1964 Ampeg Jet Questions

[Triocd]

Hi, first post here, I just picked up my first vintage amp. I picked up a Jet 12-A in great condition but I'm wondering what might be able to be replaced to improve the sound. Below are a couple photos of the guts. I can't tell what has been replaced (all of the caps?). I know at least some caps have been replaced and it has a new Mercury Magnetics power transformer. I'd appreciate any info anyone can figure out just by looking at the guts. Also, any signs to look for to determine if it needs new tubes?

Also, what are the 2 grey things to the left of the sprague atom? They say Milwaukee on them and one has something on it that looks like tar. I can't tell if the tar stuff leaked out of it or what.

Thanks for any info!

[Leo_Gnardo]

Hi, first post here, I just picked up my first vintage amp. I picked up a Jet 12-A in great condition but I'm wondering what might be able to be replaced to improve the sound. Below are a couple photos of the guts. I can't tell what has been replaced (all of the caps?). I know at least some caps have been replaced and it has a new Mercury Magnetics power transformer. I'd appreciate any info anyone can figure out just by looking at the guts. Also, any signs to look for to determine if it needs new tubes?

Also, what are the 2 grey things to the left of the sprague atom? They say Milwaukee on them and one has something on it that looks like tar. I can't tell if the tar stuff leaked out of it or what.

Jets are great little amps, along the lines of Fender tweed Deluxe. Those two grey cylinders are power resistors, and what looks like a streak of tar, probably the glue Ampeg used to spray onto the circuit board, roasted by years of heat, nothing to worry about. I would put a little space between those resistors and nearby filter cap just to keep it from getting roasted too. Some caps are rated for 105C operation but many don't take the heat too well. Sprague Atoms, rated generally 65C or 85C. Looks like a nice rebuild has already been done. Hard to tell if that's the original multisection filter cap. If it is, best to get a fresh one in there. I put in 50+50/500V can caps and single caps for the remaining two sections. Mods? Heck I think the Jet sounds just dandy stock. Maybe a different speaker, that's about it. Seen lots of old Ampegs working just fine with original tubes too. If they're working just play & don't worry.

[Triocd]

Jets are great little amps, along the lines of Fender tweed Deluxe. Those two grey cylinders are power resistors, and what looks like a streak of tar, probably the glue Ampeg used to spray onto the circuit board, roasted by years of heat, nothing to worry about. I would put a little space between those resistors and nearby filter cap just to keep it from getting roasted too. Some caps are rated for 105C operation but many don't take the heat too well. Sprague Atoms, rated generally 65C or 85C. Looks like a nice rebuild has already been done. Hard to tell if that's the original multisection filter cap. If it is, best to get a fresh one in there. I put in 50+50/500V can caps and single caps for the remaining two sections. Mods? Heck I think the Jet sounds just dandy stock. Maybe a different speaker, that's about it. Seen lots of old Ampegs working just fine with original tubes too. If they're working just play & don't worry.

Thanks for the reply. How do I put a space between things? Do I just pry them apart and/or put some insulation between? Or do I resolder them with more space?

Is the multisection filter cap the big can in the second photo to the right of the tubes? It looks new to me because it's really shiny and new looking, but I really have no idea.

[Leo_Gnardo]

Thanks for the reply. How do I put a space between things? Do I just pry them apart and/or put some insulation between? Or do I resolder them with more space?

Is the multisection filter cap the big can in the second photo to the right of the tubes? It looks new to me because it's really shiny and new looking, but I really have no idea.

Just gently pry 'em apart with a screwdriver tip, see if you can get a quarter-inch gap but less is OK. Just as long as they're not jam up against each other.

That's the multisection all right. Even old ones can look shiny new. A little close up photo so we can see what's printed on it, maybe another shot with the inside-the-chassis view of multisections connexions, we'll know what it is pretty quick. If it is new, hooray! Hope it lasts a long time.

[Triocd]

Just gently pry 'em apart with a screwdriver tip, see if you can get a quarter-inch gap but less is OK. Just as long as they're not jam up against each other.

That's the multisection all right. Even old ones can look shiny new. A little close up photo so we can see what's printed on it, maybe another shot with the inside-the-chassis view of multisections connexions, we'll know what it is pretty quick. If it is new, hooray! Hope it lasts a long time.

The soldering of this can looks especially shiny, so it may be new soldering? I just pried the things apart. You're right, it's fried glue on the Milwaukee.

[Leo_Gnardo]

The soldering of this can looks especially shiny, so it may be new soldering? I just pried the things apart. You're right, it's fried glue on the Milwaukee.

New multisection cap all right, from Antique/CE. Note 55C temp rating which leads me to caution, don't leave your amp on for hours at a time. The power supply end of yours and similar Ampegs tends to get hot as you can see, and we want those filter caps to last a good long time.

[Triocd]

New multisection cap all right, from Antique/CE. Note 55C temp rating which leads me to caution, don't leave your amp on for hours at a time. The power supply end of yours and similar Ampegs tends to get hot as you can see, and we want those filter caps to last a good long time.

Thanks for all your input gnardo. Any recommendations for a new inefficient speaker? The amp starts to come alive around at around 5, which unfortunately shakes my whole house. Would an inefficient speak have a noticable difference in volume to make it worthwhile putting one in?

[The Dude]

If you do a speaker swap (and I wouldn't), take care to preserve that original one. There are people who would kill for that thing!

[supawah]

looks like they replaced all the caps but two, which is okay since all the astrons in that amp were probably leaking a couple of volts, at least in the last 6 of those I worked on they were, I think I would have replaced those two little electrolytics in the middle of the board, they're cathode bypass, maybe for the reverb or tremolo? they get left out some times, check the value on that first black Sprague cap, sometimes guys will put a larger value in to increase bass on that first stage, I like it at a stock value. I've had customers put celestion creambacks in those amps to gig with, and it really tightens them up, but the volume is even greater then.

[J M Fahey]

Hi, first post here, I just picked up my first vintage amp. I picked up a Jet 12-A in great condition but I'm wondering what might be able to be replaced to improve the sound.

You don't *improve* a *classic*.

Or it ceases to be that, and then, what's the point of buying a Classic to begin with?

Same as buying a '57 Strat and putting Di Marzios or EMG in it, a Floyd Rose whammy, repaint it, maybe embed some Leds in the neck, etc.

[Triocd]

looks like they replaced all the caps but two, which is okay since all the astrons in that amp were probably leaking a couple of volts, at least in the last 6 of those I worked on they were, I think I would have replaced those two little electrolytics in the middle of the board, they're cathode bypass, maybe for the reverb or tremolo? they get left out some times, check the value on that first black Sprague cap, sometimes guys will put a larger value in to increase bass on that first stage, I like it at a stock value. I've had customers put celestion creambacks in those amps to gig with, and it really tightens them up, but the volume is even greater then.

It's been a while, but I've decided that my Jet has some hum that I'd like to eliminate. I have a friend who can replace caps but probably can't diagnose the hum that well. Would you say the most likely culprits are the two small silver electrolytics? Also, I love more bass...what would you up that black sprague value to for more bass?

[52 Bill]

It's been a while, but I've decided that my Jet has some hum that I'd like to eliminate. I have a friend who can replace caps but probably can't diagnose the hum that well. Would you say the most likely culprits are the two small silver electrolytics? Also, I love more bass...what would you up that black sprague value to for more bass?

So even with all of the original caps replaced, there is still some hum?

Describe the hum. Is it changed when you turn up or down any of the controls?

[Tom Phillips]

...Also, I love more bass...what would you up that black sprague value to for more bass?

That black Sprague is the cathode bypass cap of the pre-amp stage. It is likely a 25uF cap and would therefore already be producing the maximum bass you can expect from the pre-amp stage for guitar frequencies. Usually, people complain that these small amps have too much bass response for current playing styles and that they "fart out." I'd say that the best way to get more bass is to play the amp through a bigger speaker cabinet.
Tom

[Triocd]

So even with all of the original caps replaced, there is still some hum?

Describe the hum. Is it changed when you turn up or down any of the controls?

It's a buzz and it really isn't that bad...I thought it was normal for vintage tube amps until I had my other vintage amp with the same thing recapped and now it is totally silent. It gets louder as I turn the volume up on the amp with nothing plugged in the input. It isn't too bad until around halfway, from there it is definitely louder than I think it should be.

Please see supawah's post from above...he mentioned two electrolytics "in the center of the board" that look like they haven't been replaced. Do you think he's referring to the two small silver "things"? If those indeed haven't been replaced, I think I'll start there and see how it sounds.

[Triocd]

That black Sprague is the cathode bypass cap of the pre-amp stage. It is likely a 25uF cap and would therefore already be producing the maximum bass you can expect from the pre-amp stage for guitar frequencies. Usually, people complain that these small amps have too much bass response for current playing styles and that they "fart out." I'd say that the best way to get more bass is to play the amp through a bigger speaker cabinet.
Tom

I just cracked it open. The black sprague is indeed 25uF.

The two silver things I referred to earlier are marked 12/15V. I also just noticed way up under the hood, attached to the volume and tone pots are two red "tiny chief" capacitors. I can't visually tell if they're new or replaced (still bright red), but a quick google search didn't turn up any new ones, so they are probably original. It looks like one is labeled .01 MED and the other is .002 MED.

With all that said, maybe I should just replace all 4 of these and see what happens to the hum. Any thoughts?