Jca50H / 100h/ 22h mod thread and owners club

[GRIMESPACE]

Originally Posted by clay189

? to anybody who as rebiased their Jca50h, what kinda of plate voltage were you getting and on the bias reading from the factory did it seem really on the low side.
Thanks to all.

It's been a while, but I was able to dig up a notepad entry - looks like I was probing between 480 & 503 volts on pin 3 of the power tubes, which calculated to between 34 & 36ma bias current. Hope that helps.

[GRIMESPACE]

Here's my modded JCA50H. Depth knob (killer!!!) and switches for scoop & clean (jury still out on those - need to get somewhere where I can crank it!). Wound up removing switches for bright and the cathode bypass cap that I was trying out - just not my thing, I guess. So, I have two 3/8 holes to fill... Thinking about using one for a crunch/od channel indicator. Also planning out another mod that I'll follow up on later.

Really like the metal baffle that people have been doing, but not big on the screws or the rough edges. Also thought FRPC had a great idea about velcro, so I built a custom frame for the metal that I think looks pretty cool - especially with the chicken heads. Let me know what you think!

[clay189]

Originally Posted by GRIMESPACE

It's been a while, but I was able to dig up a notepad entry - looks like I was probing between 480 & 503 volts on pin 3 of the power tubes, which calculated to between 34 & 36ma bias current. Hope that helps.

Thanks just making sure I am using a amp-head bias-plate duel probe and just wanted to check. my plate voltage is right on the mark with yours but out of the box bias was reading like 10. i retubed it with jj's and set the bias to 37 and it sounds awesome.
The grill you made looks real good what did you use for the outter edge around the metal.

[GRIMESPACE]

I don't recall if I saw my bias setting before I started changing tubes and messing with everything. So yours was set to 10ma? Man - I've heard they come from the factory cold, but that's cryogenic!

I do remember being totally blown away when I turned the amp on with the new tubes. I actually called Eurotubes and asked if something might be wrong It was a totally different beast at that point. I wasn't sure if I was happy or not, and I basically had to learn how to interact with it again. Once over that hump, I've never looked back. The thing is killer in every way, and the bargain price doesn't hurt either!

Thanks for the compliment on the grill. I'm pretty happy with it now - time will tell how well it holds up. It's actually a sandwich of two pieces of 1/4" MDF that were built up around the metal grill (same one everyone else is getting from Home Depot).

If anyone is interested, here's the primary steps I used to create the baffle:

After cutting two pieces roughly to size, I screwed them together in the center area (which would be removed later) and trimmed to final dimension. Then I used the drill press to run holes along the perimeter for dowel pins almost all the way through - not all the way through, or they would show. I cut dowels to length and temporarily pinned the pair together so that I could work on the pair as a single piece after removing the center.

Next step was to remove the center. I wanted the corners to be rounded so I drilled them first, then used a saw to cut between the holes and remove the rest. After sanding & smoothing to get everything looking right, I routed a small roundover on the topside in the center and along the bottom edges. Last thing was to separate the two halves and cut a shallow rabbet along the inner perimeter on each piece where they faced each other. When assembled these rabbets would provide a space for the metal grill.

After cutting the grill to fit the rabbet, I sprayed it with primer and a coat of paint so that it wouldn't rust - the edges wouldn't get any paint once mounted in the frame. Once the grill was dry and everything triple-checked, I glued the whole sandwich together and pinned it with the dowels. The final unit was then painted and velcroed to mount on the head cabinet.

Total time was a couple hours - not a bad woodworking project for someone with moderate skills. The biggest grief I have is that the top panel of the JCA cabinet isn't straight - it's actually bowed in quite a bit, which makes my straight lines look a little off - at least to my eyes.

[Edge11]

Originally Posted by GRIMESPACE

Here's my modded JCA50H. Depth knob (killer!!!) and switches for scoop & clean (jury still out on those - need to get somewhere where I can crank it!). Wound up removing switches for bright and the cathode bypass cap that I was trying out - just not my thing, I guess. So, I have two 3/8 holes to fill... Thinking about using one for a crunch/od channel indicator. Also planning out another mod that I'll follow up on later.

Really like the metal baffle that people have been doing, but not big on the screws or the rough edges. Also thought FRPC had a great idea about velcro, so I built a custom frame for the metal that I think looks pretty cool - especially with the chicken heads. Let me know what you think!

If you already have the hole there, why don't you do the slo style clean and a 39k/68k switch.
that looks damn good, can we gets some pics of the back side of the baffle?

[GRIMESPACE]

Originally Posted by Edge11

If you already have the hole there, why don't you do the slo style clean and a 39k/68k switch.
that looks damn good, can we gets some pics of the back side of the baffle?

That's exactly what I did - changed out the clean/crunch wiring I originally put together (clean/crunch on 1 switch, another switch to bypass the bright cap) for the simple clean switch that lets me pick either resistor. I'm actually liking that quite a bit, but not thrilled with the radical drop in volume. I still think I may have had something wrong on my original attempt, as it was affecting both crunch & OD channels, but when I thought about it, I was really only after dropping the gain so the clean function seemed like a better choice. Way easier to wire in, and is definitely only affecting the crunch channel now.

The other pair of holes were for the scoop (which I kept) and the cathode bypass (which I removed). May try out the cathode bypass later, but wanted to simplify. With two holes remaining, I'm going to probably add a blue LED that'll mirror the footswitch indicator, and am still cooking up something I haven't seen before for the next mod.

Thanks for the compliment on the baffle - I'm pretty happy with it. I'll try to put some better pics together this weekend, and might put together a couple of illustrations to better convey how it goes together (if ya'll are interested).

[Edge11]

Originally Posted by GRIMESPACE

That's exactly what I did - changed out the clean/crunch wiring I originally put together (clean/crunch on 1 switch, another switch to bypass the bright cap) for the simple clean switch that lets me pick either resistor. I'm actually liking that quite a bit, but not thrilled with the radical drop in volume. I still think I may have had something wrong on my original attempt, as it was affecting both crunch & OD channels, but when I thought about it, I was really only after dropping the gain so the clean function seemed like a better choice. Way easier to wire in, and is definitely only affecting the crunch channel now.

The other pair of holes were for the scoop (which I kept) and the cathode bypass (which I removed). May try out the cathode bypass later, but wanted to simplify. With two holes remaining, I'm going to probably add a blue LED that'll mirror the footswitch indicator, and am still cooking up something I haven't seen before for the next mod.

Thanks for the compliment on the baffle - I'm pretty happy with it. I'll try to put some better pics together this weekend, and might put together a couple of illustrations to better convey how it goes together (if ya'll are interested).

I'm interested in that. And the bypass cap is a pretty big part of the scoop mod sound.

[clay189]

Edge is there any way I could get you to post a pic of the scoop mod and the cathode bypass, I just want to see a visual of them. I am very new to this reading electronic schematics I have went so far as buying science projects from radio shack for my son and building them just so I can get my skills up with soldering resistors and caps to tiny perf boards. like the scoop mod I understand the soldering the 1m resistors in series but when you solder the cap in the middle then to ground not sure where ground is. I know thats stupid but thats my question Thanks.

[rmonroe]

I bought a JCA50h about a month ago and since changed the power tubes to Sovtek 6L6WXT+ and recently purchased 5 12AX7LPS preamp tubes. I noticed a great improvement when replacing the powertubes even though I do not have the equipment to bias them. In fact Jet City told me I did not need to bia them, but on this forum I am seeing otherwise. Now I am pretty sure there is no need to bias the preamp tubes, or at least that is what my research has shown, but should I get the power tubes biased? The problem is I do not have the equipment to do it on my own and live far from anyone who could do it for me. Also the head is pretty heavy and with my bad back I should not be lifting it. Any advice?

On a different note, I have seen in this forum that people have made their own metal baffles for their JCAs. Does anyone have a link to detailed instructions on how to so this? Thanks

[Jack Tone]

Originally Posted by rmonroe

I bought a JCA50h about a month ago and since changed the power tubes to Sovtek 6L6WXT+ and recently purchased 5 12AX7LPS preamp tubes. I noticed a great improvement when replacing the powertubes even though I do not have the equipment to bias them. In fact Jet City told me I did not need to bia them, but on this forum I am seeing otherwise. Now I am pretty sure there is no need to bias the preamp tubes, or at least that is what my research has shown, but should I get the power tubes biased? The problem is I do not have the equipment to do it on my own and live far from anyone who could do it for me. Also the head is pretty heavy and with my bad back I should not be lifting it. Any advice?

On a different note, I have seen in this forum that people have made their own metal baffles for their JCAs. Does anyone have a link to detailed instructions on how to so this? Thanks

There are a few alternatives, but I have the Weber BiasRite:

http://taweber.powweb.com/biasrite/br_page.htm

If you change tubes a lot, or have several amps, it's invaluable. I like the Weber because it reads both plate and cathode voltage. I've got the one that reads both 8 pin and 9 pin tubes, but if you scroll down the page, they now have an adapter which will still show both currents, but plugs into your multimeter (the V1 option)...pretty cool!

Also, if you like to solder, there's this kit from Tube Depot:

http://www.tubedepot.com/bt-biasrite.html

[GRIMESPACE]

Originally Posted by Jack Tone

There are a few alternatives, but I have the Weber BiasRite:

http://taweber.powweb.com/biasrite/br_page.htm

If you change tubes a lot, or have several amps, it's invaluable. I like the Weber because it reads both plate and cathode voltage. I've got the one that reads both 8 pin and 9 pin tubes, but if you scroll down the page, they now have an adapter which will still show both currents, but plugs into your multimeter (the V1 option)...pretty cool!

Also, if you like to solder, there's this kit from Tube Depot:

http://www.tubedepot.com/bt-biasrite.html

Wow - that kit is perfect. Measures both current and plate voltage, and only $16! The assembled one I got from Eurotubes worked ok, but it only measures current and I hate probing the pins for voltage reading while the amp is running.

And yes, you really should adjust your bias if you can - pretty much a consensus that JCA sets the bias 'cold', which is likely to promote tube life. Bias + JJs made a massive difference on my JCA50H. It's pretty easy to do if you're even somewhat mechanically / electrically inclined, and it'll save you $$$ the first time you do it. Just be really careful about working inside the chassis so's you don't blow yourself up! See Edge's warnings and guidelines on the first post of this thread...

As to the baffle, I posted a pretty detailed outline of how I built mine up above (see post #129). It can be even easier than that if you just want a simple grill and don't care about having to use screws or what the edges look like. Home Depot has a piece of 24" x 12" expanded metal in the hardware isle that's like $10. Cut it to size using a hacksaw, dremel, or whatever - paint - install using screws, washers, standoffs, etc. to taste, and rock out! I've also seen posts by people doing similar using rain cutter grate, rolling the edges to make it stand taller, etc.

[GRIMESPACE]

Originally Posted by clay189

Edge is there any way I could get you to post a pic of the scoop mod and the cathode bypass, I just want to see a visual of them. I am very new to this reading electronic schematics I have went so far as buying science projects from radio shack for my son and building them just so I can get my skills up with soldering resistors and caps to tiny perf boards. like the scoop mod I understand the soldering the 1m resistors in series but when you solder the cap in the middle then to ground not sure where ground is. I know thats stupid but thats my question Thanks.

Since Edge hasn't had a chance to reply (he's pretty busy with school these days, it appears), I took the liberty of putting something together, which is what I think he's talking about. I picked up ground off one of the resistors (pretty sure it was R49) near the input jack, which is where I put my switch. I'll try to get a gut shot of my hatchet job this weekend to post up. You can also run a wire to the back of the chassis and pick up ground off the speaker jacks.

Note - I haven't tried this actual wiring. I originally put in two switches so I could try them independently, and have since removed the cathode bypass. If this is right (Edge - please let me know), I'm probably going to rewire to this, based on his recommendation above.



Other particulars:
.001uf cap is ceramic, and may be labeled 1000pf (mine was).

From Edge:
"22uf is 50v or more.
the .001uf is 1kv (most common value)"

[clay189]

I am very new to this tube amplifier tinkering but I would have to second what the others have told you. I have a Amp-Head dual bias probe that measures plate voltage and current this tool is a must. I believe everything can be done by you if you are half way mechanical inclined its just like when I take my Harley to the shop and they the tech tells you it has to be done there and you find out if you have the right tools and the information to do it, it's easy to do. these guys on here can help you with anything you and are very knowledgeable. my Jca50h blew me out of the water after a tube change, depth mod and rebias.

Originally Posted by rmonroe

I bought a JCA50h about a month ago and since changed the power tubes to Sovtek 6L6WXT+ and recently purchased 5 12AX7LPS preamp tubes. I noticed a great improvement when replacing the powertubes even though I do not have the equipment to bias them. In fact Jet City told me I did not need to bia them, but on this forum I am seeing otherwise. Now I am pretty sure there is no need to bias the preamp tubes, or at least that is what my research has shown, but should I get the power tubes biased? The problem is I do not have the equipment to do it on my own and live far from anyone who could do it for me. Also the head is pretty heavy and with my bad back I should not be lifting it. Any advice?

On a different note, I have seen in this forum that people have made their own metal baffles for their JCAs. Does anyone have a link to detailed instructions on how to so this? Thanks

[clay189]

Originally Posted by GRIMESPACE

Since Edge hasn't had a chance to reply (he's pretty busy with school these days, it appears), I took the liberty of putting something together, which is what I think he's talking about. I picked up ground off one of the resistors near the input jack, which is where I put my switch. I'll try to get a gut shot of my hatchet job this weekend to post up. You can also run a wire to the back of the chassis and pick up ground off the speaker jacks.



Other particulars:
.001uf cap is ceramic, and may be labeled 1000pf (mine was).

From Edge:
"22uf is 50v or more.
the .001uf is 1kv (most common value)"


Edge - your thoughts?

Thanks Grim the depth mod is badass.
Thanks aain

[kocher]

Today I changed preamp tubes to JJs and biased the amp. I was pretty cold with something like 10mA. With a measured plate voltage of 468V I calculated a 70% value of 37mA and that's what I set to bias to.
I measured plate voltage with a DMM and used an adapter like this to read the bias:


Overall sound has improved quite a lot but still too much compression for my taste. Looking forward to use other tubes in the power section: 6L6GC-STR RCA-Style black-plate TAD PREMIUM Selected

That is a recommendation from the guys at Tube Amp Doctor for an open tone.

[kocher]

In case anyone is interested, they also suggest this, for an open but warm sound:

V1: 7025 WA
V2: 7025 S
V3-5: ECC83 WA

This combination costs around twice of the JJs that's why I postponed that for now

[Edge11]

Originally Posted by GRIMESPACE

Since Edge hasn't had a chance to reply (he's pretty busy with school these days, it appears), I took the liberty of putting something together, which is what I think he's talking about. I picked up ground off one of the resistors (pretty sure it was R49) near the input jack, which is where I put my switch. I'll try to get a gut shot of my hatchet job this weekend to post up. You can also run a wire to the back of the chassis and pick up ground off the speaker jacks.

Note - I haven't tried this actual wiring. I originally put in two switches so I could try them independently, and have since removed the cathode bypass. If this is right (Edge - please let me know), I'm probably going to rewire to this, based on his recommendation above.



Other particulars:
.001uf cap is ceramic, and may be labeled 1000pf (mine was).

From Edge:
"22uf is 50v or more.
the .001uf is 1kv (most common value)"

Correct. I use 3pdt switch so when the scoop mod is of it changes the value from 2 1ms to a 680k resistor, aka the normal sucker punch mod.

[clay189]

kocher, so your amp was set at aroiund 10ma from the factory. When i changed my tubes and rebiased I thought I was crazy seeing a 10ma reading. Nice to know I still have my sanity.

Originally Posted by kocher

Today I changed preamp tubes to JJs and biased the amp. I was pretty cold with something like 10mA. With a measured plate voltage of 468V I calculated a 70% value of 37mA and that's what I set to bias to.
I measured plate voltage with a DMM and used an adapter like this to read the bias:


Overall sound has improved quite a lot but still too much compression for my taste. Looking forward to use other tubes in the power section: 6L6GC-STR RCA-Style black-plate TAD PREMIUM Selected

That is a recommendation from the guys at Tube Amp Doctor for an open tone.

[Blakkwater]

Edge11...or anyone else...

Lately I've been trying to tweak the tone controls/depth/presence controls while playing on the overdrive channel, trying to get that bright/middy hot rodded JCM800 kinda sound, but I always find that the overdrive channel has far too much low/low-mid muscle to do the Marshall sound.

Is there a mod for a voicing switch or something similar that would be able to give the OD Channel a more Marshall flavour?

[Edge11]

Originally Posted by Blakkwater

Edge11...or anyone else...

Lately I've been trying to tweak the tone controls/depth/presence controls while playing on the overdrive channel, trying to get that bright/middy hot rodded JCM800 kinda sound, but I always find that the overdrive channel has far too much low/low-mid muscle to do the Marshall sound.

Is there a mod for a voicing switch or something similar that would be able to give the OD Channel a more Marshall flavour?

Change the slope resistor to 33k

[clay189]

Hey Edge, The depth mod kicks ass and for us beginner moders was simple and smooth so thanks for that. Now for my next rookie ? I am thinking of the Scoop mod but what does this exactly do does it bring the mids down even more than just rolling them back on the Eq. Forgive me if the ? is just plain stupid.

[isuck]

Hi looking for a little help with my sons jca22h. My twelve year old son has been playing the jca20 for about a year and his grades earned him an upgrade. Yesterday we got a 22h from an on line retailer. the crunch channel sounds great I think maybe a little fuller then the 20 sounded. The problem is the od channel. When he hits the switch it squeals like a pig in heat and the only thing that will control it is the preamp knob. I emailed jet city and there response all though fast was a little lacking in information. It said to check the tubes to make sure they are glowing. It also said that the amp was designed to plug and play so if a tube is bad you can just get the same kind and put it in. Being a total noob (or kook which ever you prefer) I have know idea where to start. I can only see 5 tubes through the grill and they all have some color some a little stronger then others but color. Any help that you may provide would be helpful. I am not totally mechanically challenged so I am willing to give this tube replacement a try just don't know where to start. By the way v1, v2 v3 etc. mean absolutely nothing to me. Thanks

[67mike]

Originally Posted by isuck

Hi looking for a little help with my sons jca22h. My twelve year old son has been playing the jca20 for about a year and his grades earned him an upgrade. Yesterday we got a 22h from an on line retailer. the crunch channel sounds great I think maybe a little fuller then the 20 sounded. The problem is the od channel. When he hits the switch it squeals like a pig in heat and the only thing that will control it is the preamp knob. I emailed jet city and there response all though fast was a little lacking in information. It said to check the tubes to make sure they are glowing. It also said that the amp was designed to plug and play so if a tube is bad you can just get the same kind and put it in. Being a total noob (or kook which ever you prefer) I have know idea where to start. I can only see 5 tubes through the grill and they all have some color some a little stronger then others but color. Any help that you may provide would be helpful. I am not totally mechanically challenged so I am willing to give this tube replacement a try just don't know where to start. By the way v1, v2 v3 etc. mean absolutely nothing to me. Thanks

V1 is the preamp tube nearest the input jack on the 22h.

I would suggest the following:

Buy 2 JJ EL84 tubes and 4 SOVTECK 12ax7wa tubes.

Unplug the amp and take the back panel off the amp. Then set the amp face down on a soft surface like a rug....remove the 4 screws on the bottom to free up the chasis....then slowly and carefully put the amp back on it's bottom and carefully remove the chassis from the cab....DO NOT touch anything under the chasis....simply slide it out and place it on the floor...this allow you to access the tubes. replace the 2 EL84 power tubes, then replace the 4 12ax7's in V1 to V4 with the sovtecks.

This should help out a lot.

[isuck]

Thank you for your help. Placing order has we speak. One other thing the metal housings on a few of the tubes do they screw of or just pull off

[isuck]

Will he notice much of a difference if I just put JJ's all the way around? thanks for your help.