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Magnavox 155B - Printable Version

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Magnavox 155B - vecher - 06-19-2022

ALL, i have 3 separate units that go with this

AMP-101A power supply and Amp
Cr-188 SW and BCST receiver
CR-206E FM convertor

I have the power supply hooked to receiver.. all seems to work correctly

But do not really know what antennas to hook up I have the loop antenna that goes with it..

There is connections for the loop and also an antenna..

Also a switch in chassis that says loop / antenna..

on convertor there are connections for a antenna and plug to the receiver. I have NO FM No noise at all.

Where to look?

Skip

RE: Magnavox 155B - vecher - 06-20-2022

OK started to try alignment.. IF's went well. but trying to adjust the bcst band .. the OSC trimmer has NO effect.

it receives well but . EX: station at 1440 khz comes in at just under 1200 on dial station at 1060 is about 950 khz .I can not get it to change..


SW seems to be very close..

any clues??? Has anyone aligned one of these??

Skip

RE: Magnavox 155B - vecher - 06-23-2022

Ok Found a bad trimmer cap for the Bcst band. replace it now able to align with no problem.. SO AM and SW now working very well..

Next Issue I have the FM Convertor. hooked it up and all I get is a bunch of crackles noise.. Like static crashes.. i can bearly hear the 10.7 mhz IF signal..when injected .. no signals hear anywhere..

Any clue to what this could be??

Skip

RE: Magnavox 155B - mikethedruid - 06-23-2022

when you inject the 10.7 signal, how is that modulated? It has to be FM modulated to push through a tone. Also, just a note, if the trimmer cap has a bad mica, you can cut a new insulator from a piece of the stiff, clear plastic they use in a lot of packaging these days, just cut it the same size with the same hole in the right place. It will usually work OK.

RE: Magnavox 155B - RodB - 06-23-2022

Hi Skip,
If the converter is a tube type then it probably has a dual triode, one for the rf amplifier and one for the oscillator. In the few FM front ends I've worked on, that tube has been weak or bad. Even when a tube tester said it is good.

RE: Magnavox 155B - Radioroslyn - 06-23-2022

For those follow this saga at home here is the service info for the FM tuner: http://www.nostalgiaair.org/PagesByModel/343/M0010343.pdf

Rod
To answer your question it uses a 6SA7 on steroids for the mixer. (6SB7Y)

RE: Magnavox 155B - vecher - 06-24-2022

Found that the 6sb7y tube was bad. no filament.. i do not have any spares..

so need to order a few .. I did try a 6sa7 but that did not work either.. Tube was good but will not work in set

Skip

RE: Magnavox 155B - RodB - 06-24-2022

Like Terry said, you need to feed it some steroids. Glad you found the bad tube, it's a hopeful sign. Not too much to go wrong in that area.

RE: Magnavox 155B - vecher - 07-03-2022

Isolated to the Disc Coil I think..

[Image: https://live.staticflickr.com/65535/52190593371_e138224134_z.jpg]

[Image: https://live.staticflickr.com/65535/52190851179_58431c24d4_z.jpg]


The caps are on bottom I think But what do I do next No clue as to values..

Skip

RE: Magnavox 155B - RodB - 07-03-2022

I looked at three schematics with FM discriminator circuits and two had 56pf and one had 60pf. I would suspect that there is a mica layer under the bottom with spring loaded contacts connected to the terminals. I've been successful in lifting a contract away far enough to render it inoperable then solder the replacement cap on the external terminals. When you bend the contact you are committed to using the external cap.

RE: Magnavox 155B - Radioroslyn - 07-03-2022

Ok so let's name the players. C-1 connects across the primary of the transformer. C-2 connects signal from the plate of the 6SB7Y to the secondary of the transformer. C-3 and C-4 create a capasitive tap to feed in signal into L-2. L-1 primary and L-2 secondary.

C-3 and C-4 are probably going to out of the equation as without C-1 or C-2 running afoul there wouldn't be any hv over there. C-1 is in parallel with L-1. It helps determines the resonate frequency along with the slug adjustment. It occurs to me that all four caps are part of that copper board cap and that all of it is going to go. C-3 and C-4 total are going equal about C-1 maybe 10-20mmf. C-2 is probably is going to be a bit smaller in value perhaps 5-10mmf. You may be able the measure them with a cap meter or check resonant frequency with GDO old skool...

ps Didn't see Rod's post so values are probably more realistic than my guesses.

RE: Magnavox 155B - vecher - 07-04-2022

Terry and Rob Ok thanks.. Terry I will send you a email.

Skip

RE: Magnavox 155B - Radioroslyn - 07-06-2022

Sent you an email in return.

RE: Magnavox 155B - vecher - 07-14-2022

Ok thanks to Radioroslyn who gave me a coil that would work.. I have to report all is Good now..Alignment went with no problems no noise.. lots of stations coming in.

Thank to all

Skip

RE: Magnavox 155B - Radioroslyn - 07-14-2022

So glad to hear you got it working!