A few simple mods for my Old Canadian Pepco

[copperheadroads]

I have one of these possibly 1 watt student amp from the 60's mine is branded "Arc" I believe it the common #801 which follows this schematic

I just curious if i could mod it to get a little more gain out of it at the input stage as using the marshall values .
I'm not going to add a 3 prong cord as i don't have an isolation transformer ,Just wanted to spice her up a little .
feel free to comment .

[olddawg]

I would guess you have 4 or 5 watts. I would recommend just trying a boost pedal. AND.. get a cheap isolation transformer.

[The Dude]

...... AND.. get a cheap isolation transformer.

^^^^^^That!

[copperheadroads]

Anyone have a link for suitable isolation transformer ?

[Gnobuddy]

Anyone have a link for suitable isolation transformer ?

Triad N68X (from Mouser Canada, $22 CAD): http://ca.mouser.com/ProductDetail/T...cYR3QIAjw5w%3d

Note that there are two primary coils, designed to use with either 230V or 115V mains. For our 115V mains, you'll want to parallel the two primaries, and make sure they are phased properly (so they don't "fight" each other and melt the transformer!).

The proper primary connections you want are:

1)Connect Blk and Red/Blk together
2)Connect Yel/Blk and Grn/Blk together
3)Run those two pairs to AC live and neutral (doesn't matter which goes to which).

Of course you should also connect the incoming AC Ground wire to the metal chassis of your guitar amp, and make sure there is a solid electrical connection to the body of the isolation transformer as well.

The N68X also has an electrostatic screen (white), which you can connect to chassis ground to reduce high-frequency noise leaking through the transformer.

N68X datasheet: http://www.mouser.com/ds/2/410/media-1067757.pdf

-Gnobuddy

[Gnobuddy]

I just curious if i could mod it to get a little more gain out of it at the input stage as using the marshall values .

Those 12AX7 anode resistors are pretty large already, in the attempt to squeeze out as much gain as possible. The little Arc amp is burdened with a pretty low power supply voltage, which isn't going to help wring out maximum gain from 12AX7s.

As already mentioned, the easy way to get more gain is to use an external FX pedal. If you prefer to have the amp self-contained, I think the next easiest solution is to use an LND150 or similar small N-channel MOSFET, and insert it as a 3rd gain stage between the two halves of the 12AX7.

With a little care in the design of the MOSFET stage, you can limit its gain and keep it from ever clipping, so you won't hear nasty solid-state clipping sounds. The MOSFET can work off the same voltage as the 12AX7, takes up very little room, and doesn't need any heater power, so it won't mess up your series heater string.

I'm not going to add a 3 prong cord as i don't have an isolation transformer ,Just wanted to spice her up a little .
feel free to comment .

You already got good advice on the isolation transformer part...please add it, it is not optional. Electrocuting yourself (or someone else) with a deadly-unsafe guitar amp is simply not a viable option. It's hard to believe such a terrible idea was ever considered legal, even in the bad old days when little was known about electrical safety.

-Gnobuddy