No19 set fuses

[James D Teel II]

What are the two fuses needed for the No19 MkII PSU? I know one is a 5A/125V, but is it a fast acting or slow burn fuse? What’s the other one? The only markings on it are “BUSS MBB 1/4”.

Thanks.

[David Dunlop]

Hi James.

The fuses and fuse holders were all Little-fuse products, out of Chicago. The fuses are still available from them under the 3AG listings on their website.

The two High Voltage fuses are 250 milliamperes (or 1/4 amp if you prefer). Not sure of the original part number at the moment.

The Vibrator circuit is protected by a 10 Amp, 25 Volt fuse. Wartime Part Number is 1081-C.

Littlefuse changed their part number system some time ago but the core number will still show up in the new one. Look for the 10 Amp one first. Once you find it, the other should also be in the same series.

To my knowledge, neither are SloBlow.

David

[James D Teel II]

Thanks, David. I’ll give them a look.

[Bruce MacMillan]

Buss and Littelfuse are competitors that produce the same product. The Buss MBB is now called AGC, Littelfuse 3AG is now the 312 series. The high voltage is a fast blow (312) but the 10A is slow blow (313 series). Look closely and you can see a spring at one end of the fuse. This allows a higher inrush current than the actual rating.

[James D Teel II]

I’m having a devil of a time looking them up. Here they are in the order described.

[James D Teel II]

Oh, and my PSU is a 1943 Philco No.1. My apologies for not making that clear.

[James D Teel II]

Well. I found a NOS pack of the 5A 125v fuses, but am still looking for the one on the right.

[rob love]

As Bruce mentioned, the MBB series turned into the AGC series a long long time ago. The AGC is a 1/4" by 1-1/4 glass fast blow fuse. So what you are after is a Bussman or Eaton AGC 1/4A fuse.



Here is a link to a page where the fuse types are discussed and the mention made of the MBB type. https://www.galco.com/techdoc/buss/mbo-8_dat.pdf


Here is a link to the specific fuse on quesiton, but you will likely find them locally. They are not rare. https://www.allfuses.com/agc-1-4

[Chris Suslowicz]

Originally Posted by James D Teel II

Well. I found a NOS pack of the 5A 125v fuses, but am still looking for the one on the right.

But those are the wrong fuses!

For the HT1 and HT2 protection fuses you should be using 250mA quick-blow fuses only. (There are different designs and "the one on the right" is a very old type, probably no longer available.)

I have 6 bags of 10 fuses each at my elbow right now. DM me your address and I'll put a bag in the post to you next week.

Best regards,
Chris.

[James D Teel II]

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