Eico 145A signal tracer schematic needed

Discussion in '"Boat Anchor" & Classic Equipment' started by WB9QVY, Jun 10, 2019.

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  1. WB9QVY

    WB9QVY Ham Member QRZ Page

    I fully intend to do a total rebuild. It would end up being less work than
    trying to fix up whats currently there. Fortunately everything seems to be there.
    I will have to make up a probe for it. And get a new 6AQ5 for it.

    To give you an idea...the guy that had it tried to make it into a lamp. I kid you
    not...it had a lamp socket mounted on the top of the cabinet.
    He wanted $10 for it. I offered him $1. We settled for $2. I figured I had nothing
    to lose for $2.

    Glen K9STH...a 3 wire power cord it will be...
  2. W5RKL

    W5RKL Ham Member QRZ Page

    There's only one area in the Eico 145A for a fuse holder and that's on top of the chassis just
    to the left of the 6x4 rectifier tube. Pay close attention since the power transformer mounts
    below the chassis in that open area above the chassis to the left of the 6x4 rectifier tube. There
    is very little room for any additional components/sockets. The space between the rear of the power
    transformer and the rear panel is small. I thought about using a 3 wire ground power
    cord but with the small space between the transformer and rear panel, I went with
    the thinner 2 blade polarized power cord/plug instead.

    Added notes:

    The 3 tubes operate as audio amplifiers. Any stray AC can be picked up as hum.
    The original AC input wiring came through the rear panel hole, routed around the
    rear of the power transformer, along the right edge to front panel switch. This kept the
    AC wires away from the audio tube inputs helping to prevent AC hum pickup by
    the 12AX7 and 6AQ5 audio stages. I used tightly twisted wires for the filament
    wiring to all tubes. The transformer's HV and filament wires were kept close to the bottom edge
    of the power transformer except when connecting to the 6x4 rectifier socket pins
    and CT ground lug on the 6x4 socket mounting machine screw.

    As for a probe, you can use a simple RF probe which is basically what the original
    probe was. I use a Heathkit PK3 RF probe and it works very well. For straight audio
    I used Velleman TLM6 RED and BLACK probes. Using this method of wiring resulted
    in no hum pickup. I also recommend installing a piece of perforated aluminum between
    the speaker and the front panel. This will help to prevent poking a hole in the speaker
    through the Black cover.

    Mike W5RKL
    Last edited: Jun 13, 2019

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