NAD: CJ's Cavalcade of New Smallish Cheapish Amps - #3

[culturejam]

Had this for a couple weeks but haven't had time to post anything. Just got some parts in for mods as well, so more to come after this.

This is a Jet City Custom 5. Single-ended octal output tube with 2x preamp tubes. The circuit is Marshall-ish but has some odd choices for values (in my opinion). I bought a mod instruction sheet that supposedly gets it really close to a JCM800 in the preamp. While I can't share the document because of copyright laws, I can share what mods I end up making. The guy who did the mods apparently is tight with the guy who owns Jet City, and he was nice enough to share the factory schematic with me. I may redraw the preamp section so I can share it as well. I feel like any modification instructions should include a schematic.

This is, apparently, Jet City's attempt to use up the leftover Pico Valve chassis and transformer stock. The circuit is derivative of the Pico, but definitely not the same. I believe the chassis is identical (which is also almost an exact fit for a Valve Jr.... and I've read that it's the same guy behind Jet City, Black Heard, and the Valve Jr), and the transformers are marked "PicoValve". Like the Pico, this one also has a 5H choke.

Apparently, the guy behind Hovercraft Amps did the circuit mods. Also apparently, all of Hovercraft's amps are modded Jet City amps or similar with a dressed up head cab and face plate. Weird.

As it is, the bass is flubby and loose. Same complaints as the Pico, although this one does sound better (I briefly owned a Pico, so I recall the problems with it). More gain on tap here, as the Custom 5 has bypass caps on the first three amplifier stages, whereas the Pico has none.

I'm going to do whatever I can to tighten up the bass (starting with the filter caps and then moving on to coupling caps). Other than that, I dig the way it sounds. Great hard rock tone. The boost switch is sort of odd, and in the bass setting really just doesn't sound remotely good. The only way it works is in the treble setting. I may muck with those values as well.

This thing is HEAVY!

[thesmokingman]

reminding me of my 5 watt phase ... had the kustom defender, a cavalcade of valve juniors, the blackheart little giant and the ant, some random chinese one called the revenge. out of all of them, I will probably get another blackheart little giant to mod the crap out of. I thought it had the best balance of tone/gain and took pedals better than a lot of amps.

[thomasha]

Is that a choke? Cool for a cheap amp...

[matmosphere]

Hey CJ. These are great little write ups keep them coming.

Any chance you've run bass through any of these? I'm thinking of moving overseas for a few years and I'm looking for a small amp that can handle double duty at least somewhat gracefully. My bassman 100 cab is not going to make the journey.

I should probably just cough up the dough for a decent one or two channel recording interface instead.

[ahiddentableau]

Is that a choke? Cool for a cheap amp...

That was exactly what I thought.  I don't think I've ever seen a budget amp with a choke, let alone one that is as big as its output transformer.

What's the volume like?  And what's your impression of the power tube sound?  Knocking a 6L6 to 5/2W is not something I've heard of before, and I'm curious how they did it and if it worked out.

[culturejam]

Yeah, it's a 5H choke. Same as on the old Pico Valve model. There are some details on this in my first post above.

In my testing, the best sounding output tube is 5881. EL34 sounds not very good, at least not with the circuit totally stock.

The 2W mode is simply the output tube operating in triode mode. It sounds kinda meh (too much loss of highs). I might convert this switch to some kind of resistive load on the output instead.

[sonnyboy27]

Nice! I have the original JCA20H and I like it. Definitely gonna mod it for some more clean headroom though. The Jet City stuff has always been fairly mod friendly which is quite nice.

Definitely interested in checking out this newer line since it's supposedly redesigned by Martin Kidd and I've liked the Victory stuff I've heard. But that also depends on how much Martin actually got his hands on stuff.