Reverb not working in my '72 SFTR

29eagle · September 4th, 2003, 09:38 AM

I just had it overhauled 6 months ago - all new tubes and most caps replaced. The reverb just went out a few days ago. I pulled the reverb tank and checked all connections - all seemed good. The amp makes the reverb noise when I move it so I think that means the tanks OK.

Any one have any suggestions for what else I can check or do myself before I take it in to the shop?

Thanks in advance for any help.

Wally · September 4th, 2003, 02:56 PM

Check the reverb tube..3rd from the right as you look at the amp from the back. It is a 12AT7. You could plug the driver tube...12AT7 next to the power tubes...into the reverb tube position as a test. SUb in your normal channel preamp tube..1st on the right... into the driver position temporarily. If this doesn't clear the problem, further examination is necessary. The tank could have a bad inductor. You could have a bad cable. The reverb circuit could have a problem. You could have a bad RCA jack.

jazzguitar · September 6th, 2003, 11:53 AM

set the volume to room loudness, adjust the reverb for "3" and lift the amp half an inch, then drop it. If you hear a sound like roaring thunder the reverb recovery is good and the problem is in the reverb "send," check the 12AT7 and go from there. Otherwise check the 12AX7A next to the reverb tranny (little tranny in the preamp tube row).

Pierce · September 6th, 2003, 12:03 PM

on if he hears the reverb when you whack on the amp the return recovery is OK..first suspect for me would be the cable,2nd the wire on the transducer on the pan..than the tube
but what do I know hehehehe

EMan · September 6th, 2003, 12:15 PM

Even if the reverb 'crashes', the tank can still be bad. As mentioned, I'd start with V3 (12AT7).

You 'can' test the reverb tank drive signal by hooking a speaker up to the tank drive output on the amp. The reverb transformer has an 8 ohm output. If you can get sound out of a test speaker hooked there...and the tank still makes a 'crash', you might have a bad tank.

Pierce · September 6th, 2003, 12:23 PM

transducer= reverb tank ..

September 4th, 2003, 09:38 AM	#1 (permalink)
29eagle TDPRI Member Join Date: May 2003 Posts: 11	Reverb not working in my '72 SFTR I just had it overhauled 6 months ago - all new tubes and most caps replaced. The reverb just went out a few days ago. I pulled the reverb tank and checked all connections - all seemed good. The amp makes the reverb noise when I move it so I think that means the tanks OK. Any one have any suggestions for what else I can check or do myself before I take it in to the shop? Thanks in advance for any help.

September 6th, 2003, 11:53 AM	#3 (permalink)
jazzguitar Tele-Meister Join Date: Mar 2003 Location: Germany Posts: 280	A few tests set the volume to room loudness, adjust the reverb for "3" and lift the amp half an inch, then drop it. If you hear a sound like roaring thunder the reverb recovery is good and the problem is in the reverb "send," check the 12AT7 and go from there. Otherwise check the 12AX7A next to the reverb tranny (little tranny in the preamp tube row).

September 6th, 2003, 12:03 PM	#4 (permalink)
Pierce Tele-Meister Join Date: Mar 2003 Location: skull island Posts: 470	my money is ... on if he hears the reverb when you whack on the amp the return recovery is OK..first suspect for me would be the cable,2nd the wire on the transducer on the pan..than the tube but what do I know hehehehe

September 6th, 2003, 12:23 PM	#6 (permalink)
Pierce Tele-Meister Join Date: Mar 2003 Location: skull island Posts: 470	read my response again.. transducer= reverb tank ..

September 4th, 2003, 02:56 PM	#2 (permalink)
Wally Friend of Leo's Join Date: Mar 2003 Location: Lubbock, TX Posts: 3,750	Check the reverb tube..3rd from the right as you look at the amp from the back. It is a 12AT7. You could plug the driver tube...12AT7 next to the power tubes...into the reverb tube position as a test. SUb in your normal channel preamp tube..1st on the right... into the driver position temporarily. If this doesn't clear the problem, further examination is necessary. The tank could have a bad inductor. You could have a bad cable. The reverb circuit could have a problem. You could have a bad RCA jack.

September 6th, 2003, 12:15 PM	#5 (permalink)
EMan Tele-Holic Join Date: Apr 2003 Location: Dallas, Texas Posts: 939	Even if the reverb 'crashes', the tank can still be bad. As mentioned, I'd start with V3 (12AT7). You 'can' test the reverb tank drive signal by hooking a speaker up to the tank drive output on the amp. The reverb transformer has an 8 ohm output. If you can get sound out of a test speaker hooked there...and the tank still makes a 'crash', you might have a bad tank.