MV13YH

[tinkerer973WI]

I'm quite sure this has been brought out several times, but it doesn't seem to have its own spot, so here goes. Hopefully someone has figured it out.

Has anybody found a good replacement/ source of the mighty MV13yh bias diode, found in lots of popular ssb rigs, one would think they should be easy enough to get. I know the MV1Y can be replaced with a 1n914, but the MV13yh seems to elude everyone I've spoken too.....Help Please

 

[sp5it]

I use 1n4148 as replacement since ages and it works as it should.
Mike

 

[tinkerer973WI]

So you used a 1n4148 in place of the MV13yh, I've heard of a 1n914 in place of the MV1y, but thought there was some series of components for the MV13yh

 

[Robb]

Not much difference between a 914 and the 4148 - IIRC.

The only time I see the MV13HY used, is when the circuit has a fully regulated bias supply.

Also - the MV13YH also has a greater voltage drop than a MV1Y.

 

[bob85]

You need more volt drop over the diodes than one single diode provides for decent tracking in that style circuit.
Two diodes in series not only throttle back bias voltage as the final heats up they also help to cancel the increased conduction of the bias pass transistor as it heats up.

 

[tinkerer973WI]

In a nut shell that's what I thought I had read a few years ago. So before I do it, and find out otherwise, cause as we all know these Mitsubishi outputs are like gold, Bob85 , you are saying 2 diodes, are we still talking 4148's, or are you just saying it takes more than single diode. I have the transistors, and I know the MV13YH is junk, I'm tring to find a replacement/alternative to the impossible to find MV13yh that aids in biasing the 1969 final.

 

[Robb]

Never had to do it yet; but you may need to 'roll your own' from a pair of 4148's.

EDIT:
And please; could you post your findings if you do this?

 

[tinkerer973WI]

I was kinda hoping Exit 13 or somebody was gonna chime in here. Looks like RFParts is carrying the transistors again, not sure where they're getting them from, but at $18 a pop, i'm leary to experiment. I have a couple chassis I could pull one from to take measurements, might be a last resort. If I do i will definitely post results.

Tinkerer out for now

 

[nomadradio]

The MV1Y has one silicon diode junction inside it. Forward-voltage drop is roughly 6/10 of a Volt.

The MV13Y has two diodes in series inside it. A series pair of 1N4148 will usually do the job okay.

I'm sure I wrote an explanation of why the Uniden radios use the MV13Y on another forum, but can't find a copy of it right now.

Dern!

But that's the deal. The "MV" diodes were designed for temperature compensation. As the driver or final gets hotter, that "6/10 Volt" drop inside the transistor between the base and emitter legs begins to fall. If you provide your bias current from a fixed source, the transistor pulls more base current as it heats up. Which makes it heat up more. And draw more bias current. Textbook name for this is "thermal runaway".

Providing the bias voltage from a diode that has the same temperature curve causes the bias voltage you feed to the transistor to drop off as temperature rises, hopefully in step with the transistor's tendency to pull more current, reducing the bias voltage as it gets hotter, and keeping the transistor's bias current from running away.

73

 

[bob85]

Tinkerer
I have never played with biasing in the old unidens & never come across the mv13yh

i have built & used plenty of different bias circuits and tested them for thermal and load regulation.
That's how i know you need more than 1 diode in that style circuit for good performance.

You don't just need to throttle back bias voltage as the final heats up.
The pass transistor also heats and conducts more.
A single diode say mv1y in that circuit will give you an idle current that rises with temperature.

Yes just about any silicon diodes will work if you make sure they have good thermal contact.
Its far from perfect but its better than what you find in most HF sets using bipolar finals.

Small diodes have less thermal mass so track faster than large diodes.

I have also used a single diode in series with the base/emitter junction of a transistor the same as the pass transistor to cancel drift in that type circuit..

 

[tinkerer973WI]

Thanks a ton guys, that's the type of explanation that makes a guy feel comfortable following someones advice, Nomad, I may have read that other post at one time, reading this one rang a bell in my head... thank you both, with any luck I'll be aligning a lightning struck President Washington later today. This has been a 3 year, fix as i have time and money, project. More for the sake of, can I, than I want to..... but ohh what I have learned along the way...... again thank you, I'll post results later.