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Hi all! I am a new owner of an 18 watt TMB model. I bought it used after only testing it a medium to low volume for a few minutes before paying and walking away with it. So, when I got it home I very anxiously removed my 800 from my 4x12 and sat my (sort of new) head on top, made sure the speaker resistance was set, plugged it into the cab, powered it up, let it warm up, plugged my guitar into it, checked levels and switched the standby to on position. So far so good! Low volume gave me a beautiful and bright clean sound... awesome! Time for some crunch I says! When I turned it up and played with the EQ I got some really great tones but in the background there is this weird pulsing electrical type of noise almost like there was a flanger in the background. The low frequencies began to come out pretty muddy and made this sound more predominant too. I then rolled back the bass on the eq and brought up the treble some. Still there, still muddy when I pound out an E chord. I swapped the mesa preamp tubes for the sovteks from my Marshall to see how that would sound. At first I enjoyed a crisper sound but again when I cranked her up a bit along came that weird oscillating sound again. I tried to ignore and tried to get that buyer's remorse feeling out of my head and jammed away for a while. Next thing I know the volume starts to drop until I can hardly hear the thing! Now I'm worried. Switch it off, switch it back on, same thing. I unplug everything and stared in the back like it would fix something. I plug everything back in, power up, plug in and the volume is back but the weird noise is still persisting. Even when I'm not playing there is a pulsing sound and I forgot to mention that it also picks up a radio station. So, I have turned it off and come here to see if anyone has had a similar problem or might know what is causing this. Also does anyone have a pdf copy of the schematic so if/when I have to bring this to my amp guy he will have something to go by? I don't know how close this circuit is to the Marshall 18 watt amps so I don't want to tell him to use it.

Thanks!

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Whaaaaat? Ohhhh...turn it down!?!?!

Sorry to hear of your problems. The schematics in the resource section are very close to the model you have, the Three holer 18 watt TMB I believe.

I would guess it's tube related given that the amp dropped in level but came back after a while.

Where are you located?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I'm in Sherbrooke, Quebec.

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Whaaaaat? Ohhhh...turn it down!?!?!

I'm guessing it probably isn't one of the preamp tubes because it happened after I had put in three good sovteks from my Marshall. Could it be one of the el84's or the rectifier tube then? I'm wondering about this pulsating electrical hum that it is making. I had an old Lifco amp at one point and it did the same thing when I turned the volume up. Could it be that there is some sort of surge going through like from a faulty transformer or something?

thanks for responding!

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Whaaaaat? Ohhhh...turn it down!?!?!

Do I have access to the resource section?

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Whaaaaat? Ohhhh...turn it down!?!?!

Yes as member, you do.

Easy for me to say, but I'd try swapping the rectifier tube, then power tubes.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks

Where might I find the resource section?

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Whaaaaat? Ohhhh...turn it down!?!?!

It's a sub-forum that is only visible in the list when you're logged on to the site.

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- This Space For Rent -

Thanks!

I was experimenting a bit today with the amp and found that when I was plugged into the TMB channel alone there was a lot less background noise than the other channel. Also, I noticed that when in the TMB if the volume is up a bit on the other one I can hear crackling and hiss as though it is bleeding into the other side. When I turned that volume down it went away! So I may have narrowed it down to an issue on the channel without the master volume. I was getting the noise really bad when I had the channels jumped and I guess I know why now. There is still the issue with that weird underlying electrical whooshing sound at higher volumes but it doesn't seem so bad on the TMB side. Incidentally, I found out today that this amp is one that has already been posted on by the previous owner. Here's the url to the post: http://trinityamps.com/phpbb/viewtopic.php?f=7&t=3027 . There are pics there of it's innards. If this is one of the first builds and they have changed since would it be worth it for me to order some upgrade parts? Also, does anyone have a round about figure as to how much someone ought to pay for a used amp (specifically this one) that has a couple "issues"? I'm thinking I might have paid too much especially if it was assembled by some guy who ordered a kit and not at the company.

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Whaaaaat? Ohhhh...turn it down!?!?!

It can't be in the power tubes or rectifier, or else yu would hear exactly the same noise level in both channels. There's a possibility that one side of V1, the one which works in the noisy Normal channel could be faulty. Alternatively it could be the side of the PI (V3) which is fed by the Normal channel. Failing that, it could be a carbon composition resistor that's gotten noisy, or even a poor ground connection somewhere in the Normal channel.

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Great tones come in small glass jars!

Thanks for your reply! It's no longer an issue though because I have returned the amp to the guy I bought it from and have decided to have a brand new one built! I'm just waiting for the go ahead from Stephen to send the first payment!
Thanks again for your input!

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Whaaaaat? Ohhhh...turn it down!?!?!