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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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Holy Ghost
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Correct mitch, thanks.

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


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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