Thread: Tube Noob, seeking education

Greetings all, hope everyone had a blessed Christmas. I have been lurking around here for a while now. I have finally put together a somewhat modern system that is pretty nice I think but I am running into a few things that are unfamiliar to me and I was hoping I could get some guidance.

So I have acquired a couple of fine pieces of Balanced Audio Technology tube gear. So far, everything is going pretty well, but I am still wandering about in the dark a bit when it comes to tube gear in general and what to expect. A bit of background info is in order. The first component was the VK-P5 phono stage. When I got it, I was driving the system with a Yamaha AX-900u integrated. It was dead quiet at idle. I didn't have balanced inputs on the 900 so I made an XLR to RCA adapter cable using the wiring instructions given to me by Victor Komenko. It worked fine but I noticed that the phono stage was a bit noisy. I figured out I had a bad 6922. Bought a quad of nos Phillips 7DJ8's and all was well. Next I pick up a BAT VK-3i. It came to me with Electroharmonix 6922eh tubes installed and a quad of JJ 6922's in the box. According to the seller, the EH 6922's had about 100 hours on them. It sounded very good but I noticed that it was a bit noisy and anytime I touched the knobs or casing of the preamp, I heard it through the speakers. Just for giggles I rolled in the JJ's. The are still noisy and microphonic but they did sound better to me than the EH 6922.

So my question. When it comes to tube gear, how quiet is quiet? As I said, the Yamaha was silent. I had read that the BAT gear was very quiet. The BAT gear out performs the Yamaha amp hands down in sound quality but should I hear noise in my speakers at idle and if I should, how much? The noise is not dependent on the volume setting. With no signal present, it is about the same no matter where the volume knob is set. I know that when buying a used unit that you never know what conditions the tubes might be in. But, if I put a couple of Franklins into a new set of tubes, will it correct the problem?

Next question, Microphonics

I have read that all small tubes in a gain stage will be microphonic to some degree. How much is generally considered acceptable? Should touching the cabinet transfer into the speakers? Will replacement reduce this?

Sorry for the long post but I know that I would rather learn first and the spend accordingly.

Thanks

Tim

Originally Posted by mep

Good tubes shouldn't be microphonic or noisy. You also have a pair of 6V6 tubes in the preamp. Do you know how old they are in terms of hours of use? Kevin Deal has some good 6922 type tubes at a reasonable cost and he has some killer 6V6 tubes also.

The 6v6 are NOS JAN Sylvanias. No idea about the hours. Also have a set of Tung Sols and what appears to be the originals, black glass. I tried all three and there is not a lot of difference.

Originally Posted by Jack

If the preamp can take 7DJ8s too I would put the Phillips in it or for a mellower sound the National branded Mitsubishi's that Kevin carries. Another excellent choice is the Tungsram 7DJ8. You can get better prices on them from Tubemonger.

My understanding is that the VK-3i doesn't do well with the 7DJ8. The work very well in the phono stage. Kevin has the Tungsram 6922 and I was considering it or the 6H23 type 3. On his website, Kevin recommends the EH 6922 for the VK-3i, I would just like to try something a bit better if I am going to spend the money.

Originally Posted by Mike

Hi Tim - welcome to AS! As to your post, a lot has to do with the amplifier design, transformer, tube type and tube brand (NOS vs Chinese/Russians new).

Some tube gear is very quiet, others, not so much.

BAT gear is typically very quiet due to its balanced design. I would call Andy at Vintage Tube Services and ask his advice for tubes.




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Thanks Mike, I suspect that the noise stems from the tubes. I was just not sure how much noise might be just normal operating noise.

Well let's complicate things a bit. While listening to some records today, I noticed a crackling sound. It was the same sound that I heard when a tube went bad in the VK-P5 before. So to isolate the noise, I opened up the VK-p5 and removed the Phillips 7DJ8's that I put in about a month ago and installed the EH 6922's that I removed from the VK-3i. The crackling went away, and the EH tubes didn't seem to exhibit the microphonics that they did in the VK-3i. Hmmmm.......... with the EH 6922's and the JJ's in the VK-3i, just touching the cabinet can be heard through the speakers with the volume on. Even touching the glass of the tubes with a pencil in the P5, there is no sound transmitted to the speakers. I have three sets of the 6v6 tubes for the 3i, I have tried all 3 and there is no change in relation to the microphonics. Can a tube be microphonic in one device and not in another?

Originally Posted by Try1256

... Can a tube be microphonic in one device and not in another?

The short answer is yes it can. Tubes are biased differently in various circuits and can be utilized moderately or pushed harder towards their maximum operating range. As such they can be more sensitive to any residual noise and/or microphonics in some applications than in others.

Thanks George. So once the high voltage is bled off, what is the prescribed method for cleaning and tightening the tube sockets? Thanks again

Thanks George. Yes, I am well aware of the voltage they carry. I spoke with Victor Komenko today. I explained the symptoms to him and he seemed to think it could be oscillation. I tried everything he told be to do to try to isolate it but it persisted. I believe I may have accidently come across a possible cause. The built in phono board. I notice that when I switch to and from the internal phono, there is a pop in the speakers and when turning the volume knob, it clicked at every step. That only happened when the internal phono was selected. I decided to remove it to see what happened. Once I took it out and the preamp back in, the majority of the microphonics went away. I think one of my 6v6 tubes may be microphonic but the whole unit didn't pick up touch. The only problem was that when I removed the phono board the right channel went away. I am not sure if that was a result of removing the board thought. When I put it back in, the right side was still out. I switched the left and right outputs and it came back. I may have not seated the connector well when I put it back in. I am going to try and speak with Victor again tomorrow and see if removing the board has an adverse effect on the preamp.

Yes, when I re-installed the phono board, the microphonics came back. Victor was very helpful. I know it is difficult if not impossible to really diagnose problems with electronics over the phone. If it is ok to operate the unit without the factory installed phono board, I will probably remove it again to see if that completely solves the problem. It will be much less expensive to ship just the phono board to BAT for repair so if they will repair it, I will probably send it to them. I am glad that I got online and asked a few questions before ordering a new set of 6922's. Not that having more tubes isn't a good thing, but I would have been very frustrated had I spent the money and the problem didn't go away.

The board plugs into a connector on the main board. 2 wires plug into the input connector board on the back.

How would I proceed to identify if it is a connector or a component on the board?

Well it seems that I have found the culprit. One of the JAN Sylvanias was microphonic in a grand way. The gentleman that I purchases the unit from led me to believe that they had been replaced fairly recently but didn't say exactly when. I guess the other 2 pair I have are bad too. I replaced them with a pair of Tung Sol re-issues. No longer microphonic to touch. They really tightened up the sound a lot. Cleaner lows and a generally much better presentation. I wiil probably replace the 6922's soon as well but for now the are working well and sound good. Thanks for all of the input and guidance.