Popping sound question

mlundy57 · « **on:** 8 Jul 2017, 11:57 pm »

My PrimaLuna Prologue 4 has started emitting a intermittent popping/crackling sound. The sound first occurs about 30 seconds after turning the amp on even if nothing else is powered up. It then continues to occur at different frequencies with no particular pattern. Again, the power amp is the only piece of equipment powered on. During playback the sound is louder and more frequent then if just the power amp is on.

The sound first started after I accidentally left the amp turned on for two days earlier this week.

Any thoughts/ideas?

Thanks

Mike

thorman · « **Reply #1 on:** 9 Jul 2017, 12:43 am »

It may be time to re-tube.........That would be my first thing to look at....Tubes tend to do that when they are on there way out.

JackD · « **Reply #2 on:** 9 Jul 2017, 01:10 am »

Mike

I agree it is tube related and more than likely the AU7's or AX7's. Is the noise from just one side or both. It would be odd for both to just go at once. If it is just one side try one at a time swapping the AU's and AX's from one side to the other to see if you can find out which tube, but if it is the small signal input or driver tubes you need to replace the pair.

JakeJ · « **Reply #3 on:** 9 Jul 2017, 02:03 am »

I agree with thorman and JackD. Most likely a tube(s) and the small signal tubes are usually the ones to do that.

mlundy57 · « **Reply #4 on:** 9 Jul 2017, 04:06 am »

Ok thanks

Ouch!!! I don't have more than 250 hours on these tubes and they cost more than the amp. The 12AX7s are Telefunkin smooth plates and the 12AU7s are CIFTEs.

The sound can come from either channel but is more often from the right. It seems to be less frequent than last night. I just finished listening to the first side of Eric Clapton Unplugged and nary a pop from either channel.

Mike

JackD · « **Reply #5 on:** 9 Jul 2017, 04:27 am »

Mike

I had a pair of "high priced" Hytron 6SN7's that did the same thing in the Mystere(PrimaLuna) amp. It was random as to when, how long and how loud it was but in the end it was one tube and was easily corrected though not cheap. Chances are it is the inside pair if they are the designated input tubes as was the case on the Mystere. In my case all four were 6SN7's so I could move the offending tube to the outside (driver) position and it was less of a problem. Eventually I just put them up and moved on. If you have the Chinese PL tubes on hand put them back in one tube at a time in the front positions until it goes away. Put the remaining good pair in the more important position and look for a replacement for the "bad" tube.

mlundy57 · « **Reply #6 on:** 9 Jul 2017, 04:59 am »

I'm not sure which tube does what between the 12AX7 and rhe 12AU7. Each channel has a 12AX7 in the center of the amp. The 12AU7s are to the outside and slightly behind the AX7s. The EL34 power tubes (2 per channel) form a row across the back.

I do have the stock tubes so it looks like some experimentation is in my future.

Murphy dictates it will be the AX7s since those are the most expensive and a matched pair no less.

Thanks

Mike

JackD · « **Reply #7 on:** 9 Jul 2017, 05:13 am »

Mike

According to the manual the AX7's determine gain so I would guess they are the driver tubes. If that is the case it may not affect the sound as much as you think but will affect the bottom line. The only way to find the problem is one tube at a time so it may take a couple of hours. Good luck!

JakeJ · « **Reply #8 on:** 9 Jul 2017, 05:14 am »

Mike,

I'm guessing you don't have a tube tester? Do you have access to one or someone that has one and will test them for you? If the answer is no then I would be willing to test them on my TV7 D/U tester for the cost of shipping only. I can test for shorts, microphonics, the % good, and longevity. I live in ZIP 99352 so go to USPS.com and calculate the round trip cost. I would recommend using Priority Mail.

One hting I forgot to ask is the popping in both channels or just one?

Or maybe there is another member closer?

Jake

Added - Run your experiments first as it will likely find the culprit and negate my offer.

rotarius · « **Reply #9 on:** 9 Jul 2017, 03:08 pm »

Hello, I used to have this amp. The 12ax7s are the ones that provide input gain and affect the sound the most. The 12au7 are the phase splitters and you really don't need any exotic ones in that spot, the stock ones are perfectly fine. You might want to remove all the NOS tubes and clean the pins with super fine grade steel wool, oxidized/dirty pins can cause noises, although that is usually a crackling type of sound but worth a shot.

mlundy57 · « **Reply #10 on:** 9 Jul 2017, 04:32 pm »

Is Deoxit good to use on pins and socets?

Mike

rotarius · « **Reply #11 on:** 9 Jul 2017, 04:54 pm »

I have been using deoxit for years without issues. Most really old tubes need a bit of abrasive action to get them back to the steel color and after that you can maintain them with periodic deoxit cleaning. If the pins have plating (new production), deoxit only. When selling tubes, I have been asked a few times how I got the pins to clean up so good. It's the 0000 steel wool

mlundy57 · « **Reply #12 on:** 9 Jul 2017, 05:04 pm »

Thanks all. During the upcoming week I'll start by cleaning the pins and sockets first. If that doesn't fix things I'll start swapping out tubes.

As a point of interest, the last 2-3 hours I had the system on last night it didn't make any popping or crackling sounds.

Mike

raindance · « **Reply #13 on:** 18 Jul 2017, 01:55 pm »

Try the original small signal tubes first.

Also run the amp in the dark and see if there is any arcing in the power tubes. Typically you would see a momentary blue spark or flash when the sound occurs. If it is affecting both channels this is the more likely culprit as any tube arcing will introduce noise on the power supply.

At certain times of year, the mains voltage runs quite high and I've seen this issue occur due to that. The only fix is to replace the arcing tube.

mlundy57 · « **Reply #14 on:** 18 Jul 2017, 05:02 pm »

Thanks all. I just noticed a different but likely related issue. The right channel is not as loud as the left. Enough so that the center image is no longer centered. It is off to the left and no amount of toe-in adjustment can bring it to center short of pointing the speaker almost 60 degrees to the Left, almost pointing at the wall.

Mike

rotarius · « **Reply #15 on:** 18 Jul 2017, 05:13 pm »

Swap out the power tubes between the channels to see if the problem follows. If not, try the small tube swap next. With the Primaluna autobias, it's hard to tell if one of your tubes is not biasing up properly.

raindance · « **Reply #16 on:** 18 Jul 2017, 05:38 pm »

Sounds definitely like you have a blown output tube that has arced over. With the amp running, feel each tube carefully - one will likely not be getting very hot. It will be your culprit.

Keithh · « **Reply #17 on:** 18 Jul 2017, 11:27 pm »

Have had no problems with my Prologue 5, but my previous amp did the same thing.
Started popping and then lost some volume from one channel. It was a power tube.

I will disagree with the one post saying the 12AU7 doesn't matter. It makes a huge
difference with my Prologue 5, with the Cifte 12AU7 being absolutely incredible with
the Wedgies. Also using a Mullard 12AX7 but it was so close to the Telefunken as not
to prefer one over the other.

mlundy57 · « **Reply #18 on:** 18 Jul 2017, 11:59 pm »

That would be my luck. I had a power tube go out a few months back and it blew the plate fuse. I replaced the fuse and got another matched quad of Svetlana Winged C EL34s. I replaced all four tubes, not just the bad one. These don't even have 100 hours on them.

On the bright side I do have three left from the other quad.

Is it just bad tube luck or might there be something wrong with the amp?

Mike

rotarius · « **Reply #19 on:** 19 Jul 2017, 12:10 am »

Where are you getting these tubes from? Top quality Winged C stock has been depleted.