Had similar issues with the same or very similar Reverb 12. Both Buzz and hum as you experienced. I also realized the buzz was being generated by the AC leads feeding the power switch picked up at the pin2 grid side of V2 by the extra long lead from the 470k resisitor acting like an antenna. The other end goes to the volume control wiper where the impedance is not nearly as high. As for the reverb hum, I could eliminate that by disconnecting the shielded cable feed from the reverb section that goes to pin 2 of V2 so i knew that was the source of the hum. Removing the reverb/tremolo tube also confimed that. First To eliminate the buzz from the AC leads i shortened the ends of the 470K resistor, connected one shortened end to pin 2 and from the other short end ran a shielded cable to the wiper of the volume control and only grounded that end to prevent possible ground loop.. Buzz issue resolved. For the reverb: I noticed that even with the volume completely down, you could still hear the reverb effect from the guitar. This is because even with the volime control fully down, there is still efectively 470k to ground at V2 pin 2 where the impedance/gain is much higher. I moved the the reverb injection point to the volume wiper side of the 470k resistor and resolved the hum as well as the reverb signal at volume down issues. For good measure and better reverb volume given the lower impedamce injection point, i bridged the 1meg resistor that feeds the signal to the now volume control point with another 1meg resistor. I did not need ro reconfigure the grounds in this one. Problems resolved. I also as i recall you did, added cathode bypass cap to V1 where there was none originally. Woke it up a bit. This one was quite challenging and super fun! Keep up the great videos...
Thanks for the video. I inherited one of these from my grandfather (along with his 67 epiphone Texan) and need to get the amp repaired. This gives me hope of what it could sound like again.
It's amazing how good a low budget thing like this can sound with just a few small improvements. Hipster gear snobs who turn up their noses at stuff like this are missing all the fun. You can't hear much if you're listening with your eyes.
I picked up this amp for a hundred bucks. It’s blowing fuses and I’m pretty certain I’ve isolated it down to the power transformer. For everything else this video is super nice to follow along to. I think I will opt for the Princeton tone circuit.
To respond to a previous comment about the reverb tank position: Yes you need to be certain the signal out side of the tank is as far away from the power xformer as possible, however in this ampl the tank is mounted far away from the chassis in the very bottom of the cab. Good info, tho.
Thanks for posting part 2 so soon. The amp sounds sweet now and OMG...the tremolo is gorgeous. It's always nice to see a 50 year old amp brought back to life. Keep up the good work!
Thanks, Duke. Yeah, it's a good sounding amp. Very clean. Kinda Blackfacey, really. Could be modded for more breakup if one wanted. Tone stack could be tweaked for more midrange to get closer to a Marshall tone, if desired. For a little 10" combo, it holds its own. I suspect I might get the amp back again to tweak that reverb though. While I was able to get the noise level down, it's still a pretty weak reverb. I am sure I could beef that up with some mods. We'll see. I told the customer I'd tweak it for free if he decides to do it. He's been a good customer.
Personally I would leave it alone as is. Reminds me of the early Magnatone amps of the 60's with that watery tremolo they were famous for. Marshall amps are good for certain things but they can't replicate the tremolo of an old low powered blackface amp...(Think Fender Tremolux). Thanks for the reply and I look forward to seeing what's next in your world of resurrecting the dead.
Thanks Buddy, as always, for watching! Got a TON of projects to work on. I think I'll make a video of all the crap I have in my project pile and let you guys vote on what to service next! Might be fun.
If you lived closer to Texas I would love you to work on my old Fender Bassman with AA165 circuitry... Unfortunately I have not found anyone in my neck of the woods that I trust to repair it correctly...
Another great video. Thanks for the grounding tip in the tone stack area. I made that mistake in the Hammond conversion I've been playing with. Just changed it to a different location and it significantly reduced the hum.
Yeah, we don't think much of grounding schemes when we're first starting out, we tend to reason 'ground is ground', but nope. It matters. Thanks for watching, Mike!
Brad. You should have labels made that have your name like. " Serviced with love by Brad The Guitologist" and like a date code line. 11/15/17. Let me know what ya think. I love your humor when fixing amps. "what were they smoking or snorting..." LOL. You're the best. Mark
I’m sure you did but didn’t show it that you checked the bias I purchased I used fender blues jr the previous owner replaced all the tubes- nice but it sounded thin checked bias way off being fixed had to increase plus a lot of circuit mods love your videos keep it up
My guess for reverb noise/hum is because the tank is so close and oriented so near the power transformer. In some amps I've had to turn the tank 180 degrees to get the send transducer away from the power transformer.
Bradologist After cleaning the RCA JACKS and cables and ohming the cables and coils ( transducers ) on the reverb tank on my Kustom 50-2 amplifier , I still have minimum sound from the tank…I switched the inputs back and forth on the tank..no difference….I get a buzz from the tank output cable going to the board….cleaned pot for reverb…Can this be in the drive section of the reverb??
I have a Kalamazoo 30 Bass amp from 68, it had a similar non-responsive tone stack. Turns out one of the resistors, which did appear to be original, was seven - 7!!! -- times the value speced in the schematic. I substituted in the proper 220K, and now the Bass and Treble respond well with full range. Note to self - always blueprint a seemingly bad circuit.
Nice video I learned a lot. I have one if those amps in mint condition. It was my first Amp I bought when I was a kid. It's time for some servicing there seems to be a lot of sizzling noise like frying something in a pan on a stove. I've read that plate load resistors can cause this. I'm not a. Certified amp tech but I've been learning and doing my own work mostly on Fender Amps for the past several years. Can you direct me to which resistors and their values are the plate load resistors, on Fenders they 100K. I can change them out and see if that might help eliminate that sizzling noise. I've also found some resistors out of spec. The electrolytic caps and 3 prong power cord have also been done. I might just try some of those mods you did to help with the hum although mine does not really seem that bad. Thank you in advance for any advice to might have. Roadhog96
Awesome vid Brad as usual! My dad has this same amp and I remember good times playing it. The tremolo isn’t working as well and I’m sure its the same issue with the foot-switch since it hardly clicks. I will see if I can figure it out.
That amp sounds sweet now! Question about the power switch on treble: if the wire was in that spring/conduit, which was connected to ground, wouldn't that actually be shielding it? Thanks for the vids...learn something new every time!
I am the proud owner of one of these amps. Mine has developed a LOUD buzz when you turn on the reverb. The buzz is louder than any musical note the amp has ever done.I'm talking way more than a bit of noise. Any suggestions for a quick fix? Thanks for this video.
This model did not have the tone sucking network? It sounds great! Not much reverb, or did you not have it all the way up? Another successful service and demo! Thankz
You are correct. The reverb is really weak, even before the service. I told the customer if he wants I'll mod that reverb circuit for him for free if he decides it's too weak. He uses a reverb pedal anyway. No tone-sucking network in this one though, so that's a plus.
Hi Brad, Good repair, sounds good. Kalamazoo looks like one to avoid. Goofy layout. Proper grounding, avoiding ground loops is all important from an LM386 audio amp to tube amps. From Uncle Doug I learned you only ground one end of your shielded cables to eliminate ground loops. Happy Thanksgiving, be good, C.
Good point on the shielded cables. One other trick I learned from using shielded cables...it's a bit more dangerous, but you can use a tube's plate voltage on the shielding and in some instances, it'll neutralize more noise than simple grounding. Of course, you'll really want to be careful doing that and shrink tube the ends so they never short out against anything.
Should have put the proper pot in the Treble position and got rid of the stupid switch. Should not have drilled on the front face as could have just used the fuse hole for the ON/OFF switch and either put the fuse holder inside of the amp or if going to drill, drill on the BACK and put near the IEC input, like normal! The .01uF in the Tremolo circuit is for Tone Shaping and does not need to be polarized. Listening to the video online, this amp sounds really good to be when refurbished back to new condition and cap job, etc., but could be SIGNIFICANTLY better if laid out better and not a rats nest with proximity issues. I may have to twist one up with a better layout.
If drilling holes will keep the goofball collectors from driving the price of a train wreck of an amp like this through the roof, then drill all the holes you can. BTW, it sounds awesome-the poor thing had to wait 50 years to sound that good!
If you cut the 68k connected to the phone input you will get a lot more gain and put in a dummy plug into the other jack on the front panel make this amp sound great. your reverb should be super strong Brad and it is not.
Had similar issues with the same or very similar Reverb 12. Both Buzz and hum as you experienced.
I also realized the buzz was being generated by the AC leads feeding the power switch picked up at the pin2 grid side of V2 by the extra long lead from the 470k resisitor acting like an antenna. The other end goes to the volume control wiper where the impedance is not nearly as high. As for the reverb hum, I could eliminate that by disconnecting the shielded cable feed from the reverb section that goes to pin 2 of V2 so i knew that was the source of the hum. Removing the reverb/tremolo tube also confimed that.
First To eliminate the buzz from the AC leads i shortened the ends of the 470K resistor, connected one shortened end to pin 2 and from the other short end ran a shielded cable to the wiper of the volume control and only grounded that end to prevent possible ground loop..
Buzz issue resolved.
For the reverb:
I noticed that even with the volume completely down, you could still hear the reverb effect from the guitar. This is because even with the volime control fully down, there is still efectively 470k to ground at V2 pin 2 where the impedance/gain is much higher.
I moved the the reverb injection point to the volume wiper side of the 470k resistor and resolved the hum as well as the reverb signal at volume down issues.
For good measure and better reverb volume given the lower impedamce injection point, i bridged the 1meg resistor that feeds the signal to the now volume control point with another 1meg resistor.
I did not need ro reconfigure the grounds in this one.
Problems resolved. I also as i recall you did, added cathode bypass cap to V1 where there was none originally. Woke it up a bit.
This one was quite challenging and super fun!
Keep up the great videos...
One of the best sounding amps you've repaired. Excellent work.
Thanks for the video. I inherited one of these from my grandfather (along with his 67 epiphone Texan) and need to get the amp repaired. This gives me hope of what it could sound like again.
It's amazing how good a low budget thing like this can sound with just a few small improvements. Hipster gear snobs who turn up their noses at stuff like this are missing all the fun. You can't hear much if you're listening with your eyes.
I picked up this amp for a hundred bucks. It’s blowing fuses and I’m pretty certain I’ve isolated it down to the power transformer. For everything else this video is super nice to follow along to. I think I will opt for the Princeton tone circuit.
To respond to a previous comment about the reverb tank position: Yes you need to be certain the signal out side of the tank is as far away from the power xformer as possible, however in this ampl the tank is mounted far away from the chassis in the very bottom of the cab.
Good info, tho.
Thanks for posting part 2 so soon.
The amp sounds sweet now and OMG...the tremolo is gorgeous.
It's always nice to see a 50 year old amp brought back to life.
Keep up the good work!
Thanks, Duke. Yeah, it's a good sounding amp. Very clean. Kinda Blackfacey, really. Could be modded for more breakup if one wanted. Tone stack could be tweaked for more midrange to get closer to a Marshall tone, if desired. For a little 10" combo, it holds its own. I suspect I might get the amp back again to tweak that reverb though. While I was able to get the noise level down, it's still a pretty weak reverb. I am sure I could beef that up with some mods. We'll see. I told the customer I'd tweak it for free if he decides to do it. He's been a good customer.
Personally I would leave it alone as is.
Reminds me of the early Magnatone amps of the 60's with that watery tremolo they were famous for.
Marshall amps are good for certain things but they can't replicate the tremolo of an old low powered blackface amp...(Think Fender Tremolux).
Thanks for the reply and I look forward to seeing what's next in your world of resurrecting the dead.
Thanks Buddy, as always, for watching! Got a TON of projects to work on. I think I'll make a video of all the crap I have in my project pile and let you guys vote on what to service next! Might be fun.
If you lived closer to Texas I would love you to work on my old Fender Bassman with AA165 circuitry...
Unfortunately I have not found anyone in my neck of the woods that I trust to repair it correctly...
Uncle Doug is in Texas.
Another great video. Thanks for the grounding tip in the tone stack area. I made that mistake in the Hammond conversion I've been playing with. Just changed it to a different location and it significantly reduced the hum.
Yeah, we don't think much of grounding schemes when we're first starting out, we tend to reason 'ground is ground', but nope. It matters. Thanks for watching, Mike!
Brad. You should have labels made that have your name like. " Serviced with love by Brad The Guitologist" and like a date code line. 11/15/17. Let me know what ya think. I love your humor when fixing amps. "what were they smoking or snorting..." LOL. You're the best. Mark
This is the nicest sound kazoo I have ever heard, and you are one hell of a kazoo player!
I was breast fed as a baby. That's how I got such strong lips.
The Guitologist Now you owe me a new keyboard. And if you're feeling particularly generous, you *could* replace the coffee too.
The Guitologist I was breast fed as an adult.
I’m sure you did but didn’t show it that you checked the bias I purchased I used fender blues jr the previous owner replaced all the tubes- nice but it sounded thin checked bias way off being fixed had to increase plus a lot of circuit mods love your videos keep it up
My guess for reverb noise/hum is because the tank is so close and oriented so near the power transformer.
In some amps I've had to turn the tank 180 degrees to get the send transducer away from the power transformer.
Great job and a lovely little amp.
Sounds great only goes to show what a really good speaker can do.
Bradologist
After cleaning the RCA JACKS and cables and ohming the cables and coils ( transducers ) on the reverb tank on my Kustom 50-2 amplifier , I still have minimum
sound from the tank…I switched the inputs back and forth on the tank..no difference….I get a buzz from the tank output cable going to the board….cleaned pot for reverb…Can this be in the drive section of the reverb??
I have a Kalamazoo 30 Bass amp from 68, it had a similar non-responsive tone stack. Turns out one of the resistors, which did appear to be original, was seven - 7!!! -- times the value speced in the schematic. I substituted in the proper 220K, and now the Bass and Treble respond well with full range. Note to self - always blueprint a seemingly bad circuit.
Nice video I learned a lot. I have one if those amps in mint condition. It was my first Amp I bought when I was a kid. It's time for some servicing there seems to be a lot of sizzling noise like frying something in a pan on a stove. I've read that plate load resistors can cause this. I'm not a. Certified amp tech but I've been learning and doing my own work mostly on Fender Amps for the past several years. Can you direct me to which resistors and their values are the plate load resistors, on Fenders they 100K. I can change them out and see if that might help eliminate that sizzling noise. I've also found some resistors out of spec. The electrolytic caps and 3 prong power cord have also been done. I might just try some of those mods you did to help with the hum although mine does not really seem that bad. Thank you in advance for any advice to might have. Roadhog96
Awesome vid Brad as usual! My dad has this same amp and I remember good times playing it. The tremolo isn’t working as well and I’m sure its the same issue with the foot-switch since it hardly clicks. I will see if I can figure it out.
nice job, good work.
That amp sounds sweet now! Question about the power switch on treble: if the wire was in that spring/conduit, which was connected to ground, wouldn't that actually be shielding it? Thanks for the vids...learn something new every time!
I am the proud owner of one of these amps. Mine has developed a LOUD buzz when you turn on the reverb. The buzz is louder than any musical note the amp has ever done.I'm talking way more than a bit of noise. Any suggestions for a quick fix? Thanks for this video.
That really sounds good!
I ended up doing a bit more work on the ground scheme and reverb after making the video. It's top notch now. Reverb is super lush as well.
I do not hear any reverb, it should be strong?
Sounds nice- once you had sorted it- for such a small combo.
This model did not have the tone sucking network? It sounds great! Not much reverb, or did you not have it all the way up? Another successful service and demo! Thankz
You are correct. The reverb is really weak, even before the service. I told the customer if he wants I'll mod that reverb circuit for him for free if he decides it's too weak. He uses a reverb pedal anyway. No tone-sucking network in this one though, so that's a plus.
I didn't see any tubes?
Hi Brad, Good repair, sounds good. Kalamazoo looks like one to avoid. Goofy layout. Proper grounding, avoiding ground loops is all important from an LM386 audio amp to tube amps. From Uncle Doug I learned you only ground one end of your shielded cables to eliminate ground loops. Happy Thanksgiving, be good, C.
Good point on the shielded cables. One other trick I learned from using shielded cables...it's a bit more dangerous, but you can use a tube's plate voltage on the shielding and in some instances, it'll neutralize more noise than simple grounding. Of course, you'll really want to be careful doing that and shrink tube the ends so they never short out against anything.
Should have put the proper pot in the Treble position and got rid of the stupid switch.
Should not have drilled on the front face as could have just used the fuse hole for the ON/OFF switch and either put the fuse holder inside of the amp or if going to drill, drill on the BACK and put near the IEC input, like normal!
The .01uF in the Tremolo circuit is for Tone Shaping and does not need to be polarized.
Listening to the video online, this amp sounds really good to be when refurbished back to new condition and cap job, etc., but could be SIGNIFICANTLY better if laid out better and not a rats nest with proximity issues. I may have to twist one up with a better layout.
If drilling holes will keep the goofball collectors from driving the price of a train wreck of an amp like this through the roof, then drill all the holes you can. BTW, it sounds awesome-the poor thing had to wait 50 years to sound that good!
Great video Brad.
Thanks Richard. Good to see you here.
Mine never sounded this good.
The tremolo is nice.
What OHM's is this amp?
Output is 8 ohms.
If you cut the 68k connected to the phone input you will get a lot more gain and put in a dummy plug into the other jack on the front panel make this amp sound great. your reverb should be super strong Brad and it is not.
seams alot quieter on the video