Bought a jet city need some help

[GCKelloch]

Sure thing, Brent. I tend to obsess on these things. It make sense if you can upgrade to something you'll like better without taking a loss. The JCA20HV isn't much more expensive if that's what you mean. It's cleaner & darker, yet more "open" sounding with a bass "Depth" switch and FX loop. I'd recommend the same tubes for that amp as well.

 

[fusedbrain]

A bit late to the party, but I have a ton of experience with the JCA22H.
A few thoughts after reading through the thread so far:
Greenbacks Greenbacks Greenbacks!!. My JCA22H and my SLO sound best through greenback speakers. There is an upper mid cut in SLO style amps that is too much combined with the upper mid cut of V30's.

Getting the bias right helps a lot, but there is no easy way to check the bias with these amps, as there are no 1ohm bias resistors on the cathodes, and it's tough to find bias probes to fit the EL84 sockets. That leaves the "transformer shunt" method of setting the bias, and that's best left to a tech who knows what the hell they are doing, as the B+ voltage is "shunted " through the multi-meter during this procedure. Best thing to do is add the 1ohm resistors if you decide to mod the amp (more on this later )

Tubes make a difference ( Duh!). The TubeStore Preferred series 6BQ5's are NOS Russian Military tubes. They sound stellar, but are pricey and are probably overkill for an amp that gets all of it's overdrive and most of it's tone shaping from the pre-amp. I have Mesa Boogie branded EL84's in mine. I think they are chinese. JJ's are OK too.
For pre-amp tubes, the stock Chinese are fine, but you can lower the noise floor by using Ruby HG+ tubes ( from ValveQueen ) in V1 & V2. The JJ version is a little less bright than the Chinese.
DO NOT use any spiral-filament Russian tubes in V3 or V4, as both these positions are cathode followers.

Overall, these amps are good value for the money, and the build quality, the transformers, and the components / PCB board quality far exceed what you would expect for the price. And while they sound OK in their stock config, with a few mods they can sound INSANELY good. There is a ton of info on mods for these amps, and the "SLO" mods that change a few component values to match an SLO schematic go a long way to creating a really great sounding amp.
There are essentially 2 levels of complexity to the various mods:
1- you can change a few resistor and cap values in the pre-amp and add a depth control without removing the PC board. Because the PC board is such high quality, with through plated holes, basic component swaps can be done from the top of the board with no issues. The "SLO" pre-amp mods done this way will significantly improve the tone of the amp and will be inexpensive, even if you get a tech to do it, as it can be done from the top of the board.
2- If you are willing to pull the board yourself, or pay a tech a bit more money to do it, you can take these amps from good to f'n incredible. This involves doing the "SLO" mods to the pre-amp, plus adding a 5 - 10h choke, and modifying the power supply filter cap scheme to match a real SLO. While you're in there, now is the time to add the 1ohm bias resistors to the cathodes of the EL84's. You'll have to cut 2 traces on the PCB, but its easy to do and well worth the effort

The only other tweak I had to make was to change the slope resistor from 47k to 56k to compensate for the extra midrange from the EL84's vs 5881's. The depth mod fills in the bottom end that the EL84's are lacking.
I have real Soldano SLO here to compare with the modded JCA's I've done and it's shocking how close you can get to the sound and feel of a real SLO with a 22watt, EL84 based amp.

 

[fusedbrain]

Just noticed that in the first 2 pics I posted, the depth pot was installed in the back of the amp, but not wired up yet, and I hadn't installed the 2 new 500k gain pots yet either.....but you get the idea....

Also, sorry for the sideways pics

 

[GCKelloch]

Those seem like excellent and well thought out mods, fusedbrain. My only quibble is with tube choices. I'm sure you know that like the Preferred Series and Groove Tubes, Ruby Tubes are just rebranded Shuguang, Sovtek or JJ tubes. All current tubes are from those manufacturers and are either tweaked or just rebranded. I know Chinese and Russian preamp tubes can be very good, but I believe the JJ models I mentioned have better clarity and sweetness for the positions I recommended. Virtually everything else being made is more mushy and/or fizzy. I suspect Soldano would be using the sweet and balanced ECC83MG and dynamic ECC803S (in the PI) if he was privy to the sound quality over the somewhat maligned ECC83S that turns some off to JJ in general. I believe the next runners up for clarity and punch in 12ax7 and EL84 tubes to be Tung Sol RI, and am curious your opinion of them. More mushy or fizzy tubes can work well for certain things, but my impression is that the Soldano sound is about punch and sweet clarity without fizz. Fine points I know, but why not spend less if the JJ's and Tung Sol meet the target sound without any drawbacks?

I may be mistaken, but I believe EL84 tubes compress less than 5881, which would mean they actually have more bass. Tube s don't really have freq response limitations within the audible range, but compression and harmonic generation can alter the spectral emphasis. The comparative lack of bass you hear could just be a combination of the lower wattage and the OT compression kicking in. If you are going to perform the more extensive mods, you might replace the OT as well with the beefy Classictone 20W+ Fender type I suggested. You may not need the slope resistor change in that case? Also, the midrange quality of the EL84's may be better left as is for single coil guitars?

"Greenbacks" are a few different types AFAIK: the 20W Heritage G12M or the darker Chinese 25W G12M. They work well for many things, but it depends on what you want. The other recommended speakers have equally valid application. Something a bit brighter above ~3.5kHz might be better for Metal or Punk. The Chinese made G12H Anni or the brighter EMI 'Wizard' are both a good match for a SLO sound -- brighter, but still sweet and woody and with deeper bass than G12M types. The WGS 'ET90' might work if you want a more crisp Fendery sound -- more punchy and ~4kHz chimey than the ET65, but not piercing. That one's a gamble. I'd try replacing one of the V30's with either a WGS Invader 50, Veteran 30, or maybe an ET65.

 

[fusedbrain]

Yeah the Ruby's are rebranded JJ's and Chinese tubes, but the HG+ versions that Laura ( ValveQueen ) sells are screened for noise and micro-phonics and burned in for 72 hrs. It makes a difference.
As far as I know, all preferred series tubes are STR tubes manufactured for the TubeStore to their specs, with the exception of the 6BQ5, which is NOS russian military. Preferred series tubes are NOT re-branded generic tubes.

I haven't tried the JJ ecc83MG, but the concept of a mid-gain tube would actually work well in many applications where you would use a 5751 to back down the gain in a super-saturated amp like a 5153 stealth etc...Could work well here in V1 as well.

I haven't tried the Tung-Sol EL84 either, but I have used the Mullard re-issue EL84 in a Marshall 18watt build, and it's very good. I would assume they are very similar.

As far as the JCA22 is concerned, there is so much cascading gain in the pre-amp that the main issue is low micro-phonics and low noise. My experience has been that changing tube brands in this application does not really make that much of a tone difference. Same thing with the power amp. All you need the 2 x EL84's to do is just amplify what comes out of the phase inverter. The signal is already so mangled that it's not a big deal what tube brand you use. If we were talking about a simple Plexi circuit, then I'm all in on what you are saying.

I also agree that the "Soldano sound" is all about clarity and punch, but it's the circuit design that gets you there. Check out the power supply in an SLO. The mojo is in the B+ scheme. The tubes are the icing on the cake.
That's why you need to mod the B+ and filtering in the JCA22H to get all the way there to the SLO vibe.

 

[GCKelloch]

Makes sense. BTW, I added more to my last post b4 you replied.

The medium plate ECC83MG is only ~5% lower gain than the ECC83S (the highest gain CP 12ax7). It's actually still hotter than most current 12ax7, but generally better balanced, sweeter and more open/articulate. The ECC803S is ~10% less gain, but higher output power. It's mostly the harmonic emphasis that changes compared to the ECC83S and other short plate tubes. They both might be nice combined with one or two of the Valve Queen Chinese Ruby 12ax7? AFAIK, they generate more high harmonics than the JJ's -- maybe better in high gain stages? I'd probably want the JJ ECC803S in the PI, but they could be swapped to personal taste. My point is not to spend more money unless for a very specific requirement. I can understand that the B+ scheme affects the dynamics substantially. I think your mods are all worth doing, but Brent may not be up for all that.

Preferred Series STR tubes are still made in the Shuguang or Reflektor factories -- tweaked version of their offerings. Their EL84 may be better, but may not be worth the price unless maybe the plate limit has been increased, as with some TAD tubes. At least one TheTubeStore reviewer likes them better than his old Sylvania or RCA 6B5Q. All indications point to a slightly cleaner/more punchy Tung Sol RI EL84, but as you say: it may not matter much with a high gain amp. That's why I recommend the cheaper Tung Sol RI EL84 -- probably just a lower grade version of the same tube for half the price, but still robust, punchy & chimey, and generally preferred over JJ or other CP tubes. The Mullard RI EL84 are reported as comparatively ratty/duller -- maybe nice for an old Plexi, but I wouldn't for a SLO sound.

Researching and considering more about the stock OT, I'm not sure (probably the Chinese?) were using quality M6 Steel back when the Jet City amps were designed, if they even do now. The stock OT also probably has plastic layer insulation. Fully grain-oriented M6 Steel has very high directional permeability, low hysteresis, and very low induction saturation. That equates to better signal clarity, less low level hash, and a more gentle saturation/compression curve. Upon first thought, plastic might seem a perfectly good insulator, but my guess is it's more prone to static build up than paper/lacquer. That can create eddy-current losses as the magnetic fluxing affects the static field. Such low level eddy-currents would likely cause "phasiness" that thins the high end. Just a hunch based on some things I learned about guitar pickups, but I wouldn't be surprised if the stock OT has those issues. If you do decide to replace it at some point Brent (just a matter of re-soldering the existing OT wires to the same points on the new OT and probably drilling a few screw holes), I'd also install a Classictone choke (involves research on where to connect a few wires and drilling some screw holes). I probably wouldn't replace the power transformer. There might be some low level eddy-current interference between circuits, but there's no guarantee a paper/lacquer PT would make an audible improvement, or that there is even a suitable replacement. That would take some research.

 

[Racerxrated]

I've tube rolled with every amp I've owned, and a couple facts stand out to me.

First fact, no new tube can match older NOS or ANOS in tone or quality. The amps that are most sensitive to tubes, vintage Marshalls or Mesas sound WAY better with Siemens, Mullard, Winged C EL34s or Sylvania 6L6. Also, Pre tubes like 9th gen Chinese, Mullard, Amperex, Tungsram, I could list many more and I'm sure you get the point. Yes, these can be spendy but you can save a TON by buying used but strong. I have over 150 total ANOS power and pre tubes now in my stash and they will last me until I kick the bucket. When I gigged 2-3 weekends a month a couple years back I never had a tube failure. Only recently one of my Chinese gave up the ghost. That's pretty good reliability. I would recommend everyone start looking for cheaper used vintage tubes and start building a stash.

Secondly, amps that are all about the power section, like an SLO or a Wizard, don't care as much about the tubes you put in...the most important factor is can they hold up to the mighty voltage the amp puts out. The wafer 5881s Soldano uses sound great AND can withstand the plate voltage. Same for the Wizard, the JJ EL34L can stand the plate voltage. I've rolled tubes in these amps when I owned them and very little difference was heard between vintage or modern production tubes, the SLO was most sensitive with pre tubes IMO. But both the Wizard and SLO still sounded great with new or vintage tubes, while a vintage Marshall can go from amazing with vintage tubes to just OK with modern production tubes. Big differences too in a Mark 2C+ if you use vintage Sylvania 6L6 and Chinese/Tungsram pres vs JJ6L6 and JJ pres. Totally different amp.

 

[GCKelloch]

Perhaps it's the preamp voltage levels that make tubes sound more similar than in a Marshall, Mesa or other lower preamp voltage amps? Maybe it's not so much the brands that matter in a SLO, but the plate structure might cause harmonic emphasis changes regardless of the voltage? FI, a long plate IE, Tungsram, JJ, Sovtek etc may still have more low end emphasis than any short plate tube at the same voltage. That's were the spectral balance, clarity and sweetness might be noticed. Have you ever compared a full set of long plate preamp tubes to a full set of short plates in a SLO? I suspect the difference might be pretty obvious at the same gain tone stack settings, but not as obvious on the OD channel. AFAIK, raising the voltage supply decreases distortion and compression, but a full set of mushy sounding Sovtek preamp tubes may still sound quite different in an SLO than a set of RCA's at the same voltage, even at the same relative gain. Crappy mushy sounding tubes are also much less likely to handle higher voltages well. Certainly old tubes are better quality, but 5 good ANOS/NOS preamp tubes can be more than $200. If it doesn't matter that much, why not just get the cheap JJ's I suggested and/or 9th gen Shuguang for ~$70? They should still last many years, no?

All that being said, I can see the value in sourcing some GE 6B5Q for as much as ~$100/pair, when TheTubeStore PS EL84/7189 cost ~$70/pair and may not last very long. I noticed that The Valve Queen is selling the long plate NOS IE brand 12ax7 for $25. Seems like worth grabbing a few for PI use while they are still available -- probably better quality and richer sounding than the JJ ECC803S.

P.S. JC does offer an OT upgrade for their ~20W amps to be back in stock in under a month here: https://reverb.com/item/3139985-bulldog ... 3cadhVccwA

That Classictone is probably equally great for less cash, but it might require drilling screw holes. The stock JC 20W OT is actually just 3.6k Ohms, so you could choose something around that value from Classictone if you don't want any high end reduction. My understanding is that higher primary impedance tightens the bass as well as reduces distortion & high end. Check this video comparison of the stock 20W 3.6k OT to an 8.4k Hammond OT. The smaller Hammond OT doesn't seem to have less bass than the stock OT, but it's hard to tell: https://www.youtube.com/watch?v=tiNuXPGiVaM

Hammond are actually very good and inexpensive. They may have some more power and impedance options at this point. I think that video shows that the low impedance stock OT is a big reason the amp is very bright. I'd at least change the OT and try a few different tubes, even if you trade for the 22WH. Just follow standard tube amp safety precautions, and solder the existing wires accordingly. Someone here might even be willing to check your work from pictures just to make sure it's OK b4 you try it out?

 

[riffermadness]

Depth mod and tubes switch both work great on these amps..I had a Custom 22 that I did the depth mod to and tube rolling and it sounded great.
You can do the depth mod yourself if you know how to drain the amps capacitors so you can work safely,after that its very easy and well worth it.

 

[BrentSSL]

Yeah I jumped ship on jet city don't think Soldano tone is my thing