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Post by ss "Shane" on Mar 22, 2018 8:20:40 GMT -7
I powered up my Therapy this morning and noticed a minor electrical sounding hum. I switched to my Ghia and it wasn’t at all there, plus it’s something I’ve never noticed before with my Therapy.
Here is what I have going on: - I still have good power and grunt at higher volumes - I think the overall tone is fine - the hum only occurs when I kick the standby switch off (up) - wasn’t there yesterday - the rectifier tube is brighter that the power tubes when on - it’s not the guitar
I’m suspecting it’s a tube going bad, maybe the rectifier tube, I don’t know. That’s why I came here.
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Post by Lefty on Mar 22, 2018 8:45:59 GMT -7
Tubes. Process of elimination.
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Post by ss "Shane" on Mar 22, 2018 9:03:19 GMT -7
Thanks Lefty, I guess I’ll have to buy all new tubes since I’m not sure which one may be the culprit. Just hope it’s nothing major.
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Post by purpletele on Mar 22, 2018 9:08:10 GMT -7
My Therapy did the same thing, it was a pre-amp tube.
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Post by ss "Shane" on Mar 22, 2018 9:17:08 GMT -7
My Therapy did the same thing, it was a pre-amp tube. That’s good to know. I love this amp so I’ll be glad to get it taken care of.
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Post by zpilot on Mar 26, 2018 20:26:38 GMT -7
Thanks Lefty, I guess I’ll have to buy all new tubes since I’m not sure which one may be the culprit. Just hope it’s nothing major. Replace them one at a time or you will not know which one is bad. Except of course the power tubes which need to be a set. You probably only have one bad tube.
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Post by ss "Shane" on Mar 27, 2018 12:32:07 GMT -7
Thanks Lefty, I guess I’ll have to buy all new tubes since I’m not sure which one may be the culprit. Just hope it’s nothing major. Replace them one at a time or you will not know which one is bad. Except of course the power tubes which need to be a set. You probably only have one bad tube. That’s what I’ll do but I think I’m just gonna order all new tubes. I believe the tube store has an all JJ set for around $69. Now the trick is to figure out how to order in $20 increments so my wife doesn’t get a text telling her I used the card. This whole “connected” world makes it tough on a married musician 😄
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Post by headshrinker (Marc) on Mar 27, 2018 20:15:22 GMT -7
I'd still replace them one at a time with the new ones. That way if the sound goes south you will know which tube caused it and can stick the old one back in. If you do all of them at once, you're in the dark. Especially with preamp tubes, even the same brand and type of tube can sound different in an amp. My philosophy with preamp tubes is if you are happy with the way your amp sounds once you change out the power tubes, don't mess with the rest. With the phase inverter, listen with the old one, put the new one in, if it sounds better, leave it and keep the old for emergencies. If it sounds the same, put the old one back in.
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Post by ss "Shane" on Sept 22, 2018 7:19:52 GMT -7
The problem was a power tube that went bad and blew out a resistor, or at least I think that’s the correct part description. I called Z repairs and he schooled me on how to remove the chassis from the amp. Then I sent some pics and he identified a resistor that was blown. I’m calling a “resistor” that little blue thing that looks like a gel capsule that’s installed under the power tube valve. Please excuse my horrible description of amp parts lol. I’m obviously not a tech! So I shipped it off to repairs and had it back in no time. This is the first time I’ve had to deal with Z amp repairs / customer service and I’m truly impressed! When it was shipped back it was packed just like new! Good job Don and thanks for getting me back up and running so fast!
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Post by Chilly Gibbons (Todd T.) on Sept 22, 2018 8:08:39 GMT -7
Yep, that’s a screen grid resistor, saves your output transformer when power tubes fail in certain ways.
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Post by ss "Shane" on Sept 22, 2018 9:48:44 GMT -7
Just so folks out there in investigative land understand....yes, I posted this thread a good while back. It didn’t take this long to get my amp serviced. I procrastinated and put it off, kind of like when my wife gives me a chore to do around the house. My turn around time was about a week and a half I believe.
I’ve missed this amp! 6L6 is definantly for me!
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Post by Chilly Gibbons (Todd T.) on Sept 22, 2018 10:42:11 GMT -7
Doc’s designs really are bulletproof. Wish he made tubes...
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