Over excited about a new vintage AC 50 purchase.

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Re: Over excited about a new vintage AC 50 purchase.

Postby fiveightandten on Tue Jun 06, 2017 6:59 pm

Dave_in_Va. wrote:Nope. I want to get it serviced before I fire it up. If it was a Fender, which I've done before I'd order the parts and do it myself, but this is a little more exotic and I'd feel better having a Vox specialist reanimate the beast.

It looks like both fiveightandten and Blind Lemon are both familiar with these. Which one of you guys want to take a crack at it? Are both of you guys set up with tech type tools or whatever? I'm ready to Fed Ex it out anytime. I have the nice packaging it came in (all bubble wrap, no plastic peanuts) and have pulled the tubes. I also have an extra batch of tubes to send along if they're needed.

Thanks guys for all of the help. Hopefully it will live again, soon.

If you're familiar with working on amps, you'll likely be fine doing the work yourself and you have the forum here as a resource. That would negate any shipping expense and any potential shipping mishaps. It always makes me nervous shipping old amps. UPS and FedEx are animals, especially with heavy packages.

You just have to be mindful that these amps have a 115V primary. Running on today's wall voltages, some of the caps in the amp are under spec. And when biasing you have to be mindful about the high plate voltages, and the fact that the amp is most likely a hybrid fixed/cathode bias design. Other than that, a lot of what you know from working on old Fenders translates here. The Vox is just tighter to work on, due to the chassis layout and design. And they liked to twist wires and leads around the tag board terminals, so removing components gracefully is more challenging.

That being said, it's your decision. BLC is very good, knows his stuff with old Voxes, and has plenty of references of forums folks that have dealt with him. I'd bet he's built more amps than me and probably had more old Voxes on his bench than me. But I have two AC-50 heads, I'm quite familiar with them, and I do very clean work. There are likely others on the forum, as well, who can give the amp a once over and re-cap it, all with similar (read: clean and reliable) end results. I don't think any of your options are bad ones, including you doing the work yourself.

-Nick
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Re: Over excited about a new vintage AC 50 purchase.

Postby Vortexion on Tue Jun 06, 2017 9:55 pm

Vortexion's "stating the obvious" moment for this week, folks:

Dave, if you do decide to work on the amp yourself, make very sure that the PSU caps are fully discharged before you let your fingers stray anywhere near that Brimistor: its ends are live to the full HT Voltage.

fiveightandten wrote:Outside of the caps, the only thing that concerns me is the brimistor on the top of the power amp chassis. That's a heavy component, and the leads could snap from being all twisted and having it lay on its side like it is. If it were my amp, I'd likely cut it back and remount it vertically.

I'd be cautious about cutting back the legs of a Brimistor. Brimar's original advice on installation of these devices was that "at least ½ inch of wire should be left at each end before soldering to a tag" - on account of the high temperatures at which they operate.
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Re: Over excited about a new vintage AC 50 purchase.

Postby pdf64 on Tue Jun 06, 2017 10:42 pm

Vortexion wrote:...Dave, if you do decide to work on the amp yourself, make very sure that the PSU caps are fully discharged before you let your fingers stray anywhere near that Brimistor: its ends are live to the full HT Voltage...
:Zap:
Damn right!
Brimistors are great but the way they are mounted on an AC50 creates a death trap; even just a stray guitar string poking through the top grille could contact them.
My band:-http://www.youtube.com/user/RedwingBand
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Re: Over excited about a new vintage AC 50 purchase.

Postby fiveightandten on Wed Jun 07, 2017 3:28 am

Vortexion wrote:I'd be cautious about cutting back the legs of a Brimistor. Brimar's original advice on installation of these devices was that "at least ½ inch of wire should be left at each end before soldering to a tag" - on account of the high temperatures at which they operate.

Good point, they do indeed get hot and definitely need some space. I mounted mine to a newer terminal strip, above the solder lugs. The leads are actually about 1/2", though I had not heard of that official recommendation before, thanks for the info.

I just get nervous when I see heavy components on long leads, springing like a diving board every time the amp goes over a bump in the car on the way to a gig. I've had a few amps over the years loose sandbox screen grid resistors while in transit on tour and that sort of thing.
pdf64 wrote:Brimistors are great but the way they are mounted on an AC50 creates a death trap; even just a stray guitar string poking through the top grille could contact them.

And the first filtering stage too! Seeing the amount of dust and crud on some of the chassis tops of these amps, I wonder if the Brimistor has been responsible for many/any fires.
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Re: Over excited about a new vintage AC 50 purchase.

Postby Dave_in_Va. on Wed Jun 07, 2017 10:42 pm

Blind Lemon, I can't seem to get a PM sent to you and I'm having trouble contacting fiveightandten. Can you email me? Thanks.

davekurzman

AT verizondotnet
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Re: Over excited about a new vintage AC 50 purchase.

Postby Blind Lemon Chitlin on Fri Jun 09, 2017 7:25 pm

Dave and I have made contact and are supposed to talk by phone soon. Thanks Nick for your recommendation and nice words as well as other members. As I sit here typing this I am looking at 5 or 6 AC50 heads on a shelf in the BLC Amplitorium and I think I have at least 2 more....one being the unit that When I never could get the amp to bias properly I made what I believe to be the first cathode bias AC 50. Jim, in his book mentions these but not one has ever surfaced. When my band was active I would include this amp in my regular rotation of stage amps and always got raves from other geetar players on it's tone. I really need to fire some of these amps up....

It sounds like many of you still use the Brimisters in your amps. I have found only 2 or 3 Brimisters in my experience to still be working properly.....most will hum badly. Are you guys using the originals or is there a new replacement ? I think I remember a thread long ago about new ones that were very close to the old specs. I would like to know.

Thanks again guys !!

BLC :jam:
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Re: Over excited about a new vintage AC 50 purchase.

Postby Dave_in_Va. on Thu Jul 20, 2017 8:58 pm

Whoa........

Thanks a MILLION to Mark (blindlemonchitlin) who got this '66 up and running. Here she is an she sounds even better than she looks. I'm not kidding. The speakers are3 P12N's and sound great.

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Re: Over excited about a new vintage AC 50 purchase.

Postby Vortexion on Thu Jul 20, 2017 9:37 pm

Fixed the logo too, I see! 8)
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Re: Over excited about a new vintage AC 50 purchase.

Postby Dave_in_Va. on Thu Jul 20, 2017 11:05 pm

Yep, the replacement from North Coast dropped right in. I love it when stuff just fits without a bunch of fiddling.

I got the next to last trolly from NCM also. I had to replace the feet on the head with smaller ones but they worked perfectly also. They drop right outside of the rails.

The cab has P12N's and sounds great but I guess I'll be wondering what it would sound like with a couple of Celestion golds.

I also got a basically mint 1964 AC 10 Twin the other day from Holland. It's all original and sounds beautiful but I guess I should re-cap it.

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Re: Over excited about a new vintage AC 50 purchase.

Postby Blind Lemon Chitlin on Thu Aug 10, 2017 1:25 pm

Glad to be of service

:cheers: e.
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