Mission 5E3 Mod Kits?

[bradduerr]

I am about ready to purchase a 5E3 kit from mission but have no idea what the listed mods do. In particular, what does the "The dual Mission Amps Switchable "Humbucker" flub/flatulence Reduction Mod Kit AND Fixed Bias Phase Inverter Mod Kit" do?

[Bruce / Mission Amps]

I am about ready to purchase a 5E3 kit from mission but have no idea what the listed mods do. In particular, what does the "The dual Mission Amps Switchable "Humbucker" flub/flatulence Reduction Mod Kit AND Fixed Bias Phase Inverter Mod Kit" do?

The fixed bias PI mod is a voltage divider biasing circuit for the cathodyne driver used in the tweed Deluxe.
It has a little better output balance between the plate drive side and the cathode drive side.
Circuits like this have been used for years and years prior to the modern amp building community rediscovering it.
I use that mod in amps where the player is looking for every last ounce of clarity and the power tube driver stage is a split load or cathodyne type.
The HB I and HB II mods are in the same package and come with misc parts to split the common cathodes and tune the two preamp stages for less bass and other RC circuits to reduce bass flab and mud so the amp can be turned up a little louder with less roaring and unusable bass.
They work well with high output pickups and humbuckers.
Both HB mods come with mini-toggle switches so you can bypass them and go back to the stock sound.

[hasserl]

Bruce, where do you mount the switches? In the case of adding holes to the chassis, are there any tips to drilling a clean hole without damaging or peeling the chrome? Or is that not a problem?

[Bruce / Mission Amps]

Bruce, where do you mount the switches? In the case of adding holes to the chassis, are there any tips to drilling a clean hole without damaging or peeling the chrome? Or is that not a problem?

The Mission Amps 5E3 chassis' are already punched for the two switches, way before the chrome plating is done... that's in case a builder wants to add the mod kits later.
The two holes are located on the socket side of the chassis.
One is right before the 12AY7 and the other is in between the 12AY7 and the
12AX7 sockets.
As far as drilling other chassis....I find high quality, super sharp drill bits used after a small 1/8" starter hole works OK for drilling chrome plated steel... cheap drill bits will slide all over the place and I always use a pointed punch to pin prick the chrome to start.

[Chuck H]

This may sound extreme...But I have done just such an operation. I also dabble in knifemaking. So I have some experience in heat treating tool steel.

It would be a good idea to experiment with a non crucial project before you try this.

You can "adjust" the hardness of most "high speed" or "for steel" drill bits by using a propane or map gas torch to heat the steel to a medium red heat (red hot is just visible in daylight) hold it there for a minute or two, and then quench it in room temperature oil. At this point the steel will be as hard as glass and almost as brittle. Then take the bit and place it in a 400* oven for an hour. This will "temper" the steel to make it tough enough to perform "some" work. The drill bit may still crack unless you get it just right. But this trick will give you the hardness you need to drill through a previously plated chrome chassis cleanly. Keep the drill nice and straight and apply even solid pressure. A press will help with this, but I have done it free hand.

I've managed to drill through knife steel hardened to a rockwell of near 60 with this trick.

Drill bits are cheap compared to chrome plated chassis. So Buy several and experiment on a non visible area first. Know the nature of the materials you dealing with.

HTH

Chuck

[hasserl]

Good info! Thanks Bruce and Chuck.

[tele-tubby]

The fixed bias PI mod is a voltage divider biasing circuit for the cathodyne driver used in the tweed Deluxe.
It has a little better output balance between the plate drive side and the cathode drive side.
Circuits like this have been used for years and years prior to the modern amp building community rediscovering it.
I use that mod in amps where the player is looking for every last ounce of clarity and the power tube driver stage is a split load or cathodyne type.
The HB I and HB II mods are in the same package and come with misc parts to split the common cathodes and tune the two preamp stages for less bass and other RC circuits to reduce bass flab and mud so the amp can be turned up a little louder with less roaring and unusable bass.
They work well with high output pickups and humbuckers.
Both HB mods come with mini-toggle switches so you can bypass them and go back to the stock sound.

e

basically then, the fixed bias PI mod kit will give a little more headroom and the humbucker mods cures the fart?

[TD_Madden]

The Mission Amps 5E3 chassis' are already punched for the two switches, way before the chrome plating is done... that's in case a builder wants to add the mod kits later.
The two holes are located on the socket side of the chassis.
One is right before the 12AY7 and the other is in between the 12AY7 and the
12AX7 sockets.
As far as drilling other chassis....I find high quality, super sharp drill bits used after a small 1/8" starter hole works OK for drilling chrome plated steel... cheap drill bits will slide all over the place and I always use a pointed punch to pin prick the chrome to start.

Unless you've got an early Tweedy that doesn't have the extra hole(s).