JCM800 blowing 0.5A HT fuse - could use some help please

[valcotone]

I cranked the amp for a bit today with T0.5A Slo-blow HT fuses in place and it holds up nicely.

Thanks Wilder, Bruce, Enzo, bluesfreak - much appreciate the help! Plus I learned a lot about troubleshooting and will never forget that Marshalls use slow-blow HT fuses!

Now I need to investigate some mods for tonal improvements... maybe clip the bright cap or tone-peaking circuit on the input... but that's another story.

Thanks again all, you've been a GREAT help!

[acorkos]

don't mod it....just play it loud. the higher you can crank the volume, the better it sounds.

[bluesfreak]

The culprit on the combo are the G12-75T Speakers, I would recommend to replace them with G12H30 or classic greenbacks or if you like harder response Vintage 30s, see also Watford Valves :: Sound Factory - Listen to our speakers before you buy! for sound info. Also you can try changing the slope resistor on the tonestack to 47k or even 56k to remove some of the dull bass but the combo will never reach the punch of a head with a 4x12 due to the open concept.

[Gibsonman63]

My main gigging amp is a Marshall 4210, basically the two channel version of your amp. 1+ on trying different speakers. I am not sure what speaker is in mine because there is no label on the back, but is has a huge magnet structure and sounds good to me. My drummer is a little hard of hearing (imagine that!) and likes me to bring a second cabinet aimed at him to gigs so he can really hear me. The one I usually bring has two vintage 30s and sounds great with this amp. On a 4x12 enclosure the amp sounds huge. Two other suggestons. First, don't scrimp on tubes. Get some quality tubes and play around with different tubes for the first preamp section to get what you want. The second thing I would suggest is to dial in more mids if you haven't played with it. On my amp, it really fattens up the guitar. In a band situation, a lot of the bottom end gets covered up anyway by the bass guitar, Kick drum and floor tom. If you don't have enough mids then all you have left are the highs, which will end up sounding tinny.

It took me a long time to figure out that the amp sounds I dial in when I am practicing by myself don't always fit well in a band mix. Reamping is a great tool for tweaking amp tone.

If you still aren't where you want to be, then mod. I tweaked the gain stages on mine a bit, but ended up fairly close to where I started after some recording and a lot of critical listening and some trial and error.