So change or switch the tubes already; I’m dyin to know…
Perhaps tonight or tomorrow…I’m away today.
Can anyone tell me if it would OK to use the 5814A and 5963 variants in the BHK??
I note that they are regarded as equivalents to the 12AU7 but I have also read that there are differences in the plate voltage of these variants.
So my question is, can they be used without burning them out prematurely (assuming they require a lower plate voltage than the BHK provides)? Alternatively if they require a higher plate voltage than the BHK can provide then will the BHK run them OK?
I am still learning out tubes so these more technical aspects are still a mystery to me.
I have used them interchangeably with multiple pieces of gear that spec 12AU7’s including the BHK with no problems. In fact the 5814’s are usually preferable to 12AU7’s as they are military spec tubes.
1 Like
Swapped tubes left for right, not the tubes. Swapped inputs, aha, dead channel follows. Rebooted and reseated outputs from DS, no change. Played from optical source into DS, all good. Rebooted music server, bingo. Normality returns, carry on.
phyew!
1 Like
I was already jonesing for music 
Short answer yes,… Long answer… when looking at alternates it’s more important to make sure that the tube in question doesn’t pull to much heater current,… A 12au7 heater/filament pulls 300ma in parallel (which is how the Pre powers them) 6922/7308 pulls 300ma. as well. This is in spec with what the BHK can provide. I would think that a margin of 50-75ma higher would be ok. When you look at other alternates as discussed earlier in posts way above here, some otherwise suitable tubes (like a 12bh7 or 6n1p, etc…) will have heater currents in the 500-600ma range. Those would most likely cause issue, if not in the short term then in the long term by premature circuit failure (over heating failure of the heater circuit). BHK actually tried using some high heater current tubes and noticed (and reported) that his unit could not provide suitable heater current and distortion went way up, so no go…
In regards to the Plate voltage, the BHK Pre is only running at ~120V which is well below max of what any tube in the 12xx or 6922 range can handle so no issue there and they are biased at only 4 or 5 ma which is well within spec of any of these tubes, more important to look at heater current. That alone will knock out many otherwise suitable tubes for use!
I have successfully used 5814’s but am finding as others have as well that the Amperex 7308 is a superb tube in this pre. I have also found that Amperex 6DJ8’s from 60’s sound almost indistinguishable if you can score a tightly balanced and quite pair. RCA blackplate 12au7’s form the 50’s are a really sweet sounding tube too… I think one of the most important aspects is to find tubes with a tight balance (gain specifically) between the triodes since the tube is splitting the polarity +/- for each channel. Hope this help! Best,
I’ve found some nice 6963 RCA tubes that work really nicely in the BHK preamp. They are a ruggedised version of the 12AU7. Nice base, quite liquid midrange and nicely balanced treble (just a tiny tad rolled off). Well priced too.
OK,
Has anyone used the Schiit Lisst solid state tubes in this preamp?
They are an equivalent to 6922. They apparently run depletion mode mosfets. That will be a nice match to my Pass Labs XA25 (class A, depletion mode Mosfets in there too).
Schiit offers a whole heap of warnings but if its an 6922 equivalent I am wondering what dangers there could be?
No, I haven’t but I understand what you’re trying to do.
I have two preamps, a nearly new BHK and a quite old Pass XP-20.
When I coupled the XP20 with my old Cary tube amp, it was nice but the BHK blew it away. But when I traded the Cary for a Pass X150.8 amp, the combination of that and the XP20 is absolutely magical. Trying to minimize the hyperbole, this combination seems to have some synergistic advantage that gives truly amazing separation, detail, deep, believable bass and silky smoothness for things like horns, which with the BHK were sometimes slightly harsh, depending on tubes.
My wild ass guess is that if I had coupled the BHK pre to a BHK amp, there would probably be a similar synergy—maybe.
Solid state tube replacements are particularly popular for replacing rectifier tubes.
I do not understand the appeal. If you want solid state, buy solid state.
Schitt caveats these as only OK in their products. At your own risk in anything else.
Ha! So you want to turn your BHK into Schitt? Just kidding, but I couldn’t resist.
Elk, everyone is entitled to your opinion obviously.
Have you stopped to consider that the bhk preamp and power amps are all hybrid devices?
I bought a 2nd hand Schiit tube preamp a while ago and sold it the next day. It was very poorly designed and it sent DC at about 2V through my power amp when I switched sources. So it really was Schiit.
Yes, the warning in the manual IS REALLY HARD TO MISS!
Well I am not afraid to try anything just out of curiosity and unlike others I am not constrained to a SS / Tube orthodoxy.
I was thinking that I’d love to hear what the addition of bypassed depletion mode Mosfets would sound like in the BHK. I am concerned about the warnings as I obviously don’t want to kill my preamp. I am game for a bit of experimentation for the sake of it but I don’t want a fried preamp.
I wouldn’t do it. Just put some Amperex 7308’s in there and enjoy the essential virtues of the BHK.