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Let’s get this fixed…
According to your voltage chart (by-the-way, thanks for that…it’s very helpful) R8 only has 1 volt dropped across it, which tells me that there is very little current flowing into pin 4, which is why TP7 only has 32mV across it. The problem seems to be with either pin 4 or 7 on the tube. The fact that you are getting no sound at all leads me to think there is an open somewhere in your circuit (probably at pin 4 on the tube). Resolder pins 4 and 7 on the tube to make sure they are solid, as well as R8 and R7. Also check to make sure the tube socket itself is making good contact with the tube pins. If you pried the tube socket contacts open too far then try to pinch them closed a bit more. When you get TP7 and TP9 fixed then the voltage on TP5 will probably normalize. Make sure you drain the caps before soldering pin 4! Keep me posted on what you find.
Good luck!
-brachChristopherM,
Thanks so much for letting us know. I just fixed it. Yesterday I uploaded a newer version of the manual an I forgot to update the links.
Anyway, it’s all good now.Thanks for the questions. Yes, the schematic for the Percolator is provided with the kit as an assembly aid and for help in troubleshooting.
Exceltent! That was very helpful.
It looks like your switch went bad in the explosion. Unfortunately, you’ll have to take the pcb out of the chassis to replace the switch. The best way to remove the bad switch is to clip the off the 3 leads and heat up the 2 front posts at the same time until you can pull the switch out of the pcb…be careful, it gets hot!
I’m glad to see that none of the switch contacts are connected to ground. But also please check the round pad on P4 to see if that is connected to ground….hopefully it’s not.
Next, you’ll have to scrape off all the carbon from the burned spot. It’s easy to do with a wire brush, but if you’re careful you can do it with a razor blade or other scraping device. You should notice that there was a trace on the pcb going from the round pad of P4 to the middle pin of the switch. Surrounding the trace on either side is the pcb ground plane (a layer of copper covering most of the board that is connected to ground). Both the trace and the ground plane are usually covered by a layer of blue paint. In the photo i have scraped off the paint on the trace and some of the ground plane so you can see the copper underneath.
The explosion was most likely caused by a short between the trace and the ground plane. Possibly a drop of solder or small piece of wire was bridging the trace and the ground plane. In scraping off the carbon it is important to make sure that there are no tiny little drops of melted copper hanging around that could possibly short it out again. You’ll have to replace this trace with a jumper wire…you can use one of the wires you cut from the transformers. cut it to length and strip off only the amount of insulation necessary to solder the ends to the middle pin of the switch and the round pad of P4 (tin both ends first). make sure there is not strands of wire or anything that could bridge to the ground plane or to other pads near by.
When you re-wire the pcb back in the chassis make sure the transformer wires are not touching anything on the solder side of the board.Thanks for answering so quickly.
Just to be clear…i’m assuming you are testing the switch with the chassis upside down (the transformers sitting on the table) while the bottom of the chassis is open facing up…is this correct? in this position was the switch up or down (down would be pointing to the word “power” on the faceplate) when you got continuity between the middle pin and the pin furthest away from the front of the chassis?
Please re-check the continuity between the middle pin on the switch and the round pin on P4. If you measured 122V on the middle pin after the explosion, you should have continuity between these two points. Make sure your meter probes are making good contact. Also please re-check to see if you have continuity between any of the pins on the switch and one of the square ground pads near the IEC power socket.
Does your meter actually make a beep noise or are you using the resistance setting on your meter to determine continuity? I’m asking because i can give you better instruction if i know what method you are using.Thanks for taking those tests.
It looks like you need a new fuse. You can get one from us, but you’d probably be better off finding one locally…it’s a pretty generic part. You need to get a 1A, 250V fast-acting (not slo-blo) fuse. I think 15mm is the length, but you can measure that yourself.
Next, your pcb needs some help. But before we get to that let me ask…when you measured the 122V (am i correct to assume AC voltage?) on the switch, when was that? Was it before or after the fireworks? Was it plugged in to the wall when you measured that? It would be helpful to know this before we proceed with the pcb repair
In the meantime you can check out the switch to make sure it is still working correctly. With your meter still on the continuity setting measure between the switch’s middle pin and both the outside pins (one at a time). It should beep while touching one outside pin, but not beep while touching the other. Flip the switch and test again. It should now be just the opposite…it should beep on the other pin now and not beep on the pin it beeped on originally. Let me know what you find (or if this is too confusing).
Good luck.
-brachThe wedding isn’t happening until later this afternoon so I have a bit of time right now to help figure this out…
First of all, sorry for the trouble. Secondly, don’t worry…we’ll get this fixed real soon and you’ll have a nice amp to play through. I’m out of state right now so i don’t have an amp in front of me, but we can get started with what i remember.
Thanks so much for the photos. That really helps. The voltages you read seem correct when the amp is plugged in to the wall and the switch is on, but from now on keep it unplugged until we get some more measurements done.
With the meter on the continuity setting (it’s the one that makes a beep when the two probes touch…not the voltage setting) test weather you have continuity between the round pad of P4 and the middle pin on the switch (it should beep if there is continuity). Also check weather you have continuity between either of these points and ground.
Also, check for continuity across the fuse to see if the fuse blew when you saw the fireworks.
Do these tests and let me know what you find.
Good luck.
-brachThanks for your question.
If the speaker can handle the proper wattage, there is no drawback at to trying it out. How it will sound might be a different issue, and that all depends on the type of 12″ speaker you use. Generally it’s going to sound good if you use a speaker designed for guitar and has a wattage rating of at least 10 watts (or so). 12″ Speakers generally have the potential to sound louder and somewhat “bigger” in the lower frequencies than a 8″ speaker (but that depends on a lot of other factors). Also, something to be mindful of when selecting a speaker is it’s sensitivity. For the Percolator, (it’s my opinion that) the more sensitive it is the better. The speaker is only being pushed by 2 watts, and it’s sensitivity has a lot to do with how many subtle harmonics you will hear. I wouldn’t suggest using a “hifi” type speaker, or any type of speaker with a “whizzer” cone. These types of speakers are designed for low distortion and a much different frequency response than what you’d typically want from a guitar speaker.
Guitar tone is so subjective and it’s always fun to explore new tone territory with other speakers, so i encourage you to try out as many different speakers as you can get your hands on (as long as they are 8 ohm). You’ll find one that really resonates with you!Thanks for asking…The Percolator has a fairly typical input impedance for an amp (~1M ohm), so interfacing with most pedals is not a problem. Modulation effects (flanger, tremolo, chorus, etc…) sound great, as well as delay effects (reverb, echo, etc…). In fact, one of my favorite things to do with the Percolator is run tremolo and reverb into it (in that order) and crank up the volume to where it just starts breaking up nicely. I could listen to that sound all day. I’m still amazed at the kind of tone this amp can put out at such low volumes. Honestly, I’ve never played the Percolator through an overdrive or distortion pedal…it already breaks up enough for my taste. With the volume at around noon it starts getting a really nice warm overdrive (that only comes from tubes) and that’s better than any overdrive or distortion box that i own. At close to full volume it’s got a good high-gain sound (think Marshall stack) and i don’t feel the need to add any distortion to it…but that’s just my personal preference.
The P8R is a great little speaker, but a bit over-priced in my opinion. A very nice sounding 8″ alnico that you might want to try is Weber’s “alnico Signature 8” (not the 8S…it’s harder for the 8S to break up under the Percolator’s output wattage). At nearly half the price of the P8R, i think it sounds as good or better in some cases…https://taweber.powweb.com/weber/asig8.htm
We are using the 6AF11…it’s a Compactron with two triodes and one sharp cutoff pentode. It’s definitely not a common tube to use in audio amplification. It was originally designed for video amplification in TV circuits, but we’ve found it sounds great in a guitar amp. I love using obscure tubes in guitar amps because of the unique tone you can get with them, and it’s fun to repurpose something that probably would never be used anyway…there’s not many working tube TV’s around anymore, but there are are plenty of these tubes left.
