SLOW BLOW FUSE

[KB5MD]

What is the advantage of running slow-blow fuses as opposed to a regular fuse?  I have an Apache that will blow a 10amp fuse after being in qso for a while. Heathkit lists it as using 7amp slo-blow.  Do 7amp slo-blow type carry more than the 10amp regular?  "Inquiring minds want to know"
    I was in qso with John, KX5JT yesterday afternoon and "bamm!!!", another fuse went off like a pistol shot.  I can't seem to find any problem with the transmitter, but "for the life of me" I can't keep fuses in the darn thing.

[WQ9E]

An Apache should definitely not need even a 10 amp fuse under normal conditions.  A slow blow is usually used to prevent "nuisance" blowing under start-up surge conditions and it is preferable to use an inrush limiter with a regular fuse.  My Valiant uses lower current fuses than this and it is rated for higher input power and has never blown a fuse.

Are your plate and modulator (resting between syllables) staying OK during long transmissions or are they creeping up? 

You need to find the root cause of this behavior before something expensive like a transformer or choke goes to BA heaven. 

An AC ammeter is useful in a case like this also.  Monitor your current draw during transmission and see if it is creeping upwards.  But I have a feeling something is breaking down during transmission causing a sudden increase in current rather than the fuse opening due to high average current.  A slo-blow fuse will perhaps carry this surge causing something much more expensive to give up.

Rodger WQ9E

[W2PFY]

It's important to know where in the fuse it blew. If it blows near either end of the fuse it could be a thermal problem associated with it's mounting hardware. It it blows in the middle of the fuse it would be more likely  a component problem in the transmitter. My guess since it takes so long for the fuse to blow, it's a hardware issue.

[KC4VWU]

Yup, I have seen cracked panel mount fuseholders that are not appearant unless you really scrutinize them. Also corrosion buildup. Possibly a flakey PA or mod tube? How's everything looking AFTER the transmittter's output connector? If nothing visually stands out, start isolating sections by process of elimination to narrow down the possibilities.
73, Phil