i obtained a pair of the tubes BHK raved about as he built the pre. The unit has jumpers to accommodate other tubes, but I need to know which to move to what settings? Can anyone help me on this?
Many thanks!
See page 10 of the manual, linked here. These instructions seem a tad vague, but might be clearer if you actually have a preamp in front of you (I don’t – I was reading the manual a couple of days ago and wondering if I can figure out a way to acquire one of these units . . . ).
Thanks I saw that but I need to know what jumper positions would be best for the Tungsram 7dj8.
The Tungsram 7DJ8 is a seven volt heater voltage tube, so move the jumpers to provide seven volts. I assume the jumper locations are labeled on the PCB and visible once you have the cover off.
And for current? I know there are two sets of jumpers. I’ll take the lid off and look. Should have before I asked, but I thought there was more than voltage to change to match the tube…?
What you do is take the black cap that is seated on pin 2 and 3 and move it to pin 1 and 2. I did the same using your 7v tubes.
magister said See page 10 of the manual, linked here. These instructions seem a tad vague, but might be clearer if you actually have a preamp in front of you (I don't -- I was reading the manual a couple of days ago and wondering if I can figure out a way to acquire one of these units . . . ).I agree. A little more detail here for those experimenting with other tubes would be very helpful.
The statement in the manual that any “acceptable” 6, 7 and 12 volts tubes are OK is an invitation to trouble. I would suggest that PSA list the acceptable tube types with the appropriate current jumper settings. The voltage settings we can probably figure out (6v for 6 and 7 series tubes, 12v for 12 series). I’ve never heard, for example, that 12AX7’s or 12AT7’s are drop-in replacements for 12AU7’s but I really don’t know much about tube internals. We know form Bacom’s prior posts that the 7DJ8’s work (and edorr seems to be using them, having just changed the voltage settings?), so presumably so do 6922’s and similar tubes. I seem to recall Bascom said 6H30’s would not work. Like woodburger100, I would like confirmation before trying anything.
There are only two possible jumper setting. The default (for 12v), and moving the cap from pin 2&3 to pin 1&2 which will support 6-7 volt if I understand correctly. The manual is not clear on the need to change the cap and how to do it, so I asked PS audio support via email before doing so.
Thanks edorr. That’s what it looked like in the manual. (I was too anxious to get mine into the rack to open it up and look when it arrived.) I assume they did not say to move the bias jumper for that tube. For that one, it looks like you just go from unjumped to jumped on JP7 and JP8 (on the other side of the tube socket from the voltage jumper) to go from 4 (the default) to 5 milliamps. I have no idea what tubes for which you would want/need to do that. I have some of the Tungsram 7DJ8’s (using them now in my BHK250) and will likely give them a try in the preamp once the unit is fully broken in.
I’ve installed the 7dj8s into the BHK pre… Don’t know how long they need to burn-in, but after about 24 hours, I think they sound wonderful. The one jumper was moved as edorr outlined above. If you haven’t looked inside, it’s very hard to get fingers around that jumper. It’s more a tweezer fit.
Is it just one jumper or one jumper per tube?
There is an identical jumper behind each tube. The both need to be changed.
Thanks. That’s what I would have guessed (and presumably would have seen if I wasn’t too lazy to pull it out of the rack and open it up; soon though).