Late 1960s Fender Deluxe Reverb Guitar Amp Issues

[captainclock]

Hello Everyone, the other day I was asked to see if I could get a late 1960s vintage Fender Deluxe Reverb up and running for a friend of mine who's son had gotten it from his school who was about to throw it out because it wasn't working. Anyways it doesn't want to put out any audio when its turned on and the standby switch is switched on.
I had already tested the B+ on the 6V6s and they tested mostly within specs and the 12AT7s tested mostly within specs and so did the 12AX7, the 7025s however tested at only -0.625 Volts which I'm guessing is where the fault lies.

Any help and tips and info to try and get this thing up and running would be appreciated.

[Ed_Chambley]

Captin,
Probably want to be more specific.  First, do both channels have the problem.  The Normal and Vibrato channels?  If so, you will want to post the voltages of all your tubes beginning with V1a which is the normal channel preamp tube.

There is a method of approach outlined Here:
http://el34world.com/schematics.htm#Servicing%20fender%20amps

Review the link and change the tubes if you have known good ones.  This is the place to start.  If it is a late 60's deluxe it should not be too hard to figure out what is wrong with the help here.

[captainclock]

Captin,
Probably want to be more specific.  First, do both channels have the problem.  The Normal and Vibrato channels?  If so, you will want to post the voltages of all your tubes beginning with V1a which is the normal channel preamp tube.

There is a method of approach outlined Here:
http://el34world.com/schematics.htm#Servicing%20fender%20amps

Review the link and change the tubes if you have known good ones.  This is the place to start.  If it is a late 60's deluxe it should not be too hard to figure out what is wrong with the help here.

Well I did have a little more detailed post but lost it when I was trying to post it on here so I had to borrow the post from another forum I posted about this amp in.
Anyways both channels are dead, no audio comes out of either the normal or vibrato channel, I had tested the B+ on the plates of the 6V6s and they tested normal (or as close to normal as they could get considering that I have 125VAC household current as opposed to 117VAC Household current like what this thing was originally designed for) and the 12AT7s all measured fine, as well as the 12AX7 but the 7025s didn't measure fine, they didn't have any measureable B+ voltage on their plates.

There were some modifications and repairs done to this amp previously of which they weren't done very well, according to the schematic/layout diagram there should be 7 25 MFD 25 Volt electrolytic caps on the main turret board but instead there are only 5 electrolytic caps on the main turret board and 4 of them are 25 MFD 35 Volt electrolytics made by Mallory and the 5th one is a 5 MFD 50 Volt electrolytic cap also made by Mallory, the other two caps are MIA.
Also there is a couple of funky resistor replacements that were redone including 2 of the original carbon comp resistors that were replaced with modern carbon film resistors and one carbon comp resistor that was replaced with another carbon comp resistor but instead of using the eyelets on the turret board to mount the new resistor they tied it to the electrolytic capacitor next to it.
Also the choke that's next to the power transformer was replaced with a modern one at one point in time, and I'm not sure if its a proper replacement for the original one or not, or if its even doing its job correctly or if its even wired up properly.

I will try to post some pictures of the amp and the repairs/mods that I'm talking about. 

[captainclock]

More pictures of the amp in question

[bnwitt]

What kind of test equipment do you have on hand?

[PRR]

> no audio comes out

Ear in the speaker:

DEAD silent? NO hiss or hum?

Or do you hear low hiss/hum but no guitar?

> didn't have any measureable B+ voltage on their plates.

So back-track.

I got no water in the bathroom. Water comes from a pipe in the cellar. See if I have water in that cellar pipe (open other faucets and see if they flow). Keep back-tracking one pipe to the one which supplies it, out to the well or street-pipe.

Electricity can be easier than water because you don't have to find or make an opening to know if it is "live".

Since you have voltage to most of the tubes, there's prolly only one "pipe" involved. Burnt resistor, bad solder joint.

However since this does appear to be a 1960s build, and you say it has been boodged, it *would* be good to go through point-by-point, verify connections, values, and list the parts which are past their best-flavor date. I love those brown doghouse caps but at 50+ years they are running on borrowed time. Yes, I just read of a guy who was given a year to live in 1969, and finally passed this week after decades of "borrowed time".... but that's rare.

Problem with that is the apparent history of neglect and disrespect. The recent owners have not valued it, and are unlikely to have the cash for a good go-over. Best path may be to buy it or trade it for a nice little recent amp off CraigsList, fix and flip it to a good home.

[Ed_Chambley]

Check to insure the fuse is correct first.  Get a 2A slo-blow if it is not.  Do you have known good tubes? 

I can see you have the old Mallory Filter caps and there are still in there.  Sounds like you are familiar with the workings.  The choke is a RF filter made for automotive noise cancelling.  You are going to need to order some parts, so just get the choke.  If you look above you will see parts going by.  Just order the correct one.  Now opinion time.

Regardless, we know the Power Transformer is working and you have a AB763 Deluxe.  There could not be enough wrong with this amp to make it not worth fixing.  They are highly sought after especially if it is a Black Face.

I would simply do a complete service and unless the Output Transformer is bad the service will probably fix the issues.  Replace all Electrolytic caps and I would also get the coupling caps as well, but they may be fine.  I can see there are 2 different types.  Use Metal Film Resistors on the B+ rail.  Personally I would replace all the resistors with Metal Film.

Basically just follow the schematic especially check voltage down the B+ to insure someone has not left the preamp filter cap disconnected.

What you have is a great amp someone has messed with, but it is worth a complete overhaul IMO.

If you do intend on just repairing what is bad, start with ordering the Electrolytics, get new plate resistors and locate any missing part by marking the schematic and each part as you go.  When all your parts are marked the schematic will show you what you need to order in addition to the things you simply replace due to age like the Filter Caps.

There is lot of things to do for general service and that is why I pointed you to Hoffmans fender service guide.  It is just too much to type, but not really much work.  Like spraying the pots with Detoxit.

Or you could simply sell it to me

I am truly joking.  That is a very nice amp and certainly not a throw away.

[Ed_Chambley]

Oh yea, the 2 guys that posted with me are much more knowledgeable than me.

Follow their lead if there is any question as to what is best to do.

[Willabe]

That is a very nice amp and certainly not a throw away.

Yep.   

[captainclock]

What kind of test equipment do you have on hand?

I have a digital Multimeter and a tube tester and that's about it as far as test equipment goes.

[captainclock]

> no audio comes out

Ear in the speaker:

DEAD silent? NO hiss or hum?

Or do you hear low hiss/hum but no guitar?

> didn't have any measureable B+ voltage on their plates.

So back-track.

I got no water in the bathroom. Water comes from a pipe in the cellar. See if I have water in that cellar pipe (open other faucets and see if they flow). Keep back-tracking one pipe to the one which supplies it, out to the well or street-pipe.

Electricity can be easier than water because you don't have to find or make an opening to know if it is "live".

Since you have voltage to most of the tubes, there's prolly only one "pipe" involved. Burnt resistor, bad solder joint.

However since this does appear to be a 1960s build, and you say it has been boodged, it *would* be good to go through point-by-point, verify connections, values, and list the parts which are past their best-flavor date. I love those brown doghouse caps but at 50+ years they are running on borrowed time. Yes, I just read of a guy who was given a year to live in 1969, and finally passed this week after decades of "borrowed time".... but that's rare.

Problem with that is the apparent history of neglect and disrespect. The recent owners have not valued it, and are unlikely to have the cash for a good go-over. Best path may be to buy it or trade it for a nice little recent amp off CraigsList, fix and flip it to a good home.

Yep, Its dead silent, no hiss or hum to be heard from the speaker using the vibrato or normal inputs. and the 7025s didn't have any measureable B+ on their plates just -0.625 volts and that was it. the 6V6s and the 12AT7s and the 12AX7 measured fine though.
So I'm guessing that the 2 missing electrolytics and dodgey resistor replacement job has something to do with it.

[PRR]

> I'm guessing that the 2 missing electrolytics and dodgey resistor replacement job has something to do with it.

Are you going to fix that resistor?

The caps aren't in it. They don't make voltage. A bad cap can short-out voltage but something will smoke. However the only caps you mention(?) are 25V caps.... these have nothing to do with a 300V B+ supply. Main effect of missing cathode cap is slightly lower gain, and two lost caps is not enough to make the rig *silent*, just hard rowing.

[sluckey]

There should be some jumper wires connecting all those points labeled "D" together. Your jumper wires may be white. Since you are missing plate voltages for ONLY the first two tubes, I suspect the #1 wire (red on my pic) is either missing, broken, bad solder joint, or soldered to the wrong eyelet.

[mresistor]

Or the last resistor on the power rail (on the cap board under the doghouse) is open. BTW your amplifier appears to be manufactured in 1973, according to the transformers.

[sluckey]

Or the last resistor on the power rail (on the cap board under the doghouse) is open. BTW your amplifier appears to be manufactured in 1973, according to the transformers.

Good point. And probably more correct. I had overlooked the fact that there are three 7025s in the amp. He's probably missing voltage at all point Ds. With that on mind, your idea sounds good. Or maybe wire from the doghouse to the main board is faulty or connected wrong.

[mresistor]

Absolutley could be wiring error or broken wire or soldering Steve, and if it were my amp I'd be unsoldering those old orange dried out Mallory caps and tossing them into file 13. I wouldn't even turn it on until they were replaced. This isn't a museum piece, as mscaggs would say.  :-)
I'm wondering "why" would someone take the caps out of the cathode bypass circuits? What were they trying to achieve? As PR mentioned.

[bnwitt]

.. if it were my amp I'd be unsoldering those old orange dried out Mallory caps and tossing them into file 13. I wouldn't even turn it on until they were replaced. This isn't a museum piece, as mscaggs would say.  :-)

Me too

[Willabe]

I'm wondering "why" would someone take the caps out of the cathode bypass circuits? What were they trying to achieve?

Less gain/cleaner and less/tighter bass.

[captainclock]

This was an institution unit originally as it had originally belonged to a high school before the current owner got his hands on it, so I'm not sure why the cathode bypass mod would even need to of been done, because its not like it was a unit that was being used by a professional rock band or anything. I'll check those wires that were mentioned and see if there was some shoddy soldering jobs done on them or see if they got damaged or disconnected somehow. I guess I'll see about replacing those old power supply filter caps as well.
I would like to try and restore this amp back to stock again so that it doesn't have those shoddy mods in it that might cause questionable functionality to the amp.

[captainclock]

There should be some jumper wires connecting all those points labeled "D" together. Your jumper wires may be white. Since you are missing plate voltages for ONLY the first two tubes, I suspect the #1 wire (red on my pic) is either missing, broken, bad solder joint, or soldered to the wrong eyelet.

By the looks of the wiring of the jumpers you're referring to, they don't seem to be wired up properly, (at least they don't look to be wired up like the way you showed that they should of been wired up on the diagram.) none of the white jumper wires are tied together on one eyelet like you showed that they were supposed to be, they are tied to seperate eyelets that aren't even close to each other.

[mresistor]

Here's the layout for an AB763 Deluxe Reverb      [url=http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-Reverb-AB763-layout.pdf]http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-Reverb-AB763-layout.pdf[/url]


The Nodes D all connect together, and it does look like one of your D wires is not connected up right. The D supply the voltage to the plates of the small bottles, notice they go to the junctions of the
100K plate resistors. Start at one end of the layout and check everything out one by one on the board , to make sure the board is wired up according to the layout. 


It looks like someone in the past replaced one of the HV filter caps with a 20uf. The DR typically uses 16uf electrolytics and Doug Hoffman sells the 16uf F&T caps in the store here  http://hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Capacitors&ORDER_ID=!ORDERID!  scroll down to the electrolytics. The F&Ts are very good caps.  I wouldn't waste my money on the Spragues.

[Willabe]

Start at one end of the layout and check everything out one by one on the board , to make sure the board is wired up according to the layout.

Here's a great way to do that;

http://el34world.com/Forum/index.php?topic=17701.0

[2deaf]

The pictures show the D connections are correct and only a slight variation to Sluckey's diagram.

[Willabe]

Trace the B+ DCV rail with a multi meter, done deal. 

[captainclock]

Trace the B+ DCV rail with a multi meter, done deal. 

I did do that, but I'm not sure where the B+ is getting lost at because all of the tubes except for the 7025s measure fine yet in reguards ro B+ plate voltage so somehow all the tubes except the 3 7025s in this amp's circuit are getting the proper B+ voltages that they need, so something in the circuit got disurbed or damaged or messed up along the way to cause the 7025 tubes to not get any B+ plate voltage which is what's causing my no audio issue presummably.

[John]

If you have the correct layout on paper, finding where it gets lost should be easy. Check each place on the board where there should be B+ voltage. But I believe Sluckey and  MrResistor already pointed you where to look.

[2deaf]

There is a hole in the chassis behind the Normal channel bass control that has a white wire coming out of it and connecting to the main circuit board.  Is there any voltage on it?

[captainclock]

There is a hole in the chassis behind the Normal channel bass control that has a white wire coming out of it and connecting to the main circuit board.  Is there any voltage on it?

I'm not sure I didn't check it yet, But I'm guessing if its the wire I think you're talking about I think its the one that comes out of the filter cap tank, which I think that wire then attaches to where the white "D" jumpers attach to the board at. If there isn't any voltage there then I'm guessing that the Filter caps might possibly be to blame in this case.

[sluckey]

I've circled and numbered all the eyelets involved. All 4 of these eyelets should be connected together by the white wires. Check the voltage at #1 on the cap board. If good, then the cap board is fine. Now check the voltage at #2. If bad then something is wrong with the white wire between the cap board and the main board. Since you have no plate voltage on any of the 3 7025 tubes, this wire is my first suspect. There may be an underboard jumper involved but your pic is not clear enough for me to tell.

A better pic of this area of the main board would be a big help. I'm attaching a clear pic of an earlier model DR for comparison. Your amp may not be exactly like this but it should be very close, except the wiring will not be as neat.

[captainclock]

I've circled and numbered all the eyelets involved. All 4 of these eyelets should be connected together by the white wires. Check the voltage at #1 on the cap board. If good, then the cap board is fine. Now check the voltage at #2. If bad then something is wrong with the white wire between the cap board and the main board. Since you have no plate voltage on any of the 3 7025 tubes, this wire is my first suspect. There may be an underboard jumper involved but your pic is not clear enough for me to tell.

A better pic of this area of the main board would be a big help. I'm attaching a clear pic of an earlier model DR for comparison. Your amp may not be exactly like this but it should be very close, except the wiring will not be as neat.

Well I just figured out part of the problem! There is a resistor on the filter cap board that had one leg that was detached from the circuit and I didn't even notice it until I took a closer look, its the 10k Ohm 1W reistor that's attached across the first two filter caps next to the 2.2k Ohm 1 Watt resistor in the filter cap board.

[sluckey]

There is a resistor on the filter cap board that had one leg that was detached from the circuit and I didn't even notice it until I took a closer look, its the 10k Ohm 1W reistor that's attached across the first two filter caps next to the 2.2k Ohm 1 Watt resistor in the filter cap board.

That totally explains no plate voltage on any 7025 tube.

[captainclock]

There is a resistor on the filter cap board that had one leg that was detached from the circuit and I didn't even notice it until I took a closer look, its the 10k Ohm 1W reistor that's attached across the first two filter caps next to the 2.2k Ohm 1 Watt resistor in the filter cap board.

That totally explains no plate voltage on any 7025 tube.

Well I'm going to reattach that resistor and the white wire (which I also noticed was detached from the circuit upon closer inspection) when I get back from my job interview I have this afternoon, and see what we get from there. 

UPDATE: I reattached that resistor, turned it on, checked voltages and sure enough, BAM! I had B+ voltages again to those 7025s!
So then I reassembled the capacitor tank and plugged in the speaker and plugged in a CD player for an audio source and powered on the unit and sure enough it was working!  Who knew that a simple loose resistor in the power supply filter cap tank was the reason why this thing wasn't working... 

[2deaf]

Who knew that a simple loose resistor in the power supply filter cap tank was the reason why this thing wasn't working... 

mresistor.

Now about the reverb driver and the vibrato.

[captainclock]

Who knew that a simple loose resistor in the power supply filter cap tank was the reason why this thing wasn't working... 

mresistor.

Now about the reverb driver and the vibrato.

What about it?

[2deaf]

The two cathode bypass resistors that are missing appear in the picture to be on the reverb driver and the first stage of the vibrato.  The cathode resistor of the reverb driver also appears to be 470 ohms.

[captainclock]

The two cathode bypass resistors that are missing appear in the picture to be on the reverb driver and the first stage of the vibrato.  The cathode resistor of the reverb driver also appears to be 470 ohms.

OK well I think if I can get the money to do it I'll get the capacitor kit for this amp over at Antique Electronics Supply so that I'll have all of the electrolytics this amp needs including the filter caps and they have the F & T capacitors in their kit. Anyways I'll see if the owner of this amp wants me to get all of the capacitors replaced in this amp for them and if they do I'll get the aforementioned capacitor kit for this amp and replace all of the capacitors including the missing ones.

[2deaf]

OK well I think if I can get the money to do it I'll get the capacitor kit for this amp over at Antique Electronics Supply so that I'll have all of the electrolytics this amp needs including the filter caps and they have the F & T capacitors in their kit. Anyways I'll see if the owner of this amp wants me to get all of the capacitors replaced in this amp for them and if they do I'll get the aforementioned capacitor kit for this amp and replace all of the capacitors including the missing ones.

If you do that, you should also consider changing the reverb driver cathode resistor back to 2.2K ohm.

[captainclock]

OK well I think if I can get the money to do it I'll get the capacitor kit for this amp over at Antique Electronics Supply so that I'll have all of the electrolytics this amp needs including the filter caps and they have the F & T capacitors in their kit. Anyways I'll see if the owner of this amp wants me to get all of the capacitors replaced in this amp for them and if they do I'll get the aforementioned capacitor kit for this amp and replace all of the capacitors including the missing ones.

If you do that, you should also consider changing the reverb driver cathode resistor back to 2.2K ohm.

I'm assuming that the resistor you are referring to is the one that was kind of replaced in a funky manner next to the one cathode bypass cap that was still in place?

[sluckey]

I think the cathode resistor on the reverb driver was changed to 4.7K (not 470Ω) to decrease the reverb drive. The bypass cap was probably removed for the same reason. I removed the bypass cap on the reverb driver in my TDR (same circuit) to reduce the 'over-the-top' reverb level. I'd probably change the resistor back to a 2.2K though and then if the reverb was still not as strong as desired, put the bypass cap back in.

The tremolo bypass cap that seems to be MIA is not missing at all. It's just not on the board like an AB763. It's directly on the tube socket. Remember, this is a later silverface, A1172 or A1270.

[captainclock]

I think the cathode resistor on the reverb driver was changed to 4.7K (not 470Ω) to decrease the reverb drive. The bypass cap was probably removed for the same reason. I removed the bypass cap on the reverb driver in my TDR (same circuit) to reduce the 'over-the-top' reverb level. I'd probably change the resistor back to a 2.2K though and then if the reverb was still not as strong as desired, put the bypass cap back in.

The tremolo bypass cap that seems to be MIA is not missing at all. It's just not on the board like an AB763. It's directly on the tube socket. Remember, this is a later silverface, A1172 or A1270.

OK that makes sense, I was wondering why there was a random cap sitting in the back of the amplifier.

[2deaf]

I think the cathode resistor on the reverb driver was changed to 4.7K (not 470Ω)

The stripe is brown on my screen, as verified by my panel of experts (wife, kids).  But whatever it is, it's significantly different than 2.2K and I think this amp is pristine enough that it should have the original values resurrected. 

The tremolo bypass cap that seems to be MIA is not missing at all. It's just not on the board like an AB763. It's directly on the tube socket.

I should have looked at the picture more carefully before posting.  Sorry.

[captainclock]

I think the cathode resistor on the reverb driver was changed to 4.7K (not 470Ω)

The stripe is brown on my screen, as verified by my panel of experts (wife, kids).  But whatever it is, it's significantly different than 2.2K and I think this amp is pristine enough that it should have the original values resurrected. 

The tremolo bypass cap that seems to be MIA is not missing at all. It's just not on the board like an AB763. It's directly on the tube socket.

I should have looked at the picture more carefully before posting.  Sorry.

Yeah I do want to try and make this unit stock again just the matter of getting the money to do so as I've only got so much money to work with being that I only do the as a side job so I'm not exactly raking in the dough.

[captainclock]

OK So new problem guys, I was able to get the capacitor kit for the amplifier and I replaced all of the capacitors that I could in here without having the proper schematic for the unit (seeing as the schematic I had found was for the earlier blackface version and not the later silverface version like I have) anyways the amp was playing trouble free for me until a friend of mine brought over his electric guitar over to test out the amp to see what it sounded like and it played fine for him but then the next day I went to turn on the unit and it suddenly developed a low volume 60 hz hum through the speaker which I thought was because the power supply caps were going to pots finally, which is why I bought the capacitor kit, anyways I replaced all of the capacitors that I could in this unit as stated earlier, I put the unit back together and fired it up and sure enough the same hum that it had before prior to the recap was still present. Any ideas as to what might be causing this hum?

[Willabe]

Is the tube chart still glued to the side wall in the cab? If so it will say which model # it is.

Link below is for Doug's tube amp library, scroll down to the D's;

http://el34world.com/charts/Schematics1.php

[captainclock]

Yes it has a tube placement chart inside the cabinet but it doesn't list a model number on it anywhere, so I have no idea what model number this amp is, all I know is that its a Fender Deluxe Reverb and its a Silverfaced model.

[Willabe]

Look in Doug's schematic library, I posted the link for you. The AB763 is the BF, the other 2 are SF models.

Print them both out and go over the amp with them to figure which 1 is your amp.     

[captainclock]

I just looked at them and none of them really came close to the way the one I have is set up on the inside.

I think mine was heavily modified from the original so it's not even recognizable, as far as what it should look like vs. what it currently looks like.

The only Layout diagram that looked even remotely similar to how the amp I'm working on looked was the AB868, because it actually had most of the same capacitor values as mine did and most of them were in the same position as mine except for the tremolo bypass cap which on mine it was attached to the tube socket that controlled that part of the circuit and then attached to a ground lug on the back of the chassis, instead of being installed on the turret board like all of the other designs showed.

[eleventeen]

"I think mine was heavily modified from the original so it's not even recognizable, as far as what it should look like vs. what it currently looks like."


No, not really. Certainly not the kinds of mods we discuss around here. The insides of late 60's Fenders is just so weird looking compared to earlier models. It's a very frantic style of wiring, if you can call it that. But the mods are not major at least to the extent you describe them. Very ordinary. Irritating to unmod w/out documentation; but you could move a load of resistors and caps around for less than $10, these are pretty cheap parts. Takes time.


A choke only has two wires which are interchangeable, it can't be wired in wrong.


The amp is worth anything you would want to do with it, it's near holy grail stuff. The issue is that I guess you are working for free?


I would not take apart solder joints with slapped-in resistors that go to other parts (instead of through the eyelets if the solder joints are clean and bright looking and look strong and stable.


Should replace all the resistors inside the metal can "doghouse" with 3 watt metal films and it would not hurt to replace all the 100K plate resistors going to the 7025/12AX7 that are arranged in those "V" formations. I kind of just shotgun those parts in, they make the amp lots quieter but they DO NOT address your hum situation. That hum could be lots of things. Some of those things are or can be tough to find but they are NOT expensive to fix!


Pull tubes, rotate controls to try to localize the hum. Bad solder joint on a ground or a repaired part.

[captainclock]

Well what I meant by that it was modified to the point of not being recognizable is that I can't recognize what the amp's original layout was supposed to look like in its current modified state vs. the original layout diagrams. I actually did try swapping out the output tubes (the 6V6s) because I thought that maybe the hum was coming from a Heater to Cathode short in one of the output tubes, but sure enough the amp is still humming even with a fresh set of 6V6s in there, so the tubes are ruled out as a possible cause, the only "grounding" issue that there might be in this amp is that there was a black wire possibly a ground wire of some sort that was attached to the negative lead of the power supply cap closest to the right side of the power supply cap tank that came out of the eyelet when I removed the old power supply cap from the hole, and I tried to reinstall that wire back into the eyelet hole as best as I could, but I don't think that wire is the cause seeing as this issue was around prior to that, so that can be ruled out as well. I really can't think of anything else that could be causing the humming issue with this amp, and considering this humming issue just crept up on its own out of nowhere randomly, I don't think that this humming issue was caused by anything I did to the amp, although with all of those unprofessional mods that were done to this amp by its previous owners (which would be whoever the school that previously owned this amp took the amp to for repairs) might have gone south but not sure.

[Willabe]

Can you post several hi-rez of the amps insides?