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PostPosted: Thu Dec 19, 2019 9:35 pm 
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Running again. :mrgreen:

My Trinity Tramp smoked a bit & quit working a couple days ago.
I had installed a 7581 and was sounding great. Cranked to the max.
Had the correct bias setting on my switches. Ran about 10 minutes, cut out, sparks in the tube slight smoke, then died.
Blew the main fuse. I replaced it, put in an EL34, switched the bias & load switch to the correct positions. Tubes glowed, but no signal.
Traced it down to a 100ohm, 5watt resistor. DC voltage before the resistor, nothing after.
Replaced with a 10watt. Now it’s singing again.

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I put the 7581 back in, was working again. When I adjusted the VRM above 5, it would start to cut out. Checked the voltages, was in spec, increasing properly till I hit 5 on the dial, then voltage dropped to 31VDC & cut out. Shut it down right away.
So now I don’t know if it was a failure of the brand new tube that caused the 100ohm - 5watt resistor to go, or if the resistor failed, & caused the tube to go.
With the new 100ohm - 10watt resistor in, I cant feel it heat up when cranked.

At least its working again now with the EL34 or KT88.


Scott


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PostPosted: Thu Dec 26, 2019 9:45 pm 
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Decided to try the PAB mod.

I used a CTS 500K push-pull.

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I first tried it with just the 500K ohm pot, when pulled, gave me a total of about 22k ohm - 380K ohms in series, when I rotate pot. 22K ohm at start because of the original resistor still in line. .

Sounds good, notice a dit of difference in boost, when I adjust the pot from Low - Hi, but trying to get a bit more boost.

Then I added a 330K ohm resistor in series after the pot. Now I get 277K ohm - 490K ohm with switched pulled & pot in circuit.

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Notice more initial boost, but very little gain when adjusting pot from Low - Hi

Maybe need to find a 1M ohm push-pull pot.

More experimenting I guess.

Any comments appreciated.

Scott


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PostPosted: Sat Jan 11, 2020 3:57 pm 
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Was playing for about 15 minutes today. Everything cranked in Tude mode.

Saw some smoke again. Shut down right away.

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Maybe need some paint-on rubber tape to stop any arcing?


Scott


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PostPosted: Sat Jan 11, 2020 4:13 pm 
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These switches on the OT primaries are causing a lot of problems. Covering the terminals with rubber insulation has helped. If you can get by without the switch, just remove it and wire the OT directly to the tube.


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PostPosted: Sun Jan 12, 2020 11:46 am 
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I have used liquid tape to insulate these terminals from arching. I think the basic issue is the switch is physically small.
I would build the switch and put heat shrink over the terminals.
I will note that in the manual as well.

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PostPosted: Sun Jan 12, 2020 3:41 pm 
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Looking at the Tramp & build manual today.

As Stephen stated in the manual, which I overlooked.

“Note: Make sure that you insulate & solder the lugs/connections at the switch in order to prevent any arcing between lugs & switch metal body.”

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Obviously high voltages.

Only a couple seconds that I noticed & switched things off. The switch is ok, fuse good, hopefully my OT & tube survived.

Lots of fun & learning.

Scott


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PostPosted: Sun Jan 12, 2020 5:16 pm 
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M, if you can do without the PAB, there is a larger switch you can use. See pg. 2 of Tramp forum, "OT Impedance Switch Arcing" thread, posted by Pharmrock. The switch can be mounted in the PAB hole. After reading it, I built both my Tramps with the larger switch, but both the large switch and the liquid insulation solutions are discussed in that thread. I did buy some Permatex Liquid Insulation off Amazon, but decided to go with the large switch. Neither of my builds show evidence of arcing. Anyway, the info is there and hope this helps. Hank PS I think there's another thread on this somewhere, but can't remember the title.

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PostPosted: Sun Jan 12, 2020 5:35 pm 
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Cleaned everything & wired the switch back up. Made sure I kept the wires away from the switch body.

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Tried it out & singing away again. :)

Now I will get some liquid tape to insulate the wires & switch posts.


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PostPosted: Mon Jan 13, 2020 10:25 am 
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Moodivarius wrote:
Cleaned everything & wired the switch back up. Made sure I kept the wires away from the switch body.
Now I will get some liquid tape to insulate the wires & switch posts.


You really just need to insulate the body to increase the gap. We are looking for a better switch for this.

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PostPosted: Tue Jan 14, 2020 2:33 pm 
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So it's arcing between the switch body and the leads, not between the terminals? Clarification on that would be appreciated, as isolating switch body from leads seems to be different than isolating leads from each other.


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PostPosted: Wed Jan 15, 2020 8:19 pm 
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natebiehl wrote:
So it's arcing between the switch body and the leads, not between the terminals? Clarification on that would be appreciated, as isolating switch body from leads seems to be different than isolating leads from each other.



Mine was arcing from the metal on the switch body to the wire. I had left too much wire stripped back past where I soldered it to the lug. So it arced from wire to metal on the switch body, then also to the chassis. I re-soldered the wire to the lugs, so the insolation on the wire was tight to the lug. I also bent the upper lugs, towards the top of the switch, & the lower lugs towards the bottom, allowing a bit more space between lugs &'wires on the switch.
I just got some liquid electrical tape, which I will apply to the switch body, lugs & wires.

Hopefully that will fix it for good.


Scott


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PostPosted: Wed Jan 15, 2020 9:03 pm 
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Applied the first layer of liquid tape.

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Planning on totally incapsolating the switch lugs & wires.


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PostPosted: Thu Jan 16, 2020 12:11 am 
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I bet that will work. If it doesn't, and if you don't expect to run the tramp with a 16 Ohm speaker cabinet, I believe you could delete the arcing switch entirely and get the 2500 Ohm impedance for the EL34 by setting the speaker impedance selector one click "higher" than the installed speaker.

As far as I understand, this works because reducing the speaker impedance also reduces the reflected impedance at the primary of the output transformer. So connecting a 4 Ohm speaker to the 8 Ohm secondary tap (or an 8 Ohm speaker to the 16 Ohm secondary tap) makes the 5000 Ohm primary tap look like 2500 Ohms.

I'm happy to be corrected if there's some subtlety I missed. In the meantime, here's a photo illustrating what I mean. In the photo, the 2.5k/5k switch is deleted, and the impedance switch label shows how to set the impedance switch so that an EL34 sees a 2500 Ohm load with an 8 Ohm speaker.


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PostPosted: Thu Jan 16, 2020 9:58 pm 
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Yes, that's right. Transformers don't have a built-in impedance, the impedance reflected from the secondary back to the primary depends on the impedance of the load.

If the 8-ohm secondary reflects 5000 ohms back to primary, the impedance ratio of this winding is 625:1. With an 8-ohm speaker connected that reflects 8x625=5000 ohms back to the primary. If you connect a 4-ohm speaker to this winding that reflects 4x625=2500 ohms back to the primary.

If the 16-ohm secondary reflects 5000 ohms back to primary, the impedance ratio of this winding is 312.5:1. With a 16-ohm speaker connected that reflects 16x312.5=5000 ohms back to the primary. If you connect an 8-ohm speaker to this winding that reflects 8x312.5=2500 ohms back to the primary.

So as long as you aren't using a 16-ohm speaker, you can get 2500 ohms at the primary just by selecting one click higher on the switch.


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PostPosted: Thu Jan 30, 2020 9:40 pm 
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My CTS 1Meg pot showed up in the mail today.

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Pulled apart the 500k push/pull & the new 1Meg pot.

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Swapped the swiper pad, from the 1Meg into the 500k push/pull.

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Installed back into the Tramp. Now I can pull the 1Meg push/pull shaft, engage the PAB, dial from original, no boost, all the way up to a very noticeable Pre-Amp-Boost.

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Now I’ll likely drill a hole in the front panel on the left side of the input jack. Then I’ll have it accessible & adjustable. :mrgreen: :lol:


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PostPosted: Mon Mar 09, 2020 10:29 pm 
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A couple of sound clips. Just taken through my iPhone.

Great sounding harmonics on this amp. Guitar straight into the amp.

Using my PAB turned up to max on my 1Meg pot.

Both in Tween mode. Clean video started on Gain of 7, then went to 8.

AC/DC video was on again of 8.

Running through a WGS Blackhawk HP Alnico in my Traynor YGL-1 cab.

https://m.youtube.com/watch?v=OQOStdLvUy8

https://m.youtube.com/watch?v=FVZP51pCFLo

Scott


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