BHK Preamp tube rolling


#1

After a bit of a search, I haven’t found much about tube rolling experience with the Preamp. It would be interesting to hear what changes have been noticed switching out of the stock tubes to, say, the Tungsram.


#2

Welcome!

The search function does not work very well.

There are quiet a few posts on swapping tubes in the BHK pre, but some are buried in the various threads regarding the amps, other observations on the pre, etc. The forum members prefer a free form, stream-of-consciousness topic organization so you will need to be a bit patient and review the various threads.

Mr. King has posted that he and Arnie Nudell determined early on that the Tungstram PCC887DJ8 is superb in the preamp. Kevn Deal of Upscale Audio carries them.

Hopefully others will chime in here as well.


#3

Yeah, we are not very disciplined here about keeping threads organized. I am as guilty as anyone. Elk’s description of us as “free-flowing” is about as kind as anything that could be said.

One good post about the Tungsrams in the pre is here (look for post #248 by DenisD). I’ve read several comments and AFAIR they have all been favorable. BHK also recommends the same Tungsram tubes for his amps. I installed a pair in my stereo 250 and they were a big improvement over the stock tubes, and even better with tube dampers.

I’ve got a pair of Tungsrams waiting for the pre – I decided to hold off installing them until the pre was well burned in and I had a good handle on its sound. After rereading DenisD’s post just now, I think I will install them this evening smiley-music005_gif.


#4

I’ve had my BHK pre for 4 weeks now. I have installed the Tungsram 7dj8s last week. I love what I hear with these. Compared to the stock tubes, there’s a more realistic presence, and I’m getting a kick out of being able to pick out individual saxophonists in a big band – something I like doing when listening to a live band!

A question: under what circumstances would one change the bias jumper? I changed the voltage, but left the bias at the factory setting. Is this a correct configuration for the Tungsrams?


#5

One more question: I noticed that it’s possible to change the volume range. What is the effect of a setting change here? If I set the volume to go no higher than 70, does this mean that the preamp will be volume limited to 70, or will the preamp achieve max loudness at 70 rather than 100 (changing the volume increments)?


#6

I’m curious about the bias jumper too. I did not change it when I went to the 7DJ8’s and don’t think anyone else who has done so said they changed it. It would be good to get a list of acceptable tube types with bias settings, or a statement that it’s basically 12AU7s or 6922/6DJ8/&DJ8s if that is the case.

On the preamp, I believe it limits absolute loudness rather than compressing the range. The idea is to avoid levels that would be too loud and possible damaging for a particular system.


#7
Jah said One more question: I noticed that it's possible to change the volume range. What is the effect of a setting change here? If I set the volume to go no higher than 70, does this mean that the preamp will be volume limited to 70, or will the preamp achieve max loudness at 70 rather than 100 (changing the volume increments)?
It just sets the upper limit of the control to protect your speakers - not the maximum volume. It's no different than setting the control to 70. It does not change the actual level.

#8
Jah said I've had my BHK pre for 4 weeks now. I have installed the Tungsram 7dj8s last week. I love what I hear with these. Compared to the stock tubes, there's a more realistic presence, and I'm getting a kick out of being able to pick out individual saxophonists in a big band -- something I like doing when listening to a live band!

A question: under what circumstances would one change the bias jumper? I changed the voltage, but left the bias at the factory setting. Is this a correct configuration for the Tungsrams?


The intent of the bias or tube operating switch was to allow for the use of the 12AU7 and the 6922 family of tubes. For the 6922 types, the current was set for 5 mA and for the 12AU7, 4 mA. It would be interesting to see what you think of the sound when set at 5 mA vs. what you observed when set at 4 mA, the factory setting for the 12AU7.

#9

BHK, thank you very much for this info, and to Jah for asking the question. I installed my set of Tungsrams two days ago and changed the voltage jumpers. I did not change the bias jumpers because I had no idea what the intent was. The manual just says that there are two settings with no indication of which is intended for what type of tube; Paul, this really needs to be clarified in the next revision of the manual.

As far as the sound goes, I immediately started noticing details I had not heard before and was able to hear more deeply into the recording – similar to what Jah expressed. The tubes are not burned in yet, of course, but definitely a worthwhile upgrade given the modest cost. I’ll update this if they change much over the next week or two.


#10

I just need to buy one pair for a pre right ?


#11

Correct, 1 pair of tubes for the BHK pre-amp.


#12

Thanks Bascom. I didn’t switch the bias when I changed to the 7DJ8s and they worked fine but now I know we should switch the bias to 5 mA as well.


#13
BHK said It would be interesting to see what you think of the sound when set at 5 mA vs. what you observed when set at 4 mA, the factory setting for the 12AU7.
I changed the bias setting last night. To my ears, the benefits of the Tungsram tubes (greater ability to follow individual instruments, more realistic tone color) got kicked up a notch; same qualities, just more in evidence. Not a major difference, but certainly worthwhile and audible with careful listening.

#14

Thanks Bascom!

I changed the bias this morning and have been listening for about an hour. I’m always amazed at how small changes can make such a big difference. The tungsrams sound with the higher bias is much more tube-like in that the midrange is better fleshed out, and the overall sound is smoother. Massed violins sound right – finally!

The sound of the tungsrams at the lower bias setting, in hindsight, was etched. I’m a sucker for etched sound because of the hyper detail; however, etching does tend to drive me to keep the volume down, which I did before changing the bias.

So, thanks again for the bias clarification!


#15
BHK said
Jah said I've had my BHK pre for 4 weeks now. I have installed the Tungsram 7dj8s last week. I love what I hear with these. Compared to the stock tubes, there's a more realistic presence, and I'm getting a kick out of being able to pick out individual saxophonists in a big band -- something I like doing when listening to a live band!

A question: under what circumstances would one change the bias jumper? I changed the voltage, but left the bias at the factory setting. Is this a correct configuration for the Tungsrams?

The intent of the bias or tube operating switch was to allow for the use of the 12AU7 and the 6922 family of tubes. For the 6922 types, the current was set for 5 mA and for the 12AU7, 4 mA. It would be interesting to see what you think of the sound when set at 5 mA vs. what you observed when set at 4 mA, the factory setting for the 12AU7.


OK, so at 194 tube hours on my BHK Pre, I installed the Tungsrams purchased from Upscale (platinum and cryo’d) and set the voltage to 6 (it really helps to use a small needle nose pliers to mover the jumpers). Prior to the switch, I totally agreed with previous reviewers about the sonic magic of this preamp. The 6922 built on this–rounder, fuller sound, holographic sound stage, etc. However, I agree with JAH, the sound was a bit etched which made treble strings a little hard. I thought this was due to new (3 hour) tubes, but after seeing JAH and Bascom’s post on the current settings, I went back in and changed the bias current from the factory 4ma to 5ma. Bingo, hard edge gone, amazing what a 1ma step up in bias will do! I would recommend the Tungsrams (get them from Kevin at Upscale Audio) highly! So yes, Bascom, the Tungsrams are a significant improvement, in my opinion.

As a postscript, I have three audio sources; turntable, CD and Satellite Audio. I used the Satellite Audio (Serius XM, etc) for background music, but was blown away on how much better it sounds coming through the BHK. Actually have been snagged several times into sitting and listening. Amazing…


#16
Jack43 said . . . amazing what a 1ma step up in bias will do!
It is quite fascinating, although as a 25% increase it should have some impact. :)
I used the Satellite Audio (Serius XM, etc) for background music, but was blown away on how much better it sounds coming through the BHK. Actually have been snagged several times into sitting and listening. Amazing...
This is amazing; satellite music is highly data compressed and is typically awful. Fun that it now sounds good enough to listen and not just as buried background.

#17

Jack43, what satellite receiver are you using? As Elk said the sound is generally awful, at least on a home system. I’ve had it in my cars for several years and have been happy with it. Tried a portable receiver at my second home and just couldn’t stand it, even on a pretty basic system.


#18
pmotz said Jack43, what satellite receiver are you using? As Elk said the sound is generally awful, at least on a home system. I've had it in my cars for several years and have been happy with it. Tried a portable receiver at my second home and just couldn't stand it, even on a pretty basic system.
I'd be interested too, mine in my car is pretty awful.

#19

I use a Polk XRt XM Tuner for Sirius using the digital output to my dac.

I listen mostly to Grateful Dead 24/7, and I occasionally use the analog output to my adc to record live broadcasts, like the Dead’s 2015/16 New Years show and the Jerry Garcia Symphonics show with Warren Haynes at Red Rocks. I listened to a lot GD on second and third generation Cassettes, so Sirius is a step up.

Overall best for background music or I find if I start a listening session with anything that wasn’t all that well recorded, I have LPs I have digitized at 24/96 that were poorly recorded 40 years ago. If I first listen to some really well recorded music then the poorly recorded it is hard to listen to, the other way around, not so bad.

If you look for a used Polk, be sure it includes the antenna with cable, as it uses an odd plug, also the remote is nice to have.


#20
pmotz said Jack43, what satellite receiver are you using? As Elk said the sound is generally awful, at least on a home system. I've had it in my cars for several years and have been happy with it. Tried a portable receiver at my second home and just couldn't stand it, even on a pretty basic system.
I have Dish with a Hopper receiver.