[Harp-L] SS to tube rectifier

[Dina Janzen and Jim Rossen <dlj@xxxxxx>]

A 5R4 tube and other tube rectifiers require a 5 volt DC heater source from
the power transformer.  The power transformer in most amps with SS rectos
does not have a 5 volt tap, so an additional small tranny for this purpose
will be needed.  You will also need an octal tube socket.  Some Fender amps
with SS rectos have a suitable hole in the chassis next to the power tubes
covered by a plate and a correctly sized tube socket fits easily.  If there
is no tube socket hole, one will need to be made.

A nice alternative is to use a Weber VST Copper Cap rectifier, which is a
solid state recto that emulates the voltage drop and sag of a tube.  Models
that emulate 5R4, 5V4, 5AR4, 5U4  and  others are available.  These do not
require the 5 volt source.  I put these into a Fender 1963 Pro and 1960
Concert.  The CC recto comes in two configurations, either with an octal
connector that plugs into an octal tube recto socket or as a small box unit
with three leads that gets attached and hard wired to the chassis.  If your
chassis can take an octal socket, the plug in config is nice as it is easy
to try different CC rectos.   This is what I did with the Pro and Concert.

The power tube bias will need to be checked and probably adjusted with any
change in recto type.   It would be wise to install a bias adjustment pot
and bias test resistors at the time of the recto mod.

Jim R

> 
> 
> Message: 15
> Date: Wed, 11 Aug 2004 12:48:08 -0700
> From: "Larry Ravlin" <sheepdip@xxxxxxxxxx>
> Subject: [Harp-L] SS to tube rectifier
> To: "Harp" <harp-l@xxxxxxxxxx>
> Message-ID: <000c01c47fdc$21bec6a0$a71ffecf@sheepdip>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> Gentlemen,
> 
> I'd like to change the SS rectifier in a 68 fender Bassman to the 5R4 tube
> rectifier.  Has anyone on the list done this or have any info on the change?
> 
> Larry