Ht fuse replacement for marshall jcm 800 2205: Fast blo or slow blo??

[jalexquijano]

Last night while learning to do the bias on my JCM 800 2205, one of the power tubes went south and at the same time the 500ma slo blo HT fuse also did. Just got a replacement at a local chinese electronic shop. However, its a fast blo 0.5 A 250V fuse. Will it do any harm to the amp not being a SLO BLO type fuse? If so i will need to order one in one of the Marshall parts website or www.tubesandmore.com.

Any recommendations? wouldnt like to blow anything else!

[Jazz P Bass]

slo blo is o/k for a test.

If something is truly bad (like a power tube) it will take it out just as quick

[nickb]

Substituting a fast blow for slow blow won't do any harm to the amp.

The problem you will face is it will blow prematurely, perhaps the very first time you turn the amp on. A big surge of current has to flow to charge up the main capacitors and that may blow the fuse, or at least weaken it so it will open prematurely. The temptation is to use a higher rated quick blow one. That may solve the repeated blowing but when a real fault happens, excessive current will flow and may result in greater and expensive damage. So don't be tempted.