WD88VA noise

[Riggers]

HI John
Problem sorted. I firstly removed and fitted the smaller signal valves a few times and even swapped sides with them but the problem recurred after about 50 mins. This time I pulled in/out a few times the small valves AND the KT88's and swapped the latter from left to right.
Result, 1and 1/2 hours of beautiful music and no noises whatsoever.
Reminds me of a similar problem I had many years ago with a computer game console that had a cartridge that fitted into a memory expansion socket, and I would sometimes have to do the pull in/out thing a few times so that a good contact was made and the computer could read the cart. Must be the high humidity we live with in Brisbane.
Anyway, many thanks again John.
Cheers
Phil.

[John Caswell]

Hi Phil,
Thats good news. It might be worth wiping the valve pins with contact cleaner, Electrolube or the like - not too much of course, its conductive - and then repeating the inserting to transfer some to the sockets, just to try to keep corrosion at bay.
It is noticeable that since we have gone over to a lead free environment this problem seems to have got worse especially with battery terminals.

John

[Riggers]

Hi John and all
I (regrettably) still suffer from the intermittent rustling noise every now and then. Sometimes after only 20 mins operation and sometimes after a couple of hours. Until such time as the noise starts the amp is performing faultlessly (ie. no hiss etc beautiful sound). It's just this one little niggle which is so frustrating as the amp definitely works very well otherwise. I find (in response to John's suggestion to remove and refit and even swap sides with the input and driver valves) that switching off the unit and refitting valves helps, and I have cleaned the pins too. But the problem is only ever on the right channel, and (surely) has to be a soldering fault with one of the joints (I'm just buggered if I can identify the offender).

As a matter of interest, I rechecked all voltages and the one level that is over spec is the anode on the U1, which measures 214 volts DC compared to the specified 185 volts +-10%. Do you think this is of any consequence?
Cheers Phil.

[John Caswell]

Hi Phil,
Hmmm! Well it may be worth examining/changing the components associated with this section of the valve namely R1 (220K) R4(1.5M) and R5 (1M). Possibly R2 but I doubt it.
Substitution is best if you have the bits, and I know to my cost these thingss can be very tricky to find.

John

[Riggers]

Hi John,
Just to check, your suggestion to replace R1, R4 and R5 is in relation to the noise problem I'm having or the anode reading I get on U1 of 214V. Just checking whether the anode reading is an issue in your eyes.
Cheers
Phil.

[John Caswell]

Hi Phil
It could relate to both if the resistor is noisy/changed value, or the following R4 & R5 have done the same.

John

[Riggers]

Hi John
I've replaced said resistors but the values at the U1 anode remains 213ish volts and the rustling noise (right channel) after a few hours reappears. I am convinced that my problem is a soldering issue, namely some stray resin from the resin core solder which has made a bridge that I can't easily see but obviously starts to conduct as things heat up inside. My next move is to inspect the underside of the right side driver board, recheck the soldering of the big caps (C9 and C9a) and pay attention to cleaning any resin residue.
BTW my mains voltage is always above 240V, the reading tonight 243V. I am sure the mains Tx is wired correctly and I wonder if the higher than 240V mains input has some bearing on the U1 anode voltage figure I get.

I'll let you know how I get on.
Cheers
Phil.

[bob orbell]

Hi Riggers, can't help with the noise problem, but I run the same amp, and my voltage is very close to the max. of 253, it never drops below 248 and I have no problems at all, so your voltage is not a problem, for what it would cost, I would replace the bad side board and all components on it. BOB

[bikerhifinut]

Forgive me if its already been covered.
Have you tried unplugging the 5687 and ecc83 when the rustle appears? (switching off the amp first of course, ahem). If it rustles then the noise is on the output valve circuitry, then likewise replace the 5687 and listen, and finally the ecc83.
just a thought and apologies if that tack has been taken.

Would trying to trace the signal with a scope probe be any use to pinpoint the source of the noise?

Andy,

[Riggers]

Hi Andy
I take it you mean switching off amp and unplugging ecc83 and 5687 from offending side and turning back on without valves in place? Is this ok for a short period? I find that when the rustling starts and I switch off amp and remove and replace the 5687 and switch on again the noise is not there (at least for the moment). The theory of poor contact between 5687 and valve base has been explored but I have swapped these valves from one side to the other, cleaned valve pins and even replaced the socket on the right side with one that has gold plated contacts and the problem still reappears sooner or later. That's why I think the problem is elsewhere (perhaps a bridge of resin or some other poorly soldered joint).
BTW I don't have a scope probe. The amp sounds great until this rustle appears so I feel I must be on the right track, its just I have one "dripping tap".