2204 Redux... rebuilding JCM > JMP

[Tortuga]

So... quick little diversion (as I always do in these builds) before getting back to amp building (hopefully over this coming weekend...

...aside from getting my youngest to help with the amp build, I got kinda busy with the boys over the rest of the memorial weekend break.

This guy (my youngest) graduated high school





My nephew (also about to graduate high school, and will be joining the military in just under 3 weeks) wanted to make a special sign for his weight training class / teacher

...gluing up and prepping the 48x24 panel







...laying out the lettering



...routing the letters





...graffitti-izing



...a LOT of tedious fucking work



...and after sanding back the failed first two passes of staining (didn't get a pic), and 3 applications later, we're getting close






Oh, and forgot to mention the light saber fight



and the trip to the bar (Joe Jost's)

[Tortuga]

Mini update - been holding off the bulk of the wiring and just doing prep work for now. My son wants to do a bunch of the wire and related installation with me, so it'll be another week or so before we get this thing fired up. For now, I'm just making sure I have all the materials we'll need, doing prep work, and general messing around (yes, overthinking, Greg )...

Thought it'd be cleaner to relocate the heater wiring to the other side of the transformer. So, after checking the brain trust on the Mojotone FB group (and got a great response from Bruce Egnater - who, besides telling me it was fine informed me that it was "unnecessary" ), I tore it down and switched things around. OCD feels better, now

Heaters are the orange/black pair on the bottom-left holes in this before-shot.


This is the way it started


This is the way it ended up (on a second transformer I had on-hand, for illustration purposes)


And here's the wiring in it's new places


I may go ahead and do the primary wiring for the power and heater circuits, so that I can test things out and make sure my prior transformer woes are behind me now, and leave the rest of the board and tube component wiring for my son. We'll see

[greatmutah]

Bruce is great hahaha. He’s has a ton of knowledge and will happily share it. Super nice guy too.

Won’t hurt to do the primary and heaters. Unless your son is really looking forward to twisting some heater wires over and over again.

[Tortuga]

On Eric's orders ...

Got some of it done tonight

Cut & extended the white output lead, as the other one was a bit too short to get to the tubes (yes, I still need to insulate the junction). Cut and hard wired both sets of switched leads from the power transformer to power and standby switches, and tied off the alternate (220V, etc) power leads. Wired the PT grounds as well. (all indicated in red arrows)



Hoping to wire the power switch, mains fuse, and power input tomorrow night, along with the heater wiring to all the tubes. Will probably start power-up testing at that point, but the main HT filtering will wait until I get the board installed with my son.

Does anyone happen to know if it's ok to run a power transformer without any real load on it? Since my first one only lived an hour, I was thinking I might just let this new one run for a while to see if there's anything out of the ordinary. Maybe let it burn in a bit?

[GuitarBilly]

A PT? Yeah it's safe. The issues with running an amp without a load are related to the OT. But even the OT is safe as long as you're not passing signal or have shorted jacks.
That said, I never heard of burning in a PT. So I'm not sure if there's any benefit to doing it. I'm inclined to say there isn't. The voltages won't be accurate until it's properly loaded anyway.

But it won't damage anything to try it

[Tortuga]

Yeah - not sure if it’s a valid way of seeing if the replacement PT will hang tough this time. Just trying to eliminate it as a possible fail point. Really don’t want to go through that again.

[Tortuga]

Last couple of nights have been busy, so not a lot done, but some progress made...

finished hooking up main power input, fuse, primary power switch, and started the transformer heater lead (see red arrows)



also started the heater wiring (tedious )



Hoping to get heater wiring finished tonight/tomorrow so I can fire up the primary power and test the PT in-circuit

[Tortuga]

Mmmmmmm..... heaterzzzzzzzzzz.......

[Tortuga]

Well... had a surprise stayover from my son tonight, so we got busy...



He started wiring up the interconnects for the main controls



...and I got busy cleaning up / prepping the main circuit board

[Tortuga]

Got some done last night...

Mainly focused on the output tubes & transformer

Plate (B+) voltage test points:



Bias test point wiring (still need to install the 1-ohm resistors and finish connections, but it's close to being finished now):



Power supply to screen grid resistors:



Output transformer wiring:



Finally, after triple-checking all the wiring, plugged the thing in and got a good test of the output transformer's various supply circuits. All voltages are on the money

...then, put the tubes in and got a full test of the heater system...

IT'S ALIVE!!!

[Tortuga]

Lunch break...

Got the bias test points hooked up with the 1-ohm resistors to ground, and most of the output selector switch wired up.



Started on the speaker jacks (which get connected to the output selector and ground), but forgot to get a pic... will probably finish those up later today.

Not very exciting, but cleaned up the wiring and dropping resistor in the screen grid supply

[ajaxlepinski]

Hey G!!!
Looking good! Especially, your solder joints... so, I gotta ask: what are you using for a soldering iron?
The two soldering irons that I own do not play well with the new, lead free solder.

[Tortuga]

Thanks, Brian!

Using a Hakko FX888D-23BY that I got back in 2014. Thing is solid AF (well, except for the slightly loose cable connection jack on the front of the power supply unit, but I'll let it pass).



As for solder, I'm using Kester 24-6040-0027 (60% tin/ 40% lead)



I read & heard enough about how shite lead-free solder is. I use a smoke absorber that my son 3d-printed for me, and it seems to work great. I guess I'll find out if/when I have any affects from the lead at some point down the line.

[Tortuga]

Just finished up doing the last few connections before I have to wait for my son to come back and work with me on getting the circuit board wired in. This thing is getting very close to being ready to fire up



I'm holding off wiring the speaker jacks (one still not installed in the pic above) and Metro effects loop board until we get V1-V3 wired to the circuit board, so we have room to work in there.

Might go ahead and start prepping the JTM cabinet (drilling mounting holes & fixing up a temporary back panel), as well as installing wire leads on the circuit board and getting everything cleaned up for the final push.

[Tortuga]

Welp...

[GuitarBilly]

This is looking great man!!!!

[MacaroniSalad]

Nearing the finish line!

What a great project

[JiveTurkey]

Great Dad status surpassed long ago

[ajaxlepinski]

Thanks, Brian!

Using a Hakko FX888D-23BY that I got back in 2014. Thing is solid AF (well, except for the slightly loose cable connection jack on the front of the power supply unit, but I'll let it pass).


As for solder, I'm using Kester 24-6040-0027 (60% tin/ 40% lead)

I read & heard enough about how shite lead-free solder is. I use a smoke absorber that my son 3d-printed for me, and it seems to work great. I guess I'll find out if/when I have any affects from the lead at some point down the line.

Thanks G!!! Incoming roll of Kester 44.
Not sure why I thought lead solder was banned?

[Tortuga]

Well, if it hasn't been banned here in califailia, I doubt it'd be banned anywhere else

[Tortuga]

This is looking great man!!!!

Thanks Bill!

Nearing the finish line!

What a great project

Great Dad status surpassed long ago

[Tortuga]

My son is coming out tomorrow, so it was time to get the board ready (he'll be installing and working with me to do the final wiring. Wanted to clean & straighten out the board & components. Had to drill a few extra wiring holes due to the change in my grounding, but that was fine.



Then started adding the leads (most of these attach to the various controls up front as well as to chassis ground)



And this is the board with all the leads connected (the last two on the lower left are already in the chassis and will be connected when the board goes in).



I think between tomorrow and Saturday, we should be able to get the rest of the amp built and (hopefully) get to work on starting it up, get bias set, etc. If all goes well, I should be able to play this thing Saturday afternoon

[Tortuga]

My son and I got the thing pretty much ready to accept the board, which we will be doing tomorrow morning, right after picking up a replacement resistor for the input that I need to get. First off, we went though all the wiring done so far and made sure everything was connected right and soldered correctly, making sure to test continuity / coil resistance across everything we could. Only found one wire not soldered. Feeling pretty good about this one

Bright caps and attenuator resistor installed on the inputs. Still need a couple jumpers & wire connections along with the 1M grid leak resistor we'll get in the morning.



SGRs (green resistors) installed



Jumpers on V2 and V3, along with the 100K plate resistor for V2 all done.



Only have a little more work to do on the inputs, filter cap (the one that lives under the circuit board), and speaker outputs. Then it will be time to go through the startup process. Really hoping for tomorrow, but we've got Sunday in reserve as well

[fretless]

Best shop practices always wear eye protection.

[GuitarBilly]

You made some massive progress this week!! Getting close to the finish line

Can't wait to hear the amp when it's done. I have a weakness for 2204s!!!