This was carefully packed and boxed and FedEx dropped it when they were transporting it. It has a loud hum when everything is plugged in or not, and then it will quit humming for a while, then the hum comes back.
When they dropped it it broke two of the cab corners and pulled the PT down a bit so the ears were bent. I got it back in place but I can't see where anything is broken. The cabinet isn't damaged and I don't see anything obvious on the chassis other than the PT mounting ears getting straightened out a little.
The reverb tank was toast, all four springs broke but I replaced it already. I'm afraid this is going to be one of those near-impossible ones to track down but I hope not. The tubes were all bubble-wrapped and they sound great until the hum decides to come back.
Thoughts?
JCM800 - 2205 hum issue
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gui_tarzan
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JCM800 - 2205 hum issue
Last edited by gui_tarzan on Fri Jun 19, 2015 1:23 pm, edited 1 time in total.
--Jim
"He's like a new set of strings, he just needs to be stretched a bit."
"He's like a new set of strings, he just needs to be stretched a bit."
Re: JCM800 - 2205 hum issue
My first thought is you've got an intermittent connection that should respond to chopsticking.
My second thought is what the hell is that photograph?
My second thought is what the hell is that photograph?
I build and repair tube amps. http://amps.monkeymatic.com
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Stevem
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Re: JCM800 - 2205 hum issue
What is the manufacture date on those paper cased filters , they must be very old, not that there are your hum issue, just wondering!
Also that selenium rectifier for the bias must be from the late 50s to mid 60s!
Start with trouble shooting 101, install the output tubes first and check for the hum and them continue with loading the amp with the preamp tubes untill the hum shows up and then you atleast have the issue pinned down to a section of the amp !
Also that selenium rectifier for the bias must be from the late 50s to mid 60s!
Start with trouble shooting 101, install the output tubes first and check for the hum and them continue with loading the amp with the preamp tubes untill the hum shows up and then you atleast have the issue pinned down to a section of the amp !
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: JCM800 - 2205 hum issue
Wrong pic, that's not a JCM800. Check the filter cap grounds. I've seen the ground wires break when the amp gets bounced around.
Jerry
Jerry
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gui_tarzan
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Re: JCM800 - 2205 hum issue
Sorry, I don't know why I attached that photo.
I did the chopstick test all over the wires, board, tubes, etc. and nothing changes. I know it's TS101, I was so tired when I wrote that last night I had to shut everything down and go to bed. That was after zapping myself on the IEC jack leads. Dammit.
I did the chopstick test all over the wires, board, tubes, etc. and nothing changes. I know it's TS101, I was so tired when I wrote that last night I had to shut everything down and go to bed. That was after zapping myself on the IEC jack leads. Dammit.
--Jim
"He's like a new set of strings, he just needs to be stretched a bit."
"He's like a new set of strings, he just needs to be stretched a bit."
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Stevem
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Re: JCM800 - 2205 hum issue
Ok, so still start off with what I posted for troubleshooting!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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gui_tarzan
- Posts: 607
- Joined: Thu Jan 16, 2014 3:10 am
- Location: The 26th State
Re: JCM800 - 2205 hum issue
I will Steve, my friend told me to take my time and do what I can, he's not in a big hurry for it. He's still trying to find out if it was insured by the guy that sent it to him so he can recoup at least some of him losses.
--Jim
"He's like a new set of strings, he just needs to be stretched a bit."
"He's like a new set of strings, he just needs to be stretched a bit."
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sonofmickel
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Re: JCM800 - 2205 hum issue
I had a nightmare repair of one of these. Hum was intermittent. Seemed to be the reverb tube, replaced that and it worked for a day or two.
Investigating the reverb circuit, chopsticking around...I found a slightly charred cheapy capacitor that is soldered "under" the leads coming off the reverb tube socket, you can not see the cap, it's hidden beneath the wires. It had burned through one of it's leads and was intermittent, sometimes wiggling the reverb tube made contact and it would work for a while. I soldered in another higher voltage cheapy cap = happy amp.
So, look for a hidden, burnt capacitor on the reverb socket.
Investigating the reverb circuit, chopsticking around...I found a slightly charred cheapy capacitor that is soldered "under" the leads coming off the reverb tube socket, you can not see the cap, it's hidden beneath the wires. It had burned through one of it's leads and was intermittent, sometimes wiggling the reverb tube made contact and it would work for a while. I soldered in another higher voltage cheapy cap = happy amp.
So, look for a hidden, burnt capacitor on the reverb socket.
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Stevem
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Re: JCM800 - 2205 hum issue
Yup, the short ground leads off of the can filters can break off if the chassis takes a good hit.
Also look to see if any of the grounding screws at those caps have backed off from the impact.
You might also want to first test if the AC ripple voltage at the least preamp node changes as the issue comes and goes, and this would pin it down to a filtering issue.
Also look to see if any of the grounding screws at those caps have backed off from the impact.
You might also want to first test if the AC ripple voltage at the least preamp node changes as the issue comes and goes, and this would pin it down to a filtering issue.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!