NAD

[Duesentrieb]

I've also bought a JCA100H yesterday and couldn't resist to add some features.

 

I've added two switches, one (left) for a (much) cleaner variation of the first channel. The "mod" comes off the original SLO, which also has this clean/crunch switch (this version is simplified though). I've used a different value here though . . .

 

Also (I've owned/played a HRPlus for years and years in the 90s) I always missed a manual switch for the channels - so I've added it, plus a LED (lead channel). This needed some additional internal wiring of course - and a new switching jack.

 

And IMO Soldano-ish amps are crying for a depth mod, so I've installed it.

 

The amp needed proper biasing too . . . .

 

Here are some pics:

 

the new front with two switches and channel LED

 

the clean mod comes off the SLO with a simple resistor taking signal to ground, I didn't use the original 39k but a 68k for some more "meat" here

 

left clean/crunch, then channel 1/2 and the LED

 

here a pic how it looked one hour ago . .

 

 

I dig it

the built quality JCA sells is very cool IMO.

 

will be continued . . .

[Dolf]

Oooooh

[Duesentrieb]

wut?

[groovetube]

nice work. i'd love to have some time to learn amp modding skills.

 

sound/video clips would be killer when you get a chance

[MatchFive]

Yes, I am also interested in a simple how to with pics on putting a clean / crunch switch in a 100H or 50H.. I am thinking about getting the 50H later on..

[Duesentrieb]

Thanks guys. I will try to post some vids during the weekend incl. how to wire that switch.

You need a set of resistors (to try which you personally prefer - like 39k, 47k, 68k, 100k), a SPDT toggle switch, some wire, an iron - and to try, two croco wires.

[Ron Burgandy]

Great work, Olaf

 

 

 

I wish I was in Germany, so I could take my Jet City to you personally. Your endorsement is the sole reason I went back and gave Jet City another chance. The first one I played didn't thrill me, but I think something was wrong with it, looking back. The issues I had with the first one were undefined, muddy tones, but that's hardly been an issue with the subsequent Jet City amps I have played.

 

I have the 20 watt combo on it's way, but I'm considering a move to the 100 watt head depending on how the 20 watt sits in with my band.

 

 

Thanks,

 

Dave

[Duesentrieb]

Thanks Dave.

Personally I wouldn't use a single channel with a band (but thats me, a lot of guys are doing it), I need two or better three footswitchable sounds . . . The 20H is a very nice crunch machine, not sure about the combo - I hoep your pickups aren't too strong, you know . . .

And please check the bias of the tubes. While my 20H was almost perfect biased, this 100H was way too cold biased. Let me know if you have questions when you get it, I will show you how to bias it.

[Ron Burgandy]

I have always gigged with 1 channel NMV amps, so this won't be too much of a stretch for me.

 

I want to start using the Tweaker for my low/mid gain stuff, and A/B/Y with the Jet City for dirt. But I'm also lazy and love carrying my entire rig in one trip from the car, so... we'll see if that idea makes it's way to the band.

 

 

My pickups are really low output, so don't see that being an issue.

 

I do like that the Jet City can run on it's own, where the Tweaker I definitely prefer to use my Fuzz pedal for dirt.

 

Thanks for the offer of help, and I will be taking you up on it

[MatchFive]

 

Thanks guys. I will try to post some vids during the weekend incl. how to wire that switch. You need a set of resistors (to try which you personally prefer - like 39k, 47k, 68k, 100k), a SPDT toggle switch, some wire, an iron - and to try, two croco wires.

 

 

Thanks man, you rock!!

[Duesentrieb]

No prob.

[guitarbilly74]

oh man clips please!!!

 

 

also, any chance to make the clean/crunch switch footswitchable?

 

Any volume drop when you go from clean to crunch??

[guitarbilly74]

I have always gigged with 1 channel NMV amps, so this won't be too much of a stretch for me. I want to start using the Tweaker for my low/mid gain stuff, and A/B/Y with the Jet City for dirt. But I'm also lazy and love carrying my entire rig in one trip from the car, so... we'll see if that idea makes it's way to the band. My pickups are really low output, so don't see that being an issue. I do like that the Jet City can run on it's own, where the Tweaker I definitely prefer to use my Fuzz pedal for dirt. Thanks for the offer of help, and I will be taking you up on it

 

JCAs clean up REALLY well when you roll down the volume so it won't be an issue at all.

[Duesentrieb]

oh man clips please!!! also, any chance to make the clean/crunch switch footswitchable? Any volume drop when you go from clean to crunch??

With this simple mod thats not possible - there would be two ways to do it though:

 

a) add another gainpot and volume

[Edge11]

I'm surprised you didn't change the crunch channel to the spec of the x88r (provided it desnt mess with or bleed through to the lead channel).

I support you 100% on the depth comment, after the depth mod my 20 came alive.

 

With this simple mod thats not possible - there would be two ways to do it though:   a) add another gainpot and volume

[Duesentrieb]

I will do that when I have a good idea about a "real" clean channel

[guitarbilly74]

Let me know if you have questions when you get it, I will show you how to bias it.

 

I'm interested, please.

[Duesentrieb]

The 100H? Sure.

Do you have a multimeter?

[Duesentrieb]

 

I'm surprised you didn't change the crunch channel to the spec of the x88r (provided it desnt mess with or bleed through to the lead channel). I support you 100% on the depth comment, after the depth mod my 20 came alive. I'm assuming for #2 your adding a new "fender" style channel right? Dues I just got a peavy windsor today and your already making me regret not saving my pennies and getting a 100h.

 

Yeah, a fenderisjh clean, but that would mean that the clean channel bypasses the loop (for me thats not a problem), because the Loop-Input-Stage would "{censored}" the clean-ess up too much (or to say it the other way round: the channel would be too hot if I'd go into the loop). Also the switching would become pretty complex - I think it is easier to take off the signal from the first coupling cap, then tonestack, then 1/2 tube and an additional relay in front of the PI's 22nF - which gives another "problem" - the switching circuit comes off the heaters and has only 3.5 Volts - I need to find a relay which is able to work with that supply - or install an additional transformer for 6-9 Volts . . .

 

And the next hurdle is room - there is room between the board (input side) and the side of the chassis for a tube and some hiwattish-soldering-sockets, but on top of the chassis the room between the output transformer and the headshell is very limited . . . I'll see . . .

 

Yeah, the 100H eats the Peavey for breakfast, thats for sure . . .

[guitarbilly74]

 

The 100H? Sure. Do you have a multimeter?

 

 

Yes I do.

[Duesentrieb]

here a pic how it looked one hour ago . .

Set DMM to read 200mA DC (often you need to put the red probe into another socket for this) and locate the brown and blue/white wires coming from the right corner of the amp (OT) when the amp is flipped, pots facing you.

Switch it on, volumes set to "0" - now read the current (mA) between brown and either blue or white. Rotating the bias trimmer (middle of the PCB) into the direction of the pots = increasing mAs - rotating dir. backpanel = decrease the mAs.

 

You are reading the idle current of two tubes !

 

With a plate voltage of 460V (mine, check yours by setting the DMM to 1000V DC, black probe to chassis (blank! - f.i. one of the screws which hold the boad) and red to the brown wire) you should calculate your bias like this:

 

30 Watt * 600 / 460V = 40mA/tube or 80mA for the pair. To be safe I'd use 70mA max. here . . . (not sure if the 6L6 really can handle 30 Watts, when calculated with 25 Watts the result for a pair would be around 70mA per pair)

 

The problem is to get a good access to the point where the brown is soldered to the board, other cables, which are stiff, make that a pain.

 

If thats too scary for you I might be able to offer a different method soon, but it may need the replacement of the four jumpers on the board (PIN8 to ground), which, when replaced with 1 Ohm Rs, would make life much easier, but I need to check that first.

 

Still the easiest way is to buy an adaptor from Weber

[guitarbilly74]

Set DMM to read 200mA DC (often you need to put the red probe into another socket for this) and locate the brown and blue/white wires coming from the right corner of the amp (OT) when the amp is flipped, pots facing you. Switch it on, volumes set to "0" - now read the current (mA) between brown and either blue or white. Rotating the bias trimmer (middle of the PCB) into the direction of the pots = increasing mAs - rotating dir. backpanel = decrease the mAs. You are reading the idle current of two tubes ! With a plate voltage of 460V (mine, check yours by setting the DMM to 1000V DC, black probe to chassis (blank! - f.i. one of the screws which hold the boad) and red to the brown wire) you should calculate your bias like this: 30 Watt * 600 / 460V = 40mA/tube or 80mA for the pair . To be safe I'd use 75mA max. here . . . The problem is to get a good access to the point where the brown is soldered to the board, other cables, which are stiff, make that a pain. If thats too scary for you I might be able to offer a different method soon, but it may need the replacement of the four jumpers on the board (PIN8 to ground), which, when replaced with 1 Ohm Rs, would make life much easier, but I need to check that first. Still the easiest way is to buy an adaptor from Weber

 

Man I cannot begin to tell you how much I appreciate your posts. I always learn a lot from you. :thu:

 

I will give this method a shot. Thank you very much.

 

One more question, if you don't mind: is it true that the entire range of the bias pot is safe and there is no risk in damaging the tubes with this amp?

[Shenaniganizer]

That's what FRPC told me when I asked if I could just drop in KT88s.

[Edge11]

 

Yeah, a fenderisjh clean, but that would mean that the clean channel bypasses the loop (for me thats not a problem), because the Loop-Input-Stage would "{censored}" the clean-ess up too much (or to say it the other way round: the channel would be too hot if I'd go into the loop). Also the switching would become pretty complex - I think it is easier to take off the signal from the first coupling cap, then tonestack, then 1/2 tube and an additional relay in front of the PI's 22nF - which gives another "problem" - the switching circuit comes off the heaters and has only 3.5 Volts - I need to find a relay which is able to work with that supply - or install an additional transformer for 6-9 Volts . . . And the next hurdle is room - there is room between the board (input side) and the side of the chassis for a tube and some hiwattish-soldering-sockets, but on top of the chassis the room between the output transformer and the headshell is very limited . . . I'll see . . . Yeah, the 100H eats the Peavey for breakfast, thats for sure . . .

 

Well I'm pretty sure that it does it eat it for breakfast, but i got the peavey for 200$ and the 100h is about 4 times as much.......

I'd still rather have a 100h but I'm modding the windsor, actually I'm thinking of adding another tube so i can do a fenderish clean channel and a 4 gain stage build.

[Duesentrieb]

Well, the screen grid resistors are (just) 470R - if you use something different than 5881 or 6L6 I would definitely change them to at least 1k. (those four big resistors on the back of the board - where I've hooked the OT-second.).

 

Yeah, FRCP throwed in KT88s, so it should - I couldn't check that (yet), but I guess that I have a couple of 6550 somewhere

 

@ guitarbilly: be careful, lethal voltages - but I guess that you know that.