AC15TB(X) Korg era 5Y3 caution

xinu

Member
Messages
60
Retubed my Korg era AC15TBX and it failed after just a few months. As those of you with experience with these will know they are a PITA to replace the tubes since it requires removal of the chassis.

To make a long story short, do not use the JJ 5Y3S rectifier. It is physically longer than the 5Y3GT. When you replace the tube shielding cover with a 5Y3S inserted, the cover will push against the top of the tube with apparently enough stress to break the glass over time. Unless you are aware of this it's not obvious when you replace the shield and just a matter of time and always at the worst time.
 

metropolis74

Member
Messages
805
Yeah isn't that tube shield obnoxious? I took the shield off my AC15TBX the day I bought it (used of course) a few years ago and it's not going back on. Tube changes are easier now since I don't have to remove the chassis.

About the 5Y3, well there was a JAN 5Y3 in mine when I got it and I assume that's what it came stock with in 1997 since the amp was in mint condition when I got it. Still had the Marshall branded preamp tubes and some funky eastern European EL84's. I got another NOS JAN 5Y3 as a backup but it seems to be doing just fine after 17 years of use.
 

strings777

Member
Messages
347
I bought my AC15TBX new from Elderly Instruments and it came stock with EI EL84's and EI preamp tubes. The rectifier had a brown base and no name brand or any other markings on the glass, but I swapped it out with an RCA 5Y3GT which is still working fine. Just my two cents, but I would purchase a NOS 5Y3GT instead of a Sovtek...they're really inexpensive and will last a lot longer.
 

xinu

Member
Messages
60
Yeah isn't that tube shield obnoxious? I took the shield off my AC15TBX the day I bought it (used of course) a few years ago and it's not going back on. Tube changes are easier now since I don't have to remove the chassis.

About the 5Y3, well there was a JAN 5Y3 in mine when I got it and I assume that's what it came stock with in 1997 since the amp was in mint condition when I got it. Still had the Marshall branded preamp tubes and some funky eastern European EL84's. I got another NOS JAN 5Y3 as a backup but it seems to be doing just fine after 17 years of use.
Thanks for the advice.

Even with the tube shield off how are you able to change the tubes without removing the chassis? Do you get your hand or something through the top vents somehow?
 

metropolis74

Member
Messages
805
Thanks for the advice.

Even with the tube shield off how are you able to change the tubes without removing the chassis? Do you get your hand or something through the top vents somehow?
I just reach in from the back of the amp under the back panel and view through the top vents. It's awkward and a little uncomfortable giving the amp a ....um...'reach around', but sure beats taking the chassis out.
 

xinu

Member
Messages
60
I just reach in from the back of the amp under the back panel and view through the top vents. It's awkward and a little uncomfortable giving the amp a ....um...'reach around', but sure beats taking the chassis out.
Way to go. Talk about being touch sensitive. I don't have enough 4 letter words in my vocabulary to do it that way:) The 5Y3 maybe... but not the others.
 

gtr777

Silver Supporting Member
Messages
1,838
I tried to put TAD EL84's in once and they don't fit either. The glass is thicker then Ei ,JJ's and other EL84's and they won't fit through the cut outs
 

Jimmy MAck

Member
Messages
789
Yeah, on mine, I opened the box when I received (brand new) it, it didn't make a sound. Before returning it, I checked and the tube shield had pushed against the first or second EI pre-amp tube. Thin glass too!!!

Replaced the tube (good to have spares) and never put that stupid shield back.

I could change the tubes without removing the chassis. Had to replace the stock rectifier tube, it blew 3 fuses but not right away.

Nice amp but ............
 

xinu

Member
Messages
60
......

Nice amp but ............
The Korg AC15 comes by that weird quirky chassis layout honestly. It has been that way since the 60's (sans tube screen). Korg simplified and straightened out the AC30 chassis design during their reign.
 

Blue Strat

Member
Messages
30,206
What type of 5Y3 do you recommend

Any luck with Sovtek GTs?

Don't use the Sovtek! They're not real 5Y3s and put out too much voltage. This will shorten the life of the EL84s.

There are much better, slightly more expensive, options that will last decades.
 






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