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 Post subject: B+ Reads 0 volts
PostPosted: Wed Apr 03, 2019 10:40 pm 
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Hello there!

I just built up my OSD and I was running through the final testing phase. I can’t seems to get any voltage at B+ (100uf cap / 5w 500R) junction. The relay works great. Heater wires are correct on the tube sockets. The 2 red wires (secondary) read 333v each, they seem to progressively step down with each diode in the rectifier section. Where they connect I’m getting 0 volts... bad diodes? Anything past that point gets 0 volts. The diodes seemed to test ok on the forward voltage.

I tried disconnecting the output transformer at B+, thought that might have something to do with it, but no.

Any tips would be greatly appreciated. I’ve attached an image hope you can see it. I checked everything over, but must be missing something. Thanks!

The stray red wire is the output transformer which I disconnected.

-Ralf


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 Post subject: Re: B+ Reads 0 volts
PostPosted: Thu Apr 04, 2019 9:55 pm 
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Holy Ghost
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AC volts measured across the 2 red wires on the board?
DC voltage measured from any diode to ground and at the junction? the reason they are daisy chained is for safety factor is all.
Is there a 500 ma fuse in the HV fuse holder?
If the standby is off, the fIlter caps are not in circuit yet so not part of the equation.

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 Post subject: Re: B+ Reads 0 volts
PostPosted: Thu Apr 04, 2019 10:57 pm 
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coco wrote:
AC volts measured across the 2 red wires on the board?

AC to ground on each

coco wrote:
DC voltage measured from any diode to ground and at the junction? the reason they are daisy chained is for safety factor is all.

AC to ground, just trying to find where the problem comes from. Where the 2 diodes connect I get 0 volts.

coco wrote:
Is there a 500 ma fuse in the HV fuse holder?

Yes. Fuses in and also swapped out with new ones just in case. If I check continuity across the fuse we are good. I’ve check the whole circuit for continuity, seems good. Triple checked against the layout and schematic.

coco wrote:
If the standby is off, the fIlter caps are not in circuit yet so not part of the equation.

Standby is on. I even tried tubes in it and get very low volume and farty sounds when I play.

Totally at a loss here what might be going on.

Thanks for the response.


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 Post subject: Re: B+ Reads 0 volts
PostPosted: Fri Apr 05, 2019 4:27 am 
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Location: Qualicum Beach, BC
Make sure the Standby switch has continuity when it's supposed to be ON. Check all your wiring to the Standby switch, the fuse holder and the board. Make sure all the solder joints are good. The soldering for the eyelet with the 500 R resistor, the 100uF capacitor and the wire from the fuse holder looks suspect in your picture.

As Stephen said, if the Standby switch isn't on and you don't have good connections to the filter capacitors, the capacitors won't be in circuit and you won't have good DC at B+. At best it would be pulsating DC at 120Hz and it won't read well on a meter.


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 Post subject: Re: B+ Reads 0 volts
PostPosted: Fri Apr 05, 2019 7:50 am 
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Holy Ghost
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Where you measure 0V, you do set to DC?

If you are getting AC into the rectifier and no DC out, I would normlly suspect bad diode. What is the continuity through each diode leg, forward and reverse?

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 Post subject: Re: B+ Reads 0 volts
PostPosted: Fri Apr 05, 2019 11:24 pm 
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Whelp, I’m a dumbass and I was reading AC voltage not DC voltage. Guess I’m still new at this. Thank you both for your responses. Also the farty sounds were because the trimmer was not set in the middle. I assumed it was because I was not getting the right voltage which led me down an totally unnecessary path of debugging. Well... learned stuff. :oops:

I am getting a bit of pops and crackles but I assume that is from not having the amp in the cab yet. I’ll report back when I get some time to wear this guy in a bit.


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 Post subject: Re: B+ Reads 0 volts
PostPosted: Sat Apr 06, 2019 5:42 pm 
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Spent some time debugging the popping and crackling. The popping and crackling is not affected by the amp master volume so that leads me to believe its in the power section of the amp. It seems to be the trim pot. If I turn it the popping gets worse. If I use a chopstick and tap it I get lots of popping and crackles. It also doesn't seem to have much resistance when I turn the pot and am able to turn it 360 degrees. Anyone know what part number this pot is I think I will try to replace it?

I found this on Mouser which looks similar:
https://www.mouser.com/ProductDetail/Amphenol-Piher/PT10LV10-502A2020-PM-S?qs=sGAEpiMZZMvygUB3GLcD7usKL8k3H%252BdSdvsenJyqHEM0nZ1ZiV%2FqGQ%3D%3D


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 Post subject: Re: B+ Reads 0 volts
PostPosted: Sat Apr 06, 2019 7:19 pm 
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Holy Ghost
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We can send you a replacement to try

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 Post subject: Re: B+ Reads 0 volts
PostPosted: Wed Apr 10, 2019 11:20 pm 
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Ah thanks man. I actually ordered the one above because I needed to order some
Other components for some other projects. It came today and I swapped it out and all the popping and crackles went away. The amp is working great now. Time to play!


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 Post subject: Re: B+ Reads 0 volts
PostPosted: Thu Apr 11, 2019 7:37 am 
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Holy Ghost
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Location: Brighton, Canada
Good to know your solution worked!

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