Help! Sick valve amp.

[Infinitely Baffled]

Hello, all. I need some suggestions about tracing a fault in my amp.
It's an Audio Note single ended jobbie with 300B power valves. I built it myself from a kit donkey's years ago and it has served very well. Trouble is, though I built it I have no idea how it works - I just followed the instructions. Anyway, it was working fine and I took it out of my system a few months ago, since which time it has just been sitting on a shelf doing nothing. I put it back into the system today, thinking it would be nice to hear it again. But what do I find? One channel has nothing but a rustling sound coming out of it - fairly gentle, not a cone-splitting sound. It takes twenty seconds or so to become apparent after switch-on, and it does not vary with the volume pot position. I have of course swapped valves out, swapped them round and generally faffed around with the possible easy fixes, but no joy. Any ideas where I ought to start looking inside for my problem?
IB

[Jazid]

Hello, all. I need some suggestions about tracing a fault in my amp.
It's an Audio Note single ended jobbie with 300B power valves. I built it myself from a kit donkey's years ago and it has served very well. Trouble is, though I built it I have no idea how it works - I just followed the instructions. Anyway, it was working fine and I took it out of my system a few months ago, since which time it has just been sitting on a shelf doing nothing. I put it back into the system today, thinking it would be nice to hear it again. But what do I find? One channel has nothing but a rustling sound coming out of it - fairly gentle, not a cone-splitting sound. It takes twenty seconds or so to become apparent after switch-on, and it does not vary with the volume pot position. I have of course swapped valves out, swapped them round and generally faffed around with the possible easy fixes, but no joy. Any ideas where I ought to start looking inside for my problem?
IBHi, is it both channels or just one? This may help narrow the problem to PSU or signal section. Also have you swapped out the valve rectifier to make sure that is behaving properly? My instinct is dodgy solder joint, dry capacitor, that kind of thing.

Sent from my GT-I9195 using Tapatalk

[RothwellAudio]

Rustling sounds are often caused by an anode load resistor play up. However, you usually still get sound, just with added rustling.
Anyway, I'd check the DC voltages around each valve just to narrow things down a bit. Have you still got the circuit diagram?

[Infinitely Baffled]

Thanks for this. In answer to the first question, yes, it is just one channel so I interpret that as an indication that it is a signal section issue, not power supply (but please correct if the assumption is wrong).

Yes I have still got all the assembly instructions, but if I recall correctly, they were in the form of clear, but rather unscientific drawings of different parts of the overall unit, rather than a comprehensive circuit diagram that a real EE would want to see. It was definitely a hobbyist's kit. I'll dig out what I have got, but also in the meantime I'll do some current measurements. Thanks for the suggestions so far!
IB

[Ali Tait]

There should be test points detailed in the instructions, check these with a meter.

[anthonyTD]

Turn it off, wait for it to cool down, and pull each valve out of its holder one by one, and push them in and out of their socket a few times, if it was working when you last used it, it may just be slight contamination on the valve pins, try this first, it often works. also, sometimes if this happens after the amp has been on a while, the valve pins in the sockets may have lost their tightness agains the valve pins, and if the valve socket pin expands more than the valve pin, it can make an intermittent connection, and cause the noise your experiencing.
Hope this helps.
A...

[Infinitely Baffled]

Hurrah for De-Oxit!
It looks like the problem must have been crusty valve pins. I now have both channels back nice and clear. This is a good thing because otherwise the job looks like it would very quickly have got beyond me. I took some measurements from the innards of the amplifier. Referring to the build instructions, there is a section on tests to carry out once you have completed the construction, and before using it. These tests are to be done without the valves in place and consist of a number of voltage measurements - some AC and some DC - between various points within the works. I fared reasonably well on these - the amp measuring up to spec in all cases except one, which we won't go into here given the happy outcome. Then, in the back page of the build booklet, there was as Ali suggested a list of check points with prescribed values. These were all expressed in terms of DC with respect to ground. I tried them all and didn't get a single millivolt's worth of reading out of my meter. Mind you, I had not put the valves back in to do these tests. The checklist did not say whether it was meant to be valves-in or valves-out, and frankly I am not keen on fiddling around up an amplifier's bottom with valves in, current running and only a pair of Marigolds between me and eternity. Don't know why, but it struck me as a far riskier thing to do than the valve-out tests. Can anyone tell me, should those tests have been conducted with the valves in? Because if not, I appear to have built the first amplifier that runs on fresh air.

Anyway, many thanks to all. This was a great example of AoS community spirit and helped me a lot. Cheers.
IB

[Firebottle]

If you run into problems in the future that you can't overcome I'd be happy to look at it for you.

:)

[Infinitely Baffled]

Thanks, Alan. I already had you in mind if this turned nasty. Would be nice to catch up.
Cheers
Gary

[sumday]

I had a similar problem a few weeks back with my Little Dot valve preamp.
A low motor boating on just the left channel. I tried swapping over the tubes, speaker leads, phone leads and even took it out of curcuit
Tried replacing my better tubes with the supplied junky Chinese tubes and still the chugging noise stayed.

Then, in a moment of ahem...clear lucidity....I remembered i'd recently moved my virgin modem closer to my kit to tidy the frkkin rats nest of Ethernet cables behind.......

Moved it away and all was well.......I used ALL my extensive library of swear words before the night was over.

I'm still puzzled by the sound being on only one channel though.

[Haselsh1]

Turn it off, wait for it to cool down, and pull each valve out of its holder one by one, and push them in and out of their socket a few times, if it was working when you last used it, it may just be slight contamination on the valve pins, try this first, it often works. also, sometimes if this happens after the amp has been on a while, the valve pins in the sockets may have lost their tightness agains the valve pins, and if the valve socket pin expands more than the valve pin, it can make an intermittent connection, and cause the noise your experiencing.
Hope this helps.
A...

Yeah, I have had my Prima Luna combo for about a year now and around a month ago I had to do just that because of a rustling sound from the speakers. Pull them out, put them back and all is well.

[Lawrence001]

Happened to my with my little dot, turned out one of the pin clamps in the valve socket was loose and not making proper contact. (This also caused a crackling noise when I gently swayed the valve and the pin made contact, which helped me identify which socket.) I solved this by examining the socket and identifying the loose clamp, and forcing the clamps back together by pushing a needle between the clamp and the ceramic.

Sent from my NEM-L51 using Tapatalk

[RothwellAudio]

Then, in the back page of the build booklet, there was as Ali suggested a list of check points with prescribed values.
Er... I think I suggested you do that in post #3
Perhaps I was assuming too much prior knowledge, sorry.

These were all expressed in terms of DC with respect to ground. I tried them all and didn't get a single millivolt's worth of reading out of my meter. Mind you, I had not put the valves back in to do these tests. The checklist did not say whether it was meant to be valves-in or valves-out, and frankly I am not keen on fiddling around up an amplifier's bottom with valves in, current running and only a pair of Marigolds between me and eternity. Don't know why, but it struck me as a far riskier thing to do than the valve-out tests. Can anyone tell me, should those tests have been conducted with the valves in? Because if not, I appear to have built the first amplifier that runs on fresh air.
Yes, the tests should be done with the valves in. Current flows from the HT through the anode load resistor, through the valve and through the cathode resistor (though the electrons actually flow the opposite way). The current causes voltage drops across the resistors and they're what you measure. However, without the valve in place there can be no current flow and therefore no voltages to measure.

[Infinitely Baffled]

Er... I think I suggested you do that in post #3
Perhaps I was assuming too much prior knowledge, sorry.
Indeed you did, Andrew. My apologies.
And yes, assuming any prior knowledge is assuming too much. Kits should not be sold to people like me!
(Though, having said that, I got absolutely addicted to the making of it, getting up at stupid hours in the morning to get in my soldering "fix" before going to work.)
IB

[forsell]

Indeed you did, Andrew. My apologies.
And yes, assuming any prior knowledge is assuming too much. Kits should not be sold to people like me!
(Though, having said that, I got absolutely addicted to the making of it, getting up at stupid hours in the morning to get in my soldering "fix" before going to work.)
IB

Kit seller should provide a good overall instruction how to build up a kit incl. detailed instruction how to test it. If this is not the case -going by your info posted here there was a second test to be done but not clearly specified whether WITH or WITHOUT valves plugged in- then the kit seller is to blame for it. IMO.

[anthonyTD]

Glad to hear it was as simple as that.:)
A...
Hurrah for De-Oxit!
It looks like the problem must have been crusty valve pins. I now have both channels back nice and clear. This is a good thing because otherwise the job looks like it would very quickly have got beyond me. I took some measurements from the innards of the amplifier. Referring to the build instructions, there is a section on tests to carry out once you have completed the construction, and before using it. These tests are to be done without the valves in place and consist of a number of voltage measurements - some AC and some DC - between various points within the works. I fared reasonably well on these - the amp measuring up to spec in all cases except one, which we won't go into here given the happy outcome. Then, in the back page of the build booklet, there was as Ali suggested a list of check points with prescribed values. These were all expressed in terms of DC with respect to ground. I tried them all and didn't get a single millivolt's worth of reading out of my meter. Mind you, I had not put the valves back in to do these tests. The checklist did not say whether it was meant to be valves-in or valves-out, and frankly I am not keen on fiddling around up an amplifier's bottom with valves in, current running and only a pair of Marigolds between me and eternity. Don't know why, but it struck me as a far riskier thing to do than the valve-out tests. Can anyone tell me, should those tests have been conducted with the valves in? Because if not, I appear to have built the first amplifier that runs on fresh air.

Anyway, many thanks to all. This was a great example of AoS community spirit and helped me a lot. Cheers.
IB

[Infinitely Baffled]

Kit seller should provide a good overall instruction how to build up a kit incl. detailed instruction how to test it. If this is not the case -going by your info posted here there was a second test to be done but not clearly specified whether WITH or WITHOUT valves plugged in- then the kit seller is to blame for it. IMO.

My kit was bought a very long time ago - 2002, I think - when Audio Note kits came from PQ in Brighton. The whole Audio Note kit operation has been divested since then and is now run under the ANK banner by a very helpful chap in Canada or the US (can't remember which). I think the whole presentation of the kits: the promotional material, the instructions (now including a supporting DVD I think), the support etc. has been massively enhanced and is of a very high standard. Mind you, in fairness to the old Brighton operation, they can't have been doing too much wrong if they can get complete tyros like me through the build process, with a very nice amp at the end that has worked well for years.

Many thanks to all for the help with this.
IB