JCA OWNERS!!! (RE)JOIN THE JET CITY LOUNGE!!!

[tucsonsound]

I just converted my Jet City 50 combo to be able to use the swappable 2x10 and 1x12 baffles from my custom pine Blues Breaker cab. I love the Jet City with the 2x10!

[mesa3077boogie]

tucsonsound, nice work. What 10's you using? I absolutely love the eminence red coat ramrods. I like them more than greenbacks, G12 75's and Vintage 30's. They can be had for $80 shipped (each) Im gonna pick up another pair in the next couple of months.

[trimix]

I've got two oddball Celestions loaded, a G10C-35 (from GK's 4x10 guitar cab) and a G10D-25 (from the Marshall Lead 12 mini-stacks.) Love the crunch of these cheap OEM Celstions, works great in the two amp set-up blended with the ET65 in the pine 1x12.

[mrfret]

Hello all! I've been lurking awhile, learning a few things. I'm kind of a newbie but I've done a couple of mods (fly heater wires and front panel switch and LED for jca5012c). I really love the tone I get from both the JCA5012c and the 20h.

Here's what I want to do: I want a master volume for the 5012c. I've never liked the constant fight to keep the 2 channels even during a show. I've been researching and found several ways to implement a MV on different amps and I THINK I should be doing the PPIMV mod. I think I even know where to cut in and back out but if someone could give me specific instructions for the 5012c so I don't screw it up, I would be most obliged!
TIA

mrfret

[mesa3077boogie]

Hi I havent seen anything on installing a MV on the smp. whats the PPIMV mod?

[mesa3077boogie]

Hello all, Im wondering about the clean VS the decadence mod for my JCA22H. My Jca22H shows my R5 (R42 on the 100 and 50 heads) to be a 1M cap. The SLO clean changes the 1M to a 470K resistor, adds a 470K resistor on a switch and adds a 39 or 68K resistor on a switch to ground.

When the switch is on it uses one 470K resistor and grounds one leg of the 39K (or 68K your choice) resistor.

When switched off it connects both of the 470K resistors in series to equal about 1M which is the original value so that you can retain the "stock" crunch tone.

The schematics for the JCA50 & 100 both have a 270pf cap in series with R42 (R5 on the JCA22h).

Since the JCA22H doesnt have the 270pf cap in series with R5 (R42 on the 50 & 100) should I add a 270pf cap to the 470K resistor that the switch will switch to in the "on" position (while it also switches to the 39K or 68K to ground) ? Or should I not bother? What is that 270pf in parallel with R42 on the 50 & 100 models doing in the first place as far as tone goes? If its adding high end I want it.

Lastly, the decadence mod removes the 1M R42 (R5 on the JCA22H) and uses a 1.5M (instead of 470K in the traditional clean mod) for the off position, and uses a 470K with a 100K (instead of the 39K or 68K in the traditional clean mod) to ground in the on position. When off it combines the 1.5M with the 470K resistor and states if gives a "better" crunch sound". Does increasing the resistance from 1M to nearly 2M increase the gain or something? The mod also claims it gives a better clean tone. Does the increased resistanceof going from 39K/68K up to 100K give less gain all together? Will further increasing the resistance keep lowering the gain?

Thanks

[mrfret]

Hello all! I've been lurking awhile, learning a few things. I'm kind of a newbie but I've done a couple of mods (fly heater wires and front panel switch and LED for jca5012c). I really love the tone I get from both the JCA5012c and the 20h.

Here's what I want to do: I want a master volume for the 5012c. I've never liked the constant fight to keep the 2 channels even during a show. I've been researching and found several ways to implement a MV on different amps and I THINK I should be doing the PPIMV mod. I think I even know where to cut in and back out but if someone could give me specific instructions for the 5012c so I don't screw it up, I would be most obliged!
TIA

mrfret

So I dove in headfirst and it worked! Here's a link to the post in the DIY section:
http://www.guitarampboard.com/forum/viewtopic.php?f=53&t=25109

[mesa3077boogie]

Nice work, did it add any new noise?

Does the fly heater wires really help with noise all that much for your?

[mesa3077boogie]

sounds nice, can you explain the mods?

[overdrivenel34s]

On my 2212c ive been now using an option 5 destination bump through effects loop on a pedalboard on top of the amp with a diamond looper pedal and use the remote input for a footswitch to turn it on and off. Works out great as solo boost. The destination bump pedal has a mini level pot that stays put and near impossible to accidentally change the setting. The level pot also has slow smooth range so so easy to dial in just the amount of level boost needed.

Before the effects return in the ampI have a malekko spring reverb left always set subtle since the amp doesn't have reverb and i like a drop depending on the room i'm in. So essentially on floor next to my mic stand i have channel footswitch and remote footswitch that serves as solo boost.

Would be cool if amp just had built in reverb and footwitchable boost with pot on amp to dial in the perfect amount of level boost. That would make it a perfect grab and go amp. However, this work around set up doesn't take that long to set up.

[mesa3077boogie]

Hello people. This message is in regards to the JCA scoop mod.

I did the scoop MOD for my JCA22H bypassing the cathode resistor R4 (2.2K) with a 22uf electrolytic 450V cap.

I replaced R10 (stock value 1M) with 2x 1M resistors in series as the instructions call for. For those same 2 resistors I bypassed both of them with a 150pf cap (instructions say to use 120pf). Then I grounded a .001 cap where the 2 1M resistors meet. The only result I can hear is a reduction in volume with no audible scoop.

Are you supposed to notice an audible increase in volume when doing the cathode bypass on your JCA amp?

Regarding the scoop mod:
The JCA50 has a 2.2M resistor for R34
The JCA22 has a 1M for the equivalent resistor R10

The scoop mod instructions for the JCA50 say to replace R34 with 2x 1M resistor in series, etc etc..

Question: since the JCA22H has a 1M resistor in R10, would I then replace the stock 1M R10 resistor with 2x 475K resistors instead?







Thanks,

mesa3077boogie

[Lance-a-not]

So I am grabbing a 2112RC (I think that is right, the combo with reverb?)
This evening... Can I hang with y'all??

I have lurked in here a few times and heard some great tones, looking forward to tweaking a bit

----------

Edit,

Got it, hate it, returning it... But you guys sound good with it!

Continue on!

[mrfret]

That was quick! LOL

[mesa3077boogie]

So I am grabbing a 2112RC (I think that is right, the combo with reverb?)
This evening... Can I hang with y'all??

I have lurked in here a few times and heard some great tones, looking forward to tweaking a bit

----------

Edit,

Got it, hate it, returning it... But you guys sound good with it!

Continue on!

What did it sound like that you didnt like?

What were you expecting that didnt line up?

[8Len8]

New JCA50H owner here. It'll take me a few days to go through all of the good info here. In the mean time, does anyone have any info on the "bright cap" mod? Id searched and could only find one vague reference to it...

[maynardo]

Hi, I'm new here . For several years, I am the owner and rebuilds jet city. I would like to show you one of them

[video]https://www.youtube.com/watch?v=lig4NeNu0DA[/video]

Sounds excellent. Where did you find the schematics for the hulk mod?

[maynardo]

I found on the internet, I built and modified
First post "zip file"
http://forum.metroamp.com/viewtopic.php?f=4&t=38678

That's just the cali/chupacabra thing with a tonestack after the first stage. I thought you actually had the real Hulk Mod.

If you changed it, give yourself some credit man, don't call it something that is not. It's your mod and it sounds great.

[HavPT]

Hi guys is there any way to know the outgoing voltages in the loop of the jca100hdm? Can I do it with a multimeter and a jack cable connected to the jacks on the loop? Sorry my ignorance but i don't know almost nothing about electronics .

[8Len8]

Can anyone tell me if the scoop mod effects both the JCA50's crunch and overdrive channel, or just the crunch channel?

[Tortuga]

Sorry, HavPT - not sure what you're looking for on the loop. There's no "voltage" on the jack unless there's a signal present, and that signal is A/C, which varies according to the strength and frequency of the sound being generated by the pickups.

8Len8 - scoop is crunch channel only.

[Thundarius]

I have been debugging a nasty buzz issue in my JCA50H for the last 2 days and I'm at a loss and seeking help. I put in new power tubes and biased the amp, installed a MM 3H choke, and raised the heater wires. Afterwards my amp was operating with a considerable amount less buzz/hum, almost non-existant.
I also installed a slope resistor mod but I was in a hurry and lifted a pad from the top I thought all was fine until I noticed that my bass and middle controls became far less usable than before. I pulled out the board and discovered the trace side pad had lifted to, so I hardwired it in. I had bought and planned to install the UF5408 Rectifier diodes as midnightlaundry suggested. I did those while the board was out. I also reflowed some connections including my tube sockets.
When I put her together and turned her on I had my bass and middle control back but the buzz was worse then before I made any changes. Gain, bass, middle, treble, and presence all seem to intensify the buzz and change it's sound.

nothing in the input, swapped out tubes, bypassed the toggle for the slope resistor, I pull all but the PI(v5) preamp tubes and I still get buzz(tone controls don't effect it without tubes though), with no PI the buzz is gone so i don't think it's coming from the power section. I was thinking maybe I missed something there. I wouldn't think that the diodes are bad I ordered them from mouser and they checked out okay on my dmm. Does anyone have any ideas?

[copperheadroads]

A quick question ,what resistor is the the Slope resistor on the jca20h ? I've found picks of the mod which is R24 but i think it is the jca50 ....... I believe it was R26 on my JCA22H .

[overdrivenel34s]

Here are a few comparison clips of my jet city 2212c stock speaker vs wgs reaper. The recording of the stock speaker actually sounded better then it did in person in the room but the reaper sounded way better in person and imo on the recording as well. These are clips from recordings of random playing before and after changing the speaker last month.

stock
https://hearthis.at/yw3cbrj7/jetcitystocktrain-verbadded/

reaper
https://hearthis.at/yw3cbrj7/jetcityreapertrain-verbadded/

Guitar was an epiphone sg. Mic was an sm 57. Recording interface was focusrite 18i8. Drop of reverb added in audacity (anwida dx reverb light plugin on default with something like 10% mix) prior to converting the clips to mp3s.

[8Len8]

I made some mods (slope, depth, scoop) to my JCA50H and have some questions, just to make sure I did things right.

- For the depth mod, you remove the red wire going to the FB point on the PCB, wire the 0.1uF cap end of the circuit to the PCB, and the pot end of the circuit to the red wire?

- A little goes a long way with the depth mod. It seems like turning the pot just 1/4 turn has a big impact.

- With the depth at 1/4, and both the scoop and slope mods enabled it seems like there's too much low end on the crunch channel. I included a 22uF across R45. I wonder if that's boosting the lows too much?

- The Crunch channel seems to sound a little "quacky" with the scoop and slope mods on. Anyone try playing with the values in that notch filter?

[mesa3077boogie]

I made some mods (slope, depth, scoop) to my JCA50H and have some questions, just to make sure I did things right.

- For the depth mod, you remove the red wire going to the FB point on the PCB, wire the 0.1uF cap end of the circuit to the PCB, and the pot end of the circuit to the red wire?

- A little goes a long way with the depth mod. It seems like turning the pot just 1/4 turn has a big impact.

- With the depth at 1/4, and both the scoop and slope mods enabled it seems like there's too much low end on the crunch channel. I included a 22uF across R45. I wonder if that's boosting the lows too much?

- The Crunch channel seems to sound a little "quacky" with the scoop and slope mods on. Anyone try playing with the values in that notch filter?

Yes 22uf anything on this amp is too much. Lower the cathode bypass caps as low as .047 or .068 ( think Im using my gain channel at .0047 and its plenty bassy and thinned out compared to stock