|
|
Post by spellcaster on Mar 6, 2022 7:10:59 GMT
I discovered yesterday that I have problems with my Twin Reverb, but the tech tells me he can't do anything till Monday at the earliest. I decided overnight that since I have a day and not much planned, I should see what I can do. Frankly, I hate working with this kind of stuff, but I figure I should try to cover as much ground as I can before the meter starts running with the tech. I procrastinated almost all day, and finally got around to moving the microwave and other stuff off my kitchen table, which is about the only work space I have available in this studio apartment. I got as far as moving the head onto the table, my Ampeg cabinet for testing under the table, and a guitar on a stand to test with. First thing I did was try to duplicate what I thought was wrong yesterday. What puzzles me is that the Normal channel now sounds okay, but when I plug into either of the inputs into the Vibrato channel, there's the same really ugly distortion I heard yesterday. I didn't get any further because my second ex-wife called and we spent about three hours gabbing on the phone (before my cell battery ran out, lol) and it's late enough that I can't do much more testing until a more reasonable hour tomorrow. Knowing what I know now, I think the logical think to do is dismount the chassis and have it upside down on the table where it's easy to start swapping tubes. Since the Normal channel sounds okay, I know the power tubes are okay and what I'll be doing is substitutions of the preamp tubes. That's a real bear when the chassis is in that tight head cabinet, but it won't be too bad with the chassis out so I can see what I'm doing. I bought two new Groove Tubes 12AX7's from Long and McQuade last summer for V1 and V2, so an easy start with be using the proven-good tube from V1 in the Vibrato channel/V2 to see if it's faulty. If it's not, it becomes a bit more challenging because I no longer have any of my backup tube stock. I like Rob's suggestion of using the 12AT7 from V3/Reverb driver as a substitute for V6/Phase inverter, although since the Normal channel isn't distorting, I suspect V7's okay. If the phase inverter isn't the issue, I can only assume it's the Reverb driver V3 or Reverb return V4. I'm pretty sure V4's also a 12AX7, but I'll need to search online to find out if I can use a 12AX7 as a temporary substitution for a 12AT7 in V3, unless somebody out there knows and can advise me. So, things are now on hold till tomorrow, but I'd like to see if I can resolve things before Monday when the amp goes to the service shop.
|
|
|
|
Post by Die Bullen on Mar 6, 2022 13:39:12 GMT
I discovered yesterday that I have problems with my Twin Reverb, but the tech tells me he can't do anything till Monday at the earliest. I decided overnight that since I have a day and not much planned, I should see what I can do. Frankly, I hate working with this kind of stuff, but I figure I should try to cover as much ground as I can before the meter starts running with the tech. I procrastinated almost all day, and finally got around to moving the microwave and other stuff off my kitchen table, which is about the only work space I have available in this studio apartment. I got as far as moving the head onto the table, my Ampeg cabinet for testing under the table, and a guitar on a stand to test with. First thing I did was try to duplicate what I thought was wrong yesterday. What puzzles me is that the Normal channel now sounds okay, but when I plug into either of the inputs into the Vibrato channel, there's the same really ugly distortion I heard yesterday. I didn't get any further because my second ex-wife called and we spent about three hours gabbing on the phone (before my cell battery ran out, lol) and it's late enough that I can't do much more testing until a more reasonable hour tomorrow. Knowing what I know now, I think the logical think to do is dismount the chassis and have it upside down on the table where it's easy to start swapping tubes. Since the Normal channel sounds okay, I know the power tubes are okay and what I'll be doing is substitutions of the preamp tubes. That's a real bear when the chassis is in that tight head cabinet, but it won't be too bad with the chassis out so I can see what I'm doing. I bought two new Groove Tubes 12AX7's from Long and McQuade last summer for V1 and V2, so an easy start with be using the proven-good tube from V1 in the Vibrato channel/V2 to see if it's faulty. If it's not, it becomes a bit more challenging because I no longer have any of my backup tube stock. I like Rob's suggestion of using the 12AT7 from V3/Reverb driver as a substitute for V7/Phase inverter, although since the Normal channel isn't distorting, I suspect V7's okay. If the phase inverter isn't the issue, I can only assume it's the Reverb driver V3 or Reverb return V4. I'm pretty sure V4's also a 12AX7, but I'll need to search online to find out if I can use a 12AX7 as a temporary substitution for a 12AT7 in V3, unless somebody out there knows and can advise me. So, things are now on hold till tomorrow, but I'd like to see if I can resolve things before Monday when the amp goes to the service shop. If only one channel is bad, a preamp tube is the most likely culprit and should be ready to isolate |
|
|
|
Post by infant on Mar 6, 2022 16:46:25 GMT
Swap V1 and V2 and see if the distortion follows the tube. Then you’ll know which tube is bad.
You can swap the 12AT7 tubes if you want but if it’s determined that the distortion is in the preamp, then leave them be. Just get a new phase inverter tube when you have some spare coin.
Have you ever had the filter caps replaced? If you don’t use the amp a lot, they tend to dry out and the electrolyte will start leaking out until they blow up and make a mess of the amp. They are located under the stamped steel “doghouse” on 5he chassis. You can check them to see if they are leaking or bulging but do not touch any of the leads as they can hold up to 500V and can kill you. I always keep one hand in my pocket when going into the doghouse. I replace mine about every 10-12 years.
Finally, all 12A_7 tubes are interchangeable. Many people use 12AY7, 12AU7 and 12AT7 as preamp tubes to tame their amps. They all have different outputs with the 12AX7 being the strongest. I prefer to keep my amp as stock and so I don’t play around with changing them. I have heard that if you only use the vibrato channel, you can just pull the normal channel tube (V1) to give you some cleaner headroom. Same same can be said if you only use the normal channel. If you don’t use the reverb or vibrato on the amp, swap out the 12AX7 tube from one of those circuits with the bad tube. You never know but the bad tube may work fine in the vibrato or reverb circuit.
I’m not an electronic tech by no means but I bought 2 tube amp books when I first started buying tube amps 30 yrs ago and studied up on them. Aspen Pittman, the founder of Groove Tubes, wrote “The Tube Amp Book” and Gerald Weber, the founder of Kendrick Amps, wrote “A Desktop Reference of Hip Tube Amps”. These are both great books for learning about tube amps. They have schematics for almost every vintage tube amp and they both helped me out when I rebuilt my sons Silverface Champ.
Good luck!
|
|
|
|
Post by spellcaster on Mar 6, 2022 19:02:18 GMT
 I spent this morning fiddling while I was doing my laundry and got everything torn down and hooked back up with the open chassis on top where I can see things properly. It sure is tight trying to get the nuts undone for the chassis straps on one side. I need to have three of the power tubes removed and there's just enough room to slide the tip of my social finger up there to hold the nut when I unscrew the bolt. It's even tougher going back together....The only way I've been able to do this is to wrap my social finger in masking tap, sticky side out, stick the nut exactly in the center of the finger tip, and very slowly and carefully drop the chassis screw through the chassis strap, the cabinet top, and then through the chassis. If everything's perfect and the stars are aligned, sometimes you get lucky and get the nut in the right spot to start by twisting the screw counter-clockwise until you feel the thread drop into place so it can be tightened. I started diagnosing by duplicating what I had last night....verifying that if the guitar's playing plugged into either the first or second input of the normal channel, things sound okay. And, with the guitar plugged into either the first or second input of the Vibrato channel, things sound distorted. Next step will be to reverse the 12AX7's in V1 and V2 and see if the problem follows the tubes or remains consistent.
|
|
|
|
Post by spellcaster on Mar 6, 2022 19:47:40 GMT
Okay, tried reversing V1 and V2. The distortion is consistently in the Vibrato channel. So, I think it's safe to assume that both the new 12AX7's in V1 and V2, and the NOS Rogers 12AT7WA in V6 (phase inverter) are okay. So, that leaves V3 (reverb driver), V4 (reverb return/2nd gain stage), and V5 (tremelo oscillator) as possibilities. I'm reasonably confident that the V5 tremelo tube (NOS Rogers 12AX7) isn't in the circuit if the tremelo's not being used, and I have the footswitch unplugged, so that circuit should be dormant. Process of elimination tells me I must have a bad V3/reverb driver or bad V4 Reverb return/second gain stage tube if it's a tube problem at all....which I still don't know.
I don't have any spare tubes, so I'm thinking probably I should exchange V1 (known good Groove Tube 12AX7) and V4 (NOS GE 12AX7) and try using the Normal channel to see if it still works using the GE tube. And.....The Normal channel still works fine, so I assume the problem wasn't in V4. Just for fun, I'll try the Vibrato channel again and ensure that it's still distorted. And, yes, the Vibrato channel is still distorted. So, I think I've narrowed the problem (if it is a tube problem) down to V3/reverb send. V3's got a Groove Tubes 12AT7 in it.
I'm in a bit of a quandry.....My options here are either to swap the 12AT7 in V3 for a known good 12AX7, although I'm not sure what'll happen with a mismatched tube in there, or to swap the two 12AT7's between V3 and V6.....and I have no idea what might happen to the amp if I end up putting a bad 12AT7 into the phase inverter. I did some reading last night, and I think I remember reading that you can swap a 12AX7 into a spot needed for a 12AT7, but it won't sound right because the tube is 'mis-biased'. That seems like it might be the least likely thing to cause any harm, at least as a short-term way of testing. I want to go back and make sure I was reading the online info correctly before I try it. If anybody reading this in the next few minutes knows what the best course of action is, please feel free to chime in and share your knowledge. In the meantime, I'll go back to searching on the net and see if I can find any more information before I blunder ahead.
(Edited to add:) I've sent a message to my tech today on Facebook, hoping he can recommend the best way to proceed, and also asked the question on TDPRI, knowing there are lots of tube guys who know Fender amps there, and somebody may take pity on me and answer the question quickly. All I can do now is hurry up and wait.
|
|
|
|
Post by infant on Mar 6, 2022 20:21:53 GMT
Swap the two 12AT7 tubes with each other. It won’t do any damage.
|
|
|
|
Post by spellcaster on Mar 6, 2022 20:41:19 GMT
Ah, thank you, Rob. I'll do as you suggest.
|
|
|
|
Post by infant on Mar 6, 2022 21:05:05 GMT
Do you have any wooden chopsticks or popsicle sticks? The next thing to do would be to check for a bad solder joint in the vibrato preamp. Attached is a schematic for a Twin Reverb. I’ve marked the vibrato preamp in Blue. Disregard the red markings, they have nothing to do with what we are looking for. Use the chopsticks, with the amp turned on, and poke at the components and wires to see it any of them make noise. Remember, keep one hand in your pocket.
|
|
|
|
Post by spellcaster on Mar 6, 2022 21:08:58 GMT
I've tried exchanging V3 and V6.....No change. The Vibrato channel is still distorted. The Normal channel is still working. I guess it's safe to say that this isn't a tube problem, since I've tried swapping all the tubes and nothing seems to change. I could turn the chassis over and go looking (but not touching) to see if I could find a fried-looking resistor or a bulging/leaky capacitor, but beyond that, it won't be a problem I could solve. So, I guess the amp's going to the tech this week and he can work his magic. I'm sure getting tired of dealing with all the hassles of owning a tube amp. It might be time to start thinking about owning something solid state.
|
|
|
|
Post by infant on Mar 6, 2022 21:09:49 GMT
Also, to ensure that the problem isn’t in your reverb or vibrato circuits, pull out those tubes. It won’t hurt 5he amp. I think the sound will still bypass these circuits. See if it still distorts. Let me know what happens.
|
|
|
|
Post by spellcaster on Mar 6, 2022 21:10:54 GMT
Do you have any wooden chopsticks or popsicle sticks? The next thing to do would be to check for a bad solder joint in the vibrato preamp. Attached is a schematic for a Twin Reverb. I’ve marked the vibrato preamp in Blue. Disregard the red markings, they have nothing to do with what we are looking for. Use the chopsticks, with the amp turned on, and poke at the components and wires to see it any of them make noise. Remember, keep one hand in your pocket. I'm having trouble seeing the attachment you mentioned. |
|
|
|
Post by spellcaster on Mar 6, 2022 21:18:39 GMT
Rob, I tried your suggestion, pulling V3, V4, V5. The Normal channel still works. The Vibrato channels is silent. I kind of expected that because the second gain stage for the Vobrato channel is dead with no tube in V4. I might still try your suggestion using the one hand/chopstick method if I can find a chopstick....Not all that likely since I don't eat Chinese food, and the chopsticks that were in my parts drawer went away when I gave away all my guitar parts.
|
|
|
|
Post by spellcaster on Mar 6, 2022 23:03:40 GMT
Well, there's six hours of my life I'll never get back, lol. I finally got the amp reassembled and ready to for service. I guess I should feel gratified that I at least tried to solve it, but as I suspected, this is a job for somebody that knows what they're doing. The amp had virtually zero hours since it was retubed, so I had a feeling this would be an internal issue. I'll let you guys know what it finally turns out to be.
|
|
|
|
Post by infant on Mar 6, 2022 23:29:19 GMT
Sorry….I forgot to attach it! Doh!  |
|
|
|
Post by spellcaster on Mar 6, 2022 23:38:52 GMT
Sorry….I forgot to attach it! Doh! <button disabled="" class="c-attachment-insert--linked o-btn--sm">Attachment Deleted</button> Lol, thanks. The amps all back together now, but while it was still apart, I used a light and a magnifying glass and carefully scanned the whole chassis. There were no apparent failed components, and all the solder joints looked shiny. Hopefully the tech will find the issue. |
|
|
|
Post by infant on Mar 6, 2022 23:51:59 GMT
I still want to know where you got the blackface faceplate for your Silverface amp. I’d love to put a “blackface” panel my Deluxe Reverb seeing as the anodizing on the Silverface faceplate is starting to oxidize on mine.
|
|
|
|
Post by spellcaster on Mar 7, 2022 0:31:37 GMT
I still want to know where you got the blackface faceplate for your Silverface amp. I’d love to put a “blackface” panel my Deluxe Reverb seeing as the anodizing on the Silverface faceplate is starting to oxidize on mine. I bought all my upgrade parts from Marsh Amps. I looked at their page, but it looks as if they don't carry faceplates anymore;
I got curious and took a look because I couldn't believe it was hard to find Fender faceplates. Apparently there are copyright issues that are preventing reproduction faceplates now. I did find a bit of info - Apparently original and reissue faceplates for Deluxe Reverbs are not interchangeable. I did find this....
|
|
|
|
Post by infant on Mar 7, 2022 14:05:13 GMT
Yes, I heard this too. It’s too bad because my DR is in near mint shape and the panel is the only thing that looks a little “ratty
|
|
|
|
Post by spellcaster on Mar 7, 2022 23:26:26 GMT
I took my amp to the tech this morning to drop it off for service. I expected to just drop it and run, but he wanted to bench check it while I was there. Having described Normal channel fine, Vibrato channel distorted, I expected him to be able to duplicate the symptoms I'd experienced. He plugged into the Normal channel, and as soon as the amp came off Standby, there was an immediate dull roar in the background that sounded like a bad cap unloading. Other than that, the signal was clean. He plugged into the Vibrato channel and the same cap-unloading sound appeared, but the signal, again, was clean. He tapped all the preamp tubes but didn't have anything change, but when he tapped the power tubes, one of them seemed to have a sensitivity, which he speculated was an issue with a faulty tube socket. The cap-unloading noise diminished over a period of about two minutes and eventually, the amp sounded fine. He just shrugged and said he'd test it a few times from a cold start, remarking that sometimes these issues are temperature-related. When I think back to the hours I spent yesterday, which really would have been chasing my tail, I'm glad I just sent it to him which was my original intention. I told him that there was no rush to finish it because I can't pay him till I get my pension check on the 29th.
|
|
|
|
Post by spellcaster on Mar 7, 2022 23:41:54 GMT
Yes, I heard this too. It’s too bad because my DR is in near mint shape and the panel is the only thing that looks a little “ratty I agree. I've seen a minty old faceplates, but most of them, even on an otherwise well-kept amp, tend to look like they've been through a great war. The faceplate on mine, when I originally bought the chassis on eBay, looked discoloured, oxidized, and bent.
A new faceplate makes all the difference in how an amp presents itself. It surprises me that Fender doesn't offer them as a part.
|
|
|
|
Post by infant on Mar 8, 2022 0:26:37 GMT
I took my amp to the tech this morning to drop it off for service. I expected to just drop it and run, but he wanted to bench check it while I was there. Having described Normal channel fine, Vibrato channel distorted, I expected him to be able to duplicate the symptoms I'd experienced. He plugged into the Normal channel, and as soon as the amp came off Standby, there was an immediate dull roar in the background that sounded like a bad cap unloading. Other than that, the signal was clean. He plugged into the Vibrato channel and the same cap-unloading sound appeared, but the signal, again, was clean. He tapped all the preamp tubes but didn't have anything change, but when he tapped the power tubes, one of them seemed to have a sensitivity, which he speculated was an issue with a faulty tube socket. The cap-unloading noise diminished over a period of about two minutes and eventually, the amp sounded fine. He just shrugged and said he'd test it a few times from a cold start, remarking that sometimes these issues are temperature-related. When I think back to the hours I spent yesterday, which really would have been chasing my tail, I'm glad I just sent it to him which was my original intention. I told him that there was no rush to finish it because I can't pay him till I get my pension check on the 29th. Or until you unload the Gibson cabinet now that you’ve picked up the other 15” cab. I wouldn’t look at the number of hours that you spent yesterday as a waste of time. It’s called troubleshooting and sometimes, you will find a simple fix and save yourself some money. |
|
|
|
Post by spellcaster on Mar 8, 2022 23:27:34 GMT
I got a call from the tech today and ended up going to pick up my amp. He had cleaned and retensioned the pins on the output tube sockets, and he diagnosed an intermittently bad 12AX7 in the reverb return/second gain stage amplifier circuit (V4). He replaced it with a new JJ and the amp sounds great again. He was really fair on the cost of service too...Charged me 50.00 parts and labour, so there was just enough left in my bank account to pay him now. I'm going to hook the amp up tonight and spend a bit of time listening.
|
|
|
|
Post by infant on Mar 9, 2022 5:10:24 GMT
I got a call from the tech today and ended up going to pick up my amp. He had cleaned and retensioned the pins on the output tube sockets, and he diagnosed an intermittently bad 12AX7 in the reverb return/second gain stage amplifier circuit (V4). He replaced it with a new JJ and the amp sounds great again. He was really fair on the cost of service too...Charged me 50.00 parts and labour, so there was just enough left in my bank account to pay him now. I'm going to hook the amp up tonight and spend a bit of time listening. That’s great!! $50 is a great deal as JJ tubes cost about $25 CAD to start so he only charged you another $25 to diagnose, repair and retention the sockets. 👍👍👍👍👍 |
|
|
|
Post by infant on Mar 9, 2022 5:26:30 GMT
Yes, I heard this too. It’s too bad because my DR is in near mint shape and the panel is the only thing that looks a little “ratty I agree. I've seen a minty old faceplates, but most of them, even on an otherwise well-kept amp, tend to look like they've been through a great war. The faceplate on mine, when I originally bought the chassis on eBay, looked discoloured, oxidized, and bent.
A new faceplate makes all the difference in how an amp presents itself. It surprises me that Fender doesn't offer them as a
after seeing your old faceplate, mine doesn’t look too bad. There’s a few scratches on mine and a little “ding” on the edge but I guess it still looks pretty decent….however not as clean and shiny as the new Fender’68 Custom Deluxe Reverb. Besides, the “Pull Boost” on the vibrato channel volume no longer exists as I replaced that pot last year with a standard pot. The pull boost just added a few decibels of hiss this is my amp  |
|
|
|
Post by spellcaster on Mar 9, 2022 5:40:33 GMT
I think your amp looks great, Rob. It's not nearly as beaten and battered as so many of the older amps get after they've been gigged for a while.
I got my amp hauled up from the car and hooked up, but I'll save the trial here at home for tomorrow when I'm not so tired. I did get to listen to it in the tech's shop when I picked it up and it sounds great. I was impressed all over again just how quiet the noise floor is even at higher volumes. By the way, the tech played it through a 12" Celestion and it was really a fine sounding speaker. I don't foresee going out and buying any more cabinets at this point, but if I were going to, that Celestion would definitely be one I'd consider.
|
|
|
|
Post by infant on Mar 9, 2022 16:39:52 GMT
I think your amp looks great, Rob. It's not nearly as beaten and battered as so many of the older amps get after they've been gigged for a while. I got my amp hauled up from the car and hooked up, but I'll save the trial here at home for tomorrow when I'm not so tired. I did get to listen to it in the tech's shop when I picked it up and it sounds great. I was impressed all over again just how quiet the noise floor is even at higher volumes. By the way, the tech played it through a 12" Celestion and it was really a fine sounding speaker. I don't foresee going out and buying any more cabinets at this point, but if I were going to, that Celestion would definitely be one I'd consider. It’s a ‘79 and the previous owner basically kept it in his basement. I’ve basically done the same until about 5 years ago. My son took it one time to go and jam and it came back with a slight “pull” on the grill cloth….pissed me right off! I replaced the speaker with the hemp cone Cannabis Rex by Emminence. It really tamed the “paint peeling” treble and tightened up the “farty” bottom that I was getting with the original Pyle speaker that came with it. I had it serviced late in 2019 as I wanted to make sure it was gigworthy. I had all the electrolytic capacitors replaced, new 12AX7s in V1 and V2 and new 6V6 power tubes and had it rebiased. When I picked it up the tech told me that it was the best sounding Deluxe Reverb that had ever come across his bench and asked if I would be willing to sell it as he new some guys who would be really interested. That was all I needed to hear to know that I had one of the “special ones”. |
|
|
|
Post by johnreardon on Mar 9, 2022 17:48:00 GMT
I think your amp looks great, Rob. It's not nearly as beaten and battered as so many of the older amps get after they've been gigged for a while. I got my amp hauled up from the car and hooked up, but I'll save the trial here at home for tomorrow when I'm not so tired. I did get to listen to it in the tech's shop when I picked it up and it sounds great. I was impressed all over again just how quiet the noise floor is even at higher volumes. By the way, the tech played it through a 12" Celestion and it was really a fine sounding speaker. I don't foresee going out and buying any more cabinets at this point, but if I were going to, that Celestion would definitely be one I'd consider. I have a Celestion Vintage 30 in each of my two cabinets. Great sounding speakers. I used to have a Celestion Gold, which was amazing. |
|
