.

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Thanks Watchdog for sharing that, I’ll have to check out that thread to learn more…

I think the problem is current draw from the 6SN7 I used a 6F8G which is the same tube with a top cap for a plate connection. Worked great but the whole house smelled like toasted components. My wife and my daughter thought that it was on fire.

what was your amp/volt settings when you run your 6F8G tube Watchdog? Was the overheating problem as bad when you run it at a lower bias current?

I think the problem was Independant of the setting if I’m not mistaken

Does anyone know if the Pre requires balanced tubes where both triodes in a single tube have to have close to the same plate current (Ia) measurements?

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Yes, I understand it is desirable to have as close as possible balance between the triodes within each tube.

Whether it’s required depends on the circuit. It seems the pre is sensitive to balance, at least between tubes but perhaps also triodes within the tubes too.

@BHK Perhaps Bascom could weigh in on the need for balanced triodes?

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That’s a great question @vee. Another dimension to tube rolling.

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Because the BHK Pre is balanced my guess is each half of the triode amplifies each side of the balanced signal so my guess is yes you need ideally both halves matched in the tube

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Although a different breed…In my classic mid sixties
McIntosh MX 110z all tube tuner preamp there were
2 tube postions for which I always used balanced internally
and balanced triode to triode and low noise…

In a Ah! 4000 cdp always equipped it with internally balanced
matched and balanced , and matched to each other as well.
The unit uses 2 6dj8 variants…

So my .02 thinking don’t fiddle fadle …when you purchase
tubes specify internal matching triode to triode, if using 2
then the same plus matched to each other…

Amazingly both the Ah! and the MX110z would reflect this
aspect of things …balance between channels

Hope this helps
Best wishes

That makes sense, though it’d be great to get confirmation.

@BHK Another question is in what range the plate I(a) curves should also be “matched” between tubes/triodes for the best sound quality. Can a circle can be drawn on this graph to indicate the ideal place where triodes and tubes should be tested and matched?

Per Telefunken’s ECC82 datasheet, typical operation calls for Vp = 250, Vg = -8.5 producing an Ia = 10.5 – but tubes’ Ia varies as Vp varies, so if we wanted to get real precise – which Vp range should be tested for matching?

I’ve installed a pair of Tungsram 7DJ8’s in my BHK Preamp and I’m enjoying the results so far!

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Let us know how they sound in a couple hundred hours. Mine only lasted about that long. Both pairs from Uncle Kevin.

Will do! Thanks for the tip