Vox Cambridge 30 Reverb Twin combo mods

[dusty fretz]

Following the re-acquisition of my old Burns Vibra Artist, I decided to see if I could partner it with the same sort of gear I employed in 1964. This nostalgia-induced idea was really all about looks rather than re-creating the actual sound, which wasn't anything special as I recall, although it kept me gainfully employed!

My set-up back then was a Vox AC10 Twin combo plus the ubiquitous Copicat, but I also used a strap-mounted Topaz effects unit that delivered treble boost or tremolo. I've given up on finding a surviving example of the latter little box, while very limited cash means I can't even consider forking out around £500 for an appropriate era Copicat - the thing was rubbish back then and I know it won't be any better now! The same penny-pinching pragmatism has to apply to the Vox AC10 Twin, which was a 50-quid combo in 1964 and sounded like it, but these days this model apparently attracts almost reverential awe and equally misguided prices of about £1500!

My reality-based reluctance to play the inflated-value vintage game has prompted me to purchase a Vox Cambridge 30 Reverb Twin. I'm fully aware this circa-2000 2x10 combo is a Korean-made piece of c--p, but appearances are roughly right and therefore make it a much more attractive and affordable alternative to the 'real thing'. Unsurprisingly, it certainly looks a lot better than it sounds, but I've seen mentions of various mods that can soup up the sonic side and for comparatively little cash. While not expecting any miracles, I would like less distortion on the supposedly clean channel, along with a little more output and a tremolo that makes some discernible difference.

Can anyone on here provide the necessary info, relevant schematics etc. to achieve these aural improvements? Armed with this knowledge I can confidently then pass the task to my local amp repairer, so any help would be much appreciated.

[panchodiaz]

Hi Paul,

Let me know your email address and I´ll send all the info to you. I have one of those Cambridge TR and it sounds quite well in my opinion. I did the power mod (up to 56 watt) by myself and I think it´s not difficult to do. I didn´t change the optocoupler because my amp had that mod made from the factory.

Pancho

[Didier]

Can anyone on here provide the necessary info, relevant schematics etc. to achieve these aural improvements? Armed with this knowledge I can confidently then pass the task to my local amp repairer, so any help would be much appreciated.

I also have the documentation about the power module change, either 58W or 68W.
Another possible improvement (but more expensive) is to replace the original Bulldog speakers by more efficient ones, such as the Celestion G10 Vintage (with this model no mechanical modifications are needed, the speaker chassis is the same).

Didier

[panchodiaz]

Didier is right. Actually to modify it to 56 W is because the original speakers have the power limit in 60 W but you can rise to a power of 100 W (using another compatible cheap chip) choosing the Eminence Red Fang 10".

[Didier]

Didier is right. Actually to modify it to 56 W is because the original speakers have the power limit in 60 W but you can rise to a power of 100 W (using another compatible cheap chip)

What about the power supply, does it deliver enough for much more powerful output modules ?

choosing the Eminence Red Fang 10".

They are suppossed to have higher efficiency than the G10 Vintage !

Didier

[dusty fretz]

My sincere thanks to Francisco and Didier for your kind offers to help sort out the very apparent aural problems affecting my recently bought early Vox Cambridge combo, I've sent an appropriate pm to each of you.

I've seen suggestions about changing the optocoupler, but apparently this has already been done on my amp, using a Fender example. However, the sound is still unsatisfactory and I feel a power upgrade should give me more headroom, hopefully reducing the distortion present on the clean channel. I've tried an extension cab equipped with better, higher wattage speakers, but the break-up is still apparent, so I'm happy to stick with the original Celestions for now. This combo is intended purely for personal private use at home, rather than as part of my on-stage arsenal, so I don't need or expect too much in the way of watts or tone, but I'm sure it should sound a bit better than at present - I don't remember my old AC10 Twin being quite this uninspiring!

[panchodiaz]

Hi Paul,

I have sent an email to you with all the info I´ve got. Anyway I think you can improve the Cambridge sound with a better valve (I put a 5251 and it was spectacular). Other interesting thing is to tweak the internal pots VR11 and VR12 to your liking.

I hope this helps.
Pancho

[dusty fretz]

Hi Francisco,
I've received your email, although I can't open the attachment, so is there any chance of sending it in a different format that might prove more friendly to my computer?

Thanks too for the additional information on ways to improve amp performance. I'll take your advice and replace the valve, as well as try my hand at tweaking those internal pots, if I can find 'em! Am I correct in thinking these two might affect parameters such as volume, gain and tremolo operation?

[Bill Bowley]

Paul,

Found this in my 'junk
files, may be of use to you. All due acknowledments to the author, etc of course!

[Twangaway]

What is the full spec or name of the suggested valve 5251 ?
Can't say I can find any info as to whether it would work on other amps too.