Tube Converter

One of the biggest challenges to working on vintage electronics is getting the right component, tube, or the right substitute tube. Some tubes like the tubes 6AN8 or 6AN8A are hard to get or don’t have a substitute tube. However you can make a substitution by finding a compatible tube and rewiring the tube socket or using a tube adapter to make a substitute.

When I started this Instructable I was unable to find a tube converter for the 6AN8 tube I wanted to replace. In this Instructable I will be demonstrating how to make the simplest tube adapter.

Supplies

Solder

Wire

Tube

sockets

Soldering Iron

Multi Meter

Spacers

Large Shrink Tube

Tube

Substitution Guide

Tube Data Book

Tektronix 515A

1. I got my hands on a Tektronix 515A oscilloscope, that wasn’t working.

2. From the manual I figured out the 6AN8 tube wasn’t up to snuff.

3. I opened the case by turning two screws just one turn and removing the side panel.

4. I removed the tube cover.

5. Then I removed the 6AN8 tube and tested it.

The tube was bad.

A Tube to Convert

Looking at my supply of tubes I found I didn’t have a replacement tube and checking my Tube Substitution Guide, the only substitution is a 6AN8A tube which is just a more modern 6AN8.

Next I found the datasheet for the 6AN8 tube. It is a Triode Pentode tube.

Pin 1 triode plate.

Pin 2 triode grid.

Pin 3 triode cathode.

Pins 4 &5 Heater. 6.3 volts, 450 mA

Pin 6 pentode plate.

Pin 7 pentode grid 2.

Pin 8 pentode grid 1.

Pin 9 pentode cathode, grid 3, and shield.

The first number in the tube part number usually denotes the heater voltage.

Substitution Guide

Go back to the Substitution Guide and look up the tube you need to substitute.

Under the Basing column there is a number 9DA, the 9 stands for the number of pins.

Go to the Basing Diagrams in the back of the Substitution Guide and look up 9DA, remember what a Triode Pentode tube looks like.

Then start at the beginning of the 9 series record all the Triode Pentode tube diagrams.

9AE, 9DA, 9DC, 9DZ, 9EX, 9FZ, 9HX, 9JE, 9JF, 9JT, 9KZ, 9LC, 9LY, 9LZ, and 9QT.

Finding All the Triode Pentode Tubes

Finding all the Triode Pentode Tubes in 6 volt heaters is easy.

Go back to the Substitution Guide 6 series tubes and check under the Basing column for all the tubes with the Basing Diagram codes, 9AE, 9DA, 9DC, 9DZ, 9EX, 9FZ, 9HX, 9JE, 9JF, 9JT, 9KZ, 9LC, 9LY, 9LZ, and 9QT.

I found 6BM8, (9EX), 6FY8, (9EX), 6GE8, (9LC), and 6GW8, (9LZ), all of which had no substitutes.

Then I found 6GH8 and 6GH8A, (9AE8A) which had ten substitutes.

Selecting a Tube to Convert

The A at the end of the part number is just a newer manufacture.

Since the 6GH8-A, have about ten tubes you can plug and play substitute I stopped there.

The internal plates and grids of 6GH8, are similar in value as 6AN8 just a different pin out.

The heaters are the same voltage and current, so it doesn’t matter if all the heaters in the vintage electronics are connected in series or parallel.

However to substitute a 6GH8 tube for a 6AN8 tube you do need a tube converter.

The Tubes

6AN8 VS 6GH8, remember vacuum tubes are like transistors they only need to be in the ball park.

6AN8-A

Pin 1 triode plate.

Pin 2 triode grid.

Pin 3 triode cathode.

Pins 4 &5 Heater. 6.3 volts, 450 mA

Pin 6 pentode plate.

Pin 7 pentode grid 2.

Pin 8 pentode grid 1.

Pin 9 pentode cathode, grid 3, and shield.

6GH8-A

Pin 1 triode plate.

Pin 2 pentode grid 1.

Pin 3 pentode grid 2.

Pins 4 &5 Heater. 6.3 volts, 450 mA

Pin 6 pentode plate.

Pin 7 pentode cathode, grid 3, and shield.

Pin 8 triode cathode.

Pin 9 triode grid.

To make a converter you just need to connect the pins from the 6AN8 tube socket to the pins of the 6GH8 tube socket.

The Converter

To make the converter I used two nine pin sockets nine pins and a spacer.

To make the male fitting I simply soldered 9 steel pins into a 9 pin socket, then ground the sides so it would fit inside the tube shield.

Solder the wires carefully to avoid missed or cross connections and shorts.

Then it is just a matter of making the connections.

Pin 1 on the 6AN8 socket to pin 1 on the 6GH8 socket.

Pin 2 on the 6AN8 socket to pin 9 on the 6GH8 socket.

Pin 3 on the 6AN8 socket to pin 8 on the 6GH8 socket.

Pin 4 on the 6AN8 socket to pin 4 on the 6GH8 socket.

Pin 5 on the 6AN8 socket to pin 5 on the 6GH8 socket.

Pin 6 on the 6AN8 socket to pin 6 on the 6GH8 socket.

Pin 7 on the 6AN8 socket to pin 3 on the 6GH8 socket.

Pin 8 on the 6AN8 socket to pin 2 on the 6GH8 socket.

Pin 9 on the 6AN8 socket to pin 7 on the 6GH8 socket.

Test the Converter

Using a multi meter check the connections between the two sockets, make sure you have continuity only between the socket pins you need continuity. Use shrink tubing to prevent shorting.