Odd thing, last night I swapped the JJ 12au7 tubes for the Tungsram 7dg8 and it was fine. No pulsing. A bit more noise tho, the JJ’s are super quite. Not sure if the 12au7 just have less noise in general?
Odd how it is erratic??
Curious if you put back the JJ’s and hear if the pulsing returns.
davek saidWith the JJ 12au7 ( red printed font ) it is dead quite. I just tried some JJ E88CC 6922 ( gold pin ) and there isn't pulsing, but a bit of buzz noise mainly from right channel. Also these JJ's ( E88CC 6922 ( gold pin ) are not good at all in the BHK, thin weak base. Terrible really.Curious if you put back the JJ’s and hear if the pulsing returns.
Welp, they tossed a new board in and pronounced it healed:
Our technicians could not replicate the issue of pulsing with the included tubes.
The BHK Pre’s performance is effected by different tubes and as such the unit does not test within our limits.
That being the case it’s worth mentioning that both channels tested the same.
They replaced your main board and successfully tested your Pre with a pair of 12AU7 tubes.
I tested your Pre at my desk with your Tungsram tubes and could not hear the pulsing in either channel after 30 minutes of playback.
We feel the issue is likely systemic and not specifically related to the BHK Pre.
We are shipping back to the following address unless you need me to correct anything:
My response:
> We feel the issue is likely systemic and not specifically related to the BHK Pre.
Jeremy - let me add that this weekend I took the PCA2 out of the equation and ran the DS Dac straight thru to the Clayton M300's. No pulsing/noise.
Please expand on the statement above - the "issue" does not exist w/o the BHK Preamp in the chain w/ 6/7 v tubes. Give me some ideas to troubleshoot w/ if the unit exhibits the same behavior when I get it back.
Note that this was a second wave beta unit - not sure what yours is.
darrenv1070 saiddavek saidCurious if you put back the JJ’s and hear if the pulsing returns.
With the JJ 12au7 ( red printed font ) it is dead quite. I just tried some JJ E88CC 6922 ( gold pin ) and there isn’t pulsing, but a bit of buzz noise mainly from right channel. Also these JJ’s ( E88CC 6922 ( gold pin ) are not good at all in the BHK, thin weak base. Terrible really.
I only seem to have issue with 6922 tubes, and the MA jumper does not seem to matter what position it’s in. I still just get an unstable unit with ANY of the 6922 tubes I have tried. NOS and new productions. Alto the NOS are the most problematic.
Are they from several sources or just one ?
Darrenv1070, have you tried the JJ tubes on your BHK250 yet? Just want to know how they sound compare to the Tungsram.
thx.
I bought tubes from: Upscale Audio, The Tube Store, and The Tube Dept.
I just rolled in a pair of JJ ECC802S gold pin 12AU7 tubes. I just noticed a slight right channel pulse thumb noise. I power ALL my gear from a pair od PSA P-5 units. Most power cables are PSA AC-5 and Wireworld Equinox 7. I have tried setting the P-5 at 115 volts, and also 120 volt. Also tried the Sinwave and Multi. Even tried the preamp direct into wall. That seemed to be the worst.
a25105 saidDarrenv1070, have you tried the JJ tubes on your BHK250 yet? Just want to know how they sound compare to the Tungsram.
thx.
I have not. I am not currently using the BHK 250 in my set up. I am using a Emovita XPR-2. The BHK 250 is not connected.
I toggled power on the BHK preamp, now it’s stable…
darrenv1070 saidI have not. I am not currently using the BHK 250 in my set up. I am using a Emovita XPR-2. The BHK 250 is not connected.
I was toying with the idea of selling the BHK 250 Silver
Anyone try the Brimar CV4003 / 12AU7 or the Mullard M8136/12AU7 in the BHK preamp yet? Any feedback!
TLDR: Are there clearer instructions on changing bias current before I open my BHK Pre?
Bought my Tungsrams from Upscale Audio - dropped them into the 300 Monos and everything works fine (and sounds wonderful)
Dropped them into the Pre, and no sound. Took them out and put in the original Psvane set, and it worked. Okay, I remember that they need a jumper bias change - confirmed here.
Following are the instructions in the manual <<>>
To use a +6 or 7 volt tube, you must change the lament voltage. This can be accomplished by moving two jumpers, labeled JP11A and JP12A, inside the BHK Preamplier. <<>> 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. <<>>
Still, moving jumpers is easy - I just need to know if the JP7/8 jumpers are already in the pre, or in the box, and what to do with the JP11a/12a.
The jumpers come installed in the pre-amp. Page 10 of the manual has an illustration outlining their exact locations.
Inside the pre the existing jumpers sit on their pegs (or sockets) to facilitate 12V and 4mA, in the picture it shows the voltage jumper sitting over the right hand side of 3 pegs - that is the 12V position - to connect the jumper to 6V it needs to be pulled (up) off the RH peg and reconnected to the centre and left peg (6V).
Similarly for current increase, the jumper (blk plastic ‘bridge’) can be seen to be sitting on the RH peg (4mA) - to change it again pull the jumper up and re-seat it on both pegs - this will provide 5mA.
This is most easily accomplished using tweezers and of course with the tubes removed. It takes a coupe of minutes at most.
a bit of editing to help
Don’t forget to unplug the unit as well. Rear power switch off BEFORE unplugging. I like to wait a few minutes are well to make sure the cap voltage drops off as well. Red LED will go out. Also if you have a ground strap on wrist wouldn’t hurt to be a safe as possible.
Needlenose pliers worked very well for me when moving the jumpers.
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I recommend that everyone pull the tubes and look at the jumper position. When I changed tubes I found one tube bias setting on 4ma and one set on 5ma. Glad I only waited a couple of weeks. Center imaging improved.
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