Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Rubrburnr on March 01, 2016, 08:53:44 pm
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Ok... frustration has set in :BangHead:. Time for the initial startup test without the tubes in the sockets and it's a no-go. I have double and triple checked all of the wiring and still can't get the high voltage readings on any of the initial voltage tests. With no tubes in the sockets I am getting .38 - .4 volts at pins 1 & 6 at the 12AX7 tube socket. I have added some pics for reference...If you need a specific picture of something, I'll be glad to take it.
The ONLY thing I can think it is, is that I am using the HT and Filament center taps going to ground and not the 2 100ohm resistors. When I flip the switch, the lamp lights up as normal and I am getting 300V (AC) to pins 4 & 6 at the rectifier socket. I realize I need to "bundle" some of the wiring together with zip-ties but I wanted make sure everything is working correctly before all of that.
So... What ya thinkin?
Thank you in advance!!
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You must have the rectifier tube plugged in before you have any B+ voltages.
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Nailed it Sluckey!! :worthy1: I'm a total noob with the electronics part but I am getting better. 400V holding steady... Thank you!!
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Well done !!!
:m14
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You are running BOTH your 5VAC (yellows) and HVACs (reds) completely across the chassis, and back...?
Judging by the two jacks on the "front" (bottom of pix #2) your 5V and thus your unfiltered rectifier output are led right past, and I mean RIGHT past the 1/4" guitar input and the vol & tone control.
I hope the gods of hum are happily disposed towards you. I doubt I'd get away with that. That wiring dress is solidly in the "asking for trouble" category. But you might as well finish it out as is. Assuming you've wired it correctly [this being the difference between wiring and layout] It won't blow up or anything but it may have incurable and really loud hum with the current parts positioning. OTOH, if it does and you move the 5Y3 and it fixes the problem, you'll have learned an important lesson so there you go.
It's my prediction that you'll have to move the 5Y3 but I could be wrong. I'd be planning and probably even cutting that hole in the chassis before going much farther on the amp.
At the risk of discouraging you and I do not wish to do that at all, it *may* be necessary to cut a hole on the opposite side of the chassis and move the 5Y3 into a position where the 5V & HV wires don't cross the whole chassis. Fortunately, if that should prove necessary, it looks like you could do so reasonably easily. The only hard part would be making the hole for the octal socket.......usually irritating enough but worse when all the other stuff is already mounted to your chassis. Wiring changes would be easy as pie. It looks to me like you have an unused dual-RCA jack or some bakelite something in pix #2 (the pics just above this post, not way back at the top) in between the PT and the fusepost. if so, maybe you can tear that bakelite thingy out and locate your 5Y3 in its footprint.
If you move the 5Y3 and you only need 2-3" of PT wires to get to it, do not cut those red & yel wires that short. Figure out a way to loop those wires and tie wrap or tape them somehow so you're not cutting them real short < 6".
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Thanks for looking out and great explanation eleventeen!! No discouragement at all. I would rather make the move now than get everything "done" and have a hum. You have prevented the on-going potential issues on this build and me continuing with issues on this post or starting another "hum" post.
No cutting will be necessary, I have my OT sitting where you saw the brown bakelite thingy. Seems pretty straight forward; move the OT, unsolder the 5Y3 socket and relocate, re-solder and find a new place for the OT... then retest.
I'll post up a picture after the 5Y3 move is done...
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If you already have a cutout for the tube and it's an easy matter to move it, I'm subtly suggesting that you build it the way it is, then move the 5Y3 so you can see and appreciate the difference. Excellent learning exercise; you won't forget it.
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The move is already done. Basically I had swapped locations with the 5Y3 and the OT. Just finished testing it, still holding strong at 400V!! Worked out really well, the OT wires will run down along the edge of the chassis to the speaker jacks it was was a short distance to the 6V6 tube. Now I need to find my zip-ties and start tidying things up a bit..
Agreed...excellent learning exercise and I'm definitely not going to forget it!!
Thanks again!!!
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Any reason for two red wires running back to your rectifier?
I'm guessing they are connected to the same pin on that tube.
If so, you could just connect the red wire from the OT to that turret.
Electrically, that would have the same effect. :icon_biggrin:
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I guess I took the layout a bit too literal. Correct, they are connected to pin 8. As soon as I was reading your response, I was thinking why couldn't I connect the wires there. Great tip!! It will certainly clean things up a little. That will be done tomorrow!!