BHK 250 misbehaving


#1

Ive had the BHK 250 for six months and everything seems to be progressing nicely , I don’t think has run in as yet , it’s a little difficult to tell as I’ve been swapping out new cables and the BHK Pre arrived a couple of months back . Yesterday I turned everything on ( full hand of PS gear ) and after a minute or so there was a pop followed by some crackling and then I noticed the speaker cone in the left channel was slowly moving out in rather extended fashion as if there were dc being slowly fed to the speaker . I think I turned the pre down and then everything seem to return to normal and remained so for the rest of the day . Then the same happened again this morning . What do you think ?

Leigh


#2

Time to send that one home for a tune up.


#3

Maybe. If the preamp affects the outcome, it may be your preamp that has the problem. Try swapping output channels from the preamp to the BHK and see if the problem moves. If it does, it is likely the preamp. If it doesn’t, then yes, maybe we should look at the amp.


#4

Yikes! I guess it’s not necessarily DC. How low of a frequency will the BHK 250 pass?


#5

Ok , did as you suggested plus turn the power amp on first , then after a few minutes turned on the pre with the channels swapped on its output and yes after a few minutes the familiar pop then the crackling from the right channel and the speaker cones moving slowly out then back in . Only one cycle of movement as it were . Thanks Paul I shall get onto the man .

Regards

Leigh


#6

Yes, good you sorted that out. While no one likes their equipment going south, it’s better to know which one’s failing. And I assume it’s eazsier to move the preamp than the BHK!

As you can see, the BHK will reproduce very low frequencies, below 1Hz.


#7

Just a quick comment and maybe a question.

Fom the very beginning of owning separates, I have always understood the proper procedure is preamp on first and amp last. When shutting down, amp off first, and preamp last.

This was to protect your speakers from any transient thumps coming through to the speakers. I know the above was done while troubleshooting, but does the above policy still hold true today?


#8

It’s still good advice so it really depends on the products. With the BHK amp and preamp the routine doesn’t matter since they are both well engineered and protected.

But nothing wrong with good habits.


#9

After I logged off last night I turned amp and pre off and then on to see if it would happen again , of course no , it seems the pre has to be off overnight for the fault to show itself . It could prove to be an interesting fault to find .


#10

Power amp definitely ain’t misbehaving , it was a valve in the pre , which is a good thing , don’t have pack it and send it off and gives me an opportunity to try out a few other brands , I hear EAT are very good if you can afford them .


#11

beer_gif


#12

I’m starting to experience a popping noise in the right channel when the preamp mutes it or shuts down. At first I thought it was a bad coupling capacitor in the preamp that’s letting some DC through, but when I swapped output channels from the preamp to the amp the pop stayed in the right speaker. So it’s not the preamp.

Next thing on my troubleshooting list is to try the tubes, perhaps the Telefunken PCC88 (with iron pins) is starting to rust again? I’d cleaned them off with pin cleaner when I first put them in, but can a bad tube connection cause the popping?

I suppose I can change the tubes outright just to check, and if it still pops I’ll change speakers and see if it is the amp (pop moves to other channel) or speaker (pop remains in right channel after speaker cables swapped)

Anything else I should check?

–SSW


#13

OK, it looks like it was the tube. I had some telefunken E88CC and swapped them out this morning and the pop went away. I’ll try cleaning the pins on the old tubes (they only had 624 hours on them) and try them again, but I’m surprised I was seeing a glitch with them so soon after installing them. The problem with the PCC88 is the pins aren’t gold plated, so I may be seeing a corrosion problem even though I cleaned them with DeoxIT before I installed them.

Oh well.


#14

A festival of faulty fire bottles.