Help identifying coupling caps and dead caps ( pics )

[mildew]

Hello Amp Garage

I am the proud owner of an Ecofan Super Audion MK3 - EL34 PP amp, input valves ECC88 type (actually PCC189's), phase split valves 6cg7's. The amp builder ( Murray Dick ) is now deceased.

Stereo.jpg

It was originally all transformer coupled, but after a swap of the input stage from 12v valves to ECC88 type, it now has one stage of capacitor coupling from the input buffers to the phase splitter valves.

I want to swap out these coupling caps for some posh ones, but im not sure which ones are the coupling caps.

So, gutshots -

Ecofan gutshot.jpg

Two pics of the area where the input valves connect to the phase splitters ( i replaced the phase split valve sockets myself, so its MY horrible soldering not Murrays )

Sockets 1.jpg

Sockets2.jpg

The orange non polarized caps leading to a resistor leading to the pin are .47uf - are these the coupling caps?



Also, i think there are some electrolytics that are swollen/leaking -

Swolen cap.jpg

Is that what a "swollen to the point of leaking electrolyte" cap looks like?

And one more total beginner question - on a diagram of a valve pinout, is the numbering with the valve pins facing towards you, or away from you?


thanks in adv

[R.G.]

Yowza. That's some amplifier.
Here's a good source for tube data; the link is for a page on the 9A pinout, which includes the 12A?7 series.
How old is the amp? Or, more to the point, how old are the electrolytics? Electros degrade over time, and they degrade more slowly when used regularly. For a regularly-abused guitar amp, ten years is a good time to start thinking about re-capping the amp, although many electrolytics last longer, even far longer. If I am working on older equipment, I replace any electro that shows ANY hint of swelling or leaking at all. New electrolytic caps are far, far cheaper than rebuilding after one electrolytic spills inside the chassis.
For a rare (from what I can tell from the scarcity of info on the web) beast like this, I would be very tempted to replace them one at a time, testing after each replacement.
Not having any kind of schematic, I can't tell anything about which film caps are for coupling, and which are for stability, or frequency response shaping.

[sluckey]

I want to swap out these coupling caps for some posh ones, but im not sure which ones are the coupling caps.

Don't fix it if it ain't broke.

[mildew]

I want to swap out these coupling caps for some posh ones, but im not sure which ones are the coupling caps.

Don't fix it if it ain't broke.

Thanks for the responses - oh yes, its broken. Left side works properly, but right side has broken frequency response ( less mids and bass ), loud mains hum issues that i reset by powering the amp off then on, and bacon sizzling sounds on hot days. Can caps are completely unbalanced capacitance between left and right side - im guessing one of the caps in the cans has failed.

So far i cant even work out how to remove the cans over the can caps. Adding some tantalum caps to balance them might be my best option.

Its still very fun to listen to - i just had a quad of new Gold Lion KT77s arrive, and they sound better than the NOS Mullard fx3 B codes EL34's that its had for the last decade - perhaps less "mystical music vibes", but more clean watts and more detailed treble.

Trying to fix / upgrade it without breaking it - im going to have to try and find a schematic. After Murray passed away all his schematics were shared with a local electronic shop, i have emailed them to request a copy.

[B Ingram]

... oh yes, its broken. Left side works properly, but right side has broken frequency response ( less mids and bass ), loud mains hum issues that i reset by powering the amp off then on, and bacon sizzling sounds on hot days. ...

... After Murray passed away all his schematics were shared with a local electronic shop ...

You would be best served by having that local electronics shop repair the amp, which will likely involve replacing the many electrolytic caps in the amp.



Because even after you install your new "posh caps" the amp will still have issues needing repair.