Output Problems with a Dr. Z Prescription RX amp head
- Thread starter Pigbenis27
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Pigbenis27
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Dudes you all rock. JMFahey, Fazer, Abbey Road and PRR Thank you all for the help and Advice!!!! I'm stoked to get these new readings and I'll be back to post them! Thank you guys for taking the time to help though I grealty appreciate it!!!!!
Pigbenis27
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Hey There Everybody!
So sorry it took so long to get back to this thread. Hope you're all still around to help me decipher some of these readings I got for ya. So i took some time to do a little reading on Transformers and I still got alot of reading to do but from what I can tell it looks like one of the Transformer's secondary Windings may have a problem. What Kind of problem I don't know but I was hoping you all could help out since I'm still in the thick about learning all of this. Okay so here's all of the readings I have from various parts of the power circuit:
Voltages at PSU Secondaries:
2x Leads going to the heaters of Output Tube 7 (EL84) read: 3vac for each.
2x Leads going to pins 4/6 (Plate) of the 5AR4 Rectifier Tube read: 307vac each.
2x Leds going to pins 8/2 (Filament) of 5AR4 Rectifier Tube Read: 0vac each; but the rectifier tube still lights up??
Voltages After Rectifier Tube:
lead off of Pin 8 of 5AR4 (this lead goes to the standby switch) reads -.89vdc
Lead off of Standby switch reads the same; this lead goes to the HT fuse
Voltages at Filter Cap Nodes:
positive side of Caps 1,2 and 3 all read - .86vdc
Negative Side of Caps 1,2 and 3 all read 0vdc.
From there onward all of the distribution resistors and plate resistors are reading the same -.86vdc and all of the Heater pins for both the EL84 output tubes and 12AX7 preamps read 2.9vac. So There's all of that. Does this mean my problem lies in the Transformer or the Rectifier? the Transformer leads were tested with all secondaries disconnected and the rectifier was tested with the whole circuit connected at the nodes fo each connection. I'm doing research into testing resistance on transformer windings and I found an article on how to find shorts in them as well so I'll be doing that here soon once I'm all read up but in the meantime any more help or advice you guys can afford would be much appreciated!
Thanks again for all your help!
So sorry it took so long to get back to this thread. Hope you're all still around to help me decipher some of these readings I got for ya. So i took some time to do a little reading on Transformers and I still got alot of reading to do but from what I can tell it looks like one of the Transformer's secondary Windings may have a problem. What Kind of problem I don't know but I was hoping you all could help out since I'm still in the thick about learning all of this. Okay so here's all of the readings I have from various parts of the power circuit:
Voltages at PSU Secondaries:
2x Leads going to the heaters of Output Tube 7 (EL84) read: 3vac for each.
2x Leads going to pins 4/6 (Plate) of the 5AR4 Rectifier Tube read: 307vac each.
2x Leds going to pins 8/2 (Filament) of 5AR4 Rectifier Tube Read: 0vac each; but the rectifier tube still lights up??
Voltages After Rectifier Tube:
lead off of Pin 8 of 5AR4 (this lead goes to the standby switch) reads -.89vdc
Lead off of Standby switch reads the same; this lead goes to the HT fuse
Voltages at Filter Cap Nodes:
positive side of Caps 1,2 and 3 all read - .86vdc
Negative Side of Caps 1,2 and 3 all read 0vdc.
From there onward all of the distribution resistors and plate resistors are reading the same -.86vdc and all of the Heater pins for both the EL84 output tubes and 12AX7 preamps read 2.9vac. So There's all of that. Does this mean my problem lies in the Transformer or the Rectifier? the Transformer leads were tested with all secondaries disconnected and the rectifier was tested with the whole circuit connected at the nodes fo each connection. I'm doing research into testing resistance on transformer windings and I found an article on how to find shorts in them as well so I'll be doing that here soon once I'm all read up but in the meantime any more help or advice you guys can afford would be much appreciated!
Thanks again for all your help!
scott2000
Well-known member
Bumping ......
Looks like the rectifier is not doing its job. Maybe the heater voltage is not there, you should check the voltage across pins 2 & 8; you should measure 5Vac. Beware that there is potentially high DC voltage there.
Or the 5AR4 is duff, have you tested it elsewhere?
Or the 5AR4 is duff, have you tested it elsewhere?
Pigbenis27
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- Sep 26, 2017
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Hey There Abbey Road!
Thanks once again for the helpful response! So I went ahead and checked the ac voltage across pins 2 & 8 of the rectifier and I am in fact getting the correct heater voltage you mentioned. 5vac exactly. And no I haven't checked the 5AR4 anywhere else! Sounds like I might need to try replacing that guy and seeing what happens unless you would have a better suggestion for me?
Thanks once again for the helpful response! So I went ahead and checked the ac voltage across pins 2 & 8 of the rectifier and I am in fact getting the correct heater voltage you mentioned. 5vac exactly. And no I haven't checked the 5AR4 anywhere else! Sounds like I might need to try replacing that guy and seeing what happens unless you would have a better suggestion for me?
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