AKG BX10 Power Transformer

[CroyTone Audio]

Hey Everyone.

I have a AKG BX10 spring reverb unit in for repair. Doesn't turn on, blows fuses.

I have tracked the issue to a toasted power transformer and I got in contact with AKG on the of chance they may 1. have a replacement (nope...), or 2. have specs on it (also nope...). The only thing they were able to send me was a service manual which is helpful but has no info on voltages within the unit or the specs of the power transformer. searching the web with the AKG part number didn't give me anything either... anybody have any idea what I can replace this mains Power transformer with?

Thanks

 

[thomasdf]

Depending on what's the power needs (which are pretty basic I assume) maybe you'd be better of rebuilding a new power supply. Given the age of the design, you could easilly build a much more quiet and efficient one, the audio would only benefit from that !
Edit: it's true the service manual https://www.akg.com/on/demandware.s...rman/default/dw770713bc/pdfs/BX10_service.pdf is pretty evasive regardinf the power rails tension. But I guess it can be found out. When my repairs are too much of a bummer with very specific power supplies, unless there is a real aesthetic/mojo I really consider using SMPS power supplies in semi conductor units... Super silent, super powerful, low consumption and small package.

 

[dmp]

That document describes it exactly, 26V. A 12v center tapped transformer should work. Current mains voltage is typically high and you will get power rails of about 12v I expect. A toroid would be a good choice if it would fit.
Also re-cap the PSU, C1-C6, a bad cap may have taken out the PT.
If you post a picture of the current transformer it would help in finding a replacement that would fit with minimal issues.

 

[CroyTone Audio]

Thank you very much dmp, I was looking over to Service Manual they sent me and I noticed that the power supply voltage page is MISSING! from the official AKG source no less... thank you very much for finding something I could have found fairly easily if I found a better copy of the document... Nothing like a forum to make you feel dumb about your question sometimes hah. But I'm a lot further for asking.

I can post pictures tomorrow when I'm back in my shop as well as do some research on my own but the help is greatly appreciated!

 

[CroyTone Audio]

So assuming they physically fit, from the Hammond catalog I see choices between the 186D24 transformer and the 1182k12 transformers for 24v center tapped transformers. If these would work electrically, would the extra expense of the toroidal PT be worth it sound wise?

 

[dmp]

A toroid has less of a magnetic field to induce hum in the audio part of the circuit. You can get induced hum in other transformers or the reverb pickups.
It would be fine to look at what is in there, probably a EI type, and install a replacement the same way (same orientation). Assuming it worked without any hum in the audio previously.

 

[nsalis]

"It would be fine to look at what is in there, probably a EI type, and install a replacement the same way (same orientation). Assuming it worked without any hum in the audio previously."

In addition, toroidal transformers have a higher inrush current, which may require a different primary fuse and additional circuit measures.

Please refer:

https://www.ametherm.com/blog/inrus...urrent can,failure of the transformer itself.
or

https://tinyurl.com/4ctax79h
"Also re-cap the PSU, C1-C6, a bad cap may have taken out the PT."

The bridge rectifier (B40 C800) must also be checked.

ns