Hiwatt build voltage issues

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playonit
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Hiwatt build voltage issues

Post by playonit » Mon Sep 11, 2017 1:12 am

I just finished building a dr103 using the Schematic and layout for the early 70's circuit from the Hiwatt pages. after measuring my voltages I found the plate volts on V4 (12AT7) measured 480vdc? I have changed tubes re-flowed a few joints and retraced the circuit a few times with all checking out... I am at a loss here not being able to put my finger on the cause. I have included my voltage chart with my measured voltages in bold.. I am a lot perplexed at this point and feel the need to reach out to see if I am missing something? Thanks for looking..



http://hiwatt.org/Layouts/DR103hiwattlayout.pdf
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xtian
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Re: Hiwatt build voltage issues

Post by xtian » Mon Sep 11, 2017 1:44 am

Check the HT dropping resistor between the power tube screens node and the PI node, and check the PI plate resistors. Confirm the proper value in each case and proper connections.

Are you getting sound?
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playonit
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Re: Hiwatt build voltage issues

Post by playonit » Mon Sep 11, 2017 2:09 am

xtian wrote:
Mon Sep 11, 2017 1:44 am
Check the HT dropping resistor between the power tube screens node and the PI node, and check the PI plate resistors. Confirm the proper value in each case and proper connections.

Are you getting sound?
I am getting high voltage on both sides of the 91k and 82k plate resistors over 400vdc on both sides checked the values and they are within tolerance. Do you mean the power supply dropping resistor on the board? if so, one side measures over 400vdc and the other side about a 100 volt drop at about 326vdc.. and I am not getting any sound?
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xtian
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Re: Hiwatt build voltage issues

Post by xtian » Mon Sep 11, 2017 3:27 am

playonit wrote:
Mon Sep 11, 2017 2:09 am
Do you mean the power supply dropping resistor on the board? if so, one side measures over 400vdc and the other side about a 100 volt drop at about 326vdc
Double check this. You're saying you read 326v at that node--doesn't this same node feed the PI plates? Not possible, since you see 400+v on your PI plates. Is this the issue? You're feeding current to your PI from the same node as the power tube screens?
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playonit
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Re: Hiwatt build voltage issues

Post by playonit » Tue Sep 12, 2017 12:19 am

xtian wrote:
Mon Sep 11, 2017 3:27 am
playonit wrote:
Mon Sep 11, 2017 2:09 am
Do you mean the power supply dropping resistor on the board? if so, one side measures over 400vdc and the other side about a 100 volt drop at about 326vdc
Double check this. You're saying you read 326v at that node--doesn't this same node feed the PI plates? Not possible, since you see 400+v on your PI plates. Is this the issue? You're feeding current to your PI from the same node as the power tube screens?
I think I am confused here... I was talking about the 22k power supply dropping resistor that is mounted on the board... After reading your reply I wonder if you are talking about the 470r and the 1k 2w resistor that the screen/grid from the power tubes go to?? I really appreciate you taking the time to help me understand this...
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xtian
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Re: Hiwatt build voltage issues

Post by xtian » Tue Sep 12, 2017 3:16 pm

There’s too much hidden from view—I can’t see how things are connected. It looks like your HT secondary attaches directly to the cathodes of your rectifier diodes—why?

Show me the schematic you’re using and then we’ll talk. :)
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Re: Hiwatt build voltage issues

Post by sluckey » Tue Sep 12, 2017 6:44 pm

It looks like your HT secondary attaches directly to the cathodes of your rectifier diodes—why?
It's a bridge. Look at the layout to see the jumpers to the other diodes.

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xtian
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Re: Hiwatt build voltage issues

Post by xtian » Tue Sep 12, 2017 8:21 pm

OK, smartpants, then why has @playonit got 400+v on his PI plates? :)
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Re: Hiwatt build voltage issues

Post by sluckey » Tue Sep 12, 2017 9:05 pm

My first guess would be wiring error. Plate voltage that high usually means the tube is not conducting but the cathode voltages indicate it is. That wiring diagram makes my eyes hurt. Rather see a schematic for troubleshooting.

FYI, I had the same thoughts about the HT wires and the diodes. Thought the diodes were backwards but I knew from the voltages he had that couldn't be. So, I looked at the layout, then I saw that it was a bridge.

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playonit
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Re: Hiwatt build voltage issues

Post by playonit » Wed Sep 13, 2017 12:38 am

Here are the Schematics and layout I worked from.. I have traced this circuit at least 4 times and all appears correct. At this point I have to believe it is possibly a bad component.. I have ordered a new 470r 100r resistor and will replace the 2w 1k as well... Is it possible for a resistor to test within tolerance and be bad.. tested those 3 resistors out of circuit and the test ok on my meter??
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Re: Hiwatt build voltage issues

Post by Roe » Wed Sep 13, 2017 7:25 am

you haven't swapped the screens and phase inverter supply- have you?
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Re: Hiwatt build voltage issues

Post by Stevem » Wed Sep 13, 2017 1:19 pm

If he swapped supply's then his preamp voltages would also be high, is that the case?
Most times with good Amps just like it is with sex, it's best to just plug straight in!

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playonit
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Re: Hiwatt build voltage issues

Post by playonit » Wed Sep 13, 2017 2:15 pm

No they are not swapped... what would be good points to check voltages other than voltages at the pins and report those back? For example I get high voltage when I check each side of the 470r resistor that is from the screen/grid each side is 480vdc is that correct? Thanks for the help :D
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xtian
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Re: Hiwatt build voltage issues

Post by xtian » Wed Sep 13, 2017 3:51 pm

With amp off and caps discharged, please measure resistance from HT1 to HT3 as shown on power supply schematic.
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playonit
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Re: Hiwatt build voltage issues

Post by playonit » Wed Sep 13, 2017 10:33 pm

xtian wrote:
Wed Sep 13, 2017 3:51 pm
With amp off and caps discharged, please measure resistance from HT1 to HT3 as shown on power supply schematic.
I read 1k from HT 1 to HT 3...... From HT1 to HT2 I read 569 ohm ... what should I be looking for ?
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