1963 AC30 copper with panel integrated top boost MAINTENANCE

[VintageCharlie]

Hi folks,

i just got an original 1963 VOX AC30 copper panel amp with panel integrated Top Boost. I got it for around 1000gbp. Electronically it is nearly untouched - just a couple resistors changed. Everything else, including the electrolytics of the Jurassic age are still in there.
It has original Albion transformers, the mains transformer has had a bit of a wax leak - i suppose nothing major, as i have seen pics of much more drastic cases that still got the job done well. I had a test-drive with it tonight and most of it went surprisingly well.
I was told by the seller that the vibrato channel does not work. In fact the channel itself works rather fine and sounds great, but the vibrato/tremolo effect probably doesn't. I'm not sure - don't have the foot switch yet and didn't want to play around with it's connection wires without really knowing, what i am doing. The normal channel and vibrato channel (even though without the effect) are a blast. Easily Marshall territory gainwise, even more than my jtm 45/100 clone. Chimey, defined and bright, just as i hoped it to be. NO (perceivable/disturbing) GHOSTING - that was a surprise to me, as i've read AC30's are masters in this (and honestly, even though i love many 60's amp sounds, i do hate ghosting like hell). It is quite silent - a bit of background hum. Some hiss, when volumes are dimed and treble is set high/ cut is set low - but again, i think these are good levels, considering the brightness of such settings. Really fantastic for an amp from 1963 that has seen quite some use, but very little care.

Now to the issues:

- Vibrato/Tremolo effect (according to seller) not working.
- Not mentioned by seller: Brilliant channel has very low gain. Maxed out it is still totally clean (top and lower inputs) and too low volume for it to be right (from what i know, the Brilliant channel is the top boost channel and should have the most gain). Maybe a tube or something else...
- Amp had some crackles while warming up - for a minute or so - they were not affected by any of the channel volume controls - all were turned to 0 initially. Then the crackles that were not overly loud disappeared and did not come back during 30 mins of testing. It's not a pot - pots didn't affect it. Could it be those stone-age electrolytics in the filter sections crapping out?
- Mains transformer has had a slight wax leak, as mentioned. Is this something to be concerned with? Is a new mains transformer a good idea, a necessity? Or is this not a sign of impeding armageddon? How dangerous is a PT failure for anything else in the circuit?
- This is my first VOX and this might be a major fail question - treble and bass controls affect the Brilliant channel (which is what i expected, as afaik - normally it's the top boost channel and only that one has these controls (at least in the factory Top Boost add-on versions)), as well as the Normal channel - this i did not expect. Maybe a mod has been performed - i haven't looked at the input wiring yet. Or maybe the panel integrated top boost amps should be like this?
- The amp is quite dirty. Transformer laminations are in very good shape - almost no noticeable rust at all. Very little rust on the chassis, but the steel chassis part is covered with a black/grey gooey layer of dirt/dust/dead insects and other fun stuff. It is sticky - not easy to clean off. Almost like the layer that you get on things close to a gas heated oven - that gas residue type of thing. What is the best way to clean this stuff off without damaging the surface, coating, metal, etc.? Some kind of alcohol? (in Latvia, we cure most of things in life with alcohol - so it must work with amps too!)
- It looks like at some point there might have been a bit of a campfire around the last output tube in the chain - or maybe it is a hot spot and there is more sign of heat accumulation over the years.
- The 50ohm resistor (in the 63 era it was 50ohm vs 82ohm, right?) has been changed - so i guess there has been an incident at some point that involved the PT, the output tubes and that 50ohm resistor (i am a dumbass in electronics, but i have read that some AC30's go through a scenario, wehere an output tube fails, the amp starts to run hot, the PT heats up (and often releases it's waxy goodness all over the place) and the 50ohm resistor then goes. If this is a standard scenario, might be that this one has went through that too. What consequences does it have in the long run? Anything to look out for in particular?

Love the sound of the amp and, other than these issues, it seems to be very potent and i'm sure it will be even more of a gem after a proper restoration and some love.

Please share your wisdom on these amps, as you see, i am a VOX noob and would be grateful for any advice and shared experience about the issues that i've mentioned and then some that i might not foresee.

See pictures below.

Thank you very much fort any help/comments!

Kind regards,

VintageCharlie



[img680]http://i802.photobucket.com/albums/yy30 ... 0023-1.jpg[/img]

[img680]http://i802.photobucket.com/albums/yy30 ... 0024-1.jpg[/img]

[img:680:1024]http://i802.photobucket.com/albums/yy30 ... C_0016.jpg[/img]

[img680]http://i802.photobucket.com/albums/yy30 ... C_0015.jpg[/img][/img]

[billyz]

I would replace the power supply electrolytics. Also move the cathode bias resistor away from the parallel cathode capacitor. It will cook it and cause failure. After that as needed.

[Masco]

The treble and bass controls should only work w/ the brilliant channel.
You amp has been modified from stock. I see a cap in the photo on the plate of the brilliant channel pre to ground that doesn't belong.
Find a Vox worthy tech to reverse the mods and do what Billyz says.

[Stevem]

Your noise at warm up is likly preamp tube related.
If they test good gm wise, live with the noise, as the tubes if still N.O.S likly sound great, just do not bang the amp aorund ( or take it out of a cold environemnt as fire it right up) as many times this noise is the start of a tube(s) going microphonic.

[gingertube]

I did a restore of one of these old copper panel jobs recently.

Tremlo/Vibrato did not work and then the owner blew the entire power section.

Rebuilt the power section.

The Tremlo/Vibrato turned out to be simple. One of the B+ dropping rsistors to the 12AU7 was open circuit (R42 = 22K). Also found 3 or 4 other of the old carbon composition resistors which had gone rediculously high in value (like X2 or more original).
AND
A wire in the wrong place from a previous repair attempt by someone not up to the task. This one took me hours and many expletives to find.

Cheers,
Ian

[VintageCharlie]

Thanks for all the advice and input guys!

I have to get some cash together and order some of the parts that have to be replaced. I have most of the spares at hand - some cc resistors that are WAY off spec, and some that are above 20% tolerance (8-10 resistors) etc.

I'm not turning it on anymore before it is returned back to spec as i do not want a cataclysm.

Btw. in regard to the initial higher level of hum and the sporadic medium loud crackling noises (they sound similar to the noise that you get from a bad guitar cable contact) that it produced for about 1-2 minutes during warm-up - if it would be a preamp tube issue, would it still appear if ALL of the channel volumes are turned to 0 (this is what i tried when testing)? Or might this point to the output tubes?

[Stevem]

I would also change that output cathode resistor to a five watt higher rating while moving it and going to a non inductive type is not a bad move either.

[jaysg]

The Tremlo/Vibrato turned out to be simple. One of the B+ dropping rsistors to the 12AU7 was open circuit (R42 = 22K). Also found 3 or 4 other of the old carbon composition resistors which had gone rediculously high in value (like X2 or more original).

The way the phase shift oscillator works, I would expect problems with carbon comp resistor drift, which is always upwards.

[rooster]

What are you using for a camera? I wish your pics were better quality and I also wish you could take a picture of the PT and OT from the exterior side for documentation reasons.