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 Post subject: Grundig Satellit 6001 thermistor (?)-what is it?
PostPosted: Jan Tue 30, 2018 4:50 pm 
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Location: Santa Cruz mountains
I'm working on a 6001 for someone at my radio club.

The problem I am having is Bands 2-9 will play for some short period of time and then start fading out and eventually the reception dies completely. Switching to LW/ AM / SW1 or FM for a few minutes or turning the set off and then back on after a few minutes will allow bands 2-9 to work again, and then slowly die as before.

I've determined that the 2nd local oscillator gets weaker and weaker, eventually stops oscillating, which is why the reception dies.

After considerable observation of the circuitry in operation, I've determined that the problem is probably being caused by this thing:

Attachment:
component.jpg
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Attachment:
schemer.jpg
schemer.jpg [ 143.07 KiB | Viewed 279 times ]



It is the diode shown in the schematic snippet above, next to T3.

It shows as a diode on the schematic, but it ain't exactly that. it appears to be a component that varies resistance by temperature. When I google the number shown on the schematic, the (very few) hits that come back reference a "non-linear resistor".

What is a modern replacement for this device? I see some vendors selling a FAMILY of components under the 2322574 number shown on the schematic, listing several different values of components instead of a specific one. I'm assuming the bands on the body mean something, but I can't find a color code for this device. Does anybody know?


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 Post subject: Re: Grundig Satellit 6001 thermistor (?)-what is it?
PostPosted: Jan Tue 30, 2018 7:04 pm 
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Location: Amsterdam
This is not a thermistor. The symbol is quite different.


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 Post subject: Re: Grundig Satellit 6001 thermistor (?)-what is it?
PostPosted: Jan Wed 31, 2018 12:20 am 
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OK, it is not a thermistor, it is a varistor.

I found this in a 1974 catalog for Mullard passive components:

Attachment:
mullard_VDNLR.jpg
mullard_VDNLR.jpg [ 128 KiB | Viewed 250 times ]


So, where do I get the equivalent component in modern times? Most varistors I see online are the type used in power strips and power supplies to absorb line spikes.

This is obviously very different from that. It's supposed to change its resistance a bit in accordance with small changes in the applied voltage. I'm assuming that this was put in there to compensate for variations in battery voltage as the D Cells run down. It seems to be breaking down slowly as power is applied to the circuit and pulling critical voltages in the 2nd converter oscillator down enough to stop oscillation entirely.

If the part is NLA, I'm wondering if a couple of diodes in series might do almost the same thing.


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 Post subject: Re: Grundig Satellit 6001 thermistor (?)-what is it?
PostPosted: Jan Wed 31, 2018 3:46 am 
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Joined: Jan Tue 31, 2012 1:55 am
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Location: Mountains of Mourne. Ireland.
There are three of those puppies in your radio.
one at the base of T9 RF board, and one at the base of T12 FM tuner board.

https://www.doctsf.com/grandlivre/fiche ... 046&ori=ps

Greg.


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 Post subject: Re: Grundig Satellit 6001 thermistor (?)-what is it?
PostPosted: Jan Wed 31, 2018 8:45 am 
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Location: Ashhurst, New Zealand
IMHO they are forward biased diodes that have a specific voltage drop across them- not necessarily the 0.3 or 0.6 volts that you would expect,

_________________
Cheers - Martin ZL2MC


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 Post subject: Re: Grundig Satellit 6001 thermistor (?)-what is it?
PostPosted: Jan Wed 31, 2018 1:51 pm 
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Location: Mountains of Mourne. Ireland.
Image
Image: https://ia800700.us.archive.org/BookRea ... 4&rotate=0
from: https://archive.org/details/CircuitDesi ... edCircards

Greg.


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 Post subject: Re: Grundig Satellit 6001 thermistor (?)-what is it?
PostPosted: Jan Wed 31, 2018 1:57 pm 
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Joined: Jul Wed 22, 2009 3:07 pm
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That diode with T3 composes a current source for the T4 transistor, which looks to be a grounded base oscillator stage.
The schematics shows 1.25V voltage drop across that diode (it is biased in the forward direction). I would replace that component with two regular Si diodes (1N914 or similar) in series.

Peter


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 Post subject: Re: Grundig Satellit 6001 thermistor (?)-what is it?
PostPosted: Jan Wed 31, 2018 8:02 pm 
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Joined: Mar Thu 16, 2017 11:14 am
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Location: Amsterdam
seems to be hot everywhere right now...

https://www.radiomuseum.org/forum/grund ... ellit.html


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