Maybe not. Weird. It looks better before uploading it?

I think this one is better.

You don't need there to be crossover distortion to find the sweet spot with the ammeter. The scope is just there for detail. Honestly you just need to monitor current flow with a meter then find the sweet spot and back it of a touch. Try it on some amp one day and you'll see just how easy it can be.

MEF will be back up I am sure of it.

The Enzo method is good enough to keep your job. You dial in crossover distortion of a test signal 1k by making the bias pot set to coolest setting. You will need to measure current with an ammeter as you adjust the bias pot. Now turn up the bias pot while watching the scope wave form and the ammeter. As you increase the bias you will see the wave form become more linear on the scope. There will be a sweet spot where raising the bias pot causes the ammeter to register current flow. You will see the current meter start to rise and when it is in that sweet spot you just back it down a hair. So it will be idle and safe.

There is a lot of information about this on MEF but it's CURRENTLY down.

Acoustic 470 or 450?

I should make a few and put them up on eBay! At the same time I should make myself a more suitable one as well. The LBL's are easy to make but I have to wonder about liabilities selling something like this? We'll compared to the Chinese crap main's wiring I have seen I am sure anything I build would be better.

Please post the forum where they posted about it. I would like to read what they posted.

Oh yeah The Dude said it. Scrape off the green stuff and bridge the crack. I sometimes use a piece of stiff wire to make the connection with solder. If it is a big trace I have even used scraps of solder wick and that works amazingly well.

Remove the speaker from the amp. If there is DC voltage leaking into your speaker it may damage it. Next use a multimeter set to read dc voltage across the speaker leads. What does it read? We don't want to accidentally short them together and definitely remove the speaker. If it is not DC voltage on the output it may be something right in the preamp. But first test the power amp side to be careful.

Q11 & Q12 caught my eye too but understanding each transistors role in a circuit is difficult. I don't know what Q11 & Q12 actually do but it never stops me from guessing. Are they current limiting the circuit in case of overload? Not sure if they are pre drivers for the outputs or what. I'm curious to know how bad of a guesser I am. 

The 30 vac refers to the AC voltage but after rectification to DC voltage it will be higher. 30vac * 1.414 = 42.42vdc.

There are amps out there like Mesa boogie simulclass where they have a pair of each EL34's & 6l6's. But these are pairs of tubes and the amp is designed to allow this arrangement. No amp that I know of uses one of each different tube as a pair. It just doesn't work in a balanced way. People spend all day trying to create a matched pair of tubes for their amp circuits. EL34 tubes require a power transformer that can handle the current demand which is more than a 6L6 demands on a circuit.

Just a quick reply but perhaps study up on crossover distortion in a solid state amp. The symptoms you describe are similar. Play soft and it sounds fine. A hard attack signal will reveal the crossover distortion. It might be biased cold but that might not be what is going on. Just something to consider.

Quote from: mr.death on May 22, 2024, 04:11:09 PM

Quote from: DrGonz78 on May 19, 2024, 12:19:47 AMWhat method did you use to make the conclusion that the transformer is shorted?

I watched a dlab vid. He shows how to check the transformer. I did his test and it failed. Also when I turned the amp on I could hear the transformer frying, bubling sound. Its toast.

Okay just had to ask or we might have let someone trash a power transformer. I like D-Lab a lot and he is a solid provider of good services. I never heard a bad transformer make bubbling noises. I mean I have heard a buzzing sound from old worn out transformers. But most bad transformers and we're talking fuses blowing when turned on.

I mean from the description of what caused a failure of the amp we have little to go on. What is the status of the main transistors? We have no idea what traces you bridged. With so little information I personally can't say go buy a transformer. With more information then I might have more of an answer.