Can I enlist a little help, crackle in valve amp

[toms wait]

I was not suggesting you check the actual voltages in the amplifier, just that you take a look inside the amplifier with no power and check the voltage rating of those capacitors which will be written on the capacitor body.

Ah I thought you meant measure it.

Have put it on tonight having put in and taken out all the left hand valves a few time and so far no crackle!
It is being taken out of the rack tomorrow for works on the rack so may well have another look based on all the suggestions above, thanks guys

 

[rabski]

With 'granny knows best' hat on. If you're not experienced with working on valve amplifiers and if you aren't sure what some of the suggestions here refer to, then I'd suggest if it still makes a noise, get it to someone experienced. Maybe whoever did the work previously.

Apart from some basic checks, any proper investigation here would involve some bench testing powered up. There are plenty of voltages in unlikely places inside there that would spoil your day very quickly.

 

[toms wait]

With 'granny knows best' hat on. If you're not experienced with working on valve amplifiers and if you aren't sure what some of the suggestions here refer to, then I'd suggest if it still makes a noise, get it to someone experienced. Maybe whoever did the work previously.

Apart from some basic checks, any proper investigation here would involve some bench testing powered up. There are plenty of voltages in unlikely places inside there that would spoil your day very quickly.

You are right of course. I know enough to recognise loose wire, duff solder joint etc but not enough to poke about with a volt meter. Cleaning out valve bases pins etc is also in my capability.

So far tonight having pulled valves in and out a couple of times, no crackle!

 

[tackleberry]

I borrowed one of these units years ago with a similar problem, eventually one of the channels went down. When I opened it up (a very busy amplifier) it turned out to be a dry joint, which took a bit of finding with T&E, as I had no test gear.

 

[toms wait]

Had a dry joint a few years ago with a similar but subtly different sound.
That time is what more intense and longer crackle almost permanent.
This time it is quieter and more intermittent.
As Juancho suggests valve bases and or pins.

 

[toms wait]

Output valves failing or dirty pins?

I tried cleaning pins/valve bases by jiggling a valve in the socket appeared to work.
More jiggling to be done.

 

[toms wait]

Dental sticks and contact cleaner, a blokes shopping list.

 

[Juancho]

You've ruled out the main driver valve as the cause by removing it and the problem remains, So I would look very closely around the pahse splitter and output valves on that side. It is almost impossible that a crackle is caused by a coupling cap, so would seem to narrow it down to the resistors. I know you changed the 100r screen resistors, so I'd check around there. The phase splitter anode resistors are massively over-specced Kiwames, so I'd be really surprised if a Kiwame had failed run well within tolerance. But that's not to say they may have bad connections /dry joint.

Finally, I had a track on a curcuit board on a 500 fail completely. The amp was restored and tested perfectly. By the time it had completed its cosseted travel by courier, and was tested, a valve glowed red as the track supplying bias had failed on the journey. It's not bias in your case but track failure is a possibility!

 

[toms wait]

You've ruled out the main driver valve as the cause by removing it and the problem remains, So I would look very closely around the pahse splitter and output valves on that side. It is almost impossible that a crackle is caused by a coupling cap, so would seem to narrow it down to the resistors. I know you changed the 100r screen resistors, so I'd check around there. The phase splitter anode resistors are massively over-specced Kiwames, so I'd be really surprised if a Kiwame had failed run well within tolerance. But that's not to say they may have bad connections /dry joint.

Finally, I had a track on a curcuit board on a 500 fail completely. The amp was restored and tested perfectly. By the time it had completed its cosseted travel by courier, and was tested, a valve glowed red as the track supplying bias had failed on the journey. It's not bias in your case but track failure is a possibility!

thanks David
OK when it is next on the bench/kitchen table I'll carefully look under all the circuit boards.
A very brief clean last night seemed to stop the crackle last night and the pins are dirty. I stuck a dental stick in one this morning and even dry it came out dirty.

Intend to get some electric joint cleaner and have a proper clean, can't harm.

Reluctant to sell/lose it because of a minor crackle.

 

[Juancho]

thanks David
OK when it is next on the bench/kitchen table I'll carefully look under all the circuit boards.
A very brief clean last night seemed to stop the crackle last night and the pins are dirty. I stuck a dental stick in one this morning and even dry it came out dirty.

Intend to get some electric joint cleaner and have a proper clean, can't harm.

Reluctant to sell/lose it because of a minor crackle.

Keep the faith! It's definitely solvable!

 

[toprepairman]

Definitely recommend getting it to someone who knows what they are doing, it'll be a lot cheaper than a funeral.

 

[toms wait]

Appears so far since last night to be cack in the valve bases.
Been busy with other stuff today but tomorrow some cack cleaning.

 

[karlsushi]

I had a similar thing with a valve buffer a little while back which after much faffing, turned out to be interference from my TPlink powerline adapters (which use the mains electricity circuit to transmit an internet signal).

Just a thought.

 

[toms wait]

This is now a slight fizzing with the occasional pop.
Completely random and only on the left channel.
It is inside the amplifier, too low level and random to be interference from anything.

 

[Juancho]

This is now a slight fizzing with the occasional pop.
Completely random and only on the left channel.
It is inside the amplifier, too low level and random to be interference from anything.

I wouldn't bank on that: I had a hard drive giving a low level crackle on one channel on a 300b amp. The ECC88 phase splitters go way up to rf so potentially could pick up something with eg a longer lead on one valve

 

[It Cost How Much!?!]

If you plan to open the amp up, make sure it's disconnected from the mains for at least an hour, those caps store a lot of energy.

 

[audio_PHIL_e]

If you plan to open the amp up, make sure it's disconnected from the mains for at least an hour, those caps store a lot of energy.

Try discharging them through a 10R resistor of high wattage, amongst other things beware of discharging to chassis ground which may not be signal ground

 

[toms wait]

I wouldn't bank on that: I had a hard drive giving a low level crackle on one channel on a 300b amp. The ECC88 phase splitters go way up to rf so potentially could pick up something with eg a longer lead on one valve

There is nothing in the room that wasn't before.
Admittedly its on the ring main so maybe I put a decent extension lead to plug into.
Actually 5 things into 2 sockets! I calculated the amps and not everything is on at the same time.

 

[audio_PHIL_e]

Try discharging them through a 10R resistor of high wattage, amongst other things beware of discharging to chassis ground which may not be signal ground

My apologies, the resistance I tried was 100R, 10W

 

[toms wait]

no fizz tonight dammit, did a brief clean of sockets but the cleaner melted the picks!
ended up using 50mm of bike brake cable, amp off 12 hrs beforehand, otherwise ooouch