Hi Everyone,

This is my first post on GF (quite a long one). I am looking for some help with regards to an amp I bought.

I have bought a 60`s AC30 off gumtree and is totally thrilled. The amp is broken however. It is the AC30/6 top boost, it looks like it has most of its original components. Woden trannies and the tolex looks original but in bad shape (doesn't bother me in the least). The front grill was swapped for a black cloth, and the original speakers was replaced with Chinese speakers, the handles is also removed. Electronic wise the signal caps look original except for the vib/trem that was removed and a solid state rectifier was installed.

A bit of background I have studied Electronic engineering but have no solid knowledge of valve amplifiers whatsoever.

I have switched it on and there is a faint hiss, as I understand this indicates that the output transformer is fine, or am O incorect?

When I switched the amp on after I while I smelled something hot. It is the choke that is so hot. Is it possible that the choke should run hot, or can it be that something down the line is shorting? Perhaps the 16uF/16uF cap next to it?

Also in your opinion should I replace the electrolytics now or at a later stage?

I read that the SS rectifier is a bad thing, should I swap it back to original?

Sorry for the long post, any advice or knowledge on the matter will be appreciated. I wanted to test it with you before I warm up my soldering iron.


The Amp:


Internals:


Transformers:


Suspect cap:

Hey man!

The tubes look a little rough too... I think that would also be a good start to change them. The cap could be fine, but it's likely to be very leaky... The SS rectifier isn't as such a bad thing... It's a tad more reliable than a tube rectifier, but won't give you the sag associated with a tube rectifier. That would probably come down to taste.
All of the small electrolytic caps may have to be replaced with the big can...

Edit: Welcome to the forum!! Give us some background on who you are and what other toys you have ?

Thank you very much for the reply Psyx.

I am based in Pretoria and love playing guitar, very recently I have taken an interest in recording so I have yet to complete my first track. I like anything bluesy. I wil have to update my profile soon :-[.

Yes those Sovteks are veterans, I will be replacing them soon.

I actually opened the bottom now, the one end of the 16uF/16uF can shoots right through and has been replaced with a single 32uF cap. The other side is still in tact but I suspect that it is toast. It explains the overheating choke since it shorts can short.

I am going to try and source that cap and see what happens. I see mr valve has some caps on their website.

My 1974 Marshall had leaky caps which were at the end of their lives. I had them replaced with some LCR caps. JP le Roux in Joburg did it for me and I'm not sure where he sourced them from... And I gave mrvalve a quick look and I didn't see any 16+16uF caps, so you may have to look around a bit. Quite a few guys on the forum have restored AC30's, so you're in good company!

psyx wrote: Hey man!

The tubes look a little rough too... I think that would also be a good start to change them.

Be wary of replacing old valves. New valves generally do not compare to the old ones. Replace them only if you are sure they need to be replaced.

lapdawg wrote:

psyx wrote: Hey man!

The tubes look a little rough too... I think that would also be a good start to change them.

Be wary of replacing old valves. New valves generally do not compare to the old ones. Replace them only if you are sure they need to be replaced.

Thanx Lapdawg you are right, I will first see if they work hope they do.

I found the right caps online at justradios.com. I think I will attempt to ship it here untracked since it is so expensive for the proper insured/tracked shipping.

They have the right 25mm diameter dual caps which is nice since it will fit nicely in the clamps.

If someone wants something from justradios.com drop me a line.

Once you have the amp working it will be time to replace the "Chinese" speakers if it is going to sound anything like the original