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SG101 2006-2017

SurfGuitar101 Forums » Gear »

Permalink Minor amp problem- any idea what this is?

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Hi Folks,

I’ve got a small problem with my amp, a ’65 Bandmaster. I’ve had it a few years and had a tech go over the whole thing after I got it. The problem is not a big deal, but I thought that I’d ask and see if anyone has any ideas as to what is going on.

Here is my routine required to get the amp to play:
I turn on the amp by flipping the “on” switch. Wait a minute or two for things to warm up, then flip on the “standby” switch. The amp hums a little bit from the tube area (nothing loud or inappropriate) but no sound comes out of the speaker. So I turn off the “standby” switch, unplug the guitar cable at the amp head, plug the guitar back in, flip up the “standby” switch and everything works well. Unplugging/plugging the guitar cable is a required part of the process.

Like I said, it’s not a big deal. The amp always works. But I’m guessing that this isn’t normal, right?

By the way, Jazzmaster -> reverb tank -> ’65 Bandmaster -> Weber 12F150T is about as sweet of a sound as there can be. Smile

Hi JonW - Could be the input jack. Have you tried plugging into one of the other ones to see if they work the first time you fire up the amp? Process of elimination.........

Thanks for the help! I’ve never tried to troubleshoot an amp before.

I’ve been using input #1 on the vibrato side all this time. Upon your suggestion, when the amp was cold I started out from input #2 on the vibrato side and, sure enough, it work right away. Smile So maybe it is an input jack problem on #1 vibrato. Is it an easy fix?

I noticed that #1 is significantly louder than #2. Is that normal?

Also I tried #1 and #2 on the normal side. They both worked and played at the same volume as each other. But #1 vibrato also works now that I’ve turned it on and done lots of plugging/unplugging. I’ll check the #1 and #2 normal inputs on other days, when the amp is cold.

Thanks again.

Could be a loose solder joint on that channel (maybe at the jack?, or possibly at the grid pin of the first gain stage).

If you haven't messed with tube amps before, you need to:

1) make sure the amp is unplugged from the wall before opening it up; and

2) (carefully) make sure (with your VDC meter) that the filter caps are properly discharged before starting any work on the amp. You do this by (carefully) touching the +ve end of the filter caps with one of your (insulated) meter clips, whilst the other (insulated) meter clip is connected to the -ve end of the same filter cap, and the VDC meter is set to the 'hundreds of volts' setting.

He who dies with the most tubes... wins

Surf Daddies

Last edited: Feb 21, 2012 05:42:56

Thanks, tubeswell. I'll try all the other inputs when the amp has been off for a full day to see what the story is. So this will take a few days. If there seems to be one bad jack and 3 good ones, I'll take a look inside and see if I can tell what's going on.

OK, I just tried input #1 on the normal channel and it acted like input #1 on the vibrato channel: I had to do the unplug/plug thing to get it to work. So whatever is going on is not isolated to the input jack of #1 vibrato.

I turned the amp around and took a look inside with a flashlight. I don’t know what I’m looking for but there wasn’t anything obvious like burnt electronics or anything. It looked OK as far as I could see- which wasn’t too far.

Did you try using a different guitar cable?

He who dies with the most tubes... wins

Surf Daddies

Good idea! Yes, I just tried with a different cable. Surprisingly, it worked in one of the "bad" jacks. That was just guitar-cable-amp. Before it was guitar-tuner-a few other pedals-reverb tank-amp.

It would be crazy if all of this was just a bad cable. But cheaper than an amp fix. I'll try more variations here to try and track it down some more. At most I can only try 2 different things per day because this is all when starting the amp from cold.

Thanks for all of the help!

I tried out a few more options and it doesn’t look like it’s the cable, unfortunately.

Everything works perfectly if I just go guitar -> amp.

But if I use my normal signal chain, running through the tuner, tank, etc. I still have to do the unplug/plug thing at the amp head. For that, the full chain is:
guitar -> compressor -> tuner -> wah -> delay -> reverb tank -> amp

I’m confused at this point. Hmmm...

delete each item in the path and reintroduce them one at atime and isolate the bad boy

Yup. That's what I'm trying now. It takes a while because the amp needs to be fully cold and to know it's like that I can only try things about twice per day. That said, here's where I'm at now:

Looks like it works fine:
guitar -> amp

Looks like I need to do the unplug/plug to get it to work:
guitar -> reverb tank -> amp

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