Lost my Impedance Selector Switch

[Skel]

Hi all,

I lost my impedance selector switch for my '79 Marshall 50 watt lead head. I ordered a new one a few weeks ago from "Ampwares" dot com, but they flaked out on me - e-mails are returned, won't answer phone, etc.

Today I ordered one from MojoDOTcom but it won't be here for a week or so.

Is there a fairly easy way for somebody unexperienced like myself to jury rig something in order to use the head, set at 16 ohms? I have a gig tomorrow night and would feel a lot better having this head as my main or backup head.

Thanks

[52 Bill]

Is there a fairly easy way for somebody unexperienced like myself to jury rig something in order to use the head, set at 16 ohms?

There are two ways to handle this.

We used to bend a U-shaped wire jumper that could be inserted into the holes on the impedance switch. This was then covered with gaffers tape to secure it into place and to protect it from shorting out to ground.

The problem here is that if you use a wire that is too small in diameter, it may not make a good contact thus leaving your amp with the possibility of an intermittent load, which may cause damage to your output transformer.

If you use a wire that is too large in diameter, you may cause permanent damage to the switch, by stretching open the spring contacts. If this happens, you may be able to tighten up the contacts afterwards when the replacement plug is available. If not, then you will have to replace the entire switch.

The second and safer way to deal with this, is to take the amp out of the case, turn over the amp and solder a jumper wire from the 16 ohm transformer tap directly to the output jacks, bypassing the switch. Be sure to remove the jumper when your replacement plug comes in.

[Skel]

There are two ways to handle this.

We used to bend a U-shaped wire jumper that could be inserted into the holes on the impedance switch. This was then covered with gaffers tape to secure it into place and to protect it from shorting out to ground.

The problem here is that if you use a wire that is too small in diameter, it may not make a good contact thus leaving your amp with the possibility of an intermittent load, which may cause damage to your output transformer.

If you use a wire that is too large in diameter, you may cause permanent damage to the switch, by stretching open the spring contacts. If this happens, you may be able to tighten up the contacts afterwards when the replacement plug is available. If not, then you will have to replace the entire switch.

The second and safer way to deal with this, is to take the amp out of the case, turn over the amp and solder a jumper wire from the 16 ohm transformer tap directly to the output jacks, bypassing the switch. Be sure to remove the jumper when your replacement plug comes in.

Bill, thanks for your help. The 2nd way sounds like to way to go and I'll do this. I would just leave it but I have a 16 ohm "gigging" cabinet, and an 8 ohm 2x12 cab for rehearsals, so I'll have to make sure to remove it as you said.

Thanks.