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FDP Forum / Amp Mods, Repairs, and Projects / What did I do?! HRDx 3 more problems



Nov 28th, 2016 09:25 PM   Edit   Profile  

So my previous post I was banging my head against the wall with the amp and figured out it was a bad plate load resistor (R62)...BIG SURPRISE with these amps...anyway I was putting everything back together and forgot to put in P13 and P14 the two blue wires coming from the transformer near the V5..turned it on and nopticed the jewel light wasn't on. So I looked in the back and realized I forgot to plug in those two connectors..Now it's crazy distorted and volume is extremeley low, on 12 I can talk over it. I plugged into the power amp and changed the tubes and nothing is working. Yes I have the speaker plugged into the right speaker out. Thanks in advance.

Contributing Member

Cincinnati, USA

Nov 29th, 2016 12:23 PM   Edit   Profile  

Pull the tubes before you damage something.

If you pulled the PT connections, review them to make sure all were reconnected right, both primary and secondary.

Is the correct voltage going to the rectifier?

Are the tube filaments running on half voltage?



Nov 29th, 2016 12:39 PM   Edit   Profile  

(excuse my ignorance) To clarify you want me to pull which tubes? How and where do I measure both of those things? Also when I was testing it out the tubes were pulsing heavily with the strumming of the guitar.



Nov 29th, 2016 12:47 PM   Edit   Profile  

What could have been ruined by not plugging those in and how do tell which one goes where? They're side by side and the only difference between them is one says 600v on the wire and one says 1000v.

Contributing Member

So. Cal. USA

Nov 29th, 2016 02:43 PM   Edit   Profile  

See my post in your other thread on the same subject.

Earlier schem but Fender didn't change much in the III model.





Nov 29th, 2016 02:51 PM   Edit   Profile  

Thank you, I have that schematic which was helpful. Just at the end of knowing what to test to see what is malfunctioning. I really hope its not the transformer.

Contributing Member

Cincinnati, USA

Nov 29th, 2016 04:08 PM   Edit   Profile  

Find someone to help you.



Nov 29th, 2016 04:10 PM   Edit   Profile  

I thought that's what this place is for?

Contributing Member

Cincinnati, USA

Nov 30th, 2016 07:59 AM   Edit   Profile  

You are right, this place is to share information and help each other. I'm helping you by suggesting you get local hands-on help.

You asked "How and where do I measure both of those things?" This indicates a willingness to both do it yourself and to learn.

It also indicates, to me anyway, that you could benefit from having an experienced helper with you. That's because I suggested you measure voltages in a live tube amp which will have DC in the 400 volt range. I want you to be safe and not hurt yourself or damage your amp.

So I can say 'set your meter to the right scale and touch one probe here and another here at the same time' but that leaves out all the safety precautions that someone experienced in working in high voltages should already be practicing.

I hope you understand where I'm coming from.



Nov 30th, 2016 11:19 AM   Edit   Profile  

I understand but on the contrary that is exactly what I need seeing that I have read as much about amp safety as I have troubleshooting. Knowing the safety and physically being able to solder and troubleshoot is different from being able to read schematics.

Contributing Member

Cincinnati, USA

Nov 30th, 2016 09:21 PM   Edit   Profile  

If you want to learn to troubleshoot a tube amp, read Jack Darr's book. It was written before the Internet got hung up on which of 5 ways of biasing give the best tone. It covers basics of how the different stages work and how to troubleshoot by measuring DC voltage and by signal tracing.

It was written during the early silverface era (before channel switching) so it won't have info about your specific amp model. And he thought amps were supposed to play clean but that doesn't matter. The troubleshooting techniques are transferable to all tube amps and he uses logic instead of guessing. The book is out of print but you can read it free online if you search for it.

As for your amp, you first need to figure out if you connected the PT back correctly. If the voltages match the schematic (AC and DC but not yet signal), then the PT is working and connected correctly.



Feb 19th, 2017 10:45 AM   Edit   Profile  

check your work on R62. your symptoms sound like a bad power tube screen resistor

FDP Forum / Amp Mods, Repairs, and Projects / What did I do?! HRDx 3 more problems

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