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PostPosted: Wed Jul 24, 2019 1:16 pm 
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Hi,

I've started building my TC15 and have a couple questions about testing the power supply on page 49

1. Am I correct that this step takes place before the turret board/pots is wired up?


2. Do I have the orientation of the Power Switch and Standby Switch correct? I have seen pictures of other builds of this amplifier and they have these switches placed lug side down towards the chasis, this does not seem to be the orientation of the layout however?

3. The layout states to "tie off the 110v taps" which are the dotted black and white lines, does this mean tie the ends of these wires together, or does it mean just leave them unattached to anything and covered with some heat shrink to prevent anything touching them.

4. What is the purpose of soldering the white 6.3 VAC to the terminal strip instead of just covering the end with heat shrink? It appears to go no where on the terminal strip and is not connected to anything/is isolated on that lug of the terminal strip.


Thanks!

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PostPosted: Wed Jul 24, 2019 2:34 pm 
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You can do the power transformer test anytime, but the earlier the better. No tubes in the amp.

Your switches are installed as shown in the layout. It depends on whether you want the "on" setting with the toggle up or down. "On" will be up the way you have them. It's easier to wire them that way, too.

Cover the ends of the unused wires from the power transformer with heat shrink tubing and tie them in a bundle. You can do the same with the unused white 6.3 white wire. Or you can attach it to a free lug on the terminal strip as shown in the layout. That's just another way to safely deal with an unused wire.

Welcome to the forum and good luck with the rest of your build. It looks good so far.


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PostPosted: Wed Jul 24, 2019 3:23 pm 
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Ok,

Thanks!
Performed the check and everything looks good.


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PostPosted: Wed Jul 24, 2019 6:43 pm 
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Correct mitch, thanks.

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PostPosted: Sun Jul 28, 2019 7:58 pm 
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Hi,

Did I prepare this co-ax correctly (heat shrink is shrunk and ends tinned after I took this pic)? Is the ground shielding not connected to anything on the other end?
Or does the ground shielding get combined with the inner copper wire?

Thanks!


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PostPosted: Mon Jul 29, 2019 1:22 am 
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It looks good. As long as the shielding that you separated from the inner conductor is twisted up tightly with no stray wires hanging loose. I like to put sleeving or shrink tubing over that part, too.

The shield is not connected to anything at the other end. Definitely not the inner conductor! Separate the shield as you did at the other end, but this time just cut it off. Then put some shrink tubing over the end so the shield can't touch anything.

You don't connect the shield at both ends because it carries no signal. It's only there to shield the sensitive inner signal wire. If it was connected at both ends it would become a ground conductor. The amp stage it's feeding is already grounded elsewhere so you don't need a second path. One path would have slightly less resistance than the other which would probably cause a ground loop and induce hum.


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PostPosted: Mon Jul 29, 2019 9:38 am 
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Thanks!


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PostPosted: Wed Jul 31, 2019 9:22 am 
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Ok,
so I've started doing voltage testing but I'm getting back really ridiculously high numbers.
On the large filter cap lug before the 5w 1.5k resistor, pin 7 of the EL84s, pin 1 of the 12ax7s, they are all in the 900s...! My multimeter settings only have 200v and 600v so I don't even know how that is possible...?

I have two multimeters, I can't get readings on one, the other is giving me these "9xx" readings...


Edit:

I just tried another multimeter (3rd one, more thorough meter), and it is giving oscillating readings on these points, not as high but the numbers will range up and down from 0 to 300ish back down...(B+ was going up to 270s, same with pin 1 on the 12ax7 socket)

Any thoughts?


Edit #2:

I had improper meter settings, readings are a little high but this seems normal from what it states form them being slightly high (EG 404v for 366v/386v [schematic]/[layout] B+)


The instructions tell me to install the power tubes now and the 3 12ax7, it does not mention the EF86, is the EF86 supposed to be ommited in the speaker/volume test or is this section leftover from another amp (18v Marshall)?


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PostPosted: Wed Jul 31, 2019 1:09 pm 
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Sounds good so far. The voltages should be more normal when you get the tubes in so the power supply has load. You can put in the EF86 as well.


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PostPosted: Fri Aug 02, 2019 11:01 am 
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Hooked up a speaker and installed tubes and it works!
Sounds really nice too.

A couple issues:

There is some scratchiness when adjusting the pots, is this from perhaps old pots or poor solder connections on the lugs?

The 6 pos selector switch for the EF86 channels is EXTREMELY subtle in effecting the tone/EQ, there is less bass when moving the dial in one direction but the difference between each position is hardly noticeable, only at the extreme settings can I hear that there is a little bit more bass in the starting position. Does this sound correct?


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PostPosted: Fri Aug 02, 2019 11:54 am 
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Glad the amp is working and sounding good. The Contour switch for the EF86 channel is very subtle, all right.

Scratchiness on the pots could be caused by bad connections, but it's more likely the pots themselves being dirty inside. It could also be caused by DC getting through the coupling capacitors. If everything is new, the capacitors and pots should be good.

Wiggle the wires around with a wooden stick (chopstick) to see if it's a connection problem. You could also try spraying some contact cleaner inside the pots.


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PostPosted: Thu Aug 08, 2019 9:01 am 
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I have a little bit of an issue with the pilot light, I damaged it a bit when soldering and it can act a bit intermittent and would like to replace it.
I do have a Marshall style 110v indicator light and a replaceable bulb style housing. According to the BOM the light used is a 110v although it is listed as a 120v on the actual part. Does this difference matter or is one incorrect? The Marshall style replacement indicator is a 110v, would this work as a replacement?

If not, I do have a replaceable bulb unit, would I just need the correct spec bulb? 110v 1.2mA?


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PostPosted: Thu Aug 08, 2019 12:42 pm 
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The Marshall style light should work fine. But if you end up using your replaceable bulb housing, ideally it should have a 120 volt bulb.


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PostPosted: Sat Aug 17, 2019 3:31 pm 
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New parts, check DC on your Pots. If there is any one them, trace it back to the board. There should be 0 VDC after a cap so it could be a leaky cap. Let us know what you find out. We can send a replacement cap (DCV could be caused by DC getting through the coupling capacitors)

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PostPosted: Mon Aug 19, 2019 4:39 pm 
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Ill check the coupling caps, there is a bit of hum going on that I'm trying to find out if its normal or not. The hum does increase with the volume control, so according to the manual it's best to look at the section of the amp before the volume, would this be the area around the three large caps on the left side of the board (side closest to the transformers).

I chopsticked a bit in there and one of the lugs on the first preamp tube and some of the turrets in between the 1st and 2nd preamp tube are microphonic when I tap on them, is that indicative of poor connections? I reheated and added a little more solder and it didn't really seem to change much.


The EF86 I have (brand new EHX brand) is quite microphonic as well.

I am also getting a sort of faint ticking type of sound.

The amp sounds really nice aside from this, super chimey and articulate. It's actually really difficult to play on because of how much you can hear, so all the flubs and string noise I have not heard when playing through my Princeton are right up front.


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PostPosted: Fri Aug 30, 2019 5:30 pm 
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Here is the finished amp, I need to debug the hum issue still.
I copied the look of the Benson Vincent amp more or less, did a gold plexi front though. I did the knobs in the colors of the British Flag because it's so British sounding, maybe they should be Canadian though? Maybe a small red maple leaf plaque in the corner of each cab similar to how the Benson amps have that little plaque?

Has a Celestion Blue and a Celestion Hellatone G12H30 in the cab.

8)


Last edited by Repoman on Sat Aug 31, 2019 3:20 pm, edited 2 times in total.

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PostPosted: Sat Aug 31, 2019 2:41 pm 
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I am not seeing any DC on the pots, I do see low voltage on two 1M resistors which are in between the V4 and V3, they show 47 on the layout but I am getting around 23- 24. I swapped a couple 12AX7s in this spot and it makes no difference. When I place a meter the ends of these resistors they read 1M. They are attached to pins 2 and 7 so I think these are the grid to ground resistors? Any thoughts what would cause low voltage on these? The components around this area are microphonic and the buzz definitely seems to be affected around this area. I have reflowed the solder on all the turrets on these components and this makes no difference.


These are the only two points which have voltage readings that seem to be way off what the layout indicates.
These voltages do not change from changes in the "crunch/munch" switch or boost switch.

When chop sticking on those parts, the hum does increase a bit, like the low end EQ of the buzz increases.


The filter caps seem to have readings well over 15k for resistance.

The EL84s I bought were not matched, although they were new. I swapped some older EL84s in and there is no difference there either.


Another question- what is the purpose of the two red "X" on the .01 uf cap next to the 1M grid to ground resistor on the layout?


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PostPosted: Sun Sep 01, 2019 1:41 pm 
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The cabinets look really good. The maple leafs might be a nice touch!

According to the schematic, the red "x x" on the layout shows where you could add an FX loop if you want one on the 12AX7 channel.

The 24-volt readings at the grids of V4 do seem to be low for some reason. Are the voltage readings on anodes and cathodes of V4 OK? You could also check the 47k and 1k2 resistors in this area to make sure they are the right values.


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PostPosted: Sun Sep 01, 2019 2:29 pm 
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The voltages for the anode triode and cathode triode are good. The 1.2k and 47k resistors check out.

When I clip the meter ground to chassis and then take the measurement for the grid to ground resistors the sound cuts out.

I have an ancient 5Y3 I stuck in place of the 5AR4 and a lot of the hum seems to have lessened...voltages are a smidgen lower across all points.

Is this a no no?

I also remeasured some points on the pots and was able to get a reading of 0.05v on one lug of the master cut potentiometer.


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PostPosted: Sun Sep 01, 2019 5:45 pm 
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I tried measuring the V4 grid voltage with a different method (top of the 1.2k/intersection of the 2 1M, 1.2k and 47k) and got 48v with the 5Y3 rectifier, 57v with the 5AR4.
The hum seems to have lessened a considerable amount over the past couple hours while I've been poking about with it, the most prevalent noise issue now is a faint, fast ticking noise.

Do large capacitors get "seasoned" or "broken in" in a way to start functioning better (IE the filter caps)?

Is the purpose of a choke to reduce noise and would a choke be a thing to consider for this amp?



http://youtu.be/eCXflOrpAl0

here is a vid


Last edited by Repoman on Mon Sep 02, 2019 6:28 pm, edited 1 time in total.

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