Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => AmpTools/Tech Tips => Topic started by: FKitchen on May 14, 2008, 07:43:45 am

Title: Epiphone EA 33RVT amp
Post by: FKitchen on May 14, 2008, 07:43:45 am

I have an epiphone amp EA 33RVT for over thirty years. When it turns on it hums loudly.After looking inside the one tube looks burnt.Looking at the schematic it appears to be V4 (6AQ5).I do not see any reference to this tube ,maybe it is so old that it changed I do not know all of this is new to me.HELP!!!!!!!PLEASE!!!!!!

Title: Re: Epiphone EA 33RVT amp
Post by: FYL on May 14, 2008, 11:21:21 am

The hum is probably caused by dead filtering caps, something pretty normal after 30 years. Have the amp examined and serviced by a qualified tech - IMO changing a few caps and fitting new tubes will bring her back to her full glory.

Here's a full schemo:
http://www.schematicheaven.com/gibsonamps/ea_33rvt-galaxie.pdf

Title: Re: Epiphone EA 33RVT amp
Post by: FKitchen on May 14, 2008, 01:56:48 pm

DO YOU KNOW WHAT THE CURRENT TYPE OF TUBES ARE THAT ARE USED IN THIS AMP?

Title: Re: Epiphone EA 33RVT amp
Post by: FYL on May 14, 2008, 02:23:09 pm

Quote

DO YOU KNOW WHAT THE CURRENT TYPE OF TUBES ARE THAT ARE USED IN THIS AMP?

They are listed on the schemo.

Changing tubes isn't a viable option: the amp should be fuly checked by a qualified technician. And your <CAPS LOCK> key is stuck...

Title: Re: Epiphone EA 33RVT amp
Post by: RicharD on May 14, 2008, 02:29:36 pm

http://www.mif.pg.gda.pl/homepages/frank/vs.html

6AQ5 = EL90 = 6005
Dieing tubes don't hum, they crackle followed by silence.

Cap job.

Title: Re: Epiphone EA 33RVT amp
Post by: DummyLoad on May 14, 2008, 04:36:15 pm

Quote

http://www.mif.pg.gda.pl/homepages/frank/vs.html

6AQ5 = EL90 = 6005
Dieing tubes don't hum, they crackle followed by silence.

Cap job.

how is it that you know that?  :D

Title: Re: Epiphone EA 33RVT amp
Post by: RicharD on May 14, 2008, 05:00:23 pm

Experience.... recent experience.

What was the final death toll again?
 :'(

Title: Re: Epiphone EA 33RVT amp
Post by: DummyLoad on May 14, 2008, 06:44:08 pm

Quote

Experience.... recent experience.

What was the final death toll again?
 :'(

i lost count...  :(

Title: Re: Epiphone EA 33RVT amp
Post by: Iannone on May 15, 2008, 04:05:03 pm

I agree that you should look to the power supply cps first.  However, if you find yourself needing new output tubes, you might look at:

http://www.vacuumtube.com/guitar.htm

While the 6AQ5 is no longer in production, there are still some reasonably priced NOS bottles available.