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 Post subject: New TriWatt Build....
PostPosted: Mon May 06, 2013 9:02 pm 
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Hi I have just completed the wiring of the Triwatt.
I did the 1 second test and the light was bright.
I then proceeded to verify the voltages at each of the tubes and this is when things looked very weird...
Note these values are without tubes in:

V1 12AX7 P1 440 P2 0 P3 0 P4 NA P5 NA P6 440 P7 0 P8 0 P9 NA
V2 12AX7 P1 448 P2 0 P3 0 P4 NA P5 NA P6 440 P7 0 P8 0 P9 NA
V3 12AX7 P1 449 P2 147 P3 0 P4 NA P5 NA P6 420 P7 0 P8 0 P9 NA
V4 12AT7 P1 455 P2 0 P3 0 P4 NA P5 NA P6 455 P7 0 P8 0 P9 NA
V5 6V6 P1 0 P2 NA P3 468 P4 461 P5 -2 P6 -2 P7 NA P8 0
V6 6V6 P1 0 P2 NA P3 467 P4 462 P5 -2 P6 -2 P7 NA P8 0

I am not sure what to check for to get the voltages on Pin 1 of each of the 12A? Tubes down to the lower values...

I did have the tubes in for 10-15 seconds to see what would happen, but, all I noticed was V6 starting to glow the other tubes
did not show any signs of the orange glow... I did not want to leave it on too long to damage the tubes...

Thanks for any help....

Andrew


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PostPosted: Wed May 08, 2013 10:15 am 
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Guessing that its a heater issue. You can go back and meassure AC voltage across pin's 2 and 7 of the v6 and v5 as well as pins 4/5 and 9 of the others. Tubes don't need to be in. Might want to start at v6 since you had glow there and work your way down


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PostPosted: Sun May 19, 2013 1:06 pm 
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Checking your heater voltages at the sockets is part of the check out procedure.
Voltages on tube are always measured with tubes in. They won't even be close with not tubes I . So check that the all have correct heater voltages. And then plug them in and test again.

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PostPosted: Sun May 26, 2013 10:37 am 
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Thanks Guys;

I just did a check of wiring and everything looks okay...
All the heaters check out at 6.63 - 6.66 volts...

I just read about having the tubes in for the voltage check...
That explains why my numbers are so far out.

When putting the tubes in, do they stay in?
Do you have to put significant force to get them to insert into the sockets?
I do not want to push to hard and break a tube...

Thanks again,
Andrew


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PostPosted: Sun May 26, 2013 10:57 am 
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They do stay in.
Line the pins up and slightly rotate the end of the tube while pushing down. They take some force but I've never broken one doing that.

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PostPosted: Sun May 26, 2013 12:58 pm 
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Tubes are in and the amp is working.... I am not sure if the mid/treble controls are working.... overdrive, bass and presence seem to be working. both normal, bright and link channels are working. but the bias for the tubes seems weird... 142mv - I need to go back and check voltages at each pin to see if there is an issue.

I noticed that the 6v6GT tubes do not have pins in 6 and 2. would this cause the bias to be weird?

thanks...


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PostPosted: Sun May 26, 2013 4:08 pm 
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Hi Guys;

The tubes are in.
These are the measurements that i get on the pins...

V1 12AX7 P1 108 P6 93
V2 12AX7 P1 137 P6 88
V3 12AX7 P1 187 P2 48 P3 50 P6 130
V4 12AT7 P1 179 P2 48 P3 50 P6 179

V5 6V6 P3 364 P4 270 P5 -1.6
V6 6V6 P3 363 P4 270 P5 -1.6

Something seems a little out...

Any ideas on what I should look for?
I am able to play my guitar through the amp.
There is no hiss or noise at all..
Sounds Okay, my only concern is the mismatch in observed voltages and the fact that I do not see a change to the bias voltage when turning the pot.

Thanks for any help,
Andrew


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PostPosted: Sun May 26, 2013 6:58 pm 
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How do i add a picture?
I think that I have found my problem...
I think that I have two caps in backwards...

Thanks,
Andrew


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PostPosted: Sun May 26, 2013 7:02 pm 
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Okay I am going to try to add as an attachment...


Attachments:
File comment: Caps In Backwards?
IMG_4448.JPG
IMG_4448.JPG [ 5.86 MiB | Viewed 12534 times ]
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PostPosted: Sun May 26, 2013 11:34 pm 
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Yes they are in backwards which means you have no bias control.

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PostPosted: Tue May 28, 2013 7:27 pm 
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Okay after swapping the two caps, and setting the bias to 22.5, which was the maximum I could get, these are the voltages that I measured....

V1 12AX7 P1 150.2 P2 0 P3 1.11 P4 NA P5 NA P6 129 P7 0 P8 0.9 P9 NA
V2 12AX7 P1 186.6 P2 1.5 P3 1.55 P4 NA P5 NA P6 117 P7 0 P8 0.3 P9 NA
V3 12AX7 P1 263 P2 64 P3 68 P4 NA P5 NA P6 185 P7 0 P8 1.5 P9 NA
V4 12AT7 P1 252 P2 68 P3 71 P4 NA P5 NA P6 250 P7 61.6 P8 71 P9 NA

V5 6V6 P1 0 P2 NA P3 428 P4 396 P5 -35.3 P6 -35.3 P7 NA P8 0.022
V6 6V6 P1 0 P2 NA P3 426 P4 395.5 P5 -35.3 P6 -35.3 P7 NA P8 0.019

How much of a variance is okay on these pins, Underlined pins are the ones that see different by more than 10 percent...

It looks like my main concern would be v4 pin 1 & 6

Thanks for any help....
Andrew


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PostPosted: Tue May 28, 2013 11:23 pm 
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The amp should be working, correct? You should be able to get a little more bias but you are pretty close. Is the selector in the correct position for 6V6?
The lower pin 1&6 are not too much of a concern AFAIC. Those voltages we taken with NOS 12AT7 in V4. Otherwise, 10% on voltages is good!

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