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marconi 157 - Printable Version

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RE: marconi 157 - Arran - 11-25-2016

 Capacitor C39, a .1 mf cap, is another to check, it should be connected to a 20,000 Ohm resistor and one of the tube socket terminals, with the other end grounded. Capacitor C30 is another, it's a .01 mf cap, it's connected between the oscillator coils and a 50,000 Ohm resistor, and ground. One thing that does not help on Canadian Marconi schematics is that they do not number or label the terminals on the tube sockets, many manufacturers will mark these out with a ring of circles around the tube diagram, with a letter to indicate what element is what like "K" for cathode, "P" for plate, etc. in each circle, it's rather annoying.
Regards
Arran

RE: marconi 157 - the picker - 11-25-2016

(11-24-2016, 05:03 PM)morzh Wrote:  C19 is from the minus of the battery to the GND, C21....no good way to describe but one end is at the top lug of the volume pot (if you face the rear of the pot and the lugs look down then the leftmost lug, if the lugs look up, then it is the right one) , and the other C21 pin goes between the two resistors on the sch.

here is a pic of the battery the red is positive lead and green negative correct or not

RE: marconi 157 - the picker - 11-25-2016

(11-24-2016, 05:03 PM)morzh Wrote:  C19 is from the minus of the battery to the GND, C21....no good way to describe but one end is at the top lug of the volume pot (if you face the rear of the pot and the lugs look down then the leftmost lug, if the lugs look up, then it is the right one) , and the other C21 pin goes between the two resistors on the sch.
here is a pic of the volume control which one does c-21 connect to thanks

RE: marconi 157 - morzh - 11-25-2016

The yellow wire. As I said, lugs looking up, the rightmost one.

RE: marconi 157 - morzh - 11-25-2016

As for the battery I am not sure. The minus goes to pin3 which is the grid.
In your case I cannot tell as you have some octal tube in that socket.

It is actually a bit hard to look at photos without knowing what's what and try to extrapolate it to what it is.

RE: marconi 157 - the picker - 11-25-2016

(11-25-2016, 11:40 AM)morzh Wrote:  As for the battery I am not sure. The minus goes to pin3 which is the grid.
In your case I cannot tell as you have some octal tube in that socket.

It is actually a bit hard to look at photos without knowing what's what and try to extrapolate it to what it is.

going back to the battery the two original connection points were pin 6 of tube 6k7 and a terminal lug that has a .1 mfd cap that goes to ground a blk wire that goes to a if transformer a white wire that goes to tube 6u5 and another white wire going to a terminal lug that goes on to connect to the band selector so which is positive and negative

RE: marconi 157 - the picker - 11-25-2016

(11-25-2016, 01:09 AM)Arran Wrote:   Capacitor C39, a .1 mf cap, is another to check, it should be connected to a 20,000 Ohm resistor and one of the tube socket terminals, with the other end grounded. Capacitor C30 is another, it's a .01 mf cap, it's connected between the oscillator coils and a 50,000 Ohm resistor, and ground. One thing that does not help on Canadian Marconi schematics is that they do not number or label the terminals on the tube sockets, many manufacturers will mark these out with a ring of circles around the tube diagram, with a letter to indicate what element is what like "K" for cathode, "P" for plate, etc. in each circle, it's rather annoying.
Regards
Arran
right what I believe to be c-39 is connected to pin4 of tube 6k7 which also has a 27 k resistor connected to it which should be the 20k resistor and the other end is connected to pin 7 of tube 6k7 which is wrong correct or not

RE: marconi 157 - the picker - 11-26-2016

I also noticed in checking plate voltage on pin 3 of tube 6q7 I get lots of static in the speaker and the voltage is 135dc v instead of 100

RE: marconi 157 - the picker - 11-26-2016

just wondering if someone has some advice where to trouble shoot next thanks

RE: marconi 157 - Phlogiston - 11-26-2016

There are so many variables that this could go on for some time.

You didn't indicate having a signal sniffer/tracer or not. They can really help with this kind of problem.

RE: marconi 157 - the picker - 11-26-2016

I have a conar signal tracer but never ever used one before and I am not sure how to use it

RE: marconi 157 - Phlogiston - 11-26-2016

(11-26-2016, 01:40 PM)the picker Wrote:  I have a conar signal tracer but never ever used one before and I am not sure how to use it

Well, I am not sure about that one. The only concern I would have is if it's input was protected from B+. The old Heathkits that I use are good to "sniff" just about anywhere, B+ included.

You just start at one end - antenna or output - and look for where the problem (motorboating) starts or where the signal disappears. So you could start on the grid of the first tube, which is tuned, and should be able to hear stations. Moving on from there, from plate to grid, you should notice some gain in each stage - until you encounter your issue.

RE: marconi 157 - the picker - 11-26-2016

do I set the tracer on rf or af

RE: marconi 157 - the picker - 11-26-2016

I started to trace and good signal at antenna then pin 3 of 6k8 good then pin 3 6k7 poor and the pin 3 6q7 no signal

RE: marconi 157 - Phlogiston - 11-26-2016

(11-26-2016, 02:07 PM)the picker Wrote:  do I set the tracer on rf or af

AF. Likely will work either way.