volume loss on my 74' Model t

[django7866]

I was in the middle of recording when I had a sudden drop in volume. I had my model t running through a 16 ohm cab, turned up to 6. The amp was distorted and it would not get any louder from 3 to 10 on the volume. When this happened I checked to see if I had the ohm select switch at 16 ohms, which it was. Then I started to phase out pedals thinking it might be a battery going dead, that was not it. Then I tried running the guitar strait that was not changing the the situation. So I started to think it was the output of my guitar so I tried it through a different amp, so it is not my guitar. I took it in to an amp tech and he check it out and said he could not find anything wrong with it. He clean and re-tightened the tube sockets, re-biased the tubes, and cleaned the pots. I tried it out this pass weekend. I let the amp warm up for about 5 minutes. turned the stand by off and started playing my guitar, which at this point I just ran the guitar strait. I was sniffing around to make sure nothing was burning, when I notice 2 of the power tubes(closest to the output transformer) were running hotter then the other 2. It sounded the same as it did when I loss volume initially, but more distorted.The drummer in my band has a friend who has a tube tester and can re-bias tubes so on Sunday we took my amp over to him and spent about 2 hours testing and re-biasing the tubes. He played through 2 different cab and still the same problem. He seems to think it is one of two things, either the caps are going bad or the out put transformer is starting to go bad. We looked at the guts and he noticed some of the caps have been replaced, but not all of them There was no burn marks and it looked real clean.  I would like to see what you folks have to say to see if maybe it could be something else. If anyone has had this happen to them, could you let me know what remedied the problem. I am hoping it is just the caps, as that would be the cheaper one to fix. If in fact it may be the output transformer does anyone know of where to get them for cheap?
Thanks for any info or help it will greatly appreciated.  

[doomedfuzz]

Find a good tech who has been in the biz for years -- the reason I say this is that if they are a Mercury Magnetics re-seller, the program they have for them allows for them to get some deep discounts if they've bought a ton of product through the years. That way you can get one for cheap if the tech is cool and not worried about making some extra scratch on top of his cost. I am going to upgrade my newer Orange this year to Mercury and my guy told me about their reseller program and that he gets things super cheap and would just pass the direct cost over to me.

The other choice you have is to have the transformer rebuilt, and again Mercury can do this. However, it's not cheap. But for a classic amp if you want to keep it as stock as possible, it's not a bad idea.

Good luck!

[biltmore]

If your output transformer needs to be replaced, I'd go through Heyboer to get it rewound, rebuilt, ect. Myself, and quite a few others here in town have been really pleased with their work. They're cheaper than Mercury too, which is quite nice. I'm not a fan of Mercury at all really. I find most of their stuff to be really overpriced.

[mckinnon audio]

  Hi there,I think the key to your problem is that 2 outputs are running hotter than the other 2,could be :bad tubes,bias problem,screen resistors,power supply.I think that if your output trans. was on the way out,it would be blowing fuses by now.Good luck,Mel.

[django7866]

Thanks for the help! I took it to a reputable tech, Still waiting to hear back as to what the problem might be. There has not been any problems with the fuse blowing. I had the tubes checked and all of them are good, the guy that tested them said that the tubes were biased to run really hot. after he tested them he biased them to the spec on the schematic.When he tested the amp through each of his cabs the tube were all glowing the same. if it is the output transformer I will definitely look into getting it re-built or re-wound.
 

[johnk]

if your tubes checked out okay, then sounds like an output tranny to me. i too have dealt with heyboer, and they are great to deal with and can rewind your's back to spec.

[Isaac]

I don't agree. I don't see how the output transformer could affect the output tubes differently.