rodr
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Posts: 8
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Post by rodr on May 2, 2019 17:20:47 GMT -7
Hi All! I've been a lurker for a while, and just recently got my second Z! I've used a Route 66 for a while and I really really love that amp. I Just got a real good deal on a really nice condition Galaxie + red Z best cab. Couldn't pass! Everything is in really good shape. Both channels sound amazing, and it's a monster volume wise.
BUT... it does have some hum. It's certainly more noticeable than in my Route 66 (which has a little hum but nothing out of the ordinary), and I tried the cab with my ampeg GVT15H, and that's dead quite. I tried other combos in the same outlet and none has Hum this noticeable. When playing, the hum is masked and I got beatiful tones, but as soon as I stop playing, it's noticeable. The amp hums with volume all the way down, and with nothing plugged in. As soon as the standby switch is flicked to ON, the hum comes up. If it's any clue, the channel indicator LED is not completely OFF when in clean channel, you can see a dim light. So far I tried: -Other amps with same cables and cab. No hum. -Replacing pre amp tubes one at a time with known good one.
-Replacing both power tubes with known good ones. -Replacing the rectifier (EHX) with NOS GE. -Different speaker cable. No luck so far. I think I could live with the hum in a real live situation, but for recording it might not be acceptable. So I come here for your expertise and advice! Shipping the amp to the good Doctor it's cost prohibitive, since I am outside the US. I have electronics experience and have rebuilt/restored/maintained my own and friend's amps. Cap jobs, three prong conversion, etc. I know it could be a bad filter cap, that would take me a while to source good material to replace it. Finally, I took some pics inside the chassis (which looks immaculate with impeccable workmanship) and a video showing the issue, if it's any help. First the family pic!: Now the guts: And the vid (hum better heard with headphones): Thanks y'all!
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Post by zpilot on May 3, 2019 2:45:37 GMT -7
Sounds like 120Hz hum which indicates a filter cap is bad or has a bad solder joint. For reference 120Hz is approximately a B flat at the first fret of the 5th string on your guitar. Pull the tube just before the phase inverter and see if it goes away. If it is still present then it is probably in the caps for the B+. If it stops then it is probably one for the preamp. It could also be the cap for the bias supply. Sometimes that cap will not be replaced when a cap job is done and it is just as important as the other filters.
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rodr
New Member
Posts: 8
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Post by rodr on May 3, 2019 7:28:39 GMT -7
Man, that is great info. Thanks zpilot! I will try doing that debug when I get home. I hope I have some EL caps with the right values in my stash. If any of those is 47uf, I´m SOL. I think I have some sprague and F&T in 30 and 20 uf...
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rodr
New Member
Posts: 8
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Post by rodr on May 3, 2019 14:30:28 GMT -7
So I pulled V2. Hum still there, so time to check B+ filters and bias supply caps.
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rodr
New Member
Posts: 8
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Post by rodr on May 3, 2019 15:49:51 GMT -7
Another question. Could a bad switching relay be the cause of this hum? I'm wondering about that indicator LED not turning off completely...
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Post by zpilot on May 4, 2019 1:00:34 GMT -7
Sorry, I'm not familiar with the Galaxie. That issue with the LED sure does not sound right though. Relays are the reason I don't care for channel switching amps. What I offered was just general trouble shooting procedure.
I know from working on other amps with relays that you can tap on the relay (with a non-conductive tool) and sometimes that will cause it to make proper contact. If you find the relay is bad a TEMPORARY fix, until you can install a new one, is to access the inside and blow it out with some contact cleaner. Some relays have a top that you can pry off. Some you need to grind off a corner to be able to get the cleaner nozzle tube to blow inside and maybe another corner to allow it to flow out.
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rodr
New Member
Posts: 8
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Post by rodr on May 4, 2019 10:08:42 GMT -7
Thanks again zpilot. I'll keep in mind all your advice when troubleshooting this amp. It's perfect other than the hum and the LED, which hopefully will get sorted without too much effort.
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Post by jkramsey1991 on May 4, 2019 16:33:42 GMT -7
A galaxy is old enough that I would definitely suspect a filter cap. Unfortunately they go bad no matter how great the amp is made
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rodr
New Member
Posts: 8
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Post by rodr on May 7, 2019 9:36:03 GMT -7
Anybody know what the filter cap values are so I can start shopping for some replacements? I can't see them when opening the amp (the part of the cap with the values is facing the board), it would save me having to desolder them to look in there.
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rodr
New Member
Posts: 8
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Post by rodr on Jun 7, 2019 17:44:02 GMT -7
Ok, so I replaced the filter caps and the relay. Replaced the two 47uf and the one 22uf IC filter caps with F&Ts. Hum still present. I figure I would give it a try replacing the relay due to the issue with the LED being always faintly ON even when no footswitch is attached, but no dice, same LED behaviour. Odd. Any other ideas guys?
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Post by "Z" Steve on Jun 7, 2019 18:26:43 GMT -7
I just have to confess, whenever I read this thread title I immediately think of "Air On a 6 String". Sorry, I am no help re the hum.
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Post by zpilot on Jun 8, 2019 7:23:25 GMT -7
I acquired a 40 year old Princeton Reverb about a year ago. It did not hum but it had it's original filter caps so I did a complete cap job just because I felt it was time. It sounded fine when I was finished. Now, a year later, it has developed a 120 Hz hum. I used the best quality cap can I could find and formed them properly. I've been doing this for quite a while. My point is caps quality can be a problem. There was a period where Illinois Capacitors were junk. I have seen photos of Sprague Atom caps cut open to reveal actually a very small cap inside. Your new cap may be bad. It's a possibility. I'm fishing here also because it is difficult to troubleshoot over the internet.
One other thing. Isn't a Galaxie fixed bias? Sometimes when caps are replaced the bias cap is neglected.
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Post by T-R☼CK ♫ on Jun 8, 2019 8:22:31 GMT -7
The LED being always faintly "on" is normal for the Galaxie. Good luck w/the hum situation. I have #3, and after a LOT of play time, it's still dead quiet at idle.
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rodr
New Member
Posts: 8
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Post by rodr on Jun 8, 2019 10:54:19 GMT -7
Hmmmmm it's interesting about the LED. If that's normal then I can stop chasing that red herring. I will get to the bias caps too. Maybe it's just the power at my place? But it's weird my other amps don't have this kind of noise, they run quiet, maybe a little bit of hiss on the oldest ones. Maybe the Galaxie is more sensitive to this?
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Post by Chilly Gibbons (Todd T.) on Jun 9, 2019 8:16:19 GMT -7
Make sure all of your pots, jacks, everything is tightened down firmly and the jacks cleaned. Also make sure the tube sockets are tidy.
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Post by zpilot on Jun 9, 2019 19:58:46 GMT -7
Hmmmmm it's interesting about the LED. If that's normal then I can stop chasing that red herring. I will get to the bias caps too. Maybe it's just the power at my place? But it's weird my other amps don't have this kind of noise, they run quiet, maybe a little bit of hiss on the oldest ones. Maybe the Galaxie is more sensitive to this? That is 120Hz hum. It is a filtering problem. It's not your house wiring.
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Post by premiumplus (Dave) on Jun 10, 2019 7:24:28 GMT -7
The Nova has a switching relay as well, and it's LED remains dimly lit when it's "off". I don't think you have a relay problem.
It's a long shot but I've seen (badly) mis-matched output tubes cause hum.
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