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Post subject: Hot Rod Deville Troubles
Posted: Sun Mar 31, 2013 11:18 pm
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Buddy brought me a Hot Rod DeVille he bought from some cat on Craigslist. Not surprisingly it has issues. :| Crapped out on him during his first gig with it...

He told me it blew the fuse during the last song of his band's set. I checked the tubes, all three 12AX7's were toast -- I've never seen preamp tubes deader than these. I figured they were stock though as they were a mix of Fender-branded Groove Tubes.

My over-eager friend had a gig the next day and me, being busy with personal issues, wasn't thinking too hard and I gave him a cautious go-ahead to take the amp back with some new tubes and a new fuse. The JJ Tesla 6L6GC's he supplied wouldn't bias properly, starting at 22mv or so and only allowing me to bias as high as 54mv, both sounding awful. That raised some red flags in my head but I chalked it up to a bum tube in the pair. I put in some Sovtek WXT+ 6L6's I had laying around and biased them at 69mv. It sounded as great and loud as another Fender DeVille I'm working on for another friend. Aside from tube swapping I wasn't given time to do anything else with the amp and I cautioned him to use the amp at a rehearsal, as opposed to the gig in question. He didn't heed my warning and guess what, it blew again that night.

That was Friday. I checked everything last night and ONCE AGAIN the preamp tubes are completely dead. These were brand new JJ Tesla tubes!!

The solder joints on all 5 tube sockets look terrible...dull and cloudy, mixed with burnt flux. Would a bad solder joint on one of the pins of a power tube or, say, the PI tube cause this type of failure? I've had a couple HRD's come to me with bad power tube solder joints that have taken that one power tube and the fuse with them, but never the preamp tubes as well. I would like to help my buddy avoid having to keep shelling out money for preamp tubes.

I haven't flipped the main board so I'm not sure what the 330ohm resistors look like and from what I can see without flipping the tube board the plate load resistors aren't split open,as I've read they are prone to do. The filter caps aren't leaky but the bottom half of C36 is deformed. Not bulging though, it's actually kinda flattened. I'm not sure if this is an indicator of failure or not.

Thanks! :)


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Post subject: Re: Hot Rod Deville Troubles
Posted: Mon Apr 01, 2013 12:51 am
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OilBreath, welcome to Forum on a sour (or oily) note.

IME, when signal tubes like 12AX7 and 12AT7 short out in bunches, you have BIG issues. My guess is the heater line (which draws the most current) or the main B+ line feeding the anodes --- or both are shorting to ground somewhere and drawing a lot of current through the tubes. Which are acting as $$$ fuses, at the moment.

The sockets maybe toasted. As well as any resistor or cap nearby.

Also, the JJ 6L6GC has not been kind to me. I have had QA issues. With unstable biasing and arcing. But, this alone should not fry the 12AX7s and 12AT7s. You may now have shorting issues with the PT or output tranny.

I am not too familiar with the HRD. Not as much as others on this Board. But, I would NOT try any more tubes --- until you can yank the chassis out and throughly inspect the circuitry.


Good luck! Looks like time to break out the DVM and do some section-by-section troubleshooting. Prolly starting from the PT and working through the PS caps to the main B+ feeds onto the output tranny and anodes. Plus, the heater lines. These are the big current carriers in most amps. And cause the biggest catastrophes, when their circuits short-out.


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Post subject: Re: Hot Rod Deville Troubles
Posted: Mon Apr 01, 2013 2:07 am
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BMW2002Ti wrote:
IME, when signal tubes like 12AX7 and 12AT7 short out in bunches, you have BIG issues. My guess is the heater line (which draws the most current) or the main B+ line feeding the anodes --- or both are shorting to ground somewhere and drawing a lot of current through the tubes. Which are acting as $$$ fuses, at the moment.

Good luck! Looks like time to break out the DVM and do some section-by-section troubleshooting. Prolly starting from the PT and working through the PS caps to the main B+ feeds onto the output tranny and anodes. Plus, the heater lines. These are the big current carriers in most amps. And cause the biggest catastrophes, when their circuits short-out.


+1

My money's on a P/S related issue.

Arjay

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Post subject: Re: Hot Rod Deville Troubles
Posted: Mon Apr 01, 2013 3:44 am
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Thanks! I'm by no means a professional, really. I have been doing LOTS of reading and hands-on work ever since my friends and acquaintances got wind that I have even a passive understanding of amps late last year. I still have lots to learn though. That said, please have patience with me. :mrgreen:

By P/S you are referring to the filter caps, correct? A lot of the technical short-hand on forums eludes me. I drained the filter caps and I can push the outside film a bit inward on C36, the .22uf 500v capacitor I mentioned before. Clearly that's not right and it needs to be replaced. One of my primary questions in the original post was whether or not a single bad filter cap in the amp could cause issues such as this, or would it be more prone to produce issues such as fizzy ghost notes, excessive and or oscillating hum etc?

No 12AT7's in the DeVille either, at least by design. Just 12AX7's.

For what it's worth the brand new JJ's in question were not physically damaged. The filaments still heat up inside the glass but just read pitifully low on my little Dyna Jet 606. The two times the amp died were not explosive firework shows, either. There doesn't appear to be any scorching or splayed-open components anywhere on the board. Well, tube board anyway. Again, I'm in the process of disassembling the amp now though so I may yet find something ugly on the reverse side of the main power board.

On that note, BMW2002Ti, I assume the "toasting" would not be literal and instead would be something found only by taking components out of circuit and reading them one-by-one with a DMM as you suggested, correct?

Hope I don't come off as clueless. I'm eager to learn what needs to be done.


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Post subject: Re: Hot Rod Deville Troubles
Posted: Mon Apr 01, 2013 9:20 pm
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Anybody else out there that can offer ideas? :|

I'm ordering new caps. I figure at worst I'll save some somebody more knowledgeable a bit of work if I can't fix the issue plaguing this amp.

The 330ohm power resistor on R79 is loose on the board....it has more side-to-side play more than R78 next to it. The amp wasn't exhibiting the random channel switching, "motorboating" or other myriad of issues troublesome power resistors cause though, so I'm not sure if the solder joints needing help on R79 would cause any of this. Ordering replacements and mounting them up off the board with silicone sealer is on the "to-do" list.

I've yet to flip any boards. I'll have a more useful update later. I tried yesterday with the power board and it was giving me issues, more than the other three Hot Rod-series amps I've worked on in the past and I didn't want to break any of those crummy ribbon cables.


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Post subject: Re: Hot Rod Deville Troubles
Posted: Wed Apr 03, 2013 3:19 am
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Flipped the boards. Power resistors look good, replaced the .47 100v caps as a couple had legs that were barely connected to the rest of the cap (!!!). Waiting on a replacement filter cap for C36.

Here comes the chorus of a thousand eyes rolling in unison. :x I started on the power tube sockets and after only 5 minutes a pad was lifted off the board by my solder sucker. Completely. It's one of the pins that isn't sitting on a trace, number 6 underneath the tube. This is a dummy pad, correct? Would I be ok ignoring this pad or do I need to jump it to an adjacent pin or component? Where to?

I can see I'm not getting a whole lot of help here. That's fine as I realize I more or less blew off two knowledgable posts and insisted the fault lie in anything but what those members suggested. That said, I tested the preamp tubes again, giving them a few minutes to burn in and only one of them is actually reading in the red, not all three as I initially said. It's possible my friend got a bad tube. So, all the tubes are actually functioning. Filaments burn and they are structurally together. Because it's looking like no tubes were harmed either physically or electrically when the fuse blew would it be safe to say this rules out a transformer issue?

Thanks again, everyone. I hope somebody can take the time to hold the hand of a young guy looking to get into repairing this stuff. It's not my first amp but perhaps I've just been incredibly lucky and this is where I really need to buckle down and take my knowledge further.


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Post subject: Re: Hot Rod Deville Troubles
Posted: Wed Apr 03, 2013 5:23 am
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Yes, pin 6 is not used for a 6L6, no need to worry about it.

When you re-tubed, what type of fuse did you use for replacement? Many times, a blown fuse indicates a problem in the power supply section, such as the caps, or in the output section, such as output tube(s). It is not unusual for some tube types to have a low bias in this amp, not an indication of bad tubes, just that some tubes are rated at a very low current draw. The cap that you said was soft/deformed/flattened should definitely be replaced. If you are troubleshooting, you should also monitor the current of both output tubes, not just the test point, to make sure that both output tubes are functioning properly.

Have you checked all of your power supply voltages and compared them to the schematic?

Original:
http://support.fender.com/schematics/guitar_amplifiers/Hot_Rod_DeVille_schematic.pdf

Version III (Black face plate):
http://support.fender.com/schematics/guitar_amplifiers/HotRod_DeVilleIII_410-212_schematic_Rev-B.pdf

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Post subject: Re: Hot Rod Deville Troubles
Posted: Tue Apr 16, 2013 3:23 am
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Howdy shimmilou! Reviving this thread after letting the amp sit and giving me time to mull over what may be wrong with the amp.

The tubes in question that would not bias correctly were JJ Tesla 6L6GC's. Currently I have a pair of Chinese Shuguang 6L6GC's in it. Some people love them, some people hate them. Me, I love 'em!!! Super cheap and durable. :mrgreen:

I put a fast blow 3A 250V fuse in. Have been using one all along.

I pulled the boards and replaced the filter cap that appeared to have suffered some sort of internal leak with a brand new replacement.I also re-flowed the solder joints on the power tube sockets, preamp sockets and the power resistors. Standard procedure.

I then put the amp back together and nothing, no sound. I also noticed that now V3 wasn't even burning. I tried a couple different tubes and all had the same result. Nothing. Feeling defeated, I left the amp sitting for a week and told my buddy he'd have to take it to a real professional when he had the money.

Well, I took another stab at it a couple nights ago, reflowed the joints on V3, put a tube in and success!!! She roared. Now, was it blowing fuses still? I played the amp for a combined 2 hours and no fuses have blown. However...

After 10-15 minutes of playing with the amp's volume in the 6-7 region (ridiculously loud, I know) the output would suddenly get fizzy and fade out. I peeked in the back of the amp and V3 was out again. I put her in standby, carefully twisted and pushed the PI tube back into the socket and it started burning again. A-ha!!! Went over the joints one more time with a magnifying glass and re-tightened the pins. The bass must be so heavy from this amp that it was causing the tube to become dislodged. :shock:

I'll know if this fix worked tomorrow, but it seemed promising after 20 minutes of playing.

I believe that the amp was initially blowing fuses all along because the power tube sockets needed attention. One power tube would shake loose and trip the amp's mains fuse as a result. The owner of this DeVille has a Hot Rod Deluxe that had the same problem and I fixed that one too. I don't know why it didn't occur to me.

I also want to note that in the end 2/3rds of the NEW JJ Tesla preamp tubes my buddy bought were bum out of the box. The amp was not draining them of their current or physically destroying them. :evil: I may stop suggesting my friends buy from ARS here in Van Nuys, CA.


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Post subject: Re: Hot Rod Deville Troubles
Posted: Tue Apr 16, 2013 4:23 am
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I bought an american BD a few years ago (1993) which is also a brick. Very low volume with lots of distortion on the clean channel. If remember correctly, the drive channel sounded correct as to volume, but was also overly distorted and not usable. Not tube problems.
It sits there now to remind me of the Fender promise to reliability.
Luckily, my drri with it's printed circuit board has had no such issues.


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Post subject: Re: Hot Rod Deville Troubles
Posted: Tue Apr 16, 2013 4:39 am
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yomammaaho, sorry to hear that. Being as old as it is have you looked inside for leaky filter capacitors? It may be due for a recap in general.


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Post subject: Re: Hot Rod Deville Troubles
Posted: Wed Apr 17, 2013 5:07 pm
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OilBreath wrote:
yomammaaho, sorry to hear that. Being as old as it is have you looked inside for leaky filter capacitors? It may be due for a recap in general.


Thanks for that idea.
I would neverhave suspected that pwr. supply filter caps could be bad after only 16 or 17 years (since I purchased it and found the problem). Hell.........I've got an old Alamo Capri that still works flawlessly with it's original cap can.
But since the blond exterior looks like brand new and I purchased it used off an old man who probably never used it, that could very well be the problem.........as I understand none-use also helps break down caps.
When I get time, I'll dive into it.


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Post subject: Re: Hot Rod Deville Troubles
Posted: Thu Apr 18, 2013 3:56 am
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Amp was still crapping at rehearsal. The PI tube was still becoming dislodged from the socket. I've tightened the sockets twice now....shrugged my shoulders and lined the inside of the black plastic insert surrounding V3 with some thick 3M tape. This seems to have cured the problem.

yomammaaho wrote:
OilBreath wrote:
yomammaaho, sorry to hear that. Being as old as it is have you looked inside for leaky filter capacitors? It may be due for a recap in general.


Thanks for that idea.
I would neverhave suspected that pwr. supply filter caps could be bad after only 16 or 17 years (since I purchased it and found the problem). Hell.........I've got an old Alamo Capri that still works flawlessly with it's original cap can.
But since the blond exterior looks like brand new and I purchased it used off an old man who probably never used it, that could very well be the problem.........as I understand none-use also helps break down caps.
When I get time, I'll dive into it.


If your amp is that old it is probably well-due for service, even if it has been played at lower volumes. Fender unfortunately chose very cheap components for this amp and the filter caps are well-known for becoming leaky.


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Post subject: Re: Hot Rod Deville Troubles
Posted: Thu Apr 18, 2013 4:00 am
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OilBreath wrote:
Fender unfortunately chose very cheap components for this amp and the filter caps are well-known for becoming leaky.


Fender uses those very same IC electrolytics in their high-end pro tube and custom hand-wired models as well.

:shock:

Arjay

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Post subject: Re: Hot Rod Deville Troubles
Posted: Thu Apr 18, 2013 4:32 am
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Retroverbial wrote:
OilBreath wrote:
Fender unfortunately chose very cheap components for this amp and the filter caps are well-known for becoming leaky.


Fender uses those very same IC electrolytics in their high-end pro tube and custom hand-wired models as well.

:shock:

Arjay


Distressing. :(


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Post subject: Re: Hot Rod Deville Troubles
Posted: Thu Apr 18, 2013 3:35 pm
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Retroverbial wrote:
OilBreath wrote:
Fender unfortunately chose very cheap components for this amp and the filter caps are well-known for becoming leaky.


Fender uses those very same IC electrolytics in their high-end pro tube and custom hand-wired models as well.

:shock:

Arjay


Someone eluded in another thread concerning Fender's "business model" pertaining to Fender refusing to offer stainless steel frets.
And then I unfortunately buy a Blues De-brick which DID have a broken ribbon wire (I went around it and soldered a bypass onto the if board.........but That was'nt the problem.
IF it turns out to be bad caps.........or the pwr. tranny taken out by them, then it's yet another example of what I suspect Fender's "business model" really is.

Get the product out the door designed to hopefully..............(just) outlast the warranty. And the customer returns for a new guitar and/or amp.

I know......I know. There's prob. more to it. But not entirely IMHO.
I suspect my spec. edit. wine red drri may buck this trend, but that's prob. because I rarely take IT out of the house.


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