There are a few different recommendations I've found for these common anode replacement diodes.
Is the NTE 5991 400Volt 40Amp the current recommendation or are there others that are preferable?
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I just did my two ZW's about a month ago. I used 1N1190RA, 600V 35A. Available from Mouser Electronics as 844-1N1190RA. Although your NTE number looks like it would work just fine as well. Definitely made my postwar whistles a lot more responsive.
Despite what I saw on YouTube of several attempts to poorly explain and demonstrate the conversion, I found it fairly simple and straight forward. Took me about an hour to do my first ZW, and about 45 min for the second ZW.
@CJ Meyers Thank you for your recommendation and advice.
One of the better how to replace videos I've seen is the one by Jim Barrett in the OGR video section. He made it look easy.
Here's a link to it: VIDEO - Replace the Whistle Diode in a ZW Transformer
@gunrunnerjohn Do you have any thoughts on this question you might wish to add?
Only at the currents in play here, 35-40 amp diodes seem over kill. Also, though I can't find it, someone published a technique using Zener diodes that worked better for activating the whistles than the standard silicon diode. I think I'd look for that technique before I settled on the part.
Also note that I believe you need a reverse polarity diode, the anode to the case.
Here's a great page on replacing the diodes, and I know Kent has a lot of experience: Tranz4mr’s ZW Page
@Windy City posted:
It would be a lot more useful if he actually said how they were installed.
John and WindyCity, thank you. That linked thread provided this part number which is currently in stock at Newark. Is this what you're thinking about?
Manufacturer: SOLID STATE Part No: 1N3311B Zener Single Diode, 12 V, 50 W, DO-5, 5 %, 2 Pins, 175 °C, Anode to case
@gunrunnerjohn posted:It would be a lot more useful if he actually said how they were installed.
Are you thinking it might be different from the typical anode to case diode installation?
@SteveH posted:Are you thinking it might be different from the typical anode to case diode installation?
Likely, they're using the Zener voltage to establish the DC offset, and I'm pretty sure the Zener diode installation dispensed with the resistor as they didn't need it.
Without knowing the correct zener diode replacement procedure for certain, I'm somewhat inclined to go with what is known to work and which would be better than the non-functioning selenium rectifiers I have now in both all original ZWs. The NTE rectifier is a little less expensive and I'm also eager to place a few different parts orders which will include one of these types of diodes.
NTE5991 = $7.10ea x 4 = $28.40
vs.
1N3311B = $9.22 x 4 = $36.88
If anyone can provide the correct installation method to use a zener and is certain of improved whistle characteristics, I'd be willing to try that. Will probably place orders in the next few days.
I thought I would watch the video that SteveH provided a link to, as I need to replace a couple of diodes in my old ZWs.
I got this for a message:
@CPF3 posted:I thought I would watch the video that SteveH provided a link to, as I need to replace a couple of diodes in my old ZWs.
I got this for a message:
Sorry about that. I guess the Video's are available to OGR Digital Subscribers. Is there's a way for other members to view?
The link GRJ provided is also a very good step-by-step including pictures.
Here is that Link again: http://www.tranz4mr.com/ZW_Whistle_Diodes.html
Steve,
Which zener diode did you end up buying?
How did it work?
Did you remove the resistor? Many posts say to remove the resistor but Tranz4mr's page says not to remove the white wire (the resistor). Which is correct?
Thanks all for your help.
Don
