ST-120 What Kind of Fuse Is This ?

Which of the following three kinds of fuses do I need to use on the ST-120;

1) fuse1

2)  fuse2

3)  which other kind do you recommend if the above two are not the right kind?
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I think the amp is fixed now, hopefully maybe anyway.  I have not yet heard any music out of it.  I unscrewed the driver board and snipped off several of the wires that might have been a little too long (not sure if that was it tho).  Then I turned the amp open side down and used cans of compressed air to blow it out of any possible bits of wire or anything in there.  I replaced the rectifier tube with a JJ GZ34.  So then I turned it on and everything was fine for 5 to 7 minutes as I read the instructions to bias the amp.  All eight tubes lit up perfectly and no noise, all seemed great.  Then I biased the first tube to 0.550 and then as I was turning up the bias on the second tube the fuse blew.  I think it might have blown because I needed an extra hand to hold the ground probe on the chassis and so I didn't get a good meter read on the bias and so i think i went too high.  So now I need to find a source for this fuse, which is definitely blown.

Kind thanks,
Eddie

fuse3

this one looks a little different and maybe a better match as far as looks more like the one that Bob shipped with the ST-120, just don't know if it should be a 5-20 or a 1 1/4 x 1/4. The glass measures 5 x20 but the overall is 1 1/4 x 1/4

Measure the entire length of the old fuse end-to-end, it's likely 1/4 x 1 1/4. Get the Littelfuse 5 amp slow blow. It's a high quality product at 1/2 the price of the Cooper/Bussman.

And I strongly suggest you lose the JJ 5AR4/GZ34. They are not very reliable. If the budget allows get a new production Tung-Sol 5AR4 or Genalex GZ34. Both will be far better in the application. I'd also suggest you do the diode mod that Bob recommends - just use UF4007 diodes instead of the noisy 1N4007s.

#2

Amp calls for a 3AG fuse type, which describes the body style and size. An AGC also works ...

PS ... make sure you get the correct rating for your amp and NOT slow blows or fast acting ... Good old fashioned "standard" is the way to go.

CORRECTION > > The VTA amps do use slow blow fuses. My bad ...   

Little trick for the ground probe ... Prop the chassis up a bit with a chunk of scrap wood or whatever that's non-conductive, and just slip the probe tip between that and the chassis. Voila ... you just grew an extra hand ... use it wisely.  

sKiZo wrote:#2

Amp calls for a 3AG fuse type, which describes the body style and size. An AGC also works ...

PS ... make sure you get the correct rating for your amp and NOT slow blows or fast acting ... Good old fashioned "standard" is the way to go.

Little trick for the ground probe ... Prop the chassis up a bit with a chunk of scrap wood or whatever that's non-conductive, and just slip the probe tip between that and the chassis. Voila ... you just grew an extra hand ... use it wisely.   

According to Bob Latino's post on 9/22 of 2013 "The 5 amp slo-blo fuse should be fine with either KT88 or KT120 output tubes in either pentode ultralinear or triode mode."

So your advice to not use a slow blow fuse contradicts the amp's designer. Are you saying Bob was not correct with his recommendation?

My bad ... never had the privilege of blowing a fuse in mine and didn't bother to check.   

Not sure as I'd still need one, having an inrush limiter on mine?