Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jyant50 on February 27, 2015, 03:36:36 pm

Title: Schedule 40 GA 5 build
Post by: jyant50 on February 27, 2015, 03:36:36 pm

I am getting ready to order parts for a Schedule 40 GA 5 build.

I have a '60's Gibson GA 5 Skylark Crestline that's not working.  This is the model with 6EU7, 6C4, 6X4 and 2-6AQ5's. 
I want to rebuild this using Doug's GA 5 schematic.  My question involves the PT and OT from my Gibson amp.  The OT is stamped with TF-18-01,  5496345,  and the PT is stamped with TF-5A-P, 9966349.  Can I use the Gibson OT and PT with the Schedule 40 GA 5 build, or will I need to order the OT and PT on Doug's parts list?  I haven't been able to find any reference info on the Gibson transformers.  Any help will be appreciated.   
 

Title: Re: Schedule 40 GA 5 build
Post by: sluckey on February 27, 2015, 04:49:59 pm

Those GA-5 amps are totally different. They have nothing in common except the name "GA-5". One is a single ended amp and the other is a push/pull amp.

Your amp is very simple and straight forward. Why not just fix it?

Title: Re: Schedule 40 GA 5 build
Post by: shooter on February 27, 2015, 05:24:49 pm

Agree with Sluckey, I have fixed 2 and the results are well worth the effort.  They are a nice amp and easy to work on, I believe the "antique" value is good also.  FWIW

Title: Re: Schedule 40 GA 5 build
Post by: jyant50 on February 28, 2015, 09:39:11 am

Thanks for the response guys!  The amp I have doesn't follow any schematic I can find.  I've read on other forums, Ampage in particular,  that Gibson was particularly notorius for not following schematics back in the day.  This amp is a testament to that.  So, the amp as wired is above my skill level!!  I do appreciate the vintage value as everything is cosmetically good.  After rethinking this, I will take in to a amp tech in Dallas and see what he thinks.  Thanks again!

Title: Re: Schedule 40 GA 5 build
Post by: sluckey on February 28, 2015, 10:02:17 am

Quote from: jyant50 on February 28, 2015, 09:39:11 am

Thanks for the response guys!  The amp I have doesn't follow any schematic I can find.  I've read on other forums, Ampage in particular,  that Gibson was particularly notorius for not following schematics back in the day.  This amp is a testament to that.  So, the amp as wired is above my skill level!!  I do appreciate the vintage value as everything is cosmetically good.  After rethinking this, I will take in to a amp tech in Dallas and see what he thinks.  Thanks again!

This schematic follows your amp. It's about as plain Jane as you can get. Not much room for Gibson to muck it up too badly. You may want to print this schematic and put a copy inside your amp. Your tech would appreciate it.

http://el34world.com/charts/Schematics/files/gibson/Gibson_ga5_crest.pdf (http://el34world.com/charts/Schematics/files/gibson/Gibson_ga5_crest.pdf)