212Mavguy Posted March 7, 2018 Posted March 7, 2018 Just did a successful repair on my RedPlate Blues Machine. I used relentless application of logic and a bit of deduction to come up with a guess... and that ended up being what was wrong, once I found out, was the easiest fix ever. The amp was making what is called shot noise, a roaring kind of sound that often comes when a bad tube has a short in it. The noise happened when the amp was taken off standby to operate, at first fireup it would last up to thirty seconds, then fade to nothing. If a chord was hit hard and them muted, the sound would start, last several seconds and then fade. If the dirty channel was engaged and the player were to play continuously the noise would gradually build and take over some of t he tone the guitar was trying to send, causing a muddy mess instead of clearer notes. I tried swapping out every tube in the amp, no joy. Was a PITA to swap and rebias the power tubes for no joy. Then I thought about how I had heard a dirty pot do that in Igor, my Frank-en-Champ. So I started turning every single front panel pot knob I could, back and forth thirty times from stop to stop...No joy! AAAAAAUGH! What could it be? I tried to figurre out what part of the amp it was coming from, I hot socketed every preamp tube from first through the phase inverter, noticed the noise happened each time a freshly inserted tube got hot enough to start to pass current. I turned off the reverb circuit, no joy. I removed both reverb tubes, no joy. I removed the loop effects buffer tube, no audio and no joy...The next morning I got up and had the day off, I was going to do the dreaded thang, take the chassis out of the cab and put it on the amp cradle to see if anything visible or electronically measureable was happening. There were two small trimmer pots inside the chassis, one for the tube effects loop buffer level, and another for balancing the sides of the phase inverter. I was thinking that perhaps the pot for the loop buffer was misbehaving. I put on a powerful LED headlamp, disconnected the speaker jack, disconnected the reverb tank, and unscrewed the chassis. Carefully, I slid it out of the cabinet and placed it on the amp cradle. started looking over the main board, the headlamp was a great help to illuminate all the parts inside, an amazing amount and variety of them...then I looked at both trimmer pots, the socket in the center of each where the screwdriver blade went was white on the PI trimmer, and gray on the loop trimmer. I had a suspect...then I noticed the sheet medal radio frequency shield glued to the inside top of the speaker cabinet that covered the top of the chassis when the chassis was installed. There was a gray splotch of discoloration an inch and ahalf across, right over where the loop trimmer pot was. Both these trimmers were made by Piher in spain, a maker of the uber high quality resistors used in early Hiwatt and Harry Joyce amps. Top shelf stuff, so was not worried since nothing looked charred or melted. RedPlate uses super high quality parts and wire in it's amps, nothing is compromised. They are a full on boutique builder of fantastic tone machines. I fired up the amp, had the reverb and presence knobs turned off, they are a part of the feature set of the RedPlate Blues Machine for picky players to tailor their tones. Those features on or off made no difference...no joy. The speaker jack was connected with a six foot speaker cable to a 2/12 cabinet close by. Took the amp off standby, and the dreaded noise ensued for a good thirty seconds, reliable and aggravating, well, it at least it was consistent...Then I touched the very narrow screwdriver blade to the pot, some loud crackling happened. Eureka! I had found it! when I turned tha pot back and forth from stop to stop a LOT of noise came out of it. I kept turning it back and forth, after the sixth repetition all was silent...so to make sure I turned it from stop to stop around thirty times more. Take that! Then I put the amp on standby, crossed my fingers, and flipped that standby switch to play...dead silent...the noise was GONE! I played that amp for a few minutes, took it on and off standby a half dozen times, and all was good. Turned it off, waited a few minutes for the power tubes to cool so I wouldn't get a blistering skin burn when trying to reinsert the chassis into the cab. Slid that sucker in, inserted and snugged the bolts, hooked up the cab speaker and reverb tank,then turned it on, waited thirty seconds, and turned the stanbly switch to "on". All good! I noticed quite a bit more clarity in the tones than before, had so much fun that I kept playing through it quite loudly for a full hour, gleefully making some loud noises with it as the speaker was still new and needed some pummeling to finish breaking it in. I decided that from now on every time I play a guitar I'm going to cycle the volume and tone pots back and forth twenty or thirty times to keep the wiper and plate from gunking up. There is a change in the tone towards clarity when the pots are kept clean from use...That amp had sat unused for several months because I was playing and working on a couple other amps in the harem. At least I know where that noise is coming from the next time it happens, if it ever does again!
Boytbpc Posted March 8, 2018 Posted March 8, 2018 Go buy some pot cleaner and give them a good spray and turn them from end to end again. That will really make sure they are clean. I had an amp that was doing the same thing, dirty pot.
212Mavguy Posted March 9, 2018 Author Posted March 9, 2018 I have pot cleaner, thanks. Am thinking that a previous owner might have used some that left a residue behind. All the other pots are dead silent. A note to RP about what happened resulted in a same day response indicating that trimmer had been an issue in other amps, now they do the loop buffer with a fixed value resistor in place of the trimmer. I do like the customization in response by having that trimmer in the circuit. From now on any time I have the chassis out I'm going to cycle both trimmers back and forth. Those RP guys packed a lot of features into my Blues Machine. I played it out last night and it flat out ROARED! Had some singing sustain notes that were easily controlled for as long as I wanted as well. Having a Tone Tubby Nashville ceramic in it was a definite upgrade. Thanks for your advice, BTW
212Mavguy Posted March 16, 2018 Author Posted March 16, 2018 Haaaaaaaaaaaaaah! Luuuuucky! And would some folks please start posting in this area of the forum? it's too damn quiet. Time to stir up some amp drama. There already is plenty of drama written about the 225 Parsons Street sh...tuff. Somebody please get ornery and start an amp argument...or SOMETHING!
AP515 Posted March 16, 2018 Posted March 16, 2018 10 hours ago, 212Mavguy said: Haaaaaaaaaaaaaah! Luuuuucky! And would some folks please start posting in this area of the forum? it's too damn quiet. Time to stir up some amp drama. There already is plenty of drama written about the 225 Parsons Street sh...tuff. Somebody please get ornery and start an amp argument...or SOMETHING! My Hot Rod Deluxe can beat your Dumble in a tone contest any day of the week!
JeffB Posted March 16, 2018 Posted March 16, 2018 14 hours ago, 212Mavguy said: Haaaaaaaaaaaaaah! Luuuuucky! And would some folks please start posting in this area of the forum? it's too damn quiet. Time to stir up some amp drama. There already is plenty of drama written about the 225 Parsons Street sh...tuff. Somebody please get ornery and start an amp argument...or SOMETHING! Good Idea.
212Mavguy Posted March 17, 2018 Author Posted March 17, 2018 13 hours ago, AP515 said: My Hot Rod Deluxe can beat your Dumble in a tone contest any day of the week! Haw haw haw! Which one? I have six d-styles... BTW, I asked for it, and just got it! Way to stir up the pot! hehehe!
AP515 Posted March 17, 2018 Posted March 17, 2018 1 hour ago, 212Mavguy said: Haw haw haw! Which one? I have six d-styles... BTW, I asked for it, and just got it! Way to stir up the pot! hehehe! Glad you liked the little funny. Of course you know I'd take the Dumble clone any day. Here's a real one. I've got a hand wired PRS amp and a PRS amp designed to be just like the first one but with a PCB and they both are killer amps. I can't say they are exactly alike because the PCB version has EL34's in it and the High End one has 6L6's. Right now I'm liking the PCB one better but it might be due to the EL34's. My point being the amp does not suffer from the PDB.
212Mavguy Posted March 17, 2018 Author Posted March 17, 2018 58 minutes ago, AP515 said: Glad you liked the little funny. Of course you know I'd take the Dumble clone any day. Here's a real one. I've got a hand wired PRS amp and a PRS amp designed to be just like the first one but with a PCB and they both are killer amps. I can't say they are exactly alike because the PCB version has EL34's in it and the High End one has 6L6's. Right now I'm liking the PCB one better but it might be due to the EL34's. My point being the amp does not suffer from the PDB. Thinking foggily back in the not so certain memory that the PRS are/were designed and at least some early ones built by a man named Douglas Sewell...one of his amps was called the Wampus Cat, cool name! Might be wrong about that Sewell is the PRS guy. Ever investigate the amps Andy Fuchs builds? They are PCB also, designed with more common sense than the newest Mesa amps are, IMHO. They have killer tones, and great feature sets...several models have Dumble roots. In addition, if you have a spare real (vintage not reissue) Fender Bassman that you want some more versatility from, Fuchs amplification does the Bassman to Dumble style conversions, they have a great rep for that one. Pcb's done "right" are great sounding. Eyelet and turret board builds are better for prototyping or one off builds, PCB's are better for large production runs. My current fave amp builder besides Ceriatone is RedPlate, their main boards are a mix of eyelet and turrets, they do sing like few others clean or dirty. Their Tweedyverb trumps the 5e3 builds, more features, versatility, and wonderful tones. They are a great value on the used amp market, and the RP is a small enough operation to be able to offer great customer service.
AP515 Posted March 17, 2018 Posted March 17, 2018 Yeah, Doug is the brains behind the PRS amp designs. I've seen Fuchs amps but don't know much about them. I'm really happy with my Mesa's and PRS's and one HRD. I heard a red plate a while back with a lot of gain and was really impressed.
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