The sunn Forum
  • August 20, 2019, 01:16:32 am
  • Welcome, Guest
Please login or register.

Login with username, password and session length
Advanced search  


New members will need to be approved before they can post until we can install some improved anti-spam measures.

Author Topic: Beta Bass 1x15 Combo Repair/Refurbish Project  (Read 608 times)

0 Members and 1 Guest are viewing this topic.


  • Jr. Member
  • **
  • Offline Offline
  • Posts: 3
Beta Bass 1x15 Combo Repair/Refurbish Project
« on: February 18, 2018, 06:52:32 pm »

Found this bad boy at a sale being run by a local nonprofit.  I'm an electronics technician and huge fan of vintage audio gear, so I'm rather excited!

The tag on it just said "Broken".  Who knows what's up with it but I intend to find out!  Saw these forums and thought you guys might get a kick out of the project.  Plus when I'm finished I'll decide whether to keep it as part of my collection or sell it.

Tomorrow it will go on my bench and I'll star tearing it down to see what I'm working with.


  • Jr. Member
  • **
  • Offline Offline
  • Posts: 3
Re: Beta Bass 1x15 Combo Repair/Refurbish Project
« Reply #1 on: February 26, 2018, 06:51:03 pm »

Didn't take nearly enough pictures, but I've been working on it the past few days.

First up, the speaker seems to be original and is in fantastic shape.  No sign of any dry rot whatsoever and I hooked it up to a separate amp and it sounds great!  Pots are all extremely smooth without any gritty feeling.

Downloaded the service manual . . . the one of Fender's site is a poor scan but the archived one linked on other threads is missing a lot of pages.  I'll take what I can get.

Pulled the actual amp head out and got the boards into "service position".  3-prong plug in perfect shape.  Everything is amazingly clean. I wonder if it was just hardly ever used or if someone else cleaned it previously . . . but nothing showed any signs of ever having been taken apart..

The culprit was almost immediately apparent after a few basic tests.  I noticed a pair of TO-220 power transistors in the corner of the power board with a lot of glue, and one tested bad (Q11, a TIP30).  I'm guessing due to the crappy clip-on heatsink, and I'm pretty sure its TIP29C partner should have had a heatsink too.

Also the large input filter caps tested very poorly.  Not outright failed but not good either.  So they'll get replaced.

Since there are only two values of electrolytic buffering caps (2.2uF 50V bipolar and 10uF 35v)  in the entire unit I figure I'll replace them all while I'm at it.

And that brings us up to today.  Here are the new parts from Mouser:

I installed them all earlier.  Tomorrow I'll hook it up and see what happens!

Ryan Phelps

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 324
Re: Beta Bass 1x15 Combo Repair/Refurbish Project
« Reply #2 on: February 27, 2018, 06:18:34 pm »

Nice! Keep us posted on your progress.