April 8th, 2009, 11:15 PM
A Vox is a Vox, I guess ...
Was playing around tonight after band practice and my AC15 handwired just flat quit. Tubes still glowing, pilot light on and all.
Had it opened up (top boost side) in pentode (15 watt mode) for 30 seconds. Glorious sound. Yes, it smelled hot, but didn't smoke (I've fried enough speakers in my life to know they actually can catch fire--I once almost set a cabinet on fire with a Sunn Model T ...).
My AC15H1TV has 3 month old Ei El84s. Nice sounding tubes.
Is this a fuse? Rectifier (EZ81)? Tube? Any ideas? Anyone?
I'll start the process of elimination tomorrow. God, I love this amp, and we Vox lovers take the good with the bad, don't we?
April 9th, 2009, 12:08 AM
hmmm... we can probably diagnose this, but need a few more details. Are you getting any sound at all? All the tubes are glowing?
Usual advice is to first eliminate any other possibilities... no pedals, check guitar and cable in another amp.
April 9th, 2009, 01:30 AM
Start with checking whether the speaker cable is plugged in, or whether one of the leads fell off on the speaker terminals. If that's alright, the fuses are not blown and the tubes seem lit up, try changing all the tubes including the rectifier.
April 9th, 2009, 07:08 AM
Thanks for the quick replies!
Yes, I checked the speaker leads and chassis connection last night. I also eliminated my pedalboard and went stright in to the amp. Both channels dead.
The tubes are all still glowing as well. Anyone know the fuse locations inside this amp?
I have heard that rectifiers can go in this model. Tubes next.
April 9th, 2009, 08:22 AM
I had a rectifier tube go out on me and it was like turning off the amp....
no sound, I can't remember if the other tubes were still glowing...
I replaced the rectifier tube and been fine since... that was about four years ago...
April 9th, 2009, 10:05 AM
Does the Vox have two fuses? I had an EL84 that tested good on a tester, and would work at low volumes, but it must have had an intermittent internal short because it popped the output fuse on a Dr Z. Playing loud must have spiked the tube to short temporarily. The tubes and pilot would all stay lit even though there was no output because the main fuse didn't blow and because this particular tube wasn't actually "blown".
April 9th, 2009, 02:04 PM
Well, Now I'm stumped. Or cooked, one or the other ....
Replaced HT fuse, tried ampp without rectifier, fuse didn't blow, so I thought I had a bad EZ81.
Put a new one in, powered up, and it went off like the 4th of July!
Now it's completely dead~ no pilot light, no glowing tubes, nothing. Dead. And the fuse looks perfect.
Guess it goes to the shop now...
April 9th, 2009, 02:13 PM
It could still be a bad power tube.
The HT fuse will go but the heaters and pilot will light if a power tube pines for the fjords.
If you have another coupla of fuses, try putting the other rectifier back in, but pull out the power tubes with a new HT fuse in. If no fireworks, turn it off and see if the HT fuse is ok.
If so, suspect one of the power tubes..
The power tubes are the number one culprit in whacking the HT fuse..
April 9th, 2009, 03:39 PM
Ok ... tried that, and still no pilot. Nothing. Am I missing another fuse somewhere?
April 9th, 2009, 04:38 PM
All dead and no pilot = one or more mains fuse gone. There are probably internal fuses too.
But beware - something must be causing the rectifier and fuses to blow.
If you are not au fait with the insides of a valve amp, leave it to the expert at the shop.
April 9th, 2009, 05:20 PM
Since you got fireworks when you tried another rectifier, perhaps the rectifier was not indexed right in the socket. There are five fuses total according to the schematic. assuming this is the schematic that applies..
April 10th, 2009, 01:48 AM
I'll be darned -- AC15's use 5Y3 rectifiers now? :shock:
April 10th, 2009, 07:39 AM
Thanks for the schematic link!
However it's not for the AC15H1TV (it doesn't have a standby switch).
The rectifier is an EZ81, looks just like an EL84. I'm guessing there must be some other fuses somewhere, as I tried two different HT fuses, put the old rectifier back in, and fitted a pair of JJ EL84s I had ...
nothing. dead. No pilot. Flummoxed, I am.
By the way, I like the sound of the Ei tubes in this amp, but may not go back to them. Although for as much kudos as the JJs get here, I've fried one of them already too.
(My tech seems to ALWAYS replace every tube in the amp, including the preamp tubes. I asked him to PLEASE leave the EF86 alone, as it is an NOS (Miniwatt) that cost $50! It did fix the microphony in that channel, though.)
April 10th, 2009, 08:41 AM
The other fuses are inside..
I love the sound of Ei tubes too, the EL34 is the best ever for marshalls, but the Ei production is no more, and the tubes only sound great for a relatively short time, as they tend to poo out pretty early compared to many others.
I hope the Ei factory gets going again.
April 10th, 2009, 08:49 AM
You need to have a tech look at it.
April 13th, 2009, 10:51 PM
Wanted to thank everyone again, and just say that I got 'er running again today.
For anyone who has one of these, there is a mains fuse at the power cord input. I didn't see it until I removed the chassis to look for more fuses. Replaced the fuse (same kind as for the HT fuse), put in the old EZ81, my spare set of JJ EL84s, and it lit right up!!!
Later, I went and paid too much for a pair of Groove Tube EL84-S tubes. I did this because they seem to work well--they sound good and hold up pretty well.
For the record, I'm a pretty big fan of Groove Tubes, at least the EL84S tube, as I have had very good reliability with this tube. I know that this model is a relabeled JJ--however, my Mayfly AC15 knockoff fried a JJ at full power at two weeks of age. The GTs have taken the strain.
My AC15H1TV fried an Ei the first time I lit it up real good. We'll see if the GTs hold on when I crank the Vox--which if you didn't already know does a good OVEN imitation!:lol: