rfcii
Joined: Oct 28, 2018
Posts: 186
Quimper Peninsula, WA
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Posted on Aug 17 2021 04:32 PM
Hi there-
I haven't been using the onboard reverb in my Gomez G-Reverb amp since I like the extra control of a Surfybear. However, I just put a SurfyPan into it to see how that works, and am now wondering if there is an issue in the amp itself, maybe microphonic tubes? I have tried the "tap test" with a wooden chopstick on each tube, and do not hear anything problematic. I took a quick video, which I think most strongly displays the problems around 40 secs in. There are some quieter but very present higher-pitched harmonics, a bit like feedback but also richer, more like chords. These come and go, but do seem most easily triggered by the open G and B strings or notes in that range.
https://www.youtube.com/watch?v=DrU3xulK8CY
I would love any other troubleshooting ideas or suggestions. I don't have a good amp tech nearby but am willing to travel a bit to drop it off at some point.
A couple questions in the meantime:
Is it possible for the tubes to be the problem here AND "pass" the tap test? I can tap a little more thoroughly to isolate this.
Is this likely limited to the reverb tubes? Should I try replacing them? AFAIK, I can do this without worrying about biasing, correct?
Some further info, if it helps. I tried the tank outside of the amp, setting on carpet. Then again, with cardboard taped to the open bottom (as the original was), and enclosed in the felt bag it came in, and then finally repacked into the amp as it was originally. None of this significantly changed (improved) the situation. It does the ghost howling in all configurations.
Thanks for any pointers.
Last edited: Aug 17, 2021 16:42:02
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synchro
Joined: Feb 02, 2008
Posts: 4554
Not One-Sawn, but Two-Sawn . . . AZ.
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Posted on Aug 18 2021 04:27 PM
If yo swap the tubes, like for like, you should be safe. That’s a good starting point for a test.
— The artist formerly known as: Synchro
When Surf Guitar is outlawed only outlaws will play Surf Guitar.
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rfcii
Joined: Oct 28, 2018
Posts: 186
Quimper Peninsula, WA
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Posted on Aug 19 2021 04:56 PM
Thank you syncro!
Anyone else have ideas here? I can try to do a better recording, but i hope the recording conveys what seems a little unusual and wrong. I do have a new reverb driver tube on order. I'm not sure that is culprit, but I suppose it won't hurt to try.
Last edited: Aug 19, 2021 19:04:28
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synchro
Joined: Feb 02, 2008
Posts: 4554
Not One-Sawn, but Two-Sawn . . . AZ.
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Posted on Aug 19 2021 09:12 PM
Simple question here, what are the part numbers of the reverb pan you removed and the one you put in?
— The artist formerly known as: Synchro
When Surf Guitar is outlawed only outlaws will play Surf Guitar.
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rfcii
Joined: Oct 28, 2018
Posts: 186
Quimper Peninsula, WA
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Posted on Aug 20 2021 12:47 PM
Hi syncro - the original tank was an Acutronics 4AB3C1B, which I believe was NOS. I did have some of this "feedback" trouble with it, and thought it was perhaps how it was mounted in the cabinet. Since the amp (Gomez G-Reverb) has only a "Reverb" control, and no Dwell/Mix, I did not use it much, as I already had a SurfyBear for another amp. I decided to replace the pan with the SurfyPan to see if it had the built-in reverb more agreeable.
The new one is a SurfyPan, "an upgraded 4AB3C1B spring pan with increased quality materials for a fuller sound, a more reliable product, and a custom decay level to get a bit closer to the sound of the vintage pans."
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synchro
Joined: Feb 02, 2008
Posts: 4554
Not One-Sawn, but Two-Sawn . . . AZ.
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Posted on Aug 20 2021 03:52 PM
Well, that kills that theory. I wondered if, perhaps, the replacement was a different impedance, but that's not the case. I wish I could offer more help.
If I were dealing with this, I'd probably start by cross-checking; temporarily hooking up the OEM pan and see if the problem persists. If not, it is probably something in the amp's reverb circuit.
It could be some sort of oscillation. My next step would be to swap out some tubes and see what happens, starting with the reverb driver tube, then the reverb recovery tube. Beyond that, it could be a circuit problem and that involves a schematic and a voltmeter. (Be careful, there are hundreds of volts inside these amps and even when they are shut off, the filter caps can give you a heck of a shock.)
— The artist formerly known as: Synchro
When Surf Guitar is outlawed only outlaws will play Surf Guitar.
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LHR
Joined: Aug 23, 2006
Posts: 2123
The jungle
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Posted on Aug 21 2021 12:59 AM
Microphonic tubes squeal like pigs. Or make all kinds of nonmusical noises. Or fizz.
You, my friend, need to lower your pickups.
— SSIV
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rfcii
Joined: Oct 28, 2018
Posts: 186
Quimper Peninsula, WA
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Posted on Aug 21 2021 06:17 PM
LHR - thank you!
I replaced the "reverb driver" with a fresh tube to no avail.
However, I did just repeat the "tap test" and 1 of the 3 12AX-7s DOES ping quite a bit when tapped. The original specs of the amps say "Pre-amp tubes: 3x 12AX-7 Miniature tubes" and the one which pings the reverb quite a bit when tapped is labelled "ECC JJ 803S"
Looking that up, I find on thetubestore.com
"Note: Because this tube has a long plate structure it is susceptible to excessive microphonics and is therefore not recommended for use in combo amps or high gain stages. For these amps the JJ ECC83-S is a better choice."
This IS a combo amp - so, should I try swapping it? If so:
1) Should I do all 3 at once (a matched set)
2) Does re-biasing need to happen for pre-amp tubes? If so, will this just sound bad, or possibly damage the amp?
I did find a local tube amp tech, and am willing to drop it off and pay the $39 diagnostic. I'm also willing to try lowering the pickups. However, this is happening on 3 guitars I have, all of which were recently set up. A MIJ Jaguar, the one in the video a MIM Jazzmaster, and a Hallmark 60 Custom.
Thanks for any additional thoughts!
Last edited: Aug 21, 2021 18:29:04
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synchro
Joined: Feb 02, 2008
Posts: 4554
Not One-Sawn, but Two-Sawn . . . AZ.
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Posted on Aug 21 2021 06:52 PM
Preamp tubes are cathode biased so you do t have to worry about that. I’d just replace the one that is noisy. These are not paired, push/pull tubes that have to be balanced.
— The artist formerly known as: Synchro
When Surf Guitar is outlawed only outlaws will play Surf Guitar.
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rfcii
Joined: Oct 28, 2018
Posts: 186
Quimper Peninsula, WA
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Posted on Aug 25 2021 02:34 PM
I did lower my pickups on all 3 guitars - a Jazzmaster, a Jaguar, and Hallmark 60 - and it has definitely helped. I'm not sensing a problematic loss of tone, but it does mean that on the Jaguar, the pickups have bottomed out completely (maybe the backing foam is too thick/firm?) and on the Jazzmaster, the pickup tops are about flush with the guitar body (and the "tabs" are quite a ways below. Is this typical? I know "use your ears" is the guide for pickup height, but is this common (or secret) knowledge for surf music, to have the pickups what seems to be Very Very low? I found another thread here with lots of folks wanting them as high as possible without running into the magnetic distortion.
Last edited: Aug 25, 2021 14:34:38
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synchro
Joined: Feb 02, 2008
Posts: 4554
Not One-Sawn, but Two-Sawn . . . AZ.
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Posted on Aug 25 2021 11:23 PM
rfcii wrote:
I did lower my pickups on all 3 guitars - a Jazzmaster, a Jaguar, and Hallmark 60 - and it has definitely helped. I'm not sensing a problematic loss of tone, but it does mean that on the Jaguar, the pickups have bottomed out completely (maybe the backing foam is too thick/firm?) and on the Jazzmaster, the pickup tops are about flush with the guitar body (and the "tabs" are quite a ways below. Is this typical? I know "use your ears" is the guide for pickup height, but is this common (or secret) knowledge for surf music, to have the pickups what seems to be Very Very low? I found another thread here with lots of folks wanting them as high as possible without running into the magnetic distortion.
That sounds pretty low, to me. I’d say that the source of the problem is still undetermined.
— The artist formerly known as: Synchro
When Surf Guitar is outlawed only outlaws will play Surf Guitar.
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rfcii
Joined: Oct 28, 2018
Posts: 186
Quimper Peninsula, WA
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Posted on Aug 28 2021 09:25 AM
I did find this thread, which suggests that raising action could help:
https://www.offsetguitars.com/forums/viewtopic.php?f=11&t=117388&hilit=surfybear&sid=551b12a51d46c0d81bf2024c5d0f92d2&start=15
I will look into that this weekend. I've had all three guitars professionally set up so hadn't thought that would be a concern. I don't really have fret buzzing, but I will try anything at this point.
Sadly I live in a small town so I can't easily (or even with difficulty) find a surf guitarist to compare gear with.
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