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Thread: Help! Sick valve amp.

  1. #11
    Join Date: Dec 2008

    Location: East Riding of Yorkshire these days

    Posts: 4,779
    I'm Shaun.

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    Quote Originally Posted by anthonyTD View Post
    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.

  2. #12
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 6,869
    I'm Lawrence.

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    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

  3. #13
    RothwellAudio Guest

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    Quote Originally Posted by Infinitely Baffled View Post
    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.
    Quote Originally Posted by Infinitely Baffled View Post
    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.

  4. #14
    Join Date: Jul 2016

    Location: Welsh Borders

    Posts: 283
    I'm Gary.

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    Quote Originally Posted by RothwellAudio View Post
    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

  5. #15
    Join Date: Mar 2015

    Location: Berlin

    Posts: 50
    I'm George.

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    Quote Originally Posted by Infinitely Baffled View Post
    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.

  6. #16
    Join Date: Feb 2008

    Location: South Wales

    Posts: 9,151
    I'm NotTakingLifeTooSeriouslyTheseDays.

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    Glad to hear it was as simple as that.
    A...
    Quote Originally Posted by Infinitely Baffled View Post
    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
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
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  7. #17
    Join Date: Jul 2016

    Location: Welsh Borders

    Posts: 283
    I'm Gary.

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    Quote Originally Posted by forsell View Post
    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

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