Marshall 9005 modification

[HughF]

I have a working Marshall 9005. What do I need to do, aside from changing input and output connections, to make it into a hifi amp, change the tubes?

Cheers, Hugh

 

[DF96]

I am not familiar with the amp, but if it is like most guitar amps then you need to change the circuit and the output transformer. The valves will probably be fine as they are.

Guitar amps are not intended to reproduce sound, but to produce sound. Very different.

 

[HughF]

The schematic is there, this is just a power amp so I assume the sound production bit would be done in the valve pre that would have been before this in the rack.

 

[HughF]

After some wiki-ing I'm a bit more clued up on this now, I'll start with changing the plate resistors on the ecc83's for 220k

 

[DF96]

You will need to remove the presence control, and use flat feedback instead. Remove the Miller capacitance around V2; reduce the value of the V2 grid stoppers (unless the layout causes instability). Probably add more PSU smoothing to reduce hum. Increase the value of the balance resistor network to reduce anode load on V2. Reduce the value if the output stoppers (if possible).

You need to remember that a guitar amp only needs to go up to 5kHz or so; hi-fi needs to go to 20kHz minimum.

Much better in my view to sell the amp to someone who can use it, then use the money to make or buy some hi-fi. A conversion job, as you intend, is one of those tasks which if you knew enough to do it properly would also mean you knew enough not to attempt it.

 

[HughF]

You need to remember that a guitar amp only needs to go up to 5kHz or so; hi-fi needs to go to 20kHz minimum.

Much better in my view to sell the amp to someone who can use it, then use the money to make or buy some hi-fi. A conversion job, as you intend, is one of those tasks which if you knew enough to do it properly would also mean you knew enough not to attempt it.

Thanks for your advice, I hadn't considered the upper frequency limit...

If I could find a buyer willing to take it off my hands, I'd certainly consider putting the funds into a more suitable kit. I'll explore this avenue further.