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Question about Zener Diodes and LM307H voltages

Hey there,

Servicing an HD-130 head. No reverb with 12AX7 driver.

Recapped it, had symptom of "cuts out randomly" from before recap.

So I find a bad LM307H in ch2, think that's it. Replace it, but then another one fails. This continues.

Then I check my voltages (should have done this sooner).

Seems the LM307H's are getting +/- 46v

Someone in the past has replaced the two zeners with 1n4007's

I'm guessing my problem is that the zeners are what gets me down to +/-16v, correct?

Hoping someone confirms my suspicion before placing another parts order.

Thanks, just found this forum and it's a great wealth of info.

Edit to also ask: is the 1n4745 the correct replacement? It's not labeled on my schematic but I see it on several others and it seems to fit the bill. Is there any reason that a 5w 18v zener would be a bad idea? Lack of protection in case of a fault?



The short answer is Yes. That's what zeners do. It's best to stay with 16V and 5W if you can. Also, stand the new ones off the pc board 2mm for better heat dissipation. Here's an example: https://www.mouser.com/ProductDetail/Micro-Commercial-Components-MCC/1N5... -mgriffin
BTW: 1n4745 is a 16V 1W zener and will get too hot and fail over time. Go with 5W rating.
1n4007 is not a zener diode and it will not work in this voltage regulator application. Just sayin'.

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