Installation of the Iron Supplement for Enhanced S.E.X.
Flat tip screwdriver
Pliers
Wire cutters
Soldering iron, minimum 40W rating. A fine tip will help with the PC board assembly
your favorite solder
you may find a desoldering tool or desoldering braid useful
2 - MagneQuest for Bottlehead BHMQ-1 nickel/M3 parafeed output transformers - order from MagneQuest, 215-288-4816
2 - MagneQuest for Bottlehead BHMQ-2 plate loading chokes - order from MagneQuest, 215-288-4816
the parts below are included in the C4S upgrade available from Bottlehead:
2 - #6 lock washers
2 - C4S PC boards
4 - HLMP 6000 LEDs
2 - MJE 350 transistors
2 - 2N2907A transistors
4 - 270K ohm 1W carbon film resistors
2 - 18K ohm 1W carbon film resistors
2 - 499 ohm metal film resistors
1ft. Teflon insulated wire
You will also need to supply two of your favorite flavor of coupling capacitor with the following ratings
2uF, rated for at least 600VDC
Optional - you may also wish to upgrade the two stock 0.1uF interstage coupling capacitors with a boutique capacitor of the same 0.1uF value and 600VDC rating, as shown in the instructions below.
Removal of stock plate chokes and transformers
Begin by unplugging the amplifier and removing the tubes. Put a towel or other padding on the workbench to protect the finish.
Disconnect the twisted pair of wires that connect to terminals 4 and 5 on the stock plate chokes. The wire that connects diagonally from terminal 1 to terminal 8 on the plate choke may be left in place.
Disconnect the brown wires from the lower holes of terminals 20 and 40. Disconnect the white wire and the heavy black wire from the upper holes of terminals 5 and 25. Disconnect the heavy black wire from terminals 10 and 30.
Cut the nylon ties binding the extra output transformer leads and carefully free the leads from their bundle.
Remove the screws that mount the plate chokes and output transformers, being careful not to loose any of the mounting hardware - including the shoulder washers. Remove the output transformers and the plate chokes.
Installation of new plate chokes and output transformers
Mounting the hardware
One the power switch side of the chassis orient the transformer with the red and blue wires inboard and the black and orange wires outboards. Feed the wires through the respective grommets.
Insert one of the original #6 screws with a lockwasher thru the rear mounting flange on the transformer and put a piece of tape over the screw to hold it in place. Repeat with a second #6 screw and lockwasher thru the front flange.
Slip a shoulder washer over each screw. Carefully line up the mounting slots on the inverted chassis to allow the screws to pass through and rest the chassis on the output transformer. You may want to set a piece of cardboard under the output transformer to raise it off the work surface slightly in order to get a flush fit with the chassis plate. Place shoulder washers over each screw.
Set a plate choke over the screws, with the solder tabs of the plate choke facing inboard. Place a solder tab over the rear screw and a lockwasher over both screws. Secure each with a nut - it's a tight fit, so take your time.
Repeat this process with the other output transformer and plate choke on the headphone jack side of the chassis, but orient the output transformer so that the red and blue wires face outboard and the orange and black wires face inboard. Install the plate choke on this side so that the terminals face inboard.
Remove the 1uF parallel feed coupling capacitor from each channel - terminals 15 and A2 on one side and terminals 35 and B6 on the other side.
Now is a good time to make sure the plate choke wires are clean and well stripped and any solder lugs from which parts have been disconnected are desoldered well enough for the mounting holes to be open for the installation of new wires.
Wiring the iron
On the power switch side of the chassis, route the blue wire under the terminals strips and forward to terminal 20. Trim the blue wire to fit, strip back 1/4" of insulation and attach and solder the wire to the lower hole of terminal 20.
Repeat this procedure with the blue wire of the transformer on the headphone jack side of the chassis, attaching and soldering the wire to the lower hole of terminal 40.
Red and orange wires of the respective transformers will trimmed to fit, attached and soldered to terminal 5 on the power switch side and terminal 25 on the headphone jack side.
The black wire of the respective transformers will trimmed to fit, attached and soldered to terminal 10 on the power switch side and terminal 30 on the headphone jack side.
Scrape the terminals of the plate chokes with an Exacto knife or single edged razor blade to remove any varnish.
On the power switch side, use an ohmmeter with one probe clipped to terminal A2 to determine which of the two black wires in the twisted pair is connected to terminal A2. Attach and solder this wire to the terminal next to the dot on the kraft paper coil wrapper of the plate choke. Solder the remaining wire to the terminal with no dot.
Repeat this process on the headphone jack side, using terminal B2 to determine which wire connects to the terminal with a dot.
Parafeed capacitor wiring
These parts are to be acquired by the builder - choose your favorite flavor of 600VDC or higher capacitor
Strip back the ends of both 2uF capacitors about 1/4"
Attach and solder one lead to terminal A2, minding the connection of the blue wire. Solder the other lead to the upper hole of terminal 20.
Repeat with the other capacitor, attaching to terminal B2 and the lower hole of terminal 40.
C4S board assembly
Insert the components in the C4S board as shown in the photos. Be very careful to match the orientation of each component to the photo.
Insert the MJE350 transistor such that the metal side faces the outside edge of the PC board
Bend the middle lead of the 2N2907A transistor back between the other two leads
Insert the 2N2907A with the metal tab facing the outside edge of the PC board. Note the position of the middle lead.
Insert the first LED with the silver end facing towards the MJE 350.
Insert the second LED with the silver end facing the outside edge of the PC board.
Insert the first 270K ohm resistor. Orientation of all the resistors is not critical.
Insert the second 270K ohm resistor.
Insert the 499 ohm resistor. Turn the board over and carefully solder at every point where a lead comes through the PC board.
The completed board should look something like this. Carefully inspect the back side to be sure that no traces are accidentally bridged with solder, and that all solder pads are soldered.
C4S board installation
Cut 2 pieces of wire 2" long and strip the ends back 1/4" (output wires)
Cut 2 pieces of wire 1.5" long and strip the ends back 1/4" (ground wires)
Cut 2 pieces of wire 1" and strip the ends back 1/4" (B+ wires)
Solder wires to boards in positions shown.
Remove the 0.1uF capacitor from terminal 14 and A5 and also the 0.1uF capacitor from terminal 34 to B5.
Remove the 150K ohm plate load resistors from terminals 17 to A5 and 37 to B5.
Remove the 8.2K ohm power supply dropping resistors from terminals 11 to 16 and terminals 31 to 36.
The sockets should look like this after all the parts are removed.
Install the new 18K ohm power supply resistors in place of the old ones, with one resistor connected to terminals 11 and 16 and the other resistor connected to terminals 31 and 36.
Install the C4S boards in front of the tube sockets, on edge.
The 1.5" wire is soldered to terminal 18 on the power switch side C4S, and terminal 38 on the headphone jack side C4S.
The 1" wire is soldered to terminal 16 on the power switch side C4S and terminal 36 on the headphone jack side C4S.
The 2" wire is attached (do not solder yet) to terminal A5 of the power switch side C4S and terminal B5 on the headphone jack side C4S.
See pics above and below.
Optional
As an option you may wish to upgrade the stock 0.1uF interstage coupling capacitors with a boutique brand capacitor. Use the same value of 0.1uF and mnake sure it is rated for at least 600VDC. Solder one lead to terminal 14 on the power switch side capacitor and solder the bottom lead of the headphone jack side capacitor to terminal 34.
Solder the other lead of the power switch side capacitor to terminal A5 and solder the other lead of the headphone jack side capacitor to terminal B5.
Finished!
Resistance readings should be the same as the stock kit with the exception that terminal 20 and 40 should now read 258 ohms.
Voltage readings should remain the same as the stock kit with the exception that terminals 16 and 36 should now read 300VDC.