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Old 14th May 2018, 11:42 pm   #1
high_vacuum_house
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Smile BA148 diode. Can I use a 1N4007 in its place

Good evening,
Having issues and looks very much like this diode is conducting in both directions. It is a single diode rectifier off a winding on a LOPT to produce the A1 and focus voltages.

A 10uF capacitor on the rectified output side was changed as the diode was getting warm and no EHT was produced. Removing the capacitor the EHT sprang back to life and the diode was cold. Replacing the 10uF with a new cap resulted in exactly the same as before. There is no loading on this circuit other than a 10 megohm pot. Therefore I believe the diode is the culprit here

The PIV for this diode is 300V. Should a 1N4007 diode be ok in this position.

I have a couple of BYW96E (1KV 3A) diodes somewhere could one of these be used?

Many thanks,
Christopher Capener
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Last edited by high_vacuum_house; 14th May 2018 at 11:48 pm.
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Old 14th May 2018, 11:47 pm   #2
kellys_eye
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Default Re: ba148 diode. Can I use a 1N4007 in its place

1N4004, 5, 6 or 7 will work fine
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Old 15th May 2018, 12:27 am   #3
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Default Re: ba148 diode. Can I use a 1N4007 in its place

IN400x are slow turn-off, and in an HF supply will be inefficient and may upset the circuit operation. BA157, BA158 would be a more usual modern substitute and cost pennies but the fast-recovery BYW96E would be worth putting in if you can locate one and ought to be bullet-proof here.
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Old 15th May 2018, 12:39 am   #4
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Default Re: ba148 diode. Can I use a 1N4007 in its place

UF4007 should work. They are fast enough for SMPSUs.
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Old 15th May 2018, 7:22 am   #5
kalee20
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Default Re: ba148 diode. Can I use a 1N4007 in its place

Agree Refugee and turretslug, the types they suggest should be fine.

Try a 1N4007 only if you don't mind doing a few replacements if it doesn't work. The slow turn-off will be inefficient at best, and might take out the drive transistor or reservoir capacitor at worst.
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Old 15th May 2018, 11:01 am   #6
kellys_eye
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Default Re: BA148 diode. Can I use a 1N4007 in its place

I tend to purchase the UF4*** series as a matter of course these days. 'Same' device but faster. I should have mentioned this at the start.... sorry.
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Old 15th May 2018, 11:08 am   #7
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Default Re: BA148 diode. Can I use a 1N4007 in its place

The 1N400x series tend to turn off with a snap, radiating a lot of RF interference.... that stuff we moan about coming out of billions of SMPSs.

Counter-intuitively, using fast diodes makes things cleaner.

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Old 15th May 2018, 11:10 am   #8
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Default Re: BA148 diode. Can I use a 1N4007 in its place

Very true with the 1n400x's. You have to stick a cap across them to shut them up!
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Old 15th May 2018, 4:30 pm   #9
high_vacuum_house
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Smile Re: BA148 diode. Can I use a 1N4007 in its place

Well I fitted a new BYW 96E diode and a new 10uF 450V capacitor and this has sorted out the A1 and focus supply. The old diode once removed conducted in both directions!!.

We now have EHT in a fashion and light on the CRT though looks like there is a breakdown in the EHT overwind. The 0V wire out of the overwind has corroded away where it goes into the potting compound.

Many thanks for your help.
Christopher Capener
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