Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Oddvar on October 08, 2019, 05:36:41 am

Title: Transformer change
Post by: Oddvar on October 08, 2019, 05:36:41 am

Hi.  I was wondering if anyone could advise me on what the color codes represent in this Mesa Caliber 50.  I am about to change from 117v to 240 v power transformer.   There is also a single black going to the on/off switch in addition to the ones in the pic.  On this amp there are to 100r resistors acting as CT's, but the new transformer has two center taps, should I disable the resistors and connect the two CT's to the same point on the multi plug or just leave one of the taps unconnected?

Help is appreciated-

Title: Re: Transformer change
Post by: sluckey on October 08, 2019, 06:45:33 am

Didn't we just go through this a month ago?

Title: Re: Transformer change
Post by: Oddvar on October 08, 2019, 06:53:15 am

Possibly Sluckey, but it is not working, so...

Title: Re: Transformer change
Post by: sluckey on October 08, 2019, 06:58:50 am

Does this look familiar?

     http://el34world.com/Forum/index.php?topic=25044.msg270984#msg270984

Title: Re: Transformer change
Post by: Oddvar on October 08, 2019, 08:04:07 am

Unfortunately it didn't work.

Title: Re: Transformer change
Post by: pdf64 on October 08, 2019, 08:19:51 am

While you’re figuring it out, build a light bulb limiter and make sure to use it when you think you’ve got the PT wired up right  :w2:

Title: Re: Transformer change
Post by: Oddvar on October 08, 2019, 10:33:40 am

Quote from: pdf64 on October 08, 2019, 08:19:51 am

While you’re figuring it out, build a light bulb limiter and make sure to use it when you think you’ve got the PT wired up right  :w2:

I did that, but the MOV reacted with noise an nearly exploded.  The mov is 250v

Title: Re: Transformer change
Post by: 2deaf on October 08, 2019, 10:57:39 am

Quote from: Oddvar on October 08, 2019, 10:33:40 am

I did that, but the MOV reacted with noise an nearly exploded.  The mov is 250v

That's kind of a funny one there, too.  How would one know if an electronic part nearly exploded?  Whenever I've blown-up an electronic device it has been by complete surprise.  I did not detect the near explosion stage.

I've never blown-up an MOV, but I've blown-up plenty of other things.  In fact I got arrested for that one time.  They had to let me go, though, because I wasn't fessing-up and it seems the evidence had exploded. 

Title: Re: Transformer change
Post by: Willabe on October 08, 2019, 11:02:23 am

Quote from: 2deaf on October 08, 2019, 10:57:39 am

In fact I got arrested for that one time.  They had to let me go, though, because I wasn't fessing-up and it seems the evidence had exploded.

   
       :laugh:

Title: Re: Transformer change
Post by: shooter on October 08, 2019, 12:47:53 pm

Quote

and it seems the evidence had exploded. 

 :l2:
the smoldering mailbox wasn't good enough since time n distance was on my side  :icon_biggrin:

had a handful of Mexico-build MOV's in the '80s fail, sounds like a .22 standard round, usually the leads smoldering was a good place to start at guessing what component failed  :icon_biggrin:

Title: Re: Transformer change
Post by: 2deaf on October 08, 2019, 04:49:08 pm

First determine which GRN/YEL has continuity to the GRN's and tape that GRN/YEL off.  Then confirm that the other GRN/YEL has about the same resistance to each RED.  Then confirm that this GRN/YEL has less resistance to BLU than to the RED's.

Now confirm that BRN has more resistance to WHT than it has to BLK.  Then confirm that the resistance from BLK to WHT is way less.  Tape off BLK.

Connect the other wires as shown.

Hook the amp up to a light bulb limiter, put your goggles on, and turn the amp on.