Yip, my amp is acting weird

[Boiledrootbeer]

Hi Folks,


  I have a '76 Fender Deluxe Reverb that is making some noises.  I had it to a tech a few years back who did a full overhaul, replacing caps and resistors, removed the volume boost from the vibrato channel, rewired to AB763...  I think that's it.  Anyway, I've since replaced the tremolo pot with a switchable pot so that I can disconnect the trem (I'll attach a schematic for this, but I'm sure most of you techs know what I'm talking about).  So, that's all the work/modifications that's been done to the amp.
 Now, the noise.  I hate describing noises.  At first I thought my guitar cable was going bad, the noise sounded just like the crackle and pop of a cable with frayed wires struggling to reconnect.  Then I started to smell something hot.  Turned off the amp and removed the chassis to take a look.  I saw a bit of smoke but nothing inside looked burnt; though, around the second power tube the odor seemed more pronounced.  I took out tubes and looked in sockets and didn't notice anything.  So, I left the chassis out and turned the amp on to see what would happen... worked fine!  No smoke, no sparks, nothing interesting at all, except that I could once again enjoy playing through it.  However, I was still concerned so I checked all the tubes.  The second power tube was not glowing like the first so I replaced them both.  With the new tubes everything worked fine so I played with the chassis out for a few days to keep an eye on things.  Nice, I thought the problem was solved.  Now, I'm having a buzz again in the speaker.  It's not constant.  When it does occur, however, it seems to do it with the lower end notes.  Makes me think it's the speaker, but I'm not certain since it doesn't do it constantly and it does it sometimes when I'm not playing.  So, checked the tubes again and the second power tube is glowing blue.  I've turned off the amp and don't know what else to do.  I hope this rant makes some sense, I'm not a tech and I understand that describing something like this over the internet is probably like trying to describe the color blue to someone who was born without the sense of sight. 
Anyway, if you think you might be able to help me please chime in.  Any thing that I've left out just let me know and I'll try to fill in the blanks as best as I can.  Thanks in advance for any help you can offer. 
Also, as a side note, I do understand the risk of getting into the amp.  I understand how to properly drain the caps. 

[Platefire]

The noise your describing sounds like a grounding issue but you also made mention of something getting hot and smoking.

Did you try a different guitar cord to eliminate  that possibility or even a different guitar. I always check out the external factors before going into the amp. For the ground type noise I would start with the input jack to check grounds connections and all input wiring up to the first preamp stage. You can use a mulitimeter to check continuity of ground connections. Could be a solder joint gone bad.

On the heating/smoke. Sounds like a short somewhere with the DC power supply. Check lead dress of circuit wiring to see if the DC power supply wiring was too close to a part or wire and shorted. If you can't see any burn marks, try moving DC power wires with a chop stick that seem too close to other parts/wires to give them a little breathing room.

If your not familiar with amp trouble shooting, I would do a google search on "tube amp trouble shooting" and do a little studying especially dealing with high voltage DC that can hurt/kill you. Platefire

[Boiledrootbeer]

Thanks for the reply, Platefire.  I have tried different cables/guitars.  I played through the amp a little last night just to see if the sound would come back and I didn't notice it.  I'll get into it tonight and see if I can find a lose connection somewhere.  It is a combo so I suppose after a few years of use a crappy solder joint could have worked lose by now.  Thanks again for the suggestions. 

[eleventeen]

If you have the thing open and are buying parts and melting solder, for 6 * 30 cents each, I myself would not let the amp escape without replacing the 100K  plate resistors for the preamp tubes with 3 watt metal films. Doug sells them. They feed the plates of V1, V2, and V4 in that characteristic "V" formation. I am calling the first 12AX7, most distant from the power tubes "V1" even though there is no such designation from Fender.


I'd also go for replacing the 2 qty 470 ohm screen resistors. 60 more cents. Ooops, never hurts to replace the between-node resistors in the power supply, under the doghouse. Another 60 cents. 


I will agree with Platefire that your noise issue sounds more like a grounding issue than what I am suggesting, but replacing those plate resistors almost always cuts spurious weird noises way, way down, very noticeable. And it's kind of a thing where if you are hunting down and killing noise then you can't really say you've done the best you can w/o replacing these. With a blackface Fender I consider the replacement mandatory, on yours, 10 years newer, I would consider it only a "very strong suggestion". It doesn't matter if those R's look OK...on BF's they were typically 1/2 watt and maybe were more likely to show some heat aging. On yours they are probably 1 watts, but even so, it's not a matter of appearance...it's a matter of being carbon comps vs metal films. The carbons are noisy. This is also a good case for having a bottle of liquid flux, just to add a SMALL amount to the joints you are going to reheat over and above the flux within the new solder you will add. To me...this stuff is cheap and the problem is annoying, so if you can kill it with one sweeping effort, I prefer that method.



Back to the possible grounding issue; in most cases I have seen, you can't get away with simply reheating the solder joints of ground-related connections (and call it a *thorough* job)  because the same corrosion that foiled a proper solder joint when the amp was built still exists, except worse with age. You really have to examine those ground connections very carefully, hopefully with a magnifying glass. You have to wiggle (and in some cases replace) the bare ground wires (for the most part I am talking about BOTH ENDS of the bare wires that connect to the brass sheet metal behind the controls. It's tedious, but I know from many years of experience how irritating spurious noises are. 

[Boiledrootbeer]

Hi folks,


  I have been playing through my amp since my last post and everything has been fine.  Well, until today.  I decided to plug the reverb back in.  I normally run it through channel one on the amp and hadn't reconnected it after putting the chassis back in the cabinet because I just didn't think it would matter.  Anyway, I plugged it back into channel one and didn't have any reverb at all.  Hhhmmm…..  So, I hooked it up in the stock manner and when turning up the "reverb" knob I get an awful squeal.  The squeal changes pitch as I work the knob a little.  I've disconnected it and am not sure what to do.  I'll probably have to send it to a tech since I'm not as good in this area as I would like to be, but I thought maybe someone here might have a suggestion that may save me the time and money of going that route.  Thanks in advance for any help. 


Aaron