Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Big chief on January 13, 2016, 05:44:46 pm

Title: Fender reverb unit
Post by: Big chief on January 13, 2016, 05:44:46 pm

Does anyone have a layout of a Fender reverb unit Premier 90
I need tubes and cap for this unit made in the early 60's
A schematic would be great

Thanks

Title: Re: Fender reverb unit
Post by: sluckey on January 13, 2016, 06:12:05 pm

Fender did not build the Premier 90. Here's a schematic...

http://el34world.com/Forum/index.php?topic=14283.0 (http://el34world.com/Forum/index.php?topic=14283.0)

Title: Re: Fender reverb unit
Post by: ac427v on January 14, 2016, 07:14:36 am

I shared my Premier 90 experiences in a thread in August 2014.I can't copy the link in this post but if you do a search for "Premier 90" it should come up. The gist of my experience was that hum could be cut in half by using a bridge rectifier in the power supply. Even then, hum was still present. I hope you will share your experiences with the 90 cause it has great tone. I would build one if someone more capable could figure out better hum reduction.
Craig

Title: Re: Fender reverb unit
Post by: HotBluePlates on January 14, 2016, 07:29:20 am

Quote from: ac427v on January 14, 2016, 07:14:36 am

I shared my Premier 90 experiences in a thread in August 2014.I can't copy the link in this post ...

ac427's Premier 90 thread (http://el34world.com/Forum/index.php?topic=17492.msg175795#msg175795)

Did you ever try the ground isolation method I mentioned in that post? Or perhaps an isolation transformer on the power cord, a la Ebtech?

Title: Re: Fender reverb unit
Post by: ac427v on January 14, 2016, 08:19:02 am

Hi HBP. The answer is kinda-sorta.
I removed the ground connection from the AC plug by using a 3/2 prong adapter with the ground terminal unconnected (temporarily). That did not help. So the hum was not caused by a ground loop through the AC ground and guitar cable ground.
Craig

Title: Re: Fender reverb unit
Post by: HotBluePlates on January 14, 2016, 02:06:43 pm

Did you ever check the grounding of the reverb send/return jacks, as compared to the in/out jacks on the reverb tank?

The typical Fender reverb tank has one reverb tank jack isolated from ground (the reverb pan's chassis) while the other jack is connected to ground (again, the reverb tank's chassis). In a Fender tank, the tank input is isolated while the tank output is grounded.

The typical old Fender amp has the grounds of send/return jacks connected to the chassis (not isolated) to complete the circuit, as those amps use the chassis throughout as a grounding point. If the tank has both jacks grounded to the tank chassis, there is a big ground loop.

So consider checking the tank.

Title: Re: Fender reverb unit
Post by: Mike_J on January 16, 2016, 06:32:12 pm

I didn't have a problem when I made a stand alone reverb unit but when I made my Revibe unit it had a severe hum.  The solution to finding it was using the continuity tester and testing every ground point on the chassis to ground.  All but one indicated a low value while one was much higher.  Put some solder on the joint and it went from a loud hum to completely silent.  Don't know if that helps but it worked for me.


Thanks
Mike