Output Transformer (OT) Swap Information

Whether you mismatched ohmages and blew the OT, or simply want to revamp/improve your tone in every way, the OT change is applicable to almost any VK user. It is simply the removal and replacement of the stock iron OT that comes standard with the amp.

Please be sure to read the Warnings page before changing the OT in your amp.
"...Pulling the chassis and poking around inside the amp can be dangerous deadly dangerous...."

Installing a Custom output transformer gives the amp a tighter, more defined and articulate tone. It balances out the frequencies so the lows don't fall apart and get muddy and the highs aren't so harsh. It makes the amp more dynamic with a tighter feel. It improves the clarity and definition of what you're playing so everything isn't blurry.

The Custom choke beefs up the power supply by improving the power supply filtering which help with noise levels, improves sustain, and helps the amp stay tight and punchy.

When you try the OT the first time, you may after installation find it gives off a high pitch squeal! The solution we have found is, reverse the 2 outer primary wires and try again! Usually the blue and brown wires. It is best to try before you put the chassis back in the cabinet! Make sure a speaker is connected when you do this! It is feedback that should disappear once the wires are reversed!

(Credit Jason43)
Output transformers that will work for the VK100 and VK212:
Weber WOT100LHR
Weber WOT100HHR
Heyboer HYOT100

All three are sold through tedweber.com

VK100/VK212 installation overview:
You will need a crimping tool/wire stripper and several crimp-on wire connectors and female spade connectors. With the tubes removed to prevent breaking, pull the chassis from the cabinet. Lay it open side up and locate the wiring for the OT. The primary wires(red,blue and brown) are connected to the board with one plastic push-on connector. The secondary wires(orange, white, green and black) are connected off to the side via spade connectors. Make a note of the order that the secondary wires are attached to the board. Disconnect all of the OT wires from the board. Cut the primary wires about two inches from the plastic connector. Unbolt the OT an remove it from the chassis. Depending on which OT you bought, you may need to drill new mounting holes in the chassis. Mount the new OT and run the wires into the amp. Strip about 1/4" of insulation from each wire. Connect the female spade connectors to the end of each secondary wire and attach to the board in this order: (new wires to old wires)yellow to orange, green to white, white to green and black to black. Attach the primary wires to the on the plastic connector with the crimp on connectors, or solder them and plug the wires back into the board. Reassemble your amp and you're done.

For reference, here are the stock and Weber/Heyboer OT schematics:


Primary Secondary

blue---------- X -----------orange -16ohms
red----------- X -----------white -8ohms
brown------- X ----------green -4ohms
X -----------black -common

Heyboer/Weber OT:

Primary Secondary

blue---------- X -----------yellow -16ohms
red----------- X -----------green -8ohms
brown------- X ----------white -4ohms
X -----------black -common

Heyboer OT wiring:
external image VK004.jpg
Choke wiring:
external image VK005.jpg
Choke: (the choke replaces R201)
external image VK006.jpg

(credit Cap47)
Photos inside a VK112 with Weber WOT45HHR OT and Weber WSW-R2x4 4 pos rotary switch. Also a Weber choke W02299 photo not shown here.
external image 100_0651.jpg
external image 100_0650.jpg
external image 100_0652.jpg
external image 100_0653.jpg
external image 100_0654.jpg
external image 100_0577.jpg
external image 100_0580.jpg
Last one is position where 390 ohm was removed and choke wires soldered.

(Credit Cap47)
I installed the Weber WOT45HHR OT and the WO22699 Choke along with the WSW-R2x4 Rotary 4 position switch for cabinet choice. This is in the VK112. It has tightened up the amp. Some board disassembly was required to drill mounting for choke and selector switch. Makes the VK112 more versatile for use with various cabinets. The new OT is about 1/3 bigger and beefier than the original. Well worth the effort.

I had an issue with the standby switch popping loudly after I installed the Weber Choke. Turns out chokes do not work well with standby switches in series. It leaves one side disconnected, which creates arcs at the switch and choke (not good.)

So I moved the switch to function between the rectifier diodes and first filter cap. This improved the situation greatly.

You will be working right by them circuit wise.

Bridge the standby switch nodes so as to remove the standby switch function.
Take the two rectifier diodes, band end solder those together with a wire to one leg of the standby switch. (junction of D202 and D211)
---be sure to take it from the banded end---
From the other leg of the standby switch, run a lead into the former location of the banded end of D202 OR D211 (not both)

This will break the High voltage circuit immediately after the rectifier, which actually a better location for Standby anyways.

Refer to Valve Wizard's site on Power and Standby switches for even better ideas.