AA270 Twin Reverb, reverb on both channels

JMadson · 10-03-2006, 02:58 AM

Well, I got the vibrato working, now the only issue is the reverb and vibrato are on both the vibrato, and normal channels, not a big deal, but I went through the entire curcuit, and all is in place near as I can tell from the layout diagragm, (the amp looks stock) . What could I be missing? Once again, I seem to remember a mod that some folks would do years ago to make the amp do this intentionally. Any advice would be great...
Thanks in advance...
Jason

Tom Phillips · 10-03-2006, 04:00 AM

Hi Jason,
There is a simple mod to put reverb on both channels that is easy to miss.
Check the pin 6 plates of the first and second pre-amp tubes to see if they are jumppered together. The jumper could be connected to the tube sockets or the eyelett board. Also check around the two 220k channel summing resistors at the input to the phase inverter. If the mod I have in mind was done then only one of the 220k resistors will be connected. In the stock amp each 220k resistor is fed by a wire that brings the signal from each pre-amp.

I’m assuming that you have the layout diagram to reference. If not it’s available from Schematic heaven. If you see anything suspicious in the two areas I mentioned it shouldn’t be too difficult to put the circuits back to stock by following the diagram. Or…decide to keep it that way. It think it’s a useful mod and gives you the option of bridging the channels and/or of voicing each channel differently.

Good Luck,
Tom

Enzo · 10-03-2006, 08:05 AM

AA270 is on Schematic Heaven

JMadson · 10-09-2006, 12:26 AM

Well, I'm confused... the layout is exact, at least I've spent several hours tracing the wiring... However, I have figured a couple of things out... 1, the reverb works on both channels, although it is not as intense on normal channel, maybe 60% or so. 2, the vibrato also works on the normal channel, only it is only maybe 35% as intense as it should be. It seems like this could be a leakage thing or something. Is there a cap or something somewhere in this curcuit that could have failed and caused some of the normal channel signal to leak into the vibrato channel?
Any help would be great...
Jason

walkman · 01-08-2007, 12:04 PM

Hi, mine does this too. I have a 73 Silverface Twin Reverb. I've only recently noticed it on a couple of occasions happening, it doesn't happen all the time. I did change the phase inverter to blackface over a year ago. Also the reverb channel breaks up much earlier than the normal one , though it has always been this way since i have owned it. It still has the original filter caps , they should be changed i guess. I haven't checked to see if the reverb channel is i stock or not.

sbluestubes · 01-15-2007, 01:46 PM

Check the circled areas if the end of the .047 is connected to either of these points that's where the normal channel has been coupled to the reverb if its stock you will get continuity to the 220K resistor in the phase invertor area labeled X on the layout

walkman · 07-28-2007, 06:03 AM

Checked the circuit finally. Its a 100watt master volume version form 1977? not UL 135watt. The channels are not linked at those places.?

tboy · 07-28-2007, 08:35 PM

Quote:

Originally Posted by JMadson

Is there a cap or something somewhere in this curcuit that could have failed and caused some of the normal channel signal to leak into the vibrato channel?

V1B and V2B have a shared cathode resistor and capacitor. If the cap is weak or open, the channels will mix at that point.

ampfixer · 10-21-2007, 01:51 PM

I cannot find my schematic on how to install reverb on both channels of my SF deluxe reverb,anyone have one? I remember doing this once but cant remember. Please let me know.A drawing would greatly help.

10-03-2006, 02:58 AM	#1
JMadson Junior Member Join Date: Oct 2006 Posts: 15	AA270 Twin Reverb, reverb on both channels Well, I got the vibrato working, now the only issue is the reverb and vibrato are on both the vibrato, and normal channels, not a big deal, but I went through the entire curcuit, and all is in place near as I can tell from the layout diagragm, (the amp looks stock) . What could I be missing? Once again, I seem to remember a mod that some folks would do years ago to make the amp do this intentionally. Any advice would be great... Thanks in advance... Jason

10-03-2006, 04:00 AM	#2
Tom Phillips Senior Member Join Date: Jun 2006 Location: California, USA Posts: 676	Hi Jason, There is a simple mod to put reverb on both channels that is easy to miss. Check the pin 6 plates of the first and second pre-amp tubes to see if they are jumppered together. The jumper could be connected to the tube sockets or the eyelett board. Also check around the two 220k channel summing resistors at the input to the phase inverter. If the mod I have in mind was done then only one of the 220k resistors will be connected. In the stock amp each 220k resistor is fed by a wire that brings the signal from each pre-amp. I’m assuming that you have the layout diagram to reference. If not it’s available from Schematic heaven. If you see anything suspicious in the two areas I mentioned it shouldn’t be too difficult to put the circuits back to stock by following the diagram. Or…decide to keep it that way. It think it’s a useful mod and gives you the option of bridging the channels and/or of voicing each channel differently. Good Luck, Tom Last edited by Tom Phillips; 10-03-2006 at 05:32 AM.

10-09-2006, 12:26 AM	#4
JMadson Junior Member Join Date: Oct 2006 Posts: 15	Still 'verb on both channels! Well, I'm confused... the layout is exact, at least I've spent several hours tracing the wiring... However, I have figured a couple of things out... 1, the reverb works on both channels, although it is not as intense on normal channel, maybe 60% or so. 2, the vibrato also works on the normal channel, only it is only maybe 35% as intense as it should be. It seems like this could be a leakage thing or something. Is there a cap or something somewhere in this curcuit that could have failed and caused some of the normal channel signal to leak into the vibrato channel? Any help would be great... Jason

10-21-2007, 01:51 PM	#9
ampfixer Junior Member Join Date: Oct 2007 Posts: 4	I need to install reverb on both channels I cannot find my schematic on how to install reverb on both channels of my SF deluxe reverb,anyone have one? I remember doing this once but cant remember. Please let me know.A drawing would greatly help.

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10-03-2006, 08:05 AM	#3
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,366	AA270 is on Schematic Heaven

01-08-2007, 12:04 PM	#5
walkman Member Join Date: Jan 2007 Posts: 46	Hi, mine does this too. I have a 73 Silverface Twin Reverb. I've only recently noticed it on a couple of occasions happening, it doesn't happen all the time. I did change the phase inverter to blackface over a year ago. Also the reverb channel breaks up much earlier than the normal one , though it has always been this way since i have owned it. It still has the original filter caps , they should be changed i guess. I haven't checked to see if the reverb channel is i stock or not.

07-28-2007, 06:03 AM	#7
walkman Member Join Date: Jan 2007 Posts: 46	Checked the circuit finally. Its a 100watt master volume version form 1977? not UL 135watt. The channels are not linked at those places.?

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