Hi there,
Being a newbie to this forum (and to the 9005 as well), I'm looking for a bit of help please.
I've recently purchased a second hand Marshall 9005 Power Amp to accompany an Engl Pre-amp.
The problem comes when I try to run my 1936 2x12 Cab in Stereo as channel B on the 9005 cuts the power when taken off Standby. I can switch the Power Amp on fine with an impedance of 16 ohms on both channels, take channel A off Standby to get sound out of one of the speakers within the cabinet, but switching channel B on immediately blows a fuse and the power is lost.
Appologies if I now start to lose you as I'm hopeless with all this electrical talk but on the back of the PA in the channel B section, there are two fuses labelled:
FUSE 1. Fuse 120V - T4A. 220/240V - T2A
FUSE 2. HT FUSE T800mA
I currently have 5a and 800mA fuses in respectively. Am I correct in doing so?
A friend of mine has a 9005 as well but his are labelled as:
FUSE 1. F12a 250V
FUSE 2. 500mA 250V
Any advice at all? Are my fuses incorrect? Is it something more serious? Any help would be much appreciated, thanks.
*Edited to change description of fuse to 800mA*
Fuse 2 is labeled as 800mA, that's 0.8 amps, or 1/8 of an amp.
If you have an 8 Amp fuse in the F2 position and you're still blowing that fuse, then you're putting yourself and your amp in danger.
If the schematic I found online is correct, F2 is the tube plate voltage fuse. If you are blowing that, it means you are forcing way to much current thru the output of your tubes.
Have you tried taking only channel B off standby (leaving channel A on standby)?
Which fuse are you blowing (F1, F2, A side, B side?)
I wrapped a newspaper ’round my head
So I looked like I was deep
Hi there, and thanks for your reply. Apologies, I did actually mean that I have 800mA fuses in there!
After firing the amp up again and switching channel B on (without channel A this time), the same happened. The amp just cut out.
The fuse that immediately blew was the 'Fuse 120V - T4A. 220/240V - T2A' one, which I'd like to say is somewhat connected to the Mains. This photo may help (fuse cloest to the left) - 
The fuse that keeps repeatedly blowing in this socket is a 5a 250V. Do you think this is where I'm going wrong?
Again, thanks in advance.
Hi there, and thanks for your reply. Apologies, I did actually mean that I have 800mA fuses in there!
Ok, I'm glad that's sorted out.
After firing the amp up again and switching channel B on (without channel A this time), the same happened. The amp just cut out.
The fuse that immediately blew was the 'Fuse 120V - T4A. 220/240V - T2A' one, which I'd like to say is somewhat connected to the Mains.
Yes that is the mains fuse (it kills both A and B when it blows, right?)
My best guess would be a power supply fault.
If it was a bad tube or the output transformer, I'd expect the HT fuse to blow first.
This amp should be seen by a repair shop.
Or returned to the seller, if this is what happened when you first powered it on. You did say you were new to this amp, so I assume that it's a recent purchase.
I wrapped a newspaper ’round my head
So I looked like I was deep
Yes, it does kill A and B.
Thanks very much for your advice anyway. I've spoken to a few people now and they all seem to say relatively the same, just with an emphasis on 'take it to a tech / specialist' so that's what I think I'll do. Who knows... It might even end up 4 hours away in the Marshall repair centre.
Thanks again!
