Bought a jet city need some help

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BrentSSL

BrentSSL

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I traded a guitar for the JCAh it has the SlO overdrive channel. I have a Avatar with V30s in it and that overdrive channel is a little too top end sizzle. Does this amp work better with it's own cab possibly? It sounds to fizzy fuzzy and not very muscular and sounds kind of thin. Any dialing suggestions?
 
keep the presence at 0 and turn it up as loud as you can. These amps need volume to open up. Also, check the bias, they're biased ridiculously cold from the factory. My 50h was biased at 7mA per tube.
 
The JCA50 / 100 are the same as the Hot Rod 50+ / 100+, so not quite SLO but still very cool.

I added a depth control to mine (very easy, like 3 parts and a hole in the chassis), works great to add some thickness.

Very bright amps though, I keep treble quite low.

Biasing is critical, mine was also like 7mA to 10mA when I got it. I biased up to I think 35mA and it was like a different amp, way thicker, way clearer, way less fizz/brittleness.
 
Sweet thank you would it's own cab help tame it a bit? Or maybe gt1275s or possibly Sheffields from a 6505 cab?
 
Soldanos IMO sound way better with Greenbacks or similar. I've owned 1 HR100 and 3 SLOs, and they all hated my V30 cab.
 
BrentSSL":1n92rm0d said:
Sweet thank you would it's own cab help tame it a bit? Or maybe gt1275s or possibly Sheffields from a 6505 cab?
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Avatar cab is better quality than the jet city cabs. The eminence made speakers in the jet city cab I had weren't great either. Perhaps try a v30 with an m65 creamback, I found that combo smooth highs and added some bottom to my bogner cab vs 2 v30s
 
I don't remember where it is on the PCB, but another thing you can do to reduce the amp's brightness (besides tubes and the much needed re-bias) that's fairly easy to do is to take the treble bypass resistor out of the signal path of the gain pot; both gain pots if it's the 2 channel model. This is the exact same thing that the bright switch does on the rhythm channel and the "Haynes mod" does on the lead channel for the SLO, and what the bright switches do on the Decatone. It does make a difference. And unless your V30's and 75T's are VERY broke-in, I'd also recommend a Greenback cab since the highs aren't as strong with Greens. Just my $0.02.
 
BrentSSL":rxn5gy53 said:
Oh and mine is the 20 watt can you bias those?
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yeah you can. JCA set their bias super low for some reason, straight into crossover distortion range.

As for speakers, I use mine with Greenbacks.
 
I'm not sure how old the cab is but I went through the same thing a few months ago when I was trying out a 50 watt single rectifier with a v30 marshall cab. It seems like the v30 is really bright but when you listen to it on recordings it's not. Super confusing
 
Recordings are often EQ'd to fit a mix, and the speaker may be mic'd off-axis to roll off the high end. V30 are a relatively harsh speaker, as are the Chinese made G12T-75 . You might try the V-Type and/or G12-65, or the equivalent WGS Veteran 30 and/or ET65. They combine very well.

Lowering the Presence actually closes down the amplifier as the neg feedback squelches the dynamics. Turning the Treble way down with the Presence up reduces brightness while allowing the amp section to "breath". You could add a resonance (low end neg feedback ) knob, but the amp can sound boomy. You could try using a cap in the resonance circuit to limit the low end NF reduction to above 200~500Hz if you don't want boom, but want more mid crunch. I wrote something about the JC amps on Thu, Nov 01, 2018 2:52am you be interested in here: viewtopic.php?f=3&t=199797&p=2211771#p2211771
 
I might just go back to the drawing board I read all that info and wow that is in depth
 
Go back to the drawing board? Those JC amps are decent amps to mod. The yellow Mallory 150 caps and preamp tube compliment I mentioned should give it a fuller tone with a more clear and dynamic harmonic structure. I'm not sure the impedance of the stock OT, but I'd look into a Classictone. They're made with high quality M6 Steel and considered equal to Mercury Magnetics for less money. This 20W+ Fender type upgrade has virtually the same primary impedance used for most 2 x
EL84 amps (10% higher is barely noticeable): http://www.classictone.net/40-18087.html
It should have more bass punch and less compression than the Marshall 18W: http://www.classictone.net/40-18037.html
A deep & punchy OT is a big part of the SLO sound. The Marshall 18W OT is likely "softer" sounding. I doubt the 18W rating would be an issue, but you might ask them if you want it.

You could have a really nice amp for a few hundred bucks -- plus labor cost if you can't do it yourself. You could spend a lot more on another OT, but I'm not sure it would be noticeably better -- assuming the Classictone would sound better than the stock OT in the first place.

I missed that you said it was a 20W amp. You might consider sourcing some pre 70's era 6BQ5 (US made EL84). They are actually beam tetrodes and sound more like KT66 than an EL34 pentode, with less 3rd harmonic distortion and harmonic "swirl". The old GE are the most sought after, with the Sylvania a close second. The US made RCA are supposedly "harder" sounding with less high harmonics -- warm, but more crunchy.

P.S. Those upgrades may not make much audible difference if the preamp circuit is the SLO OD channel. The OD channel rolls off above ~2kHz, so the improved clarity and punch may not be so obvious. If so, you might consider adding another input that taps into the 2nd gain stage of the V1 tube (if the ~2kHz filtering is wired b4 that). I'd guess you could also wire a series cap b4 that stage to roll off some low end for a crisp crunch channel (depending on the gain and biasing of that tube)? Then you'd want separate Gain and Master volume knobs. You could replace the Gain and MV pots with dual concentric pots of the correct value to save space. That's still all fairly cheap and easy to do if you can grasp the circuitry. You could then use an A/B box if you want channel switching from two different pedal chains. Might be a nice little setup.
 
That is wayyyy above my pay grade and knowledge I know a little in the way of caps and how boards are built. Like the difference between old Marshall boards and new ones. How the new Marshall boards don't have the small holes at the saughter points to make them easier to work on. I also know Mesa does the same thing. However I wouldn't know where to begin with this amp. So unless there's an amp guru like you in Ohio somewhere that can do all that I'm kind of out of luck. I'll try it with some greens this weekend and if that doesn't work I'll go from there. Also in that older post you said that a dual rectifier is a direct copy of a SLO 100. I completely agree with you I had a Rev F and we compared it my friends Soldano and the Mesa could get there. However I'm having trouble finding usable tones in the Jet City personally. If I could get it close to a dual rectifier I might have something but that seems to not be the case right now.
 
BrentSSL":3e7brn6r said:
That is wayyyy above my pay grade and knowledge I know a little in the way of caps and how boards are built. Like the difference between old Marshall boards and new ones. How the new Marshall boards don't have the small holes at the saughter points to make them easier to work on. I also know Mesa does the same thing. However I wouldn't know where to begin with this amp. So unless there's an amp guru like you in Ohio somewhere that can do all that I'm kind of out of luck. I'll try it with some greens this weekend and if that doesn't work I'll go from there. Also in that older post you said that a dual rectifier is a direct copy of a SLO 100. I completely agree with you I had a Rev F and we compared it my friends Soldano and the Mesa could get there. However I'm having trouble finding usable tones in the Jet City personally. If I could get it close to a dual rectifier I might have something but that seems to not be the case right now.
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I have tried a few 2 channel Duals and the low end is too bloated, tubby to be very similar to the SLO, even after boosting. But, a 2 channel Triple was a different story...boosted it very much reminded me of any of the SLOs I owned.
 
Racerxrated":3h2f5unw said:
BrentSSL":3h2f5unw said:
That is wayyyy above my pay grade and knowledge I know a little in the way of caps and how boards are built. Like the difference between old Marshall boards and new ones. How the new Marshall boards don't have the small holes at the saughter points to make them easier to work on. I also know Mesa does the same thing. However I wouldn't know where to begin with this amp. So unless there's an amp guru like you in Ohio somewhere that can do all that I'm kind of out of luck. I'll try it with some greens this weekend and if that doesn't work I'll go from there. Also in that older post you said that a dual rectifier is a direct copy of a SLO 100. I completely agree with you I had a Rev F and we compared it my friends Soldano and the Mesa could get there. However I'm having trouble finding usable tones in the Jet City personally. If I could get it close to a dual rectifier I might have something but that seems to not be the case right now.
Click to expand...
I have tried a few 2 channel Duals and the low end is too bloated, tubby to be very similar to the SLO, even after boosting. But, a 2 channel Triple was a different story...boosted it very much reminded me of any of the SLOs I owned.
Click to expand...

It has to be one of the earlier ones with the series effects Loop. I think the Rev G was what they landed on so they wouldn't get sued LOL. If you have a REV F or earlier it can get there as long as you bypass the loop.
 
BrentSSL":29p83b66 said:
That is wayyyy above my pay grade and knowledge I know a little in the way of caps and how boards are built. Like the difference between old Marshall boards and new ones. How the new Marshall boards don't have the small holes at the saughter points to make them easier to work on. I also know Mesa does the same thing. However I wouldn't know where to begin with this amp. So unless there's an amp guru like you in Ohio somewhere that can do all that I'm kind of out of luck. I'll try it with some greens this weekend and if that doesn't work I'll go from there. Also in that older post you said that a dual rectifier is a direct copy of a SLO 100. I completely agree with you I had a Rev F and we compared it my friends Soldano and the Mesa could get there. However I'm having trouble finding usable tones in the Jet City personally. If I could get it close to a dual rectifier I might have something but that seems to not be the case right now.
Click to expand...

I kinda' figured that it was a bit much after I wrote it all. I actually just get all my info from real "amp gurus". I'm not sure I would attempt some of the mods I suggested. The OT replacement wouldn't be difficult, but it may not make much difference.

Even if different speakers do the trick, I'd still consider changing the preamp tubes for the JJ ECC83MG and ECC803S (not the ECC83S) for ~$40 from Eurotubes or TheTubeStore. The Medium Gain (MG) is like an Amperex "Bugle Boy". It's probably the sweetest & clearest new 12ax7 type tube. All reviews I've read report a smoother, yet articulate distortion compared to other CP (Current Production) tubes. The long plate (803S) in the V3/PI (Phase Inverter) pos will add girth and a sweet dynamic detail without the rasp or fizz of other CP preamp tubes. The overall effect will be a darker & sweeter, but more articulate overdrive. Some prefer the Sovtek 12ax7 LPS in the PI slot. It's a more "mushy" tube -- softer, but maybe more fizzy. You'll probably have to turn the Gain knob up a notch to get the same preamp overdrive with those JJ tubes, but the emphasis will be more in the low midrange with a sweeter and more-dynamic high end that will complement any speaker (or OT).

If you don't want to seek out some US made 6B5Q beam tetrode power tubes, the Tung Sol RI EL84 are probably the best CP EL84's. Maybe more fizzy than JJ, but I think the JJ may be "harder" sounding with less harmonics. The TheTubeStore "Prefered Series" EL84/7189 have more of a clean 6L6ish sound. My guess is they are just selected Tung Sol RI -- probably cleaner and harder sounding. The Mullard RI may be a bit muddy compared to the Tung Sol, essentially defeating the advantages of the JJ preamp tube setup. I'd try the Tung Sol RI. They can be ordered as matched pairs from TheTubeStore.com. I think you can also specify a grade. I wouldn't get the highest grade unless you want a very clean amp sound. The OT might be the weak link there.

If the amp thins and mushes too much for you when cranked, you might then consider a beefier Classictone OT. If it doesn't already have one, a choke can smooth the amp sound. Those parts are really not hard to install with a few basic tools and some know how. For future reference, there are several websites that show how to do that and much more. Some mods, like the 10% power mod, are much easier than you might suspect.

You may just want to swap out one of your V30's for something like a G12M-25 or one of the other smoother choices suggested in this thread. You'll still get the deep V30 bass punch, but you won't hear the piercing ~3kHz if it's on the bottom (unless you listen very close to on both vertical and horizontal axis). BTW, the WGS 'Invader 50' is a smooth GB-type with deeper bass punch and a bit more 5~6kHz "detail" than the G12M-25...and for less money. Again, a sweeter sounding preamp tube setup will make that high end detail sound...sweeter.

The tubes and speaker are the cheapest solutions I can think of.
 
I really appreciate all your help this is great info and I'm using it to my advantage for sure. I just need time to experiment with the amp more and I think the speaker change is where I need to start. I also know there is another head which is an upgrade from the one I have with bright switches for a similar price.
 
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