bassist_lewis Posted June 9, 2020 Share Posted June 9, 2020 Hi there BCers I just took delivery of the PF-50t today, an amp I've lusted after for years. I plugged it in and I love the sound of it, and it seems like it'll be plenty loud enough for any of my gigs. However, it's got a weird, rattle or resonance or static or interference or something when I play a C. It's very quiet, I have to listen for it. I've set the bias according to the manual, and I've plugged both the DIs into my laptop and they're absolutely silent (this implies to me that the tubes are fine but I don't know anything about electronics). Aside from big scary problems like faulty tubes, the only thing I can think of is that I was using a regular instrument cable to connect it to the cab (I've ordered a proper speakon-jack cable). Anyone more knowledgable than me know what's going on? It'll still be in warranty and I have another amp, so sending it back isn't a huge deal, but I'd rather not go through the hassle if I don't have to! Quote Link to comment Share on other sites More sharing options...
paul_5 Posted June 9, 2020 Share Posted June 9, 2020 If it’s just at one particular pitch then I’d say it was something loose that vibrates best at that frequency. Are there any loose parts on your bass or the amp? Quote Link to comment Share on other sites More sharing options...
Jus Lukin Posted June 10, 2020 Share Posted June 10, 2020 (edited) - Edited March 5, 2022 by Jus Lukin Quote Link to comment Share on other sites More sharing options...
Beer of the Bass Posted June 10, 2020 Share Posted June 10, 2020 Does it come through the speakers or is it heard acoustically from the amp? On my PF50T the phase inverter valve was microphonic, and replacing it helped considerably. You can test for microphonic valves by gently tapping them on the glass with something non conductive and listening for a ring through the speakers. On the PF50T you can do this with a wooden cocktail stick through the cage without removing anything. Quote Link to comment Share on other sites More sharing options...
bassist_lewis Posted June 10, 2020 Author Share Posted June 10, 2020 4 hours ago, Beer of the Bass said: Does it come through the speakers or is it heard acoustically from the amp? On my PF50T the phase inverter valve was microphonic, and replacing it helped considerably. You can test for microphonic valves by gently tapping them on the glass with something non conductive and listening for a ring through the speakers. On the PF50T you can do this with a wooden cocktail stick through the cage without removing anything. Its coming through the speaker. I'm waiting til the cable arrives (hopefully today) in case its anything to do with that, but I'll try that first if it continues. As I said in the OP, when DI'd there's no interference/static. Quote Link to comment Share on other sites More sharing options...
bassist_lewis Posted June 10, 2020 Author Share Posted June 10, 2020 12 hours ago, Jus Lukin said: Are there spring retainers on the power valves? I've never known those buggers not to add some mechanical 'zing' to proceedings. Otherwise, tightening every screw you can find may help, and I vaguely recall that the cage over the power valves can benefit from something to isolate it from the chassis to prevent rattles- draught strip or somesuch. can anything be done about it if it is that? I've looked and I think there's springs in the housings of the preamp valves. Quote Link to comment Share on other sites More sharing options...
bassist_lewis Posted June 11, 2020 Author Share Posted June 11, 2020 Got the new cable, made no difference. I did a bit of research into microphonic tubes and that seems to line up with the sound I'm getting. I decided to take the cage off to check. I tapped all the valves and ALL of them apart from one are microphonic! Quote Link to comment Share on other sites More sharing options...
yorks5stringer Posted June 11, 2020 Share Posted June 11, 2020 Speak to the shop you bought it from or even Ampeg? Quote Link to comment Share on other sites More sharing options...
bassist_lewis Posted June 11, 2020 Author Share Posted June 11, 2020 6 hours ago, yorks5stringer said: Speak to the shop you bought it from or even Ampeg? I'm sending it back, they're going to have a look and replace the valves Quote Link to comment Share on other sites More sharing options...
Cat Burrito Posted June 11, 2020 Share Posted June 11, 2020 Only just seen this thread. I initially had the same problem with mine when it first came out. I did a LOT of investigation and it was the valves. I have had no problems since and it's been years, so I suspect they'll sort it no worries. Quote Link to comment Share on other sites More sharing options...
bassist_lewis Posted June 12, 2020 Author Share Posted June 12, 2020 9 hours ago, Cat Burrito said: Only just seen this thread. I initially had the same problem with mine when it first came out. I did a LOT of investigation and it was the valves. I have had no problems since and it's been years, so I suspect they'll sort it no worries. I did get a little obsessed with valve shopping yesterday so part of me now just wants to buy fancy ones and replace them myself! The stock tubes are Ruby, which are apparently re-branded Shuguang valves from China. A valve savvy friend said to avoid the Chinese ones. Don't know if anyone agrees or knows better? Quote Link to comment Share on other sites More sharing options...
Beer of the Bass Posted June 12, 2020 Share Posted June 12, 2020 There are mixed opinions on the different valves available, and their performance varies between amps (some amps are more prone to microphonics than others, some have circuit designs that cause reliability issues with certain valves etc). Not all valves from the same factory are tested and screened to the same extent either. Some say the Shuguang valves are fine if you buy them from a seller who tests them. But I do feel that the stock valves with the PF50T are not great. I had my power valves replaced within a couple of weeks under warranty, and not long afterwards switched to a NOS Philips ECC82 in V3 which reduced the microphonic sounds considerably. Quote Link to comment Share on other sites More sharing options...
Jus Lukin Posted June 12, 2020 Share Posted June 12, 2020 (edited) - Edited March 5, 2022 by Jus Lukin Quote Link to comment Share on other sites More sharing options...
bassist_lewis Posted June 12, 2020 Author Share Posted June 12, 2020 1 hour ago, Jus Lukin said: Much of the cork-sniffery you will read..." don't you mean... valve-sniffery? Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted June 18, 2020 Share Posted June 18, 2020 On 12/06/2020 at 11:51, bassist_lewis said: don't you mean... valve-sniffery? I gave that up after burning my nose! 1 Quote Link to comment Share on other sites More sharing options...
afterimage Posted June 18, 2020 Share Posted June 18, 2020 On 12/06/2020 at 08:29, bassist_lewis said: I did get a little obsessed with valve shopping yesterday so part of me now just wants to buy fancy ones and replace them myself! The stock tubes are Ruby, which are apparently re-branded Shuguang valves from China. A valve savvy friend said to avoid the Chinese ones. Don't know if anyone agrees or knows better? There are lots of good valves to buy for the Ampeg buy from those who test them Quote Link to comment Share on other sites More sharing options...
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