Change 120v to 6v Indicator lamp on 1959 SLP Reissue

[liquidlew]

I have a pre-EFX loop 1959 reissue and want to change the flat 120v indicator lamp to the bigger sized 6v lamp. Can this be swapped straight out or is there some components that need to be changed/added? Why do I want to do this? Well, I used to have some old mid 70's 50w's and 100w's and I loved that indicator lamp mojo, these pre-EFX loop reissues have the skinnier flatter lamp and I just don't like the looks of it. I see that the reissues WITH the EFX loop have the bigger 6v lamp, why is that? I know it's probably a dumb idea, but I'm the king of dumb ideas. Thanks!

[MKB]

You can simply swap the lamps out, but you would connect the 6V lamp in parallel with the tube filament string, where the 120V is connected to the mains input after the power switch. You shouldn't need any additional parts, only install the bigger lamp and wire it to the filament string.

[sikter]

Do not do that yourself! Let your tech do it for you!
I'm afraid you don't see the difference between 120VAC and 6VDC.

[liquidlew]

Yeah thanks guys! That's why I asked this question, I know there's a big difference between 120 ac and 6 dc and I figured I couldn't just swap one with the other without changing something. But why does the pre EFX loop heads have the smaller profile 120v lamp, then the EFX loop models have the 6v lamp with the larger profile bulb? Seems all the heads I have ever seen have the bigger bulb, I have never seen this flatter style until I got this pre EFX loop reissue. I just gots to know!

[liquidlew]

Hey MKB, where exactly is the filament string? I don't understand schematics, but if you could put up a pic of where it should go, that would be great!

[Anitoli]

Do not do that yourself! Let your tech do it for you!
I'm afraid you don't see the difference between 120VAC and 6VDC.

But you can certainly feel it......

[Anitoli]

More seriously though if you look at this schematic it will give you an idea of how the 6v lamp is inserted into the heater string on a 1959 handwired.
As the other posters said this is where you would want it.

http://marshallroadhouse.com/download/file.php?id=3062

[MKB]

One other thing; if you connect the 6V lamp to the heater string, you will probably need a 6VAC lamp, not VDC, as most filaments run on AC. Some Marshalls have a preamp tube running on DC for noise reasons, you would not want to connect it there.

As was mentioned before, please have your tech do the installation as there are very lethal voltages inside Marshall tube amps, often the filament voltages are on terminals very close to the high voltages. If you happen to wire the bulb to a high voltage terminal, you could blow up your amp, burn down the building, or even kill yourself. This can be a dangerous modification if you aren't totally clear about what you are doing.

[michael_dba]

Hey MKB, where exactly is the filament string? I don't understand schematics, but if you could put up a pic of where it should go, that would be great!

The filament string in the pic below is the green twisted pair of wires that feeds voltage to the filaments (heater) of each tube.

[liquidlew]

THANKS!!! I still want to do this, but you all have helped me get my mind right and scared the crap out of me about the high voltage. Do not want to wind up dead. But I don't want to pay a guy to do something simple I can do either, and it would cost me double as I have 2 heads. Isn't there a way to discharge the voltage, or does it naturally dissapate over a period of time? Or should I just get over it? I'm trying to, but not having any luck so far.

[michael_dba]

Easiest way to do it is just turn it on and play some chords, then turn the power switch off....you can hear the audio decay as it winds down....the caps are now drained. To confirm, unplug the amp and put a volt meter on the caps + and - and you should read about .3vdc.....residual voltage.


Here's a youtube video about it:

[youtube][/youtube]