Magnatone Twilighter 2020--MOD BUILD-Only Tremolo

[wsscott]

Thanks. A few more things to add to my list.

[wsscott]

I checked the AES site, and their .68uf at 630V should work fine for the 500V cap, but at 0.61" it's a bit too wide for the 250V cap. I didn't see any .68uf 250V caps on their site except for one at 200V that was really expensive.  I guess I could just use long leads and have it sit above the other components, unless you have another source for the cap or another idea.

Also, I haven't been able to find a 1uf, 63V cap for the Line Out.  I have found a 50V and a 630V.  Thoughts?

And although I won't need tubes for awhile, I thought I'd ask your opinion on brands.  What about JJ tubes for this build?

[sluckey]

I checked the AES site, and their .68uf at 630V should work fine for the 500V cap, but at 0.61" it's a bit too wide for the 250V cap.

I don't know where you found a 0.61 dimension. The 630v cap I would use is 1.14 x .406 x .66 (LWH) It will fit in either position. But your 100v cap should be OK for the 250v shown on my layout. The only voltage it will see is the bias voltage.

     https://www.tubesandmore.com/products/capacitor-630v-polypropylene-radial-leads

Also, I haven't been able to find a 1uf, 63V cap for the Line Out.  I have found a 50V and a 630V.  Thoughts?

50V is fine. DO NOT USE AN ELECTROLYTIC!

     http://smallbear-electronics.mybigcommerce.com/capacitor-bc-components-1-uf-63v/

And although I won't need tubes for awhile, I thought I'd ask your opinion on brands.  What about JJ tubes for this build?

I have bought a lot of JJs.

[wsscott]

I was looking at the Metal Film Tubular caps. Your suggestion looks a lot better.  I'll be buying more than 1 of them, so is there any reason not to use a .68uf at 630V in both locations?

[sluckey]

so is there any reason not to use a .68uf at 630V in both locations?

The only reason would be if it doesn't fit.

Small Bear has several options for that 1µF film cap. DO NOT USE AN ELECTROLYTIC!

[wsscott]

Gotcha-

[wsscott]

Does anyone have a Mojotone chassis that they can tell me the specs for the angle of the front, and its heighth.  I thought it was 45 degrees and 2 1/2" but I think that's too severe of an angle for the jacks and pilot light to fit properly.

[wsscott]

I got it resolved.  Waiting to get chassis fabricated.

[wsscott]

Status update, for anyone who is interested:  Finally got the chassis design resolved, and its in the process of fabrication.  Maybe I'll get it in the next week.  Trying to do custom cabinet mod via email is difficult for my project, so I and the fabricator have decided to ship them the chassis when I get it and they will build the cabinet to fit.  Its just a few mods to a Brownface Deluxe cabinet, but not being a cabinet builder, its hard for me to think of the changes that need to be considered.  This will turn out the best way to do it for me.

[wsscott]

Well the 0.68uf 650V caps and the 82K resistor came in yesterday, and I installed them this morning. Attached is a photo.  I think the caps fit fine.  I decided to use the BIG ones for both. So the turret board is complete and waiting for the chassis to proceed.

[wsscott]

Well the Chassis came in this week, and I sent it to the cabinet fabricator to use for the cabinet design. Hopefully that will go smoothly, and maybe in a week or so I'll have it and the chassis back, so I can start wiring it up.

Sluckey, 2 questions for you.  On your layout, it shows the wire for the Negative Feedback circuit as having a different color.  Did you just do that to make it easier to see, or is there something special/different about this wire.  Also, as to the 1 ohm bias checkpoint resistors, are they just 1/2 watt like all the others or is there something special about them also?

I've never had to cut rectangular openings in an aluminum chassis before, so I wanted to ask for some guidance on the best/easiest way to do that.  I'll need cutouts for the PT and for the IEC jack.  The chassis is 0.08" aluminum.  I was thinking of drilling holes in each corner of the marked rectangle area to be cut out, and then use a fine tooth, 32 TPI, manual hacksaw to cut it out.  Thoughts? 

Thanks as always.  Stephen

[shooter]

drilling holes in each corner

I use a dermal with metal cutting wheel, take your time, then finish the fine work with a flat file

[sluckey]

Sluckey, 2 questions for you.  On your layout, it shows the wire for the Negative Feedback circuit as having a different color.  Did you just do that to make it easier to see, or is there something special/different about this wire.

Seriously? Is that really a question?

Also, as to the 1 ohm bias checkpoint resistors, are they just 1/2 watt like all the others or is there something special about them also?

Half watt is fine although I use some 1Ω/1W/1% that I got from Mouser a long time ago.

I've never had to cut rectangular openings in an aluminum chassis before, so I wanted to ask for some guidance on the best/easiest way to do that.  I'll need cutouts for the PT and for the IEC jack.  The chassis is 0.08" aluminum.  I was thinking of drilling holes in each corner of the marked rectangle area to be cut out, and then use a fine tooth, 32 TPI, manual hacksaw to cut it out.  Thoughts?

I drill corners then use Dremel with cutoff wheel and finish with files.

[wsscott]

Well Sluckey, I hate to be stupid, but yes its a real question.  It has a notation, "NFB" on it, plus it's color stands out.  Why put the notation and the colorization on the Layout if it doesn't mean something?  The schematic shows it as wired normally, nothing unusual, so that's the reason.

[sluckey]

Did you also notice that the NFB wire is smaller than the other wires? Or were you saving that for a follow-up question?   

[wsscott]

Actually, no I hadn't noticed that the wire is smaller until you mention it now.  Thanks.

[sluckey]

Old men just gotta have a little fun every now and then.   

[Willabe]

Old men just gotta have a little fun every now and then.   

 

[wsscott]

Well, as Paul McCartney says everybody needs to "Dance Tonight".  Good song.

[wsscott]

Just to let anyone who’s interested know that neither the project nor I am dead yet. The cabinet probably won’t be ready until late June, so I’m on hold until then. But since I had ankle replacement surgery last week at UVA, the cabinet build will probably fit in with my recovery schedule anyway. Hope you guys are doing well, and that you have some interesting new projects on your workbenches. Best.

[wsscott]

Well, I have arisen from the dead!  My cabinet just arrived this week, so now I have a chassis and a cabinet that fit together great.  Now that I have the chassis back I plan to start working on the layout on the chassis next week.  The last chassis I did from scratch was the Mag 10A Mod that Sluckey, Shooter and others helped me on last year.  When I drilled the holes for the controls on the front they were in pretty good alignment, but although I used a punch, and a drill press, and a stepped bit, some of them wound up being slightly off the center punch.  Not a big deal on that chassis because they were so close as not really noticeable, and I wasn't going to have a faceplate or something to go over it.  But I'm thinking of having some kind of a faceplate this time so I really want them to be accurate.  I was thinking maybe I should make a template from some fiber board or something to use as a drill guide.  Any thoughts?  Thanks again for your comments, interest and time.  Stephen

[shooter]

make a template

 


if you have a custom overlay faceplate, that "hides" many a drift on the backing plate

[sluckey]

First off. Don't start your holes with a step bit. Accurately mark with the center punch. Use a 1/16" bit to drill pilot holes. Then use a 1/8" bit to make the pilots larger. THEN switch to the step bit.

If you want to ensure the faceplate lines up with the holes in the chassis, then attach the faceplate to the chassis, mark, center punch, and drill both at the same time.

[wsscott]

Yes, last time I used a center punch, then a small drill, then step drill, so probably adding another interim sized drill would help. The faceplate would be custom so I don’t have one yet. I’m going to see if a local graphics/sign shop can do something for me. Obviously to drill the holes I’ll know what the layout is, so maybe it’s something they can do now and I can drill both together as Sluckey suggests. Problem may be finding someone local who can do it. Maybe my project for this weekend is to do the layout design.

[shooter]

see if a local graphics/sign shop can do something for me.

maybe find your local fabrication shop and see what they can do to center n drill the holes 

[PRR]

I'm thinking an all-round sign shop must have a drill. Whether they can drill better than you is a different question; my sign shop, I don't trust the young guy much but I bet the old guy can do anything he reckons he can. Or next door in the steel shop they can drill ANYthing to any spec, but they charge for tools and skill.

[wsscott]

I’m making some progress!

[sluckey]

Jacks on the left seem higher than jacks on the right.

[PRR]

> Jacks on the left seem higher than jacks on the right.

Less than 1/8".

Man, I'd shove you off the stage for pointing that out.

[sluckey]

Haha. But it's so obvious to someone who has drilled a lot of holes. Most people would never notice. Might make getting a faceplate that fits a little challenge. Good argument for not drilling until the faceplate is made, then using the faceplate as a drill template.

[Willabe]

> Jacks on the left seem higher than jacks on the right.

Less than 1/8".

Man, I'd shove you off the stage for pointing that out.

[sluckey]

Guys there was some recent discussion about hole misalignment so I though my criticism was appropriate. Not trying to be nasty.

[Willabe]

I'm laughing at what PRR said. 

[PRR]

> it's so obvious

Apple has trouble with the concept.
https://www.theregister.com/2021/06/15/m1_imac_crooked_display_issues/

[wsscott]

Any suggestions or comments on the proposed layout of the Choke and the OT as shown in the attached photo?

Also, as to the Cap can, I've never installed one before and had a question(s).  Can I just use the metal and phenolic  oval-like "washers" for mounting, and bend the ground tab(s) to hold in place, or do I also need to use the ring mount.  I have a ring mount but its too small to mount around the base of this can.  If I can just use the washers, does the metal one go on the outside of the chassis and the phenolic one on the inside, if not, how are they mounted.

Thanks as always. 

[tubeswell]

Also, as to the Cap can, … Can I just use the metal and phenolic  oval-like "washers" for mounting, and bend the ground tab(s) to hold in place, or do I also need to use the ring mount.(?)

Use a proper mount.

[Willabe]

Also, as to the Cap can, … Can I just use the metal and phenolic  oval-like "washers" for mounting, and bend the ground tab(s) to hold in place, or do I also need to use the ring mount.(?)

Use a proper mount.

Yes.
Highest dcv in the amp connects to that can. 

[sluckey]

The proper way to mount that can is to bolt the metal mounting plate on the inside of the chassis. (You will not use the phenolic mounting plate). Now position the can so the twist lock tabs will go through the slots in the mounting plate. Twist all 4 tabs 90° to secure the can to the mounting plate.

Now, solder the PT HT center tap to one of the twist lock tabs. Also solder a short ground strap wire to the same tab. Put a ring lug on the short wire and bolt it under one of the mounting screws for the mounting plate. This is your power ground point.

Look at this pic to get the idea...

[sluckey]

Oh yeah, here's a view of that same can from the top. Nice and neat. Those cans were very popular in the '60s.

[wsscott]

Sluckey, so the clamp mount isn’t really necessary?

Thoughts on the orientation and layout of the Choke and OT?

[sluckey]

Sluckey, so the clamp mount isn’t really necessary?

Thoughts on the orientation and layout of the Choke and OT?

Twist lock style cans never had a clamp. I showed you the proper way to mount that style cap. Heck, twist lock cans were so popular in the '60s that some manufacturers didn't even bother with the mounting plate. They just punched the chassis for the twist tabs to fit. Now that's really clean looking. Look at this...

     http://sluckeyamps.com/hammond_2/big_guts.jpg

Choke and OT look fine.

[wsscott]

Thanks. It certainly looks cleaner. I wonder why they started using the clamp?

[sluckey]

Clamp style cans have been around a long time too. They are much easier to change. More secure too. The twist-lock cans can be a real PITA to remove, especially if all twist tabs are soldered! I never saw a twist-lock can in any military equipment.

[shooter]

I wonder why they started using the clamp?

those came along in the 70's when all the field engineers bitched about having to replace the dog ear'd caps 

[wsscott]

Since the PT (Hammond 290BX) that I'm using doesn't have a CT for the 6.3V filament winding (see spec sheet attached), am I correct that I'll need to add a pair of 100 ohm resistors at the Indicator Lamp to create a virtual CT for this amp?

[wsscott]

I ask because the PT in the Schematic/Layout that Sluckey did for me appears to be the same PT as the one I'm using and it also doesn't show a CT for the filament section of the Secondary.

[wsscott]

I ask because the PT in the Schematic/Layout that Sluckey did for me appears to be the same PT as the one I'm using and it also doesn't show a CT for the filament section of the Secondary.  Is that because the 100 ohm resistors are built onto the turret board?  I assume so, but just want to be sure.

[sluckey]

The answer you seek is on the layout. Trust your eyes.

[wsscott]

Sluckey, in looking at your Layout, what type of Ground connection is used for the 1 ohm Bias Check resistors?  You have a ground wire running off that connection point and going to the Power Ground Point on the chassis.  Is it an insulated connection point that keeps it isolated from the chassis?

[sluckey]

The black thing that the two 1Ω resistors connect to is called a tip jack. The two red things are also tip jacks. They are all insulated from chassis. That's why there is a wire connecting the black (common ground) jack to a power ground lug. They are used to conveniently monitor bias current. Just plug your meter in.

They are not needed. You can connect the 1Ω resistors directly to the power ground if you prefer. Here's a pic of the tip jacks Hoffman sells...