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 Post subject: OSD build in Montreal
PostPosted: Thu Mar 29, 2018 12:05 pm 
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Second build. I built a trinity 5E3 a few years ago and loved it.

I’m in the testing phase with tubes in place. After some struggles I have the following voltage readings:

I have B+ as follows:

B+1 446V
B+2 441V
B+3 432V
B+4 304V (should read 333V)
B+5 296V (should read 328V)

V4 and V5 check out to around 440V on the screens and plates, -40V on the grid.

V3 is reading a little off but close.

Pin 1 316V
Pin 2 40V
Pin 3 63V
Pin 6 307V
Pin 7 41V

V1 reads 202V at pin 6 and 1.33V at pin 3

V2 reads 198V at pin 6 and 1.55V at pin 3

Now for the real issue...

With volume and master at 7 o’clock (off) with the power on, when I engage them standby I get a static scratch through the speaker that lasts about two seconds which sounds to me like a cap discharging. I have intermittent faint hum, it comes and goes, but generally at idle everything is very quiet. The same scratching occurs and sometimes lasts a few seconds longer when I power off but is inconsistent, sometimes it doesn’t happen. I haven’t plugged in a guitar yet because (paranoid as I am!) I think I have a problem. Is that something in the signal path??

With a cable plugged in (no guitar) I get a very faint tapping but no hum when I touch the end, it’s very quiet, volume and master volume increase has no effect on the volume of the tapping. In essence I have no sound as is.

The footswitch seems to be working, LED on the REL2 section of the board is in with footswitch plugged in, off when it’s disconnected. The other LED lights when the footswitch is engaged.

I do have the ground wire from the bus mentioned in the Bangkok build thread. I have a ground running from the bus bar between the input and the volume control to the PRE1 ground lug, which is also grounding the relay board, the footswitch and the 25uF polarized caps/1K5 resistors from V1.

Stephen has suggested I need to test continuity from the input jack step by step until I find the problem.

Any thoughts are much appreciated!


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PostPosted: Thu Mar 29, 2018 7:27 pm 
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An update:

I tested all of the following and have continuity across these connections:

V1
Input jack (cable in) to 33K (R1)
Pin 1 to 100K (R4)
Pin 3 to 1K5 (R3)
Pin 4 jumper to pin 5
Pin 6 to 100K (R14)
220K (R11) to volume control
Pin 8 to 1K5 (R15)
Pin 9 to V2 pin 9

V2
Pin 1 to 100K (R18)
68K (R18) on pin 2 to trim pot
Pin 3 to 1K5 (R19)
Pin 4 jumper to pin 5
Pin 6 to 100K (R22)
180K (R21) on pin 7 to level control
Pin 8 to 1K5 (R23)
Pin 9 to V3 pin 9

V3
Pin 1 to 100K (R30)
Pin 2 to 1M (R26)
Pin 3 to 820K (R29)
Pin 4 jumper to pin 5
Pin 6 to 110K (R31)
Pin 7 to 1M (R 28)
Pin 8 jumper to Pin 3
Pin 9 to V4 pin 2

V4
Pin 1 jumper to pin 8
Pin 3 to 6V6/6L6 toggle switch
470R (R39) attached to pin 4 to B+2
5.1K (R35) attached pin 6 to 220K (R33)
Pin 8 to bias test point

V5
Pin 1 jumper to pin 8
Pin3 to 6V6/6L6 toggle switch
470R (R39) attached to pin 4 to B+2
5.1K (R36) attached pin 6 to 220K (R34)
Pin 8 to bias test point

I’ve tested many of the other connections between the control knobs and their various destinations with no result. I did discover that the ground connection between the ratio control and the bus bar was not 100%, I repaired that and still have the same issue.


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PostPosted: Fri Mar 30, 2018 9:52 am 
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Can you post pictures of the controls pots, tubes side, output jacks
I will try to trace your circuit through. Confirm the impedance switch is wired correctly and to the jacks?

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PostPosted: Fri Mar 30, 2018 11:29 am 
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I traced your stuff through and it looks good. (you called Pin 3 to 820K (R29) should be 820R).

1. You should also follow the schematic and trace the signal path through the controls and switches as well. Ian do the same with the results if you like.

2.Check for a compromised shielded cable (i.e. the ground has melted through to the core during installation)

3. Measure conductivity for all the jumpers you put under the board, i.e. between part leads.

Your voltages seem OK but something is affecting B+4 304V (should read 333V) and therefore B+5 (could be a tube) but if the tube is good, it should still work.

4.Confirm the impedance switch and 6V6 / 6L6 is wired correctly. I expect it is because the voltages are reasonable on the power tubes.

5. If all that is Ok, you will need to very carefully take an insulated, small screwdriver (or insulated clip with a lead on it) , and systematically tap the grids of various tubes to see if you can get a pop or noise through it. This is a way of inducing a signal directly into the chain to see where it is broken down. Start from the power tubes and work backward following the schematic.
Just be sure to touch only the grids because there is some very high voltage close by.

I also suggest posting some hi res pictures.

Your voltages are close so I think there is a wiring error somewhere.

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PostPosted: Fri Mar 30, 2018 12:36 pm 
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Thanks, Stephen.

I won’t be able to get to this until April 9th. I’m fairly certain it’s in the signal path, somewhere the signal is being sent to ground. I started testing continuity in parts of the path and didn’t find anything in the pots, etc. but I ran out of time, I will be more systematic when I come back to it. I imagine the shielded cable would still test for continuity even if the core has been compromised by overheating as you suggest?

I rewired the impedance switch just to make sure and it checks out.

The underboard jumpers are on my mind as well, it seems (at least) that I have the same instinct that you have about where to look for the problem. It’s also possible it’s in the rock/Jazz mid boost switches, they were a challenge for me to wire cleanly.

Thanks again!


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PostPosted: Mon Apr 09, 2018 6:56 pm 
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Ok, back to work.

I checked the continuity of the under board jumpers and discovered TWO problems. The one connecting the caps from the bias/rectifier section to the power supply, also the one from 1uF cap in the phase inverter section to the preamp section. I corrected those with a jumper on top of the board (for now...I may take the whole thing apart and fix the under board jumper). I now have continuity for all the under board jumpers.

I tried another power up, same result. I checked the B+ voltages again, 4 and 5 are still just under 300V, the others are close to spec.

On the subject of shielded cables, is there a way to check them without desoldering? A visual inspection doesn’t yield much.


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PostPosted: Tue Apr 10, 2018 8:01 am 
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You need to check if the core is grounded. Do a continuity check from the core ground. On input jacks, you need to plug a cable in.

You do have a compromised signal path if all the voltages are close, so go through the schematic and layout and locate and test the continuity of signal path.

Sometimes voltages are low because of excessive current draw. You can look for causes of that on plates and cathodes and bad vacuum tubes.

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PostPosted: Tue Apr 10, 2018 8:39 am 
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A bad solder joint from second coupling cap to the relay board...I have a signal path :D ! No time to test today...tomorrow...I have a guitar signal!


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PostPosted: Tue Apr 10, 2018 12:45 pm 
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AndreDanican wrote:
A bad solder joint from second coupling cap to the relay board...I have a signal path :D ! No time to test today...tomorrow...I have a guitar signal!


Excellent. Good detective work. Looking forward to more feedback and another Video I hope!!

Check out this post on getting going. http://www.trinityamps.com/phpbb/viewtopic.php?f=21&t=5472

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PostPosted: Fri Apr 13, 2018 8:22 am 
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I haven’t had much time to further dig in into diagnosing what’s going on with my build. As I mentioned in my last post, I have a guitar signal but alas, the overdrive channel is not working. In looking through the builders guide (various) versions it seems there are conflicting versions and I may have some hybrid of those different versions. For example, in the current builders guide (v.13) the 22M resistor shows one connection on the PAB section of the board while the current layout (also v.13) shows something else. I would like to go through the whole relay board to confirm it is correct but I’m not sure what I should be using as a benchmark. Once the board is in there is very little room to work in there, a partial tear down may be in order. :(


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PostPosted: Fri Apr 13, 2018 10:35 am 
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For the latest check this out.

http://www.trinityamps.com/wp-content/u ... ut-v13.pdf

Does PAB footswitch work??

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PostPosted: Fri Apr 20, 2018 8:37 am 
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Good news/bad news. I rewired the relay board to conform to the latest version. My work was so spread out over weeks that I had some kind of mixed up composite of earlier versions. Fired up the OSD and I had sound! Overdrive and PAB working. Sounding good. As I began to experiment with the tone knobs with no OD or boost, the wires at the 6v6/6l6 DAP switch burst into flames, power off! This only took about two minutes for the heat to reach such a level. A short?


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PostPosted: Sat Apr 21, 2018 8:16 am 
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My small fire was the insulation of two wires, specifically the area where the w brown/white wire from the output transformer and the brown wire to V5 leave the DPDT switch. I unsoldered those two wires along with the blue/white wire, which was also damaged, from the output transformer. My plan is to clean it up, resolder, test for continuity and see if I can get it up and running. I’m not understanding why the heat would reach such a point at this location, is there something wrong with the 4K primary of the OT?


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PostPosted: Sat Apr 21, 2018 5:59 pm 
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There is nothing wrong with those leads AFAIK. Disconnect them, measure the resistances and I will measure a set here and we can compare them.

You could temp just use the 8K and bypass the switch.

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PostPosted: Sat Apr 21, 2018 8:13 pm 
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Check the switch, too. Could be the contacts have become highly resistive thereby generating a lot of heat. Could be a bad connection where the brown wires attach to the switch, too.


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PostPosted: Sun Apr 22, 2018 12:11 am 
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+1 on the switch too. :thumbsup:

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PostPosted: Sun Apr 22, 2018 8:13 am 
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Red Center tap - brown/white primary: resistance measures 116.1 ohms
Red Center tap - blue/white primary: resistance measures 123.2 ohms

At first glance this seems normal. Any thoughts on what’s next?


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PostPosted: Sun Apr 22, 2018 8:15 am 
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Mitch m I think the switch and the connections there is the problem. I’m going to try to clean that up a bit and recheck all the connections.


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PostPosted: Sun Apr 22, 2018 6:04 pm 
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AndreDanican wrote:
Red Center tap - brown/white primary: resistance measures 116.1 ohms
Red Center tap - blue/white primary: resistance measures 123.2 ohms

At first glance this seems normal. Any thoughts on what’s next?


What are the measurements of the other tap? Blue / Brown

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PostPosted: Mon Apr 23, 2018 8:10 am 
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Red-brown 162.3 ohms
Red-blue 176 ohms

I’m assuming the higher impedance on these 8K windings is normal as they are further from the red Center tap than the 4K windings...


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