This topic contains 10 replies, has 2 voices, and was last updated by Hyllej 1 year, 3 months ago.
April 4, 2018 at 2:24 pm #3197
I recently purchased the Percolator kit and when it came time to test, I get no sound. More specifically, I get an audible scratch when I turn the volume knob and that’s it. Upon reviewing the test points, I discovered everything within range, except TP9 was about 43Vdc and TP7 was at 0!! I have tried going back over the tube pins, and making sure they have a tight fit. The tube lights up but it has a rattle in it. Any suggestions?April 4, 2018 at 3:47 pm #3199
Make sure that the feedback wire is connected to the correct lug of the output jack. If it’s connected to the ground lug instead of the positive lug of the output jack then it would exhibit symptoms like those. Let me know what you find.
-BrachApril 4, 2018 at 6:27 pm #3201
The FBL is on the correct lug, I ended up removing the PCB and discovered solder has bridged a cap which I repaired. After reassembling the chassis, all the DC readings are spot on, and I’m now able to get some feedback when I install an input cable. However I still can’t get sound from an instrument; and when I unplug the speaker, I get a high pitched very audible buzzing from the chassis.April 4, 2018 at 9:40 pm #3202
Let me elaborate a little more: the amp is quiet up until 1/2 volume, then the buzz starts and gets louder and higher pitched as you increase towards full volume. And again, this is WITHOUT the speaker being plugged in. When the speaker IS plugged in there is slight hum which I expect, and when I make contact with an installed instrument CABLE I get the feedback I would expect, but plugging in an instrument itself produces no sound nor hum.April 5, 2018 at 10:54 am #3207
The fact that all the tube voltages are correct is a good sign that the tube circuitry is functioning properly. The first thing to do is to tighten the tube socket. To do this you just need to get some sort of sharp, pointy tool and gently pry the tube socket contacts closer together to help them grip the tube pins better. Sometimes they get spread a little to far apart in the “loosening the tube socket” step, and they don’t make good contact with the tube pins.
If this doesn’t work then you probably need to re-flow (re-solder) the solder joints again. I know it’s a pain, but the fact that you had one bad solder joint is a sign that other’s could be bad as well. At first, just re-flow the resistors from the top (component side) of the board so you don’t have to take out the PCB. If that doesn’t work then you’ll have to take out the board and check really closely for solder bridges (shorts) and re-flow the capacitors and other components that you weren’t able to get to from the top of the board.
You really shouldn’t turn on your amp without a load (speaker) attached. It’s really bad for the tube. So make sure the speaker is plugged in when you test it. It’s not uncommon for properly working tube amps to behave like that when they don’t have the speaker plugged in…so i’m not worried about the buzzing with no load. The problem is that the signal is not making it through somehow. We’ll get it sorted out one way or another.
-BrachApril 5, 2018 at 6:48 pm #3211
I reflowed solder over the resistors and that appeared to do the trick. I now get hum from the speaker. Now unfortunately when I plug my guitar in, I get sound but it’s near inaudible, so something is underpowered? Where can I measure to pinpoint whatever is bottlenecking? Thank you for being so helpful, I’m super excited to get this thing running! I feel we’re close!April 6, 2018 at 7:12 am #3213
The fact that re-flowing the resistors from the top side changed something, tells me that you had another bad solder joint somewhere. Since your Percolator still isn’t working properly it makes me think that there is another bad solder joint somewhere. You may be at the point of taking the board out of the chassis again and reflowing all the joints and double checking for solder bridges (shorts).
Have you tightened the tube socket yet? If so, did you tighten the socket and re-flow the solder joints in the same step, or did you test the amp between each of those steps? I’m just wondering if it might have been fixed when you tightened the tube socket, but you didn’t notice it. If that might have been the issue or part of it then gently re-tighten the socket again…if that works it will keep you from having to remove the board from the chassis. When tightening the sockets focus on pins 3, 6, and 11 (next to R1, R6, and R11)…these are the grid pins. The “grid” is where the signal comes into the tube stage. If you have correct voltages on the other pins then it’s most likely that the signal is not making good connection to one of these pins…if it’s the tube socket at all.
I don’t know if you have one, but it really helps to get one of those solder sucker tools to remove the solder from the holes after you remove the wires. They are very helpful in putting the board back after you remove it and removing excess solder from around the pads if you have any big solder globs anywhere.
We are really close. Keep persevering!
Good luck and keep in touch.
-BrachApril 6, 2018 at 1:33 pm #3216
So I removed the pcb and reflowed every lead. All the caps are separated so no bridges. I reinstalled everything and it’s definitely louder but still super quiet on full volume and no tube break up. I have tried numerous times to retighten the tube socket but I can of course keep trying. Like I mentioned previously, I noticed a rattle in the tube but not sure if that means anything. Thanks again for all the help!April 7, 2018 at 4:16 pm #3223
The good thing is, the amp works…it’s got the correct voltages in the correct spots. The problem is some of the signal isn’t making it through somehow to the output. If I understand you correctly, every time you re-flow/re-solder some stuff on the board the amp gets louder. To me, that’s a sign that there’s some sort of connection issue…most likely it’s something that’s not making a good connection somewhere (as opposed to a short)….only letting a bit of the signal through. If you are at all un-confident about the solder joints then please check them again…look very closely at each joint. I know it’s a pain, but that seems to be what all signs are pointing toward.
Just checking, you are using an 8 ohm speaker, correct?
If all the tube voltages are correct then the tube is working correctly. Besides that, we test every tube before we send it out, so there’s very little chance that it’s a tube problem. Vacuum tubes contain a bunch of tiny parts, very close together, so often times they do rattle when they are shaken vigorously…unless you are talking about loose parts in the tube, but if that’s the case then it most likely wouldn’t have the correct voltages on the tube pins because something wouldn’t be making a connection in the tube.
Thanks for verifying that you tightened the tube socket pins. If you are pretty sure all the tube pins are making good connection then you don’t have to keep trying to tighten them. I just know in the past these symptoms have been caused by that.
You’ve probably already done this, but I wouldn’t hurt to double check the values of resistors in the signal path to make sure they are correct.
Please keep me posted with how things are going.
-BrachMay 16, 2018 at 1:46 pm #3608
I apologize for taking so long to get back on this. I have not had the time to look at the amp since last month, but I have recently purchased a desoldering pump and a more precision soldering iron. I have reflowed so many times, it wouldn’t surprise me if that was the issue. I think the best place to start is to re-do the soldering points. I will do that over this weekend and let you know the results!May 17, 2018 at 9:22 pm #3623
Got it working! Removed all the solder from the tube pins and reflowed them. Seemed to do the trick!
Thanks for all the help, can’t wait to wrap her in some purple tolex!