The MV1Y Diode; Can it be Substituted?

[Robb]

Working on a Cobra 2000GTL for a local operator. The driver needed replacement. But it appears that there is no bias on this device. I suspect it is the MV1Y diode. But they cannot be found on the internet.

Can I use a 1N4148 or a 1N4003 diode in its place?
Will it damage the driver?

 

[unit_399]

Robb-

I think you can use a 1N914, but it will have to be epoxied to a metal tab and installed like the MV1Y, so that it functions as a thermal diode. It's too late to go down to my shop tonight, but I will post tomorrow and let you know for sure.

- 399

 

[Robb]

Thanks!

Would it be better to glue it to the driver itself?
Same thing goes with the final?

 

[unit_399]

Robb -

A 1N914 will work. Glue is ok, but epoxy will give a better thermal bond. Direct to tab on driver & final is ok too.

- 399

 

[Robb]

Great, thanks!

May I pick your brain once again here? What is the difference between the MV1Y and the MV13YH bias diode? Is it a 1n914 as well; or is it a different animal?

 

[unit_399]

different animal

 

[Robb]

I've read somewhere online that the MV13YH is actually a series of three diodes - which creates a voltage drop. Dunno which diodes nor how much drop - if I were to make my own. Probably using the same 1N914's I'll bet . . .

I went down to Halted Electronics in Sunnyvale, CA. Bought 20 1N914 diodes @ $.03/ea. Also bought 20 1N4148 diodes at the same price. I understand that the 4148's have practically the same specs.

 

[Robb]

Turned out that the driver bias pot was the issue after more examination. Requires a 500 ohm pot; but it seems it still wouldn't bias down to 25mA's. Thought something was wrong with the c2166 I put in to replace the c1306. Put in a 1000 ohm pot and used a c2312 for a driver - and now the minimum bias is 80mA; got worse.

BTW - three other VR's were also faulty; so I replaced them all for fair measure.

http://www.cbtricks.com/radios/cobra/2000gtl/graphics/cobra_2000gtl_om_main_sch_11x17.pdf

Q: where are the AGC diodes; still trying to understand this radio.

The power supply smoothing cap was waaay, waaay out of spec so I replaced it. This radio is a real candidate to have all of the electrolytic and tantalum caps replaced IMO. Might end up doing just that too . . .

Max output on the radio on SSB is 8w and 5w on AM. Haven't peaked the TX cans yet. Ordered some MV13YH diodes to replace D49. Although that diode tests OK, been reading that they can be faulty and not properly bias under load. Also replaced the c496 bias control/TR37 and no change. Weird.

This radio is a real basket case. Have repaired many things already; just a few things left to do. Radio is also getting receive coming through in the PA mode when the CB/PA is switched. Still trying to figure that one out! It's a big problem because the receive is better in PA mode than it is in CB mode. CB/PA switch and wiring check out OK.

 

[Robb]

Transmission1 • View topic - 6 band Jackson output woes

http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=MV1Y

 

[Robb]

Found a great substitute for the MV1Y. It is a NTE-610. It is a varistor that has the same specs as the MV1Y. Cost is about $.60 apiece.