Replacement part number for a 1S2687??

[Lkaskel]

Hi Everyone,
I am working on a first edition (2-button) President Washington. While I am de-moding it I found that in the PLL section one of the varactor diodes is missing. The part number is 1S2687. I have done the research and found that they are no longer available. Does anyone know of a decent replacement for this? All that I have read seems to indicate that I may be out of luck but I am hoping not.

Thanks as always!!!

 

[tecnicoloco]

Check ebay,I believe the seller is name is : littlediode

I bought a few about 3 months ago

Good luck
Andy/Tecnicoloco

 

[Lkaskel]

Check ebay,I believe the seller is name is : littlediode

I bought a few about 3 months ago

Good luck
Andy/Tecnicoloco

Andy,
I have purchased some stuff like this of of E-Bay and many times they were fake. Did the parts you purchased work out ok? Also, I would love to know if someone has used a different part and had success.

Thanks!!

 

[Handy Andy]

If you can find an SVC251 (Galaxy Varactor) it should work

Some other contenders from DIGI-KEY
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One of many "main aspects" of searching for Varactor's, once you get past your stomach over losing all your stuff to SMD - the parts bins are there and have quite a few selections to work with.

The main one is to find a large enough STARTING pF Capacitance and then works down, LOWER to a smaller value once the Voltage rises up.

Meaning - since these things are "reverse biased" the junction itself has a "MAX reverse before Breakdown - mostly 12V should do fine.

Remember too, the "Holes" on one part of the junction and the "Electrons" in the other - in the reverse bias condition - begin to separate and form a reverse bias "plate to plate" Intrinsic condition to make it appear as a variable capacitor.

 

[tecnicoloco]

Andy,
I have purchased some stuff like this of of E-Bay and many times they were fake. Did the parts you purchased work out ok? Also, I would love to know if someone has used a different part and had success.

Thanks!!

Yes they seem legit and worked for me

Littlediode_components 99.5% positive feedback

https://www.ebay.com/itm/324233338071?hash=item4b7dd01cd7:g:l7sAAOSw02JfEnAu

He is located in Anaheim, California and fast shipping

Good luck
Andy/Tecnicoloco

 

[Lkaskel]

If you can find an SVC251 (Galaxy Varactor) it should work

View attachment 45527

Some other contenders from DIGI-KEY
View attachment 45529​

One of many "main aspects" of searching for Varactor's, once you get past your stomach over losing all your stuff to SMD - the parts bins are there and have quite a few selections to work with.

The main one is to find a large enough STARTING pF Capacitance and then works down, LOWER to a smaller value once the Voltage rises up.

Meaning - since these things are "reverse biased" the junction itself has a "MAX reverse before Breakdown - mostly 12V should do fine.

Remember too, the "Holes" on one part of the junction and the "Electrons" in the other - in the reverse bias condition - begin to separate and form a reverse bias "plate to plate" Intrinsic condition to make it appear as a variable capacitor.

Thanks H.A.!!!
I found the SVC251 on Barkett's site so I am going to pick it up from him as I need to get a few other things (Robyn and Cobra 2000 meters included) to help with shipping costs. As I thought this through, I decided to take the original varactor from the USB section and put the Galaxy varactor in the USB slot. I know the owner NEVER talks on USB so that will help me sleep better knowing I should not get a call that their radio is not functioning as expected.

I always appreciate your help!!!

 

[Lkaskel]

Yes they seem legit and worked for me

Littlediode_components 99.5% positive feedback

https://www.ebay.com/itm/324233338071?hash=item4b7dd01cd7:g:l7sAAOSw02JfEnAu

He is located in Anaheim, California and fast shipping

Good luck
Andy/Tecnicoloco

I did reach out to Mrsprockets1 in California and I may buy some from him if I can't get the Galaxy varactor to work. Not that it's a huge deal but he charges $5 for shipping so it doubles the cost of the diodes from him.

Thanks again Andy!!!

 

[Lkaskel]

I did find this excellent video on how a varactor works in an oscillation circuit .

 

[Handy Andy]

As I thought this through,

Remember the issue of having the right values of the Varactor is less important - then to find the right capacitance it "varies" against in the circuit - that trim cap will help you in the "realign".

The schematic "snippet" I posted is to show you that other capacitors can be used in the Varactor tuning circuit that works in Parallel with it - ADDs capacitance to change the way or region of which, the circuit will tune with a working capacitive value to tune with, but displaces the range of tune by it's value too.

Since one cap is fixed, works a lot like a parallel circuit resistively - meaning the smaller cap will force the varactor's range to be less - no equal to - MUCH less in value than the Varactor can tune, but it is useful to help in RESOLUTION of tuning range (variable pot control) - which is why a large value Varactor even with the drifting qualities of the Galaxy chassis - is required to obtain the nuances of the tuning thru both Coarse and Fine ranges of tune with less drifting because of the larger value - that fixed cap has to work against - which makes the drifting issue actually less than to use a smaller range Varactor - which has it's own tolerance and drift changes. Remember that the lesser smaller varactor provides less capacitance - but the impact of the smaller range (Ohms law) - lessens the stability and shrinks the tuning range..