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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!
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!
Originally Posted by GRIMESPACE
The grill you made looks real good what did you use for the outter edge around the metal.
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.
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.
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!
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!
that looks damn good, can we gets some pics of the back side of the baffle?
Originally Posted by Edge11
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).
Originally Posted by rmonroe
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
Originally Posted by Jack Tone
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.
Originally Posted by clay189
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)"
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
Originally Posted by rmonroe
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?
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 aain
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.
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.
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