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PostPosted: Mon Sep 02, 2019 1:24 pm 
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Joined: Mon Sep 02, 2019 12:57 pm
Posts: 3
Hello!

This is my first build, everything went well, until I installed the power/preamp tubes. I did power it up with a current limiting light bulb, and it didn't indicate any issues so I went ahead and inserted the tubes.

As you can see, the voltage readings are quite off... I tripled checked all components / connections, and couldn't find any issues. V3 & V4 Pin 3 (Plate) voltages not being even is a bit concerning to me. :|

Here are the readings (without tubes):

V5 Pin 4 & 6 = 359v
V5 Pin 2+8 = 5.6v
V4/V3 Pin 2+7 = 6.4v
V2/V1 Pin 4/5+9 = 6.4v

Here are my readings with tubes inserted (JJ 5Y3 - without the current limiting light bulb):

B+ 340 (367)

V4, 6V6
Pin 3 = 346v (356)
Pin 4 = 251v (326)
Pin 8 = 34v (20)

V3, 6V6
Pin 3 = 327v (356)
Pin 4 = 251v (326)
Pin 8 = 34v (20)

V2, 12AX7
Pin 1 = 85v (148)
Pin 3 = 1.1v (1.3)
Pin 6 = 41v (191)
Pin 7 = 6v (17)
Pin 8 = 11.6v (45)

V1, 12AY7
Pin 1 = 110v (120)
Pin 3 = 0.86v (1.8)
Pin 6 = 99v (120)
Pin 8 = 0.86v (1.3)

Any guidance on where to start troubleshooting would be greatly appreciated. With the voltages being this out of whack, I'm not sure where to start.

I have pictures... if you think it would help, I'll be happy to post them.

Thanks a million!


Last edited by Blue Apple on Mon Sep 02, 2019 8:12 pm, edited 1 time in total.

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PostPosted: Mon Sep 02, 2019 2:18 pm 
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Experienced
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Joined: Sat Dec 04, 2010 3:42 pm
Posts: 346
Location: Qualicum Beach, BC
Hi. Welcome to the forum.

All I can say is the usual stuff. Make sure all the parts are the right values and they are in the right places. Make sure there aren't any accidental shorts. Make sure all the jumpers under the board are in place. Make sure all the grounds are good.

Check all the connections, visually and with an ohmmeter, to make sure everything is proper and all the solder connections are good. Especially around R22 (the 4k7 2-watt resistor). Make a copy of the layout drawing and highlight each component and wire as you check.

It's a fairly simple circuit, so it shouldn't be too hard to get it working right.


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PostPosted: Mon Sep 02, 2019 2:46 pm 
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Joined: Mon Sep 02, 2019 12:57 pm
Posts: 3
Thanks Mitch, I'll go through everything one more time.

Any idea as to why the V3 and V4 Pin 3 (Plate) voltage would be unbalanced? It seems like it should be even, no? There are no shorts and I've reflowed the connections just to make sure.

Cheers!


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PostPosted: Tue Sep 03, 2019 1:28 am 
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Experienced
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Joined: Sat Dec 04, 2010 3:42 pm
Posts: 346
Location: Qualicum Beach, BC
Yes, the readings at the anodes of V3 and V4 should be the same. The readings at the cathodes and screen grids are the same. Measure it again in case it was just a problem with the meter probes not making good contact. Also try swapping the two tubes and see if the anode voltages follow the tubes or stay with the sockets.


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PostPosted: Wed Sep 04, 2019 5:56 pm 
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Joined: Mon Sep 02, 2019 12:57 pm
Posts: 3
Well, it took me way too long to figure it out, but turns out that one of the .1uF capacitors (C9?) was wide open.

I replaced it and all of the voltages fell into place! No hum, no hiss, just great all around great tone.

Even though I pulled my hair out trying to figure out the issue, I loved putting this thing together. I may have to do it again. :D

Thanks again for the help Mitch!

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PostPosted: Wed Sep 04, 2019 6:45 pm 
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Holy Ghost
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Joined: Sun Mar 13, 2005 4:10 pm
Posts: 7370
Location: Brighton, Canada
Good work. Very rare to have a defective cap, and those arent the cheap ones!

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