Repaired Plexi died in 10 mins

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UPDATE: Spoiler, more problems. I picked up the `67 Super Bass yesterday after the tech had asked me to give him a second chance to “make it right.” (After his first attempted fix, the amp sounded weak and blew a fuse after 10 mins of play time.) He said he added a capacitor to the V2 cathode that wasn’t on the JTM schematic. ?? This head is a very early version of the SB. The guts and components look essentially the same as JTM Black Flag pics I’ve seen. It has no filter caps on the chassis top, etc. Still, I have no idea about this “fix.” He also repaired the indicator light and put in the right fuse values this time. Don’t get me started on the fuses. Soooo …

The amp actually sounded pretty amazing. It really nailed the Cream/ Clapton live Crossroads tone. Really rich, beefy and smooth overdrive. Not quite early Van Halen, but big sounding and very touch sensitive. Great Strat tones on neck and bridge positions. But it needed to run hot, at least 75% of volume with treble, mid and presence at around the same. Bass rolled back to about 25%. I was kind of in tone nirvana. But here’s where it took a turn for the worse …

The amp blew another fuse after about 3-4 hours of playing. Just when I thought I had finally finished my Plexi repair journey. Right in the middle of a solo it died without a sound. Just went dark. I had stress tested it and it failed. So now I’m going to call up Jeff Bober or Pete Cage in Maryland to start back at the beginning and have them go over the amp. I have all the components that were pulled/replaced by the last tech, as well as the two itemized shop receipts for what was done. Sigh. I was really hoping this saga was over — just want to play that awesome Plexi!
 

pedecamp

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UPDATE: Spoiler, more problems. I picked up the `67 Super Bass yesterday after the tech had asked me to give him a second chance to “make it right.” (After his first attempted fix, the amp sounded weak and blew a fuse after 10 mins of play time.) He said he added a capacitor to the V2 cathode that wasn’t on the JTM schematic. ?? This head is a very early version of the SB. The guts and components look essentially the same as JTM Black Flag pics I’ve seen. It has no filter caps on the chassis top, etc. Still, I have no idea about this “fix.” He also repaired the indicator light and put in the right fuse values this time. Don’t get me started on the fuses. Soooo …

The amp actually sounded pretty amazing. It really nailed the Cream/ Clapton live Crossroads tone. Really rich, beefy and smooth overdrive. Not quite early Van Halen, but big sounding and very touch sensitive. Great Strat tones on neck and bridge positions. But it needed to run hot, at least 75% of volume with treble, mid and presence at around the same. Bass rolled back to about 25%. I was kind of in tone nirvana. But here’s where it took a turn for the worse …

The amp blew another fuse after about 3-4 hours of playing. Just when I thought I had finally finished my Plexi repair journey. Right in the middle of a solo it died without a sound. Just went dark. I had stress tested it and it failed. So now I’m going to call up Jeff Bober or Pete Cage in Maryland to start back at the beginning and have them go over the amp. I have all the components that were pulled/replaced by the last tech, as well as the two itemized shop receipts for what was done. Sigh. I was really hoping this saga was over — just want to play that awesome Plexi!
Thats frustrating......tell that @$$hat what happened and you want a refund or partial refund and that youre taking it somewhere else. Good luck with it this next time.
 

Dblgun

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To me it still sounds as if the amp was never right. I don't know where you are playing but if I stood in close proximity to my 100W at 3/4 volume for 3-4 hours I'd be deaf.

I'm also curious about the fuse opening after this session. Do you know which fuse it was and did you check that the correct value and type had been used this time around?
 

StrummerJoe

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So I drove the amp over to the shop and confronted the tech in person …

I pointed out that he returned an amp that sounded weak, had a nonfunctional indicator light and a 10-amp fuse in the 1.5-amp H.T. spot. I had planned not to lose my cool but I couldn’t help getting angry. Why is this fuse in there, I asked? He said he’s been doing this type of amp repair for 40 years, has lots of amps coming through the shop each week and has NEVER checked fuses unless they’re blown. I said WHY NOT?!

He had also told me that the ‘67 Super Bass sounded “anemic” by design and was probably best used just as a pedal platform, so I explained what it’s supposed to sound like. I told him the amp obviously still had a major tone issue when he returned it. I told him I was really disappointed with the work and that we should probably part ways — and I should get at least a partial refund. He flatly refused the refund but asked me to please give him a chance to make it right. He would look at the amp again and find the issue at no charge. He called me back an hour or so later and said he found the problem with the tone, that the amp sounds right now. I thought, wow, that was fast. But he also said he can’t be 100% sure he solved the issue that caused the mains fuse to blow after 10 mins of play time. OK. He’s ordered the vintage style square indicator light and will install it.

The problem is I don’t have many other good options. My first choice was the great vintage guitar/amp shop here. But all the techs they work with — people with true expertise and talent with vintage Marshalls — have at least a 3-month waiting list to even look at an amp. That shop said it still had amps that came in in August. It’s really crazy. I suppose I could ship it somewhere? Otherwise I may not be playing it until next fall. Ugh.
Prayers to the Higher Power of your choosing to guide his hands and restore your "67 Super Bass to it's rightful glory. AMEN!

Man...I am realy sorry you are having this experience. What a nightmare.

You & your amplifier deserve to be made whole.
 

playloud

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The amp actually sounded pretty amazing. It really nailed the Cream/ Clapton live Crossroads tone. Really rich, beefy and smooth overdrive. Not quite early Van Halen, but big sounding and very touch sensitive. Great Strat tones on neck and bridge positions. But it needed to run hot, at least 75% of volume with treble, mid and presence at around the same. Bass rolled back to about 25%. I was kind of in tone nirvana. But here’s where it took a turn for the worse …

Fwiw, that sounds about right. With my SB, single coils start to overdrive with the volume around 7 (although the clean sound obviously gets loud before this!)

Pity about the fuse though. I would get the amp to one of those other guys without delay!
 

XTRXTR

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Can you post the second receipt/work order? I would love to hear Bober has this amp rocking solid soon.
The intermittent thing sucks.
Side note have you changed speaker cables recently?
 
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neikeel

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These amps are not dirty or vicious in stock form. More loud blues/rock devices. Like a JTM45 on steroids. Depending on which speakers may not be that loud (G12M greenbacks are not that efficient). Plate voltage with the dual rectifier and 8cap board is around 480v.
It will be very sensitive to the condition of the preamp tubes and output tubes, old tired ones will not flatter it.
The cap he added sounds like a common mod to boost the second gain stage (which frequency band will depend on cap value) but it is a mod.
There are a few things that can take a fuse out after that period of playing, commonest is an HT fuse popping with an output tube getting too hot. Obviously if mains fuse you will be looking at PT and diodes carefully. Problems like this can be difficult to solve and risks ripping the amp to bits.
I will emphasise my point to the disbelievers that when an amp is not working you test it and replace what is not working, not random part replacement because they might be old!!
 
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To me it still sounds as if the amp was never right. I don't know where you are playing but if I stood in close proximity to my 100W at 3/4 volume for 3-4 hours I'd be deaf.

I'm also curious about the fuse opening after this session. Do you know which fuse it was and did you check that the correct value and type had been used this time around?
I use a Fryette Power Station attenuator. Otherwise, yeah, I’d be deaf and divorced. The 3 amp mains fuse blew, same as last time. I checked that both the mains and HT fuses were the correct value before I played it.
 
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Travis, Of the three fixes that you listed the tech did on the second try, none of those "fixes" addressed in any way or shape why the amp blew the fuses both times. That fuse blowing issue has not been addressed, and you would want to convey that to your next tech.
Exactly, that’s what I’m planning.
 
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These amps are not dirty or vicious in stock form. More loud blues/rock devices. Like a JTM45 on steroids. Depending on which speakers may not be that loud (G12M greenbacks are not that efficient). Plate voltage with the dual rectifier and 8cap board is around 480v.
It will be very sensitive to the condition of the preamp tubes and output tubes, old tired ones will not flatter it.
The cap he added sounds like a common mod to boost the second gain stage (which frequency band will depend on cap value) but it is a mod.
There are a few things that can take a fuse out after that period of playing, commonest is an HT fuse popping with an output tube getting too hot. Obviously if mains fuse you will be looking at PT and diodes carefully. Problems like this can be difficult to solve and risks ripping the amp to bits.
I will emphasise my point to the disbelievers that when an amp is not working you test it and replace what is not working, not random part replacement because they might be old!!
One of the things (out of many) that aggravated me was the tech didn’t ask before he made the cap mod on V2. So I may likely have the next guy put it back to stock. Sigh.
 

neikeel

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For US is should be T4A (ie 4 amp SLO-BLO, aka anti-isurge) T3A is US for a 50w. Assuming you are running it at 120vac.
 

XTRXTR

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