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marconi 157 - Printable Version

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marconi 157 - the picker - 11-19-2016

I picked a Marconi model 157 radio and when I got it the radio had a capacitor hum only so I recapped it and now I have a motor boating sound from half volume and up and no other sound only a low hum

RE: marconi 157 - Phlogiston - 11-19-2016

Assuming that all of the capacitors were installed correctly, check the values of all of the resistors in particular a canned-ohm if it has one.

RE: marconi 157 - morzh - 11-19-2016

See if any tubes and their grid wires that are supposed to be encased in a shield are inside the shield.

Also: have you tested the tubes?

RE: marconi 157 - the picker - 11-19-2016

(11-19-2016, 10:51 AM)Phlogiston Wrote:  Assuming that all of the capacitors were installed correctly, check the values of all of the resistors in particular a canned-ohm if it has one.

I am not sure what a canned ohm resistor is but I will check the others

RE: marconi 157 - the picker - 11-19-2016

(11-19-2016, 11:47 AM)morzh Wrote:  See if any tubes and their grid wires that are supposed to be encased in a shield are inside the shield.

Also: have you tested the tubes?
tubes have been tried in working radios and none of the tubes at all have shields

RE: marconi 157 - Phlogiston - 11-19-2016

(11-19-2016, 12:57 PM)the picker Wrote:  
(11-19-2016, 10:51 AM)Phlogiston Wrote:  Assuming that all of the capacitors were installed correctly, check the values of all of the resistors in particular a canned-ohm if it has one.

I am not sure what a canned ohm resistor is but I will check the others

It is the voltage divider resistor from which is derived the bias voltages. It is often a wire-wound in a metal sleeve riveted to the chassis for heat dissipation. The wire can burn open but most often the contacts become intermittent.

In most of my recent repairs, I would estimate that 1/2 to 2/3 of all resistors had either failed or were way out of tolerance.

RE: marconi 157 - KCMike - 11-19-2016

Here's schematic for anyone helping.
http://pacifictv.ca/schematics/marconi157data.pdf

RE: marconi 157 - morzh - 11-19-2016

Russ might've meant Candohm.
It is a power resistor that is riveted to a chassis.


Ypi don't seem to have one.
Your neg bias seems to be made with a.... battery?
Is the battery good?

RE: marconi 157 - the picker - 11-19-2016

(11-19-2016, 02:25 PM)morzh Wrote:  Russ might've meant Candohm.
It is a power resistor that is riveted to a chassis.


Ypi don't seem to have one.
Your neg bias seems to be made with a.... battery?
Is the battery good?
are you talking about the 1.5 v bias cell if so yes I have it replaced

RE: marconi 157 - sam - 11-19-2016

candohm resister  looks like this
[Image: http://i117.photobucket.com/albums/o46/radioconnection/Candohm_zps3fde8706.jpg]
could be smaller or larger with more tabs

RE: marconi 157 - the picker - 11-19-2016

(11-19-2016, 03:21 PM)sam Wrote:  candohm resister  looks like this
[Image: http://i117.photobucket.com/albums/o46/radioconnection/Candohm_zps3fde8706.jpg]
could be smaller or larger with more tabs

I will look but I do not think it has one

RE: marconi 157 - sam - 11-19-2016

I don`t think you have one

RE: marconi 157 - the picker - 11-19-2016

(11-19-2016, 04:07 PM)sam Wrote:  I don`t think you have one
I looked and could not see one .

RE: marconi 157 - Phlogiston - 11-19-2016

Well, they look canned.

So never mind that, but check the voltages on the tubes starting with the 6F6.

Just curious too, does the eye tube do anything (signal indication)?

Do you have a signal tracer?

RE: marconi 157 - Radioroslyn - 11-19-2016

For us US guys here's some pic's of it:   http://radioatticarchives.com/radio.htm?radio=12521