SuperBee
6057 posts
Jul 12, 2019
8:08 AM
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It’s an old bit of junk really. Been messed with so much it’s more like a homemade amp than worthy of the name ‘ampeg’
But, it’s in an ampeg cab with the jet chassis and transformers and preamp layout and circuit features, except it’s running 5881wxt power tubes and considerably more Voltage on the power amp than you’d find in a typical J12B
When I got it the preamp had been interfered with and also the phase inverter was not the original design. It had even more gain than the original.
I gutted the preamp and tried to rebuild it to spec. I got the circuit right but the layout is not quite like the original in one area. I studied a lot of photos but one area is wrong.
Anyway, it works but I decided it was a bit more trouble than it was worth and was inclined to emphasise certain frequencies so I eventually stopped using it.
Revived it tonight, and tried out the lone wolf mojo pad deluxe. Great!
AActually sounded good with the pad at -20 dB, set to ‘normal’. Could open the amp to 12 o’clock, and I discovered it’s an amp I’d really like to use. Sounded great with LW reverb, delay, octave pedals and an early 70s CM mic
Seemed as loud as my Princeton Reverb but maybe a bit bigger thanks to the 12”.
Now I have to find a gig to suit.
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jbone
2968 posts
Jul 12, 2019
11:41 AM
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No tech savvy here really, but that sounds some similar to my Silvertone 1482. 12w, 12" speaker, trem circuit. Puts out plenty as stock, one 12au pre amp swap in p3. This amp has served very well in the duo for 15 years now and even some 4 piece band work if they kept their volume reasonable. I use a hi z transformed military EV m43u mic and run it to a Lone Wolf Harp Delay. The rest is me.
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Music and travel destroy prejudice.
Reverbnation
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SuperBee
6059 posts
Jul 12, 2019
3:41 PM
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I used it at band practice. I usually take a Silverface Princeton Reverb and while I like that, I wondered if the 12” might sound a bit nicer. Dunno why I hadn’t thought to use the mojo pad before. I obtained that to use with a hot rod Deville and kinda forgot I had this other amp.
The j12B has an octal preamp, 6SL7s iirc, and there’s a lot of gain. I could probably just tube it down but the pad seems to do the trick.
I feel a small degree of attachment to the amp as it’s the first push-pull unit I’ve built.
I asked the bass player, who was in the direct line of Fire all night, what he thought of it, and he praised it.
Old amps though, I’m always a bit nervous about gigging with them. I think I’ll pack a harp attack backup rig if I do get around to using this on a stage.
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Lou
75 posts
Jul 12, 2019
5:17 PM
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Those old Ampegs sound great IMO not sure what the deal is with them but they have a very sweet & warm sound to them. I had a 40 watt custom amp built with an "Ampeg style" transformer & the circuit based on the old Bassman tweed with 2 10's in it and it really sounds good. Also had gain staging put on it so I could use it at low volume situations kind of an all in one package so far I'm real happy with it. I've never had the will or knowledge to tear into one or try and build one ! Good Luck with amp SB
Lou
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SuperBee
6060 posts
Jul 13, 2019
3:34 AM
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Thanks,Lou.
I figure maybe the cathode biased power amp might be a little warmer than the (for instance) Princeton Reverb. And the preamp is different of course with the old octal tubes. I think Ampeg had a reputation for using unusual tubes.
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TetonJohn
355 posts
Jul 13, 2019
10:40 AM
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Sort of on the subject: I have a ReverboJet (Golden Glow) I think a J12-R; has tremelo. I got it for $100 maybe 15years ago. Power tubes are 7591. A tech tore into it pretty seriously and made it single ended, using only one of those tubes. Now the groovy meter on the front doesn't work anymore. We were trying to make it more harp-friendly; in hindsight, I would have left it alone -- let it be what it was designed for. I have not giggerd with it in a while; had a harptone+ in front (and AFB), used the accordian input. AY and AX in that order. Band leader liked the sound. Maybe I'll put it back in the rotation.
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SuperBee
6063 posts
Jul 14, 2019
4:30 PM
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sounds like an interesting amp, John. i think any amp with an input marked 'accordian' is worth investigating for harp use.
this thing of mine has octal/pentode preamp tubes and i believe i had concluded they were microphonic and i could not be bothered trying to deal with that.
It did make some harsh noises and when i read about sorting out microphonic octal tubes it all seemed like an exercise i didn't need so i shelved the amp.
i didn't notice any of these problems when i used it last friday with the mojo pad though, so now not really sure what to think about the microphonics issue. i'll deal with it if it presents. probably in the same way :)))
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Prento
55 posts
Jul 14, 2019
5:02 PM
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Hi Dave,
Is it possible that your microphonic problem with your preamp valves is related to the big signal your microphone hits it with, a bigger signal than a guitar would hit it with, and by adding the mojo pad you are reducing that signal. If the cathode resistor has a cap bypassing it you might try removing it to see it it makes a difference.
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SuperBee
6064 posts
Jul 15, 2019
4:24 AM
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I reckon that’s a factor, Prento.
I could probably redesign the preamp circuit a little. I thought about a 6SN7 pre, but they draw considerably more than a 6SL7 and I suspect my PT is already working quite hard supplying those 5881s.
Yeah there is a 100 uF bypass on the pre. I’ve messed with clipping the bypass on a couple amps. On my 5F1 it was fine, and it’s debatable whether it’s part of the design anyway. On my valve jr I clipped the preamp bypass cap and while it did make it more manageable I thought it was detrimental to the sound overall. The thing just became very muddy as it was turned up, so I reinstalled it.
I am quite pleased with the sound I was getting from the Jet with the mojo pad. I’d like to gig with it, but I think too loud for the cafe where I usually use a champ, and my other gigs can handle the Sonny Jr 2; find it difficult to leave that one at home when there’s an opportunity to use it.
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Prento
56 posts
Jul 15, 2019
5:01 AM
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Have you thought about those silicone vibration rings that you put over the valve? I’ve seen photos of valves with 2 rings to absorb the vibration.
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