Is my O.P. transformer fried

[timwhite76]

I build pedals, and repair guitars. Ive also done some mods, and replaced trannys with custom ones, but Im by no means an expert, just follow directions well and have a good soldering hand.
I got a Fender Deluxe H.R recently ( i know, they're not great). I played it for a day and a half, and it worked fine. Then i came home from work, turned it on (in standby) because a guy was coming by to pickup a pedal i built for him. When I turned off the standby, the amp made a crackling noise, then nothing. I pulled the fuse, it was gone. Like an idiot, I just put in a different fuse (using the same recommended value 3A 250V). When i turned it on, ( i took the back panel off before hand so i could see into it), it made the same crackling, but before the fuse blew, I saw inside the output transformer spark, and a some smoke.
I was planning on replacing the output transformer anyway, just not yet. Now, alas, I think I probably have to. Am i correct in believing the OP tranny is fried? Im going to bring it to a tech, because he'll put in a Mercury Magnetics, and it will cost me only $25 more than if i just ordered it myself and had to do the work.

Is there some components i should check before I drop the amp off? If its something else that can be fixed w/out replaing the tranny yet, id rather do that. I know Im going to have to replace the Power tubes.

Also, the kid i got the amp from NEVER changed the tubes, and i believe NEVER had them rebiased.

[Firestorm]

How did you see inside the OT? That would have to be one heck of an arc! Before you take the amp in for service, pull all the tubes, replace the fuse and try powering up again. If the fuse still blows, drain the power supply, disconnect the center tap of the OT (CP18) and measure the resistance between CP18 and CP19 and between CP18 and CP20 (those are your OT primaries). Readings should be similar. For the OT to take out the fuse, it probably has to have done more than just open up; it likely has to be shorting, so check the resistance between CP18 and the speaker jack ground. This amp has protection diodes on the OT so be sure to put the red lead of your DMM on CP18. Speaking of which, it's also possible one of these diodes (CR4 and CR5) has shorted. That would account for these symptoms.

[timwhite76]

Thank you, I asked this on another forum and just was flamed, but without any help. Ill do all of this when I get home. Would you mind if i PM'd you withb the results?
I didn't see the actual spark, just the flickering light in the tranny that corresponded with the crackling. Problem is, the fuse must have blown before w/the previous owner, because I saw the fuse I pulled out was a slow blow instead of fast. So I assume some unneeded damge must have occured.

[timwhite76]

When you say all the tubes, are you saying ALL the tubes? Preamp and power tubes?

[Firestorm]

Fuse should be a slo-blo; initial current surge when the amp powers up will usually take out a fast fuse. Pull all the tubes; you want to unload the amp as much as you can. If the fuse doesn't blow with no tubes, then you can put the preamps back in and see what happens then. Most common cause of a blown fuse is an output tube short, then a bad PT, then maybe a bad rectifier diode, then the OT. So I'm not particularly convinced the OT is actually the culprit. I don't know what you saw, but an OT short is rarely visible. If your DMM has a diode test function, when the amp is discharged and center tap lifted, check CR4 and CR5. A short there will pop the fuse. PM me if you want.

[timwhite76]

I don't think the OP tranny was the cause of the problem, I think it was a victim of the issue. There wass definitely sparks coming from thr OP. Transformer, it could have come from somewhere above the tranny in the chassis. Ill haveto take it apart and take a look. Id like it to be something you mentioned & would love if the transformer is still operable. So ill obviously need to bleed the filter caps first

[Gibsonman63]

Possibly from a power tube arcing? It's fairly common and can take out the fuse... and probably sounds crackly while it happens. When you pull the power tubes examine the sockets for carbon traces.

[timwhite76]

Okay, will do. If that is the problem, how difficult is the fix? BTW, again, thanks for your help. I posted this on another forum, got about 10 reponses, all indicating Im an idiot (though Ive given adive for guitars and effects that manufacturers have actually had to come onto the forum to tell them to settle down because I was right), none of them came close to giving me any useful info. Interesting how the most vocal ones, have the least to say. This very well could be the problem. Would it require replacing the sockets?

[timwhite76]

Thanks to BOTH of you.,

[timwhite76]

So i should replace the fuse with a slow blow? I figured this would allow more damage, but you sound like you know more than I. anyone needs advice on their guitars, IM here, also building custom boards, hit me up, need NOS parts; CA3080A metal can chips for Dyna Comps, CA3080E for ROss/keeley, JRC4558d for TS808's, NOS tubes, theres a guy two blocks away that has EVERYTHING. though he's expensive. He wanted $350 for 2 RCA Blackplate 6L6 or 6V6, I cant remember. I just remember my girlfriend has an old silvertone amp with the same tubes, working, tht she paid $200 for the whole amp

[Gibsonman63]

I would start with Firestorm's suggestion. Pull the tubes and see if you can power up. If so, the power down and put, your preamp tubes back in and try again. If it still powers up, but in a pair of power tubes that you know are good.

If there are carbon traces on the power tubes from arcing, they are conductive. Replacing the tube sockets would be the best fix. If you are used to working on pedals, it should be fairly easy. But it is just an educated guess on my part, so work through it systematically before you start replacing parts.

We normally don't flame people around here... unless they post that thier amplifier is better than ours and refuse to discuss it technically or post gut shots.

[timwhite76]

I will do all of these, in the order you mentioned. I have to go out and get some 6L6's though. I have none on hand, and im sure the ones in there are bad, i have to get my fathers tube checker to see. You guys have been a great help, even if it turns out that none of it works, you still have been a great help.
Ive done mods to amps, helped build one (early fender deluxe, simple circuit), replaced filter caps and tranny's. But those were done on working amps, diagnosing is a completely different beast. Im glad I logged on here adn asked. I was just going to drop it off witha tech, which in the end may happen, but Id be no worse off, that s worst case scenerio, best is its something I can do myself.

[timwhite76]

I just wish everything wasnt board mounted. I wanted to replace the pots on a Blues Jr, but that guy Bill M said it wasnt a good idea. Havent read far enough to find out why. Maybe I should get that book on tube amps. I can setup a Strat, tele, LP with my eyes closed, but amps are a new frontier. The only thing i find more difficult is certain digital effects. I have a TC Nova Delay that i want that input buffer mod done, but I cant find it anywhere online, just where to send it. Looking at that pedal, it seems like you need computer experience more than pedal or amp experience.

I have a Dumble reverb left to me in a will. I dont want my uncle to die anytime soon, but......
For now I have to just plug my Zendrive into a fender DRRI, to get close. The Hot Rod was supposed to be my beater amp, but its beating me. I traded an Egnater Tweaker, i needed more wattage. now i realize i should have kept it. But, live and learn.

[timwhite76]

Called the TV repair place down the street from me (if you can believe they still exist) the do mostly juke box repairs. ANyways, I did a transformer upgrade for them for one of their customers for free last summer. I have no other 6L6's at the house (i deal mostly with 6V6's and EL's). Asked him if he had a couple working tubes to use, just to test the amp when I think its fixed. He's giving me a couple for nothing, then said when its fixed, he'll give me a pair of NOS RCA Blackplates for $100 for the pair!
sometimes good deeds do go unpunished. Dont want those to blow though, got to fix this before i install them.

[katopan]

Best test aid you can have is a lightbulb limiter. You'll find it with a search. Acts as a current limiter for the mains going in, saves blowing fuses and lets you trouble shoot without doing any more damage.