Vox Climax (v125 combo) restoration project

AC4, AC10, AC10 Twin, AC10 Reverb Twin, AC15, AC15 Twin, AC30 Twin, AC30 Super Twin, Top-Boost, Non-Top-Boost, AC50, AC100, 710, 760, 7120

Vox Climax (v125 combo) restoration project

Postby namke on Wed Mar 05, 2014 10:24 am

Hi (New user here)

I've just acquired an early-80s Vox Climax combo amp in a particularly sorry state; an associate of the previous owner took wire-cutters to the amp's guts and removed (and sold) the transformers, tubes and large caps. The amp then spent 5 years in a shed, so, this might be more than just a simple restoration :lol: . I got the amp for free - so the price was right!

Anyway, the tubes and caps are easy enough to source and replace, but the transformers I think will prove more difficult (I'm currently looking out for spares/repair V125 heads for example).

The only schematic I can find is for the V125 head which, although closely related, is not the same as the Climax:
  • The front end is different - Climax has the (apparently awful) 'distortion' circuit
  • The combo has a speaker attached (along with a switch - what does that do?)
I'd be extremely grateful for any information which might help me with the above 'open issues' - my first task is to trace out the PCB and check that what's there is still functional!

Thanks for reading!
namke
Peasant
 
Posts: 9
Joined: Wed Mar 05, 2014 10:07 am
Location: York, UK

Re: Vox Climax (v125 combo) restoration project

Postby frankc on Thu Mar 06, 2014 10:40 pm

The Climax and the V125 heads are successors to the AC120Twin, and the circuit is closely related. The AC120 has the distortion circuit, and they probably all share the same transformers. Great amp, the AC120. I sold mine, but regret doing so. I liked the distortion. It has a dirty fuzz like character. The AC120 circuit is easy to find, so try that.

/Frank
Vox AC30, Vox Conqueror, Vox Defiant, Vox Pathfinder, Vox AD120VTH, Vox 710, Selmer Treble'n Bass, Selmer Thunderbird Fifty, Yamaha G100,http://www.etcetera-music.eu/public/instruments/Vox/
frankc
Page
 
Posts: 299
Joined: Mon Jun 18, 2001 7:01 am
Location: Denmark

Re: Vox Climax (v125 combo) restoration project

Postby namke on Fri Mar 07, 2014 10:29 am

Thank you. That's a good tip about the AC120 - I will check out the schematic.

I'm now just playing a waiting game for the transformers (I can't afford to buy new replacements, I'll have to wait for a spares/repair V125 to come up)

Perhaps I'll just use it as a cab for the time being!
namke
Peasant
 
Posts: 9
Joined: Wed Mar 05, 2014 10:07 am
Location: York, UK

Re: Vox Climax (v125 combo) restoration project

Postby namke on Tue Nov 11, 2014 10:24 pm

SO, it's been a while :)

Anyway, last week a chassis from a V125 (head) came up on eBay, and it's now mine; I also bought a almost-full complement of valves to go into it too. The past week has been spent checking, double-checking the chassis and I've now brought it up and it's functioning… kinda.

What's happening is the volume is fading in and out; doesn't matter which input I use. Looking on the web it seems that this is generally a symptom of failing power tubes, but since they're new I feel it unlikely (yes, I know that tubes can be DOA). I'm now thinking that perhaps the big smoothing caps aren't doing their jobs (they're still original, so there's a good chance that they're out of spec by now I guess).

Does this sound reasonable? I think new caps are the way to go regardless, it's just a case of whether there's going to be another cause of the volume problem.

(One of the things I'd like to do is trace out the Climax's input circuit, since it is different from the V125 — regardless of what the schematic says! No 'distortion' control on the V125, and two discrete inputs for normal and brilliant, rather than shared on the Climax).
namke
Peasant
 
Posts: 9
Joined: Wed Mar 05, 2014 10:07 am
Location: York, UK

Re: Vox Climax (v125 combo) restoration project

Postby pdf64 on Wed Nov 12, 2014 12:30 am

Smooth fading in and out is characteristic of an intermittent heater connection.
My band:-http://www.youtube.com/user/RedwingBand
pdf64
Knight
 
Posts: 1243
Joined: Thu Dec 14, 2006 9:55 am
Location: Staffordshire UK

Re: Vox Climax (v125 combo) restoration project

Postby namke on Wed Nov 12, 2014 7:55 am

Ah! Thank you — that's something to look for then :)
namke
Peasant
 
Posts: 9
Joined: Wed Mar 05, 2014 10:07 am
Location: York, UK

Re: Vox Climax (v125 combo) restoration project

Postby dlvoots on Wed Nov 12, 2014 8:33 pm

namke wrote:Does this sound reasonable? I think new caps are the way to go regardless, it's just a case of whether there's going to be another cause of the volume problem.

Hi, and welcome!

You're on the right track. Check out pdf64's recommendation with an intermittent heater. You might even be able to see the filaments on one or more tubes lighting up and then winking out. I used to work on some old data processing equipment that used tubes -- since there were several hundred of them in the box, one of the diagnostic magic tricks was to pop all of the covers off and look for dead or intermittent filaments right off the bat.

Your comments about new caps are spot on. Electrolytic caps are chemical based, and will start to slide downhill in performance in as little as half a dozen years, especially if the amp has not be played on a regular basis. The heat of being plugged in and running tends to preserve the electrolyte inside. If the chassis has been sitting in a cold shed for a number of years, there is an excellent chance that one or more caps have simply deteriorated and gone over the edge. Don't diagnose anybody -- just replace 'em all first. THEN diagnose what ever issues come up after that.

A third possibility is that one or more resistors have gone "sensitive" over the years and now want to change value depending on how hot they are. You could have one that works great when cold, and then goes wacky as it heats up. The circuit stops working correctly, the resistor cools back down, and as it cools, the circuit starts working again.....and on and on.

You don't need to "shotgun" resistors (i.e. replace them all) the way you do with caps, so the diagnostic order of the day would be to investigate the heaters first and do a cap job second. Then, if the bug is still there, trouble shoot it down to the gain stage and then to the component within the stage that is bothering the amp. The symptom you described is that it doesn't matter which input you use. That means the bug is probably beyond the preamp in the signal chain. Possibly in the mixer (assuming there is one), phase inverter, or power stage itself.

Dave
dlvoots
Squire
 
Posts: 744
Joined: Tue Aug 30, 2011 10:28 pm
Location: Dallas, Georgia (USA)

Re: Vox Climax (v125 combo) restoration project

Postby namke on Wed Nov 12, 2014 11:00 pm

Thanks Dave,
I made some more progress this evening: I reflowed all of the solder joints on the tube sockets, in case there was a dry/intermittent joint there (in fact all of the heaters are glowing, so I think that's all ok actually).

What I did start doing was measuring the power-supply levels across the board. The main B+ voltage is sitting at 495v (the schematic (http://www.korguk.com/voxcircuits/circuits/v125lead.jpg) indicates that it should be 485v), there are then series-dropper resistors all the way down to the 300v used by the pre-amp stages. I discovered that the voltages weren't dropping as much as the schematic indicated, and eventually I've found that the final dropper resistor (22k) was reading 4.5M! This meant that the bottom of the dropper chain was joined to ground through the power-supply smoothing cap (32µF + 32 µF). This would possibly explain the 'oscillation' as the capacitor tried to react to the DC. I found that when I measured the voltage across the dead resistor, the amp would 'come alive' again (presumably the internal resistance of my multimeter was shunting the capacitor).

So, I'm going to pick up a replacement 22k resistor tomorrow, and see what happens. Hopefully the new caps will arrive as well :)

Seeing as this is my first experience 'playing around'** with valves, it's all been very interesting and an education!

All the best,

john..

(** Yes, not really playing when there's just shy of 500v kicking around in there — I'm keeping my left hand firmly in my pocket!!)
namke
Peasant
 
Posts: 9
Joined: Wed Mar 05, 2014 10:07 am
Location: York, UK

Re: Vox Climax (v125 combo) restoration project

Postby namke on Thu Nov 13, 2014 11:09 pm

:D So, I soldered in the replacement 22k resistor, and the amp is now working without the fading — YES!

Now I'm not sure whether the inputs are behaving correctly; the 'Normal' input sounds Ok, but the 'Brilliant' input is pretty thin (that may be by design, I've not heard what it *should* sound like!).

Re-cap job over the weekend I think…

john..
namke
Peasant
 
Posts: 9
Joined: Wed Mar 05, 2014 10:07 am
Location: York, UK


Return to Vox

Who is online

Users browsing this forum: Google [Bot] and 3 guests