Phil-osopher10 Posted December 16, 2012 Share Posted December 16, 2012 So I recently got a blackstar HT 40 club secondhand. I asked the fella to demo it for me and it seemed grand. I bought it and brought it home, admittedly over some bumpy country roads at 60mph. It seems to have developed a fault where if I play and go to the bassier strings it starts to hum like feedback but it doesn't stop until I put it on standby. Is it loose valves? Or a more sinister problem? If it is loose valves what precautions should I take putting them in? Valve amp noob. Quote Link to comment Share on other sites More sharing options...
3below Posted December 16, 2012 Share Posted December 16, 2012 Easy check for loose valves - switch off (elf n safety), open cage or whatever that covers valves, gently wiggle them back in. See what happens. After that the next stages depend on how the Blackstar is constructed and your ability to work safely with valve amps, discharging smoothing capacitors prior to working inside chassis (or knowing whether it has bleed resistor) . If you are not ok with that stage do not attempt next bit. If it is pcb with modern push connectors, one of these may have worked loose. Check they are seated correctly. If it is point to point or similar check for any wires that have detached, if found re-solder. After these simple checks the going gets tougher, test equipment and ideally circuit diagram with test voltages needed (or a good valve amp tech). Quote Link to comment Share on other sites More sharing options...
Phil-osopher10 Posted December 16, 2012 Author Share Posted December 16, 2012 Thanks, I'll get on that to see if it helps. Quote Link to comment Share on other sites More sharing options...
3below Posted December 16, 2012 Share Posted December 16, 2012 (edited) Just some more thoughts, check the speaker wires, has one become detached? check speaker mounting bolts/screws are tight, is speaker baffle board firmly in (if bolted rather than glued), is the speaker cloth frame (again depends on construction) firmly in place. Another possibility is a valve has gone faulty due to the rough trip. To follow this up you will need a spare known to be good ECC83, and EL34. Replace each pre amp ECC83 in turn with the good one. Then do same with output EL34s in turn. This will show if it is a faulty valve. After this it is as above, [color=#282828][font=helvetica, arial, sans-serif]test equipment and ideally a circuit diagram with test voltages (or a good valve amp tech).[/font][/color] [color=#282828][font=helvetica, arial, sans-serif]Looks a nice amp, hope it is a simple fix.[/font][/color] Edited December 16, 2012 by 3below Quote Link to comment Share on other sites More sharing options...
Phil-osopher10 Posted December 17, 2012 Author Share Posted December 17, 2012 So I took your advice, back panel off and check for loose valves. everything seems tight enough. I then plug it is with the back panel off and strum enough to induce the hum, then I touch the valves to see if there are any changes.... how dangerous this was I do not know. turns out it stops when I touch one of the valves ie wiggle it. So I'm not sure if the valve is bad or the socket thing you put the valve in is. It is a larger valve and thus I assume a power amp valve. El34 I assume? Next question where is the best place to get one and how do I change it? Quote Link to comment Share on other sites More sharing options...
ezbass Posted December 17, 2012 Share Posted December 17, 2012 I had a problem like this many years ago. It appeared to be a resonance associated with a slightly loose valve seating. I seem to remember that I slipped a wooden shim next to the valve to stop the induced vibration. Probably not an 'approved' fix, in fact a bodge, but it worked fine afterwards. Quote Link to comment Share on other sites More sharing options...
3below Posted December 17, 2012 Share Posted December 17, 2012 Could be the socket, could be the valve. Swap the two EL34 valves around. If the problem goes away it was possibly a poor contact in the valve socket. Swap them back. If the problem stays with one valve, it is the valve. Sometimes just taking the valve out and in a few times can clean the contacts and rectify the problem. If it is the valve, you will need to buy a pair and are then into a whole minefield of choice. I have found JJ to be good and a fair price. Quote Link to comment Share on other sites More sharing options...
Beer of the Bass Posted December 17, 2012 Share Posted December 17, 2012 If the socket is not holding the pins tightly, you can try re-tensioning the contacts. This link has about the clearest description of the process I can find. [url="http://swartamps.com/tech/socket_retention/"]http://swartamps.com/tech/socket_retention/[/url] I would add a caveat that if you don't know how to discharge the filter capacitors, don't go poking at the valve sockets with any conductive tool, even with the amp turned off. It may still be possible to get a shock from some of the pins on the valve sockets with the amp turned off. Quote Link to comment Share on other sites More sharing options...
BigRedX Posted December 18, 2012 Share Posted December 18, 2012 Could be that one or more of the valves has gone microphonic. If taping any of the valves while the amp is running causes the unwanted noise to come and go, I'd be looking at replacing the valves in question. Quote Link to comment Share on other sites More sharing options...
Big_Stu Posted December 18, 2012 Share Posted December 18, 2012 [quote name='3below' timestamp='1355777264' post='1902699']If it is the valve, you will need to buy a pair and are then into a whole minefield of choice. I have found JJ to be good and a fair price.[/quote] It's reported elsewhere on this forum that recent JJs have been a bit hit or miss on QC. I've asked Watford valves about it & while not commenting they've now pointed me at Gold(en??) Lion valves rather than JJs; both of which they stock. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted December 18, 2012 Share Posted December 18, 2012 Can you tell if the valve socket is bolted to the chassis or just to the circuit board? Might be a resoldering to the board if its that. Quote Link to comment Share on other sites More sharing options...
3below Posted December 19, 2012 Share Posted December 19, 2012 (edited) A good point by Mr Foxen. As mentioned above if any DIY internal surgery, work safely, discharge those smoothing (filter) capacitors (and check with DMM even if the amp has bleed resistors). Life is a one time trial not a practice run, we do not get a second go. Edited December 19, 2012 by 3below Quote Link to comment Share on other sites More sharing options...
Phil-osopher10 Posted December 19, 2012 Author Share Posted December 19, 2012 I think changing valves are my limit at the moment, where can I learn about discharging capacitors etc? Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted December 19, 2012 Share Posted December 19, 2012 Caps will discharge slowly through a multimeter testing them, but a couple of crocodile clips and a resistor is what I use. I heatshrunk the resistor so totally can't tell you what value I used. Basically you connect the positive end to earth via a resistor so the charge leaves it slowly, rather than sparking. I've discharges very big 1000uf 450v caps into my arm once, its educational rather than life threatening, unless you have a weak heart or something, pretty uncomfortable. Quote Link to comment Share on other sites More sharing options...
3below Posted December 19, 2012 Share Posted December 19, 2012 [quote name='Mr. Foxen' timestamp='1355881065' post='1904068'] I've discharges very big 1000uf 450v caps into my arm once, its educational rather than life threatening, unless you have a weak heart or something, pretty uncomfortable. [/quote] I have as well, gave me quite a a shock in all senses. Once done never repeated. Quote Link to comment Share on other sites More sharing options...
Phil-osopher10 Posted December 20, 2012 Author Share Posted December 20, 2012 Hmmm.. I think i'll try changing the valves first! Is that easy done? how do you line it up so the pins go in the correct hole? Quote Link to comment Share on other sites More sharing options...
umph Posted December 21, 2012 Share Posted December 21, 2012 [quote name='Phil-osopher10' timestamp='1355677471' post='1901254'] So I recently got a blackstar HT 40 club secondhand. I asked the fella to demo it for me and it seemed grand. I bought it and brought it home, admittedly over some bumpy country roads at 60mph. It seems to have developed a fault where if I play and go to the bassier strings it starts to hum like feedback but it doesn't stop until I put it on standby. Is it loose valves? Or a more sinister problem? If it is loose valves what precautions should I take putting them in? Valve amp noob. [/quote] Hi you have a microphonic valve, let it start to squeel and pull valves out starting from the front end until it stops, then replace the last valve you pulled out Quote Link to comment Share on other sites More sharing options...
umph Posted December 21, 2012 Share Posted December 21, 2012 [quote name='Mr. Foxen' timestamp='1355881065' post='1904068'] Caps will discharge slowly through a multimeter testing them, but a couple of crocodile clips and a resistor is what I use. I heatshrunk the resistor so totally can't tell you what value I used. Basically you connect the positive end to earth via a resistor so the charge leaves it slowly, rather than sparking. I've discharges very big 1000uf 450v caps into my arm once, its educational rather than life threatening, unless you have a weak heart or something, pretty uncomfortable. [/quote] I use a 1k It's safe enough ;p Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted December 21, 2012 Share Posted December 21, 2012 (edited) 2.2K 10W wirewound for me, only cos its physically bigger, so easier/safer to hold. Before using the resistor, I run the amp with something loud, playing through it - not a guitar or bass, that could leave you earthed, try an Ipod. Then pull the mains plug, the valves will still run for a while, discharging most of whats in the caps, less of a 'flash' that way. & after the resistor, short the HT rail to chassis with a screwdriver blade to make sure. Then do it again after a few minutes or so if your still working on it, sometimes, a bit of it comes back ! Microphonic valves usually show up if you turn the amp up with no input,and then tap them with a screwdriver handle. Dodgy bases usually show up if you put a finger on the pip at the top and wobble the valve. Edited December 21, 2012 by BILL POSTERS Quote Link to comment Share on other sites More sharing options...
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