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Old March 14th, 2013, 10:15 PM   #1 (permalink)
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Calling 5e3 gurus....voltages are way high!

ladies and gents,

Got the chassis all wired up and started reading my voltages.

5.5 ac between pins 2 and 8 of rectifier and heater voltages all around 3.25-3.3 ac....looking solid, right?

With just the rectifier installed - 365 at the standby switch in the 'off' position.

installed preamp tubes, standby in 'on' position
V1 - 180dcv @ pin 1, 2.9dcv @ pin 3, 181dcv @ pin 6, 2.9dcv @ pin 8.
V2 - 349dcv @ pin 1, 5.8dcv @ pin 3, 299dcv @ pin 6, 69dcv @ pin 8

B+ (pin 8 at V5) - 363dcv w/ standby off, 472dcv w/ standby on.

Rectifier is a JJ 5Y3S, PT is MOJO756. Power section wired per Triode Electronics layout.

Thoughts? Suggestions? I didn't even install the power tubes due to fear of outcome. Should I load em and then take my readings? thanks in advance for any tips!

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Old March 14th, 2013, 10:41 PM   #2 (permalink)
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Voltages read high with no load. When you install tubes, voltages will drop.

Install the tubes (with speaker or dummy load connected).

I think you will find that things are normal.
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Old March 14th, 2013, 11:38 PM   #3 (permalink)
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awesome. most everything fell into place. looks like V2 is still off kilter. and there's dead silence except when i touch my meter lead to the V2 pins

V2 readings with power tubes in place and speaker connecter:
251dcv @ pin 1, 4.2dcv @ pin 3, 206dcv @ pin 6, and 49dcv @ pin 8.

i also have to assume i've screwed something up with my input wiring. here are a couple photos (the input jacks aren't touching the bus bar despite the photos)



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Old March 15th, 2013, 05:57 AM   #4 (permalink)
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Are the connections from the inputs to the 68K resistors under the board? I can only see one connected, second eyelet from the right?
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Old March 15th, 2013, 06:25 AM   #5 (permalink)
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Are the connections from the inputs to the 68K resistors under the board? I can only see one connected, second eyelet from the right?
Yes, I connected all of my leads on the underside of the board. I was thinking that it would result in a cleaner appearance. In retrospect, i think it's just made things a bit more cramped. The first lead is soldered on top because of a cold solder joint that I didn't catch until after I had the board mounted and started making connections.

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Old March 15th, 2013, 06:31 AM   #6 (permalink)
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Ahhhh, Ok, thought that might be too simple! I know when I started mine up, I had a cold solder joint on the V1 heater link (pins 4 and 5). Are all your tubes lighting up?
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Old March 15th, 2013, 06:44 AM   #7 (permalink)
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Yup, all tubes glow nicely. There was very slight crackling at V1 once I connected a speaker and began probing with my dmm. V2 however, was pretty darn loud while taking my readings in spite of the volume pots being all the way down. Here's a shot of my V2 wiring:

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Old March 15th, 2013, 07:26 AM   #8 (permalink)
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You should be getting this on your 12ax7's pin 1 & 6 165VDC
pin 3 & 8 1.5VDC, this was given to me by Telenut, this helped me find my similat fault on start up
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Old March 15th, 2013, 07:30 AM   #9 (permalink)
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I don't mean to insult your intelligence, but is your pre-amp ground bus terminal strip's 3 terminals connected to one other with jumpers?
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Old March 15th, 2013, 08:14 AM   #10 (permalink)
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I don't mean to insult your intelligence, but is your pre-amp ground bus terminal strip's 3 terminals connected to one other with jumpers?
Think nothing of it. This is my first build so I'm all ears and open to any and all criticism :)

I have a strip of 18awg connecting all three tabs of the grounding strip. It's tucked on the bottom. Is that what you mean?
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Old March 15th, 2013, 10:40 AM   #11 (permalink)
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If Telenut was here at this moment...here's what he'd post up ... he posted this to my build as well...
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Old March 15th, 2013, 12:29 PM   #12 (permalink)
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It is time to start doing continuity tests with an ohmmeter. IF those test show noproblem, then one starts using a voltmeter to see where the votlages go 'wonky'. In the voltage test...starting with the output tubes plates and working back toward the input, in addition to reading voltages one will also find where the signal is not being passed because the test will reveal louder and louder tests as one gets closer to the input end of thigns. If andhwne the signal drops, your problems are in that area.
Obviously, you have a voltage problem on V2. Read the circuit from voltage source to the tube and you will find the problem....if hte continuity tests didn't already reveal the problem.
One trick one can play on oneself in this type of situation is to take for granted that one has not made an error. Use an open mind and critical assessment....there is an error. Resource: "Zen and The Art of Motorcycle Maintenanc" by Robert Pursig
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Old March 15th, 2013, 04:22 PM   #13 (permalink)
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So V2 pins 1 and 3 are too high (first tetrode), pins 6 and 8 (second tetrode) are in the ball park. Have you grounded the 25uf/1.5K turret, checked the actual values of the 1.5K resistor and the 100k. Swap the 12ax7's, see if the volts remain the same, to discount a faulty tube.
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Old March 15th, 2013, 05:55 PM   #14 (permalink)
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well, I found my issue with the voltage...i had forgot to solder the lead from the 0.1uf cap to the middle tab on my first volume pot! agh! thank you guys for the assistance! All voltages are now within range.

HOWEVER, I still don't have any sound. haha. so I'm assuming (dangerous, I know) that I have an issue with either my input or output wiring. here's a pic of both. All grounds have continuity to the board/jack/pot. I did have noise from the speaker when testing the V2 pins. Does this mean my output wiring is ok?



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Old March 15th, 2013, 08:46 PM   #15 (permalink)
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Check your input wiring with the wiring on the layout.

Where are your input wires that go to the 68k resistors?

Are they connected under the board?

If so, are they shorting on the chassis underneath?
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Old March 15th, 2013, 11:19 PM   #16 (permalink)
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Looks like on the inputs you may be missing one solder on the top right jack.
All those solder joints on the jacks look like they could use more solder to me.
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Old March 16th, 2013, 10:55 AM   #17 (permalink)
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another update...

for some reason, i left off the ground at the output jacks. i had it in my head that they were grounded against the chassis . anyway, i added a ground to my bus and now i get the very slightest distorted tone from my speaker when the volume is at 10+.

back to the bench.....
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Old March 16th, 2013, 11:06 AM   #18 (permalink)
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Is the OT centertap connected? it should be soldered to the business end of the standby switch. some builders connect it directly to the first filter cap too.
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Old March 16th, 2013, 12:30 PM   #19 (permalink)
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Is the OT centertap connected? it should be soldered to the business end of the standby switch. some builders connect it directly to the first filter cap too.
Yup. That's exactly how I've got her wired.
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