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Vantage t50r guitar amp

My friend has had a Vantage T50R amp for several years, but it hasn't been working for a long time. He was going to get rid of it, so I said I'd take it off his hands. It's a 112 (8Ω) dual channel tube combo, with 4x EL84s and 3x 12AX7s and reverb. From what I gather, it's the same amp as the Seymour Duncan 84-40 (Owner's Manual PDF), rebranded for Vantage, making it a 40W, with a tone (apparently) somewhere between Fender and Vox.

I plugged the amp in and hooked up a guitar, and could just barely hear some sound coming through the speaker amid lots of hum and some crackle. I jiggled the cord in the input, getting nothing different, and tapping the housing just resulted in some reverb ping and more hum. I took a look around back to check the tubes; the power tube on the far left was lit up quite bright, the middle two not so much, and the far right looked pretty much dead. I swapped the two on the ends, and the tubes lit up as before, suggesting the issue is the tubes themselves and not the circuit/sockets.

I picked up a matched quad set of EL84s to see if I can get the amp running again and replaced one of the 12AX7s from the preamp that wasn't lighting up with an old one from the tremolo circuit in my Twin Reverb... unfortunately, that didn't seem to fix the problem, though the new power tubes all seem to be glowing to the same extent, as are the preamp tubes. I suppose I'm going to have to take the amp out of the chassis to see if there's anything obviously dead in the circuit (and maybe tighten up the input or something)... but amps can be pretty dangerous to poke around in when you're not really experienced (there are some pretty strong voltages in there, and strong capacitors to supply them), so there's not a tonne I can do at my experience.

I'd love to hear this thing in action Razz

2 blog comments below

Yep - you need to methodically trace the current through the circuit with a tester. I would start to draw-up a circuit diagram by tracing.
Here are the circuits for the VOX amps - you might find one similar (I don't know the T50R I'm afraid).

also this site might help
Bikerman on Sat May 05, 2012 9:26 pm
Thanks, Bikerman.
I finally had the energy/time to pull the amp out of the cabinet and take a look at the components... got definite confirmation on the Seymour Duncan connection, it's built with a Seymour Duncan 412480 Rev. A circuit:

I gave the board a once over visual inspection, but don't see anything obviously untoward. All the capacitors are still sealed, there are no burned resistors, the solder points seem to be solid, etc., but I haven't hit it with the multimeter yet, and I hesitate to (amplifiers can kill, after all, and I have 0 experience).

I did contact Seymour Duncan and they sent me schematics for the transformer connection for the Rev. B of the circuit, and a schematic for the Rev. C board... hopefully they're not too different from the Rev. A in my amp. If nothing else, they should help the technician I bring it to, if I bring it to someone.

Now for a photobomb of the internals of the amp!

Ankhanu on Fri May 25, 2012 6:44 pm

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