50 watt plexi voltage issues

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xlch721
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50 watt plexi voltage issues

Post by xlch721 » Sat May 16, 2015 9:59 pm

Ok so I just finished a Triode Electronics 50 watt 1987 build following the Triode Layout and using the Metro Build pdf as a guide.
I went to take my voltage readings I get 520vdc at the standby switch the rectifier and at the B+ fuse but my readings on my power tubes at pins 3,4,6 are coming up as -870 vdc . I have the same thing going on with the preamp tubes.
The bias pot seems to be working i get -33 to -57 when at min and max. All my tubes light up and appear to be working but I have no sound. I triple checked all my connections I have continuity where I should have.
I have to say that I did add the PPIMV Mod to my build could it be somethings not right with it.
All of my AC readings look great but my DC readings are all messed up. Im at the end of my rope here this things got me stumped could it be a bad output trans .
Any help at this point is greatly appreciated This is not my first build I have built several 18 watters and a couple of fender champs all of them fired up without any major issues other than a high B+ voltage that I was able to drop using a few Zener Diodes but this thing is kicking my backside.

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neikeel
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Re: 50 watt plexi voltage issues

Post by neikeel » Mon May 18, 2015 4:16 pm

Sounds like a misplaced link or poor joint from the B+ line that means you are not evenly dropping your voltage.

Also check your grounds on the rectifier and the OT centre tap etc.

I doubt a bad OT it is a new build, much more likely a daft mistake.

Mixing builds and layouts can be tricky if it is done even partly as paint by numbers.

Your bias circuit is getting a feed (that is only taken from half your ht ac feed after the switch) as you will guess the problem lies after that.

Post some pics and hope you used standard colour scheme and looped wires up over the board to the turrets :wink: ?
Neil

danman
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Re: 50 watt plexi voltage issues

Post by danman » Mon May 18, 2015 5:48 pm

Did you use the Classictone PT and OT that Triode provides with their kits? The wire colors are different from the iron used in the Metro instructions so that is one area to look into also. Do you have both red secondaries from the PT going to the diodes or block diode and the red/yellow centertap grounded properly?

xlch721
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Re: 50 watt plexi voltage issues

Post by xlch721 » Mon May 18, 2015 5:59 pm

I figured it out for myself before my post was approved but you are correct it was a missing jumper wire on the cap can in the B+ line. I found it after probing the HV line. Had 530 volts on one side of the cap can and nothing on the other side. Scrolled through the Metro Pdf and saw it there then I double checked it against the Triode Layout sure enough it was there. They sent me a copy of the layout but it was in B&W not Color. I took a jumper wire with Alligator clips and jumpered the 2 sides together sure enough I had sound and Plate Voltage. The amp sounds really good and boy can it get loud. The PPIMV is awesome I love it can get the tone without the ear crushing volume.
My only concern at this point is my B+ Voltage seems a bit on the high side at 480 VDC with the Bias set at 36 Im getting 34.5 MA on one tube and 37.2 on the other. The tubes are not red plating but it seems to be running a bit hotter than it should. I have a couple of 6.3 volt zener diodes I can add in if needed. Just wanted to get some other opinions on my B+ being so high 40 volts off from the Metro and Triode Layouts. I ran into this problem in the past on a couple of 18 watt builds and 2 or 3 zeners on a couple of tag strips solved that.
Thanks in advance for any help .

xlch721
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Re: 50 watt plexi voltage issues

Post by xlch721 » Mon May 18, 2015 6:03 pm

danman wrote:Did you use the Classictone PT and OT that Triode provides with their kits? The wire colors are different from the iron used in the Metro instructions so that is one area to look into also. Do you have both red secondaries from the PT going to the diodes or block diode and the red/yellow centertap grounded properly?
I followed the Triode layout only used the Metro Pdf as a guideline when I cut and soldered my wiring and boy did I have alot of wire left over.LOL Oh well I saved all of it I can use it some pedal builds later on so it wont go to waste. But yeah it was the missing Jumper on the cap can in the HV line that goes to the board that was my problem.

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