Peavey Delta Blues issue...won't work

[jesseallen]

Peavery Delta Blues issue revisited....

Hi all, sorry for digging this up from the depths but Google brought me here and I have had a problem similar and wanted to see what everyone thinks.

Bought the amp new in '94 and have used it a fair amount, retubed it several times, new speaker a few years back, it's generally in good shape. I have an electronics background, including repair of tube gear (worked in repair dept. of Sam Ash for several years fixing this kinda stuff) so I have a decent clue about this stuff lol.

Last night first tune of the gig, semi full house and the amp quits, no sound. Pilot light on, all tubes appear to be lit just not as bright as normal. Switch from creative brain to technical brain and begin troubleshooting:
-Plug straight into amp, bypassing pedalboard/wireless unit. Nothing.
-Plug into effects return to bypass preamp section, nothing.
-Backup guitar, nothing.
-Spare cable, nothing.

Start wiggling tubes around to see if any weren't fully seated and noticed they were lit up more than before and not only that, I had sound! Thinking something wasn't seated, I plugged back in and away I went.
First song, halfway thru the sound fades and dies out. Look in back, tubes barely lit again. At this point I recall two things:
-These amps have the tube heaters wired in series.
-I have old spares in my gig bag.

I quickly replace the power tubes, everything lights up and we have sound!!! Play the rest of the 3 hour gig with no issues except that the old tubes sound worn but not horrible. Ordered new tubes as soon as I get home from gig at 3am.

Popped it open yesterday and just took a quick look for any hotspots or burn marks around connectors and resistors etc... (didn't pull the pcb's out) but everything looked fine. Next step would be to check solder joints. After I put it all back together I played the snot out of it for a good 90 minutes at gig volume (and beyond) trying to make it cut out but couldn't.

My questions to those out there that have experience with this platform of amp:
-Since the amp worked fine after replacing the power tubes, could there be anything else to look at that caused it? Power tubes are in my opinion the weakest link of the chain and do go wonky, so maybe it was just a bad tube.
- Thermal cycling? Cold car to warming up to hot at gig and back to cold car.....
-Good time to swap out filter caps? It is close to 25 years old and all original, however they all appear to be fine, no bulges or ooze anywhere.
-Any tips for extracting the pcb assy. out of this amp? I hear they can be tricky.

Apologies again for revisiting this and sorry for the long post. Thanks in advance, I appreciate it.

This has become a "pre-historic" issue but I understand the frustration. As stated in many of the replies the problem is probably the jumper wires between the tri-fold pc boards. The wire that is used to connect the pc boards together is very thin and when the amp is on and driven the solder connection melts thus causing the amp to quit. When the amp cools down again the connection will re-connect and the amp starts working again. These amps run very hot. I finally had mine fixed (knock on wood) by my amp repair guy putting on a heavier gauge wire between the boards and so far so good. I also turn the amp off at set breaks thinking this might help a little. This was my experience anyway....good luck

[DRH1958]

I finally had mine fixed (knock on wood) by my amp repair guy putting on a heavier gauge wire between the boards and so far so good.

It's not really a heavier gauge wire issue as opposed to a flexibility issue. The existing wire's gauge is fine. It's better to replace them with stranded wire jumpers so there is less vibration transmitted to those solder connections, especially if it has been taken apart a time of two. There's less stress on the connections when handling the folded PCB sections. Stranded wire will help with this issue.

[Dr. Jimmy]

Again, I apologize for digging up an old thread.

I was actually toying with the idea of replacing those jumpers with stranded wire (of the same gauge) for more stability. I plan to remove the pcbs to check the solder anyway so I may as well do this while the boards are out. Forgot to mention that while I had it out, I cleaned and retensioned the sockets.

As I mentioned, my initial inspection showed no component damage, I rang out the screen resistors, the heater circuit resistors and bias circuit resistors (in circuit) and they were all pretty much on the nose, which again leads me to believe the issue was nothing more than a tube that flaked out on me. To be somewhat preventive, I ordered up replacement electrolytics to have on hand if I feel motivated enough to change them when I have it opened up.....

[km6xz]

Using stranded wire will help a lot, and you almost have to repair them all because of any movement as needed to get the boards out, breaks additional jumpers.Peavey redesigned later models in that series to not require those jumpers..
The main killer of filter caps is heat and if they are isolated from the heat of the tubes, they can last a long time, far longer than the internet theories of replacing electrolytics as PM automatically. Most tubes and most caps replaced still have many years life left in them. The habit developed due to finding a few going bad so assumed that all went bad at about the same time which is not true, and because it became part of internet folklore. Test them, if the ESR is reasonable and you are not getting any increased 120hz hum, you can leave them in for another decade or two. There are electrical indications when they are starting to deteriorate such as higher ESR and lower capacitance so if those are still good, it is not an indicator they are going bad.

[Dr. Jimmy]

Thanks for the replies here, they're much appreciated!

The caps all look fine and there's no odd/excess noise that would lead me to think they are worn or heading south, I was just thinking since it's an older amp and I'm going to have it open that I would swap them out. Maybe I will just leave them be and hold on to the new ones for later when I do need them.

In the meantime I will check out the solder joints at R71/R72 (maybe even replace them, I have some on hand) as well as replace the jumpers associated with them. Waiting on a new set of tubes as well, I checked my records and the old ones were about 6 months old and had been used quite a bit over that time (including transit/playing on some very cold days) so they were due to be replaced and I still think the issue may simply be a tube that was on its way out.....

[Dr. Jimmy]

Ok, an update!!!

Had the day off so I dug into this guy and got the pcb's out, not as hard as I thought, and was able to examine the solder side. Believe it or not, the jumpers looked ok, with maybe 2-3 showing very faint cracks in the solder joints. As a precaution, I resoldered all the jumper connections, plus a few others that looked borderline. On the tube pcb, I completely resoldered all the pins on all the tube sockets, I desoldered, cleaned the flux off and resoldered all of them, I noticed a few of the pins looked less than ideal so I just redid them all.

Upon further examination I noticed that the board under R71 and R72 (3ohm 5W in the heater circuit) looked discolored, not burnt, but showing signs of overheating, so I replaced both resistors and left the new ones about 1/16" off of the board to enable some airflow. Screen resistors R43/R53 looked ok, but I replaced them anyway since it seemed like a bad tube is what caused all of this.

More examination showed something really odd. R66 (15ohm 5W in the bias circuit) had what appeared to be a greenish oxidation on both leads, so I took it out and replaced it. After taking it out I rang it out and it was reading intermittently very high/open. I then replaced the caps (C45/C46) that also make up that part of the circuit.

Since I had it opened up, and had the forethought to order the parts, I replaced all the filter caps, I purchased the amp new in '94 and have used it quite a bit so I figured it was due, or would be due soon, so I swapped them out.

Cleaned all the pots, cleaned and retensioned the tube sockets, threw in new set of tubes and buttoned it all back up. Played it at gig levels for about an hour and it all seems well, a lot more clarity and high end, probably due to the new tubes. Either way, I'm going to burn it in over the next 24 to shake it down a bit and see how it goes.....