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PostPosted: Tue Jan 07, 2020 10:11 pm 
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Have you tried it with an EL34 yet? I'm not a player, so I can't describe it, but I like the EL34 tone more than the 6V6 tone.

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PostPosted: Wed Jan 08, 2020 11:48 am 
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I haven't tried an EL34 yet, but I'm excited to do so. I'd like to solve the gain question first, before I start adding more variables.

But the 6V6 has plenty of power for me, provided I can push it. And there's plenty of gain in 'tude mode. It's just tweed mode where the gain seems low to me. For example, switching from 'tude to tweed drops the output voltage across the speaker by a factor of 4 or 5 when the input is small.


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PostPosted: Wed Jan 08, 2020 8:17 pm 
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LH , Topic by No457Snowy on pg 4 of Tramp forum "Now I don't understand why would you build a Champ?" might help. He talks about using a clean boost pedal. Don't know if this helps.

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PostPosted: Thu Jan 09, 2020 7:26 am 
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Thanks Hank. No457Snowy's clean boost pedal matches my experience almost exactly. That's super helpful. I'm impressed that you remembered a relevant thread from 7 years ago.

Stephan's post in the same thread is also really interesting:
Quote:
CHAMP SET UP: MV on max; B & T mid; both 'tude & fat OFF; Power about 8 snd use only Volume control.


When I do this, with a higher output humbucker guitar, I can get a little break up with Volume on max, and the amp is sending about 1W to the speaker when I'm playing reasonably hard. I wish I had a Champ (or another Tramp) to compare to...

Thanks again. I appreciate you staying engaged on this thread.


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PostPosted: Fri Jan 10, 2020 4:17 pm 
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You're welcome. I'm retired and I try to read all the threads on amp I'm going to build in it's respective forum. May not help all the time, but it helps more often than not. Also Resources page is good, too.

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PostPosted: Sun Jan 12, 2020 2:06 pm 
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You can amp the gain up a bit if you dont want to duplicate the Champ.
1 reduce bias resistor on V2 from 2K7 . Try 2K. If you like it. Then pair it with 4K to keep same ratio as original tramp
or 1800 / 4700
2. move feedback from 8 ohm to 4 ohm

Let us know how it goes

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PostPosted: Thu Jan 16, 2020 12:28 am 
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Thanks for this response, and for the ideas about how to increase gain.

I'm embarrassed to admit that at least part of my problem was the guitar. The pickups were set way low, so the signal from the instrument was weak to start with.

I spent some time over the weekend and during spare hours this week learning about tube amp design so I can be a little less helpless. This was (and continues to be) a lot of fun. After working out expected AC voltages and gains through the amp, I'm now convinced I built it correctly. Amazing!

I do still want more gain in tweed mode, so I'll play around with the suggested mods and report back.

For now, though, I'm calling the build complete, and I'm going to spend a bunch of time playing through the amp! :)


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PostPosted: Thu Jan 16, 2020 6:44 pm 
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Whenever you get tired of playing (probably be awhile), check out Rob Robinette's page https://robrobinette.com/Amp_Stuff.htm Has some great stuff (especially Fender related) and links to other sites. Edit: Sorry was wrong about links :oops:

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PostPosted: Sun Jan 26, 2020 1:04 pm 
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Hank that's a really good link. There's lots of great information on Rob's site!

When I said I'd call this build complete I was forgetting that I still had speaker swap to do! This meant making a custom baffle so the long magnet on the Alnico speaker wouldn't interfere with the power tube on the tramp. To jog your memory, here's the clearance problem that needed fixing.
Attachment:
File comment: This shows the magnet cover installed, but even with the magnet cover removed the speaker doesn't fit.
withBell.jpg
withBell.jpg [ 194.13 KiB | Viewed 527 times ]

The normal narrow-panel Deluxe baffle shifts the speaker to left as you face the amp. I decided to make a mirrored baffle that shifts the speaker in the opposite direction. For materials I bought some 3/8 inch baltic birch plywood from a nearby Woodcraft store. I also bought a piece of "1/4 inch" birch plywood from a big box home improvement store to space the grill cloth away from the baffle. The plywood from woodcraft was great. I'm not impressed with the plywood from the big box store. I bought gold-stripe oxblood grill cloth from Mojotone.

I copied the dimensions of the original baffle and cut it out with a circular saw.
Attachment:
File comment: You don't see safety glasses in this picture because I'm still wearing them.
fence.jpg
fence.jpg [ 223.8 KiB | Viewed 527 times ]

I measured and drew the speaker cutout, then cut it out with a jigsaw. I cleaned up the shape with a wood rasp. The rasp was far too coarse for the job and caused some tearout on the plywood. Next time I'll sand out any irregularities (see next post).
Attachment:
File comment: Drawing the cuttout.
drawingCutout.jpg
drawingCutout.jpg [ 41.88 KiB | Viewed 527 times ]

I drew a few extra marks to help center the speaker on the cutout, then used the speaker frame as a guide to mark holes for the speaker studs. I used 8-32 x 1" machine screws for speaker studs. I predrilled holes with a 1/8" drill bit, then screwed the studs into the holes from the front side of the baffle. 1/8" is pretty tight for a #8 screw, but I wanted a snug fit so the studs wouldn't back out later. I was still a little worried that I'd ding the threads when putting the speaker on, and that the torque to force a nut past the dings would be enough to back the screw out, but so far so good.
Attachment:
File comment: You can see the alignment marks at 3:00, 6:00, 9:00 and noon in this picture.
alignmentMarks.jpg
alignmentMarks.jpg [ 161.11 KiB | Viewed 527 times ]

I test fit the baffle and speaker. There's lots of clearance without the magnet cover. At this point, the baffle felt super-loose in the enclosure, and I wished I'd cut it a bit bigger, but see below...
Attachment:
File comment: Looks like everything will fit!
testFit.jpg
testFit.jpg [ 352.04 KiB | Viewed 527 times ]

This post is getting long, so I'll break it into two.


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PostPosted: Sun Jan 26, 2020 1:39 pm 
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After making sure the basic fit was OK, I cut 1" strips of 1/4" plywood to give the grill cloth some standoff from the face of the baffle. I softened all the sharp edges with a piece of sandpaper, then glued and screwed the 1" strips to the baffle board. The spring clamps in the picture were what I had available, but they're the wrong tool for the job. They don't keep the wood from sliding. You can imagine picking up the baffle in the picture below. The glue hasn't set, so it's still really slippery. Gravity pulls the handles of the clamps down, and that walks the 1" strip just a little bit off the edge of the baffle. I was able to get things lined up fine, but it was finicky and frustrating. next time I'll get some small C clamps. I used #6 x 1/2" screws with 5/64" pilot hole. I used flathead screws, and countersunk the pilot holes so the heads of the screws wouldn't interfere with the grill cloth.
Attachment:
File comment: Screws and glue
gluedAndScrewed.jpg
gluedAndScrewed.jpg [ 59.24 KiB | Viewed 527 times ]

In the picture above, you can see that the bottom strip of 1/4" plywood overlaps the bottom of the speaker cutout. It's probably no big deal, but it doesn't seem classy, so contoured it to match using 80 grit sandpaper. This was much easier than I expected. It took about 3 minutes of hand sanding.

I stapled on some string to hang the baffle, masked the threads of the speaker studs with tape, and sprayed the whole thing with flat black rattle can spraypaint.
Attachment:
File comment: Ready for painting.
readyForPaint.jpg
readyForPaint.jpg [ 20.17 KiB | Viewed 527 times ]

Keeping the grill cloth tight while attaching it was tricky. Fortunately my wife is both talented and strong, so between the two of us it went pretty well. We used 3/8" T50 staples. The staple gun was just about strong enough to drive these into the plywood, but we wound up tapping quote a few of them in with a hammer to tighten them up.
Attachment:
File comment: So many staples.
grillCloth.jpg
grillCloth.jpg [ 331.65 KiB | Viewed 527 times ]

We added a second row of staples before trimming the grill cloth, but I think it was overkill.
Attachment:
File comment: Ready for installation.
ready.jpg
ready.jpg [ 279.95 KiB | Viewed 527 times ]

With the grill cloth and staples, the baffle just barely fit the cabinet. I'm surprised at how much space get eaten up. Maybe 3/16"? That's only a guess, but I'm glad now that I didn't cut the board any bigger.

I drilled holes for the screws that mount the baffle to the cabinet by holding the baffle in place, then running through the holes in the cabinet with the biggest bit that would fit cleanly (and not enlarge the holes in the cabinent). This made sure the holes in the baffle were perfectly lined up. I don't remember what size bit I used, but the mounting screws look to be 8-32.

As expected, there's not enough clearance for the magnet cover, but everything fits great without it. I"m telling myself the additional cabinet volume will improve the sound. :)
Attachment:
File comment: I did remember to install a speaker cable eventually. ;)
installed.jpg
installed.jpg [ 95.14 KiB | Viewed 527 times ]

And here's the finished (again) product.
Attachment:
File comment: For real this time.
finished.jpg
finished.jpg [ 166.51 KiB | Viewed 527 times ]

Thanks again for listening. This has been a lot of fun.


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PostPosted: Mon Jan 27, 2020 1:39 pm 
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It looks good. You would never know it wasn't the stock baffle except for the different speaker location.


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PostPosted: Mon Jan 27, 2020 10:17 pm 
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Looking great. :thumbsup:


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PostPosted: Wed Mar 18, 2020 2:40 pm 
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Thanks for the great thread! Your presentation is nice. I was wondering if you would be up for making a short thread highlighting the 3-way bias switch? You mentioned you would post about it's effects after you were done. It would be great for future builders if it was all in one place. Thanks either way!

-Daniel


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