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

[Jay]

This gets me to wanting to see about modding the JCA100H for EL34s. After finally spending time with an EL34 amp after years and years with loads of 6L6 amps, I can say I prefer an EL34 base over 6L6. Mainly due to the loose character on the lower end as opposed to a tighter more articulate character I've typically found with 6L6. I'm not a djent or metal player so I don't need 'ninja lows' or anything super tight, but being more a fan of old school Marshall recordings that's more along what I like.

Did you see the stuff we've been posting above about the voicing switch? I don't have a ton of experience with EL34-based amps, but I truly believe the voicing switch that CTN and I did get us in that realm. It sounds like we're both looking for a bit more 'elasticity' and 'feel' to the sound, which I've been experiencing with that switch. A couple bux and a couple hours' work, and you may find a bit of what you're looking for. And, if you or someone ever do successfully convert over to EL34's, I'd be extremely interested in hearing the outcome. That said, I do seem to recall the Valve Queen running KT66's in her JCA, and I think FRPC was doing same. I guess that'd be good reference links to post here, eh?

Yeah FRPC has KT66 tubes in his currently, and IMO that sort of bridges the gap between 6L6 and EL34. He did a quick demo with EL34 and I thought they sounded great, but it isn't safe to run them.

With the indexing/referencing, I think that would be a great format. Example, scoop mod gets its own 'post' in the mod thread, that way you can isolate mods and jump right to it when linking to the mod. I think all relevant schems, gut shots, tutorials, etc for that specific mod should be in the same post, unless you think it would exceed the character count. I guess we would have to weigh out how many mods there are vs how much mod specific info there is.

Maybe a new sub section on the board? Sort of how RT has manufacturer specific sub sections. That might be a better solution so the amp section here isn't 'clogged' (maybe that's not the right word) with 17 Jet City threads on the front page.

If I recall, the Tung-Sol EL34B has very similar operating perameters close to that of a 6L6, so.....those may be a very close drop in and bias, but let me check into it first. Otherwise, to run EL34s, or ANY octal powertube tube for that matter, the Power Transformer would need to be changed, a few resistor/caps need to be changed and MAAAYYYYYBEE the Output Transformer. I could into some stuff and probably put together a list of changes. That way, anyone can run any tube to their hearts content, and there is the possibility of running dual bias circuits for different pairs of power tubes.

TECHNICALLY, the KT66 is not a drop in and bias replacement, but it's very close. You have to mismatch the impedance of your cab, so if you have a 16 ohm cab, plug into the 8 ohm jack on your amp, if you have an 8 ohm cab, plug into the 4 ohm jack on your amp.

What I would need from a JCA50 and JCA100 owner is to see if there is a sticker on the power transformer that gives the Volts/Amps details. I think the JCA20H has a sticker on it that says all of the ratings. I don't know if the bigger boys do. In any case, I could still find a suitable replacement if anyone is interested in doing the swap. I think I may shut down my DIY project for a spell and try to pick up a 50 or 100 to get some of these crazy mods done.

As far as the mod threads, maybe a single thread per mod in the DIY section, with a link index on the first page here. That sounds good to me.

[racerevlon]

This gets me to wanting to see about modding the JCA100H for EL34s. After finally spending time with an EL34 amp after years and years with loads of 6L6 amps, I can say I prefer an EL34 base over 6L6. Mainly due to the loose character on the lower end as opposed to a tighter more articulate character I've typically found with 6L6. I'm not a djent or metal player so I don't need 'ninja lows' or anything super tight, but being more a fan of old school Marshall recordings that's more along what I like.

Did you see the stuff we've been posting above about the voicing switch? I don't have a ton of experience with EL34-based amps, but I truly believe the voicing switch that CTN and I did get us in that realm. It sounds like we're both looking for a bit more 'elasticity' and 'feel' to the sound, which I've been experiencing with that switch. A couple bux and a couple hours' work, and you may find a bit of what you're looking for. And, if you or someone ever do successfully convert over to EL34's, I'd be extremely interested in hearing the outcome. That said, I do seem to recall the Valve Queen running KT66's in her JCA, and I think FRPC was doing same. I guess that'd be good reference links to post here, eh?

Yeah FRPC has KT66 tubes in his currently, and IMO that sort of bridges the gap between 6L6 and EL34. He did a quick demo with EL34 and I thought they sounded great, but it isn't safe to run them.

With the indexing/referencing, I think that would be a great format. Example, scoop mod gets its own 'post' in the mod thread, that way you can isolate mods and jump right to it when linking to the mod. I think all relevant schems, gut shots, tutorials, etc for that specific mod should be in the same post, unless you think it would exceed the character count. I guess we would have to weigh out how many mods there are vs how much mod specific info there is.

Maybe a new sub section on the board? Sort of how RT has manufacturer specific sub sections. That might be a better solution so the amp section here isn't 'clogged' (maybe that's not the right word) with 17 Jet City threads on the front page.

If memory serves, Drew modded his JCA100H to KT88'S but then Doug and Mike both said "Bad Idea!!!" so he reverted it to 6L6s.

[Jay]

This gets me to wanting to see about modding the JCA100H for EL34s. After finally spending time with an EL34 amp after years and years with loads of 6L6 amps, I can say I prefer an EL34 base over 6L6. Mainly due to the loose character on the lower end as opposed to a tighter more articulate character I've typically found with 6L6. I'm not a djent or metal player so I don't need 'ninja lows' or anything super tight, but being more a fan of old school Marshall recordings that's more along what I like.

Did you see the stuff we've been posting above about the voicing switch? I don't have a ton of experience with EL34-based amps, but I truly believe the voicing switch that CTN and I did get us in that realm. It sounds like we're both looking for a bit more 'elasticity' and 'feel' to the sound, which I've been experiencing with that switch. A couple bux and a couple hours' work, and you may find a bit of what you're looking for. And, if you or someone ever do successfully convert over to EL34's, I'd be extremely interested in hearing the outcome. That said, I do seem to recall the Valve Queen running KT66's in her JCA, and I think FRPC was doing same. I guess that'd be good reference links to post here, eh?

Yeah FRPC has KT66 tubes in his currently, and IMO that sort of bridges the gap between 6L6 and EL34. He did a quick demo with EL34 and I thought they sounded great, but it isn't safe to run them.

With the indexing/referencing, I think that would be a great format. Example, scoop mod gets its own 'post' in the mod thread, that way you can isolate mods and jump right to it when linking to the mod. I think all relevant schems, gut shots, tutorials, etc for that specific mod should be in the same post, unless you think it would exceed the character count. I guess we would have to weigh out how many mods there are vs how much mod specific info there is.

Maybe a new sub section on the board? Sort of how RT has manufacturer specific sub sections. That might be a better solution so the amp section here isn't 'clogged' (maybe that's not the right word) with 17 Jet City threads on the front page.

If memory serves, Drew modded his JCA100H to KT88'S but then Doug and Mike both said "Bad Idea!!!" so he reverted it to 6L6s.

I think he had the KT88s in his HDM, which is still not a good idea. EL34s, 6550s and KT88s draw more current on the heaters and the plates/screens. I don't think the PT is rated for that much draw.

[Hipster Salad]

One mod that I'd like to do on my JCA100H and the Earhart, is add an LED light on the chassis when the 2nd channel is activated. The HDM has this stock, so would it be as simple as copying from the HDM schematic? I guess the Depth control would be copied from the HDM schematic to, right?

On the Earhart, the footswitch is 3 buttons, layout is Clean, 2nd Master, and Overdrive. All three have one LED light per switch and light up when engaged. When all lights are off, that indicates 2nd channel is active, Overdrive mode not engaged. Same on the chassis. I'd like just a simple small LED on the chassis to indicate the 2nd channel is active.

To switch from channel 1 to channel 2 on the Earhart, you just press the Clean switch. Would there be a way to have a dual color/dual mode LED on that switch to indicate what channel it's on? Instead of the LED off when it's on channel 2, it lights up a different color like yellow or blue?

[racerevlon]

Has anyone done any of the Mercury Magnetics upgrades to their Jet City amp? If so, please let us know what you think.

[Hipster Salad]

Has anyone done any of the Mercury Magnetics upgrades to their Jet City amp? If so, please let us know what you think.

According to FRPC, the OT and PT trannies are a good chunk of iron. He even mentioned that Zach from Titan Amps said upgrading to Heyboer or O'Netics wouldn't really justify the cost of doing it.

[Jay]

Has anyone done any of the Mercury Magnetics upgrades to their Jet City amp? If so, please let us know what you think.

I know they make good stuff, but it's awfully expensive. Honestly, I had two different Splawns, one with Mercury iron, and one with Heyboer, and you couldn't tell the difference. I think the appeal with the MM stuff is that they take the guesswork out and make application-specific trannies. They DO make good parts, but with a little research, you could find a really good piece for half the price or less.

[Axe]

I was just checking out some of the Jet City amps and I noticed the only one that has a 4 ohms output is the Pico Valve. I've got a 4X12 on the way that will have 4 16-ohms wired in parallel to 4 ohms. I guess I could rewire it to series/parallel for 16 ohms.

Not sure why they wouldn't have a 4-ohm option.

[Tortuga]

Good stuff about tubes right here: http://www.harmonycentral.com/t5/Amps/S ... p/33009324

Some say 66's are fine, others (including JCA, who says you may stress your transformers) have pointed out that the amp wasn't designed to be swapping tube types - apparently, the 66 pulls additional current that needs to be considered.

Of course, if you're going to spend a $$$-load of money on Mercury Magnetics transformers, you could probably have them help you factor that in. Of course, you could just about buy another amp that uses the EL34s by the time you get done paying for all that expensive iron.

My advice would be to do some searches on HCAF (I know, blasphemy) - there's a tremendous amount of experience on that forum from many of the people that are here now, who already did much of what is being discussed relative to JCAs/tubes/transformers. Check it out - then please make sure you make me aware of any good stuff you find so I can link it here. Also, write Laura (Valve Queen) or one of the other online tube outlets and/or Mercury and see what they have to say about it. My guess is that the smart money is on retaining decent-quality 6L6 variants (the wxt+ is my next tube pair) and see where that takes you.

I did record some comparison clips yesterday of the new voicing mod on my amp. I really think anyone looking to get a bit more feel / sponginess / elasticity with their amp should seriously look at this mod. I've been really surprise over how much it changes the response without making it overly muddy or tubby sounding. And, with it cranked up, I did notice a huge difference on that mod's impact over the crunch channel. Good stuff!

[Tortuga]

One mod that I'd like to do on my JCA100H and the Earhart, is add an LED light on the chassis when the 2nd channel is activated. The HDM has this stock, so would it be as simple as copying from the HDM schematic? I guess the Depth control would be copied from the HDM schematic to, right?

On the Earhart, the footswitch is 3 buttons, layout is Clean, 2nd Master, and Overdrive. All three have one LED light per switch and light up when engaged. When all lights are off, that indicates 2nd channel is active, Overdrive mode not engaged. Same on the chassis. I'd like just a simple small LED on the chassis to indicate the 2nd channel is active.

To switch from channel 1 to channel 2 on the Earhart, you just press the Clean switch. Would there be a way to have a dual color/dual mode LED on that switch to indicate what channel it's on? Instead of the LED off when it's on channel 2, it lights up a different color like yellow or blue?

Do you have a copy of the HDM schematic? That'd be awesome to have. I didn't realize the HDM had a panel indicator for which channel it's on - I'd really like to have that, too. The way the footswitch is wired leaves me to believe there's no way to control a light on the panel from the footswitch, and that you'd have to grab voltage from the circuit that energizes the relays (or something else). Maybe that's how it's done on the HDM. It'd also be cool to see how the depth control is set up by JCA (as well as the 1/2 power switch). Could you do some detailed gut shots for us?

I was just checking out some of the Jet City amps and I noticed the only one that has a 4 ohms output is the Pico Valve. I've got a 4X12 on the way that will have 4 16-ohms wired in parallel to 4 ohms. I guess I could rewire it to series/parallel for 16 ohms.

Not sure why they wouldn't have a 4-ohm option.

Which JCA amp are you using? My 50 has 4, 8, and 16 ohm jacks. Pretty sure that the 100 and 22 do, too. And it'd be pretty easy to rewire your cab to 16 ohms. With mine, I made a switchplate so that I can run it at 4 or 16, or split it into two 8 ohm pairs (stereo, or can run two heads into same cab).

[Jay]

I'm suprised JCA is more concerned with the OT than the PT. Apparently, the TungSol KT66 has electrical similarities to a standard 6L6, so they might work as a drop in. The problem is more with the Output transformer with KT66s. They like to "see" a higher resistance across the OT primary winding. 6L6 amps (and most EL34 and KT88) amps all use around 3.4k-5k for the primary for a P-P pair. KT66s prefer around 6.6k for a P-P pair. So by mismatching which impedance you plug your speaker cab into, you can "fake" the KT66s into seeing a higher primary impedance.

Otherwise, you can swap out the Power Tranny for a stouter unit to use EL34s, 6550s, KT88s in addition to 6L6s.

[racerevlon]

JCA22H only has a single 16-ohm tap and two 8-ohm taps. Bottom line, 22H won't handle a 4-ohm load. I've run 2 x 16-ohm cabs with a 22H though and it sounds KILLER!

[Axe]

Which JCA amp are you using? My 50 has 4, 8, and 16 ohm jacks. Pretty sure that the 100 and 22 do, too. And it'd be pretty easy to rewire your cab to 16 ohms. With mine, I made a switchplate so that I can run it at 4 or 16, or split it into two 8 ohm pairs (stereo, or can run two heads into same cab).

I don't own one -- they're rare as hens' teeth up here in Canada. None of the major stores near me in Barrie -- Long and McQuade, Cosmo Music, The Arts -- carry them. Same with Blackstar. Not sure why.

I checked the specs at http://www.jetcityamplification.com/heads/ and all of them except the Pico Valve list the output as XX watts into 16 ohm or 2x 8 ohm speaker outputs

[Tortuga]

It's been a while since I looked at their website. I see what you're saying on the specs list, but that doesn't jibe with the picture they have of the 50's back, which matches mine - check 3rd pic: http://www.jetcityamplification.com/2010/01/30/jca50h/ - pic for 100H looks same. Jacks are (from left to right): 2x4ohm, 2x8ohm, 1x16ohm, footswitch, effects send/receive (the two stacked on the far right).

[Tortuga]

...by the way, HDM users - I am going to start hounding you - I really want to see some gut shots, especially of switching, wiring, and circuit board connections related to depth control, channel selection light, and half-power. Bonus points for schematic diagrams!

[Jay]

I need two volunteers, one JCA50 and one JCA100 owner to measure out the bolt pattern/dimentions and wire hole locations for the power transformer and output transformer. Pleeeease!

[Jay]

Something like this would work as a replacement for the 50W JCA and be able to run 6L6s, EL34s, KT88s, 6550s. etc. Plus, it's blue!!

http://edcorusa.com/p/730/xpwr129_120

I just don't know the bolt pattern on the JCA to ensure it's a drop in replacement.

[Jay]

And this for an output upgrade.

http://edcorusa.com/p/447/cxpp60-ms-4k

[Tortuga]

Jay - this is AWESOME - I will definitely measure & photo my transformers as soon as I can - maybe tonight, but more likely tomorrow. That'll be the 50. Then we need someone with the 100 and HDM to do same. I might just do this mod later this year (if $$$ allow). It'd be incredible if someone can do this thing!

[Jay]

If you really want to get nuts, you can swap the choke for one of these.

http://edcorusa.com/p/783/cxc100-5h-200ma

or

http://edcorusa.com/p/782/cxc125-10h-200ma

[Jay]

Jay - this is AWESOME - I will definitely measure & photo my transformers as soon as I can - maybe tonight, but more likely tomorrow. That'll be the 50. Then we need someone with the 100 and HDM to do same. I might just do this mod later this year (if $$$ allow). It'd be incredible if someone can do this thing!

I'm trying to clear out some extra gear to try and pick up a JCA. I was going to go for a 22h, but I may have to try and find a 50 or 100 to do some of these more involved mods. I've seen a 50 around here or HCAF for less than $400. I'd rather do the mod forst to make sure it's an easy task. Also, I'm still going through the list for a match for the 100s. The one I picked for the 50 has the same voltage as the stock unit, the extra current to handle the different tubes, a more stout bias tap (the resistor on the amp may need to be slightly bigger) and a choice for the heaters/switching. The 7A 6.3v tap could power all of the heaters and the switching with ease, but you could divide it up. Run ONLY the heaters from the 6.3v tap, and then use the 18V tap for the switching by either adding a resistance after the rectifier or bleed some of the voltage to ground. Or just use the 6.3v as in the stock configuration and use the 18v for something fun like backlighting or a beer tap.

I still haven't found a PT to match the 100 yet, but I'm sure I can find one in that long list.

I have used Edcor stuff before and it's good. Never done an A/B test, but I like their iron.

[Tortuga]

Selfishly, I'm really hoping you go with the 50 (since I have the same). How reliable would the switching circuit be with the modified 18v leg, as you describe? Would it be better to do a voltage regulator, or might that not be able to handle the current?

I so need to learn more about this stuff - I actually have an AS in electronics (although the paper is about 25 years old), but they didn't teach us stuff like this back then...

So, here's the pics and dimensions for the power and output transformers. I put them all into a documentation thread in the DIY section (trying something new, to make it easier to find this stuff - let me know what you think).

JCA50H Documentation - Transformers

Thanks Jay - can't wait to hear some feedback on this.

[racerevlon]

Grime, your amp looks awesome!

Thanks man! I'm pretty proud of the way it turned out. I wanted to use the expanded metal for my baffle like a lot of other guys were doing, but I thought the edges looked a bit unfinished, plus they were having to screw them down, making tube changes / replacement a bit more of a pain. Decided to steal FRPC's idea of using velcro and build up a frame. It's basically a sandwich of two layers of 1/4" MDF that I joined together with dowel pins around the perimeter and a channel cut into each half that allows for the expanded metal to fit into. Turned out pretty good, and lets me see all the tubey goodness lighting up inside. Here's a couple pics, if anyone's interested.







Only thing i HATE is that my headshell came warped. The top sags down (from side to side), and makes things match up not so good - especially when I try to push my nice, straight baffle up, and have the corners not meet at all. You can kind of see it in this picture below. Nobody else notices, but I sure do.

Doug White - are you listening?!?!

Did you contact Jet City or your retailer about the warped head shell? Not cool calling out someone by name on a forum as if he were personally responsible for the problem. Why not find out who actually built the head shell and call THAT person out? Or better yet, do what the rest of the world does and use the warranty that comes with the product? I've dealt with Doug on many occasions and he goes WAY above and beyond to help me out with stuff that technically isn't really his responsibility.

One man's opinion...

[Tortuga]

Dude - that was entirely meant as a joke. I've had a few exchanges with the man, myself, and the have all been very positive. Pretty sure all my postings here and elsewhere have all been nothing but complimentary. I think Doug & Co.do a phenomenal job creating a killer product that is very affordable. If he were at all offended by my attempt at a little humour, I would offer my most humble apology. That I somehow offended you in the process, I can only offer same.

I would hope that my enthusiasm in promoting the product and contributing quite a bit of my personal time and effort in getting others involved in this great family would afford me a little slack...

[racerevlon]

OK--fair enough. Just seemed on the surface you were calling him out personally, which only gets amplified by the fact that Google picks up EVERYTHING.

Wasn't trying to put you down either... Was just sticking up for a guy who's done nothing but right by me.

Now I'm gonna go rock my 22H through my Whitebox 2x12 with WGS ET65s and put all this in the rear view.

Cheers,

Race