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In Reply to: RE: Need To Develop A Short List Of Tubes For a BHK Pre Amp posted by Mister Pig on April 20, 2019 at 09:03:37
"Need tubes for the pre amp, which can take 12a*7 family or 6922/6dj8 tubes."
What is the actual preamp? (You don't mention a name or model number)
A preamp that advertises that you can plug a 12AX7 or 12AU7 into the same socket is either going to be running the 12AX7 into the ground or running the 12AU7 so lean that it will sound like garbage. One caveat is that if the preamp in question has a bunch of dip switches to adjust the operating parameters (actual resistors in the circuit), then these tube substitutions could be done with more success.
Follow Ups:
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Hey I have seen that! It came in the box with the pre amp I bought.What info in that manual did you want me to reference? I cant tell by your post.
Cheers
Mister Pig
Edits: 04/21/19
"The BHK Signature Preamplifier features two 12AU7 dual triode vacuum tubes in the input stage that act as a zero feedback balanced input amplification pair. A unique self biasing constant current source and user selectable switch combination allows those who like to roll their own tube selections to place any acceptable 6, 7 or 12 series vacuum tubes inside the preamp. The twin hand-selected vacuum tubes that ship with the BHK are the preferred models we recommend and use in PS Audio's Music Room One reference system."
"The BHK preamplifier is supplied with 12AU7 dual triode vacuum tubes. These have a heater (filament) voltage of 12 volts (that's what the "12" in 12AU7 indicates). Replace these tubes with a similar design that runs on +12 volts for its filament voltage.It is possible to use a lower voltage tube, such as a 6 or 7 series dual triode. To use a +6 or 7 volt tube, you must change the filament voltage. This can be accomplished by moving two jumpers, abeled JP11A and JP12A, inside the BHK Preamplifier. You can also change the bias current running through the tube if you wish. The bias we use from the factory is 4 milliamperes. Using the second internal jumper set, labeled JP7 and JP8, this can be increased to 5 milliamperes by using the supplied connector to jumper JP7 and JP8 (they are normally not jumpered for 4 ma). If you don't understand these setting and terms, best to probably leave it at the factory setting. Otherwise, if you really need to know, contact our service department."
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
First I must say I have no idea what function the tube is serving in the preamp. Gain stage? Cathode follower?
That being said, my only comment would be 4ma (or 5ma) is not a good idle current operating point for either the 12au7 or the 6dj8.
I call BS. Feel free to prove me wrong. My mind is always open to good engineering explanations. But please, no voodoo talk.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I just have a minute. But in the BHK pre amp the tube is used as an input gain stage, but the heavy lifting of gain is done by Mosfet outputs. The gain of the tubes are variable and part of the volume control. I am just heading out the door, but lifted this paragraph from the Stereophile review that is descriptive of this element of the pre amp.
Then there are those "wonderful tubes"-BHK's phrase: two 12AU7 dual-triodes, which provide voltage gain and are involved in the preamp's innovative two-stage volume control. The BHK Signature's fine increments of volume adjustment (0.5dB) are achieved by altering the tube-stage gain-and every 10-12dB a relay clicks in, activating a step in a discrete stepped attenuator.
The BHK preamp is fully balanced from input to output. Its output stage riffs on the traditional push-pull design, using all-N-channel power MOSFETs in place of the more common complementary arrangement (footnote 1). The N-only topology is something King has been doing for a while in his amps and preamps. "The preamp's tube stage as well as its MOSFET N-channel output buffer are independent circuits and without global feedback," McGowan says. "They achieve their low distortion and characteristics through careful design and high voltages."
This link takes you to the measurements section for the pre amp.
https://www.stereophile.com/content/ps-audio-bhk-signature-preamplifier-measurements
Cheers
Mister Pig
Edits: 04/22/19 04/22/19 04/22/19
Sorry for being unclear. The BHK pre amp. Its a PS Audio component. Yes you can adjust voltages and current.
Edits: 04/20/19
That is helpful. There are some dubious products from overseas that claim you can just plug in what you want with no issues.
The preamp looks to be designed for the 12AU7, so I would stick with the 12AU7, 12BH7, and 6CG7 since they are all pretty similar. The manual also suggests that the current can either be set at 4mA or 5mA, so this would rule out using something like a 12AX7.
I sure would contact them about the 6922/6DJ8. The shield on the 6922 is connected to what would be one of the heater pins on the 12AU7, so if it's disconnected and left floating, that could be a problem.
Got recommendations in those families to build a short list from?
Look for big lots of random used tubes, the test and match them up as you go.
There's a lot of love for the Mullard box plate 12AU7, but honestly I would just get 10-20 used old stock 6CG7s and try those first.
There is no need to make tube changes that were not engineered for the piece. Nor was the BHK voiced with these other tube choices.
If you stay with 12AU7s you can find all manner of tones and other sound parameters. There are equivalents such as 5814s to experiment with, and my personal favorite the Amperex made 7316, (which you can find in Tube Lore). If You insist on using the 6922 family is fraught with low volume production making them expensive. They are also not great for "musical sound" in the mind of many. If you are going to with them, and I have had to. I wish you good luck. My personal pick there is very clean and strong signalling tube. It's source belies its sound, the CV2394 by Mullard, but this is no mellow tube.
Finally don't rule out trying the Gold Lion re-issues (Russian) they are as good or better than some old stock.
This is always the question of what to use for tubes in a new production component. Unless we are talking custom build one off, or limited production components, manufacturers have to select current production tubes that offer what they feel is the best value for the money. It is not going to be a NOS tube that they can only get a 100 pair of at any one time. So the choice PS Audio makes of Gold Lion or Psvane is one of the practical economics of offering a new product to the market place.
Actually the BHK 250 Signature amp comes with new production Gold Lion 6922. That is a tube GEC never produced, so its essentially a new production tube with that label stamped on it. I spent quite a bit of time listening to that tube, and I sure do not get this "as good or better than some old stock". From what I heard its a dark, grainy, and recessed sound. I had a hard time understanding what was special about this amp until I installed a pair of Siemens 6922 gold pins, 60's era. in it. That took the shackles off the amp, and if you follow some of the post by BHK, he thinks the Tungsram 6922 is a great tube in the amp, better than the Gold Lion. But to me almost anything is better than that tube.
The pre amp comes with 12au7 Psvane, and they certainly are better than the GL that came in the amp. But I do have a set of Phillips 12au7 that look to be Mullard Blackburn, and the described sound seems to fit them. They have most of the lettering rubbed off, so I am not 100% certain. They certainly are not the JAN version. What I found from my initial experiments is that the 6922 tube is a bit noisier in this circuit than the 12au7, and its noticeable because I have speakers that are 93 db efficient. A bit higher than normal, but enough to notice the difference between the two tube families.
So I think I will pursue 12au7 tubes and their variants. As much as I like the Siemens 6922, I have to wonder if I would appreciate the Siemens 12au7. I remember many years ago that I liked RCA 12au7's, but I am not sure if that would be the case today. I am really not a fan of tube warmth, and if you ask me why I have hybrid components...well I could not give you a good answer...but I prefer a more neutral presentation that most SS gear presents. However, I do like the flow and cohesive nature that tube gear can give, which is why the hybrid format of the BHK series intrigues me.
So at this point, I am going to be looking at 12au7 candidates.
Cheers
Mister Pig
Maybe I can get you to try one more current manufacture 6922? Take a chance on the JJ gold pin 6922's. The sound is very similar to the Tele 6922's I have. I've been using them in my CAT SL1 Renaissance for a few years now and have never felt like I was missing anything, or sense that the presentations wasn't right. For ~$30 a pop selected for noise and microphonics, they're tough to beat.
If those tubes are "Mullard Blackburn" they will have etched codes in the glass down low on the side of the tube. The first letter in the second line of the code will be a "B".
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I owned some and had liked them very much but they have gotten very expensive. Did you want to roll them for another tube? The vast, vast majority of my decently large collection of tubes are old stock. I liked none of the new production for many years, but my attitude regarding the New Sensor tubes has dramatically shifted. I don't collect/hoard them because I know where to get them when I want one.
I also got used to using new production with few exceptions for power tubes.
Like I said you can't argue preferences and or tastes.
Edits: 04/22/19
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