Tube Converter

13,459

76

31

Introduction: 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

Step 1: 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.

Step 2: 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.

Step 3: 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.

Step 4: 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.

Step 5: 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.

Step 6: 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.

Step 7: 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.

Step 8: 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.

Step 9: Install the Tube

Insert the converter into the socket first.

Place the tube in the tube cover and insert the tube into the converter.

Make sure the tube socket is grounded, the tube cover prevents transient signals from interfering with the tubs functions.

Place the side panel back on and test.

Step 10: PDFs

These should be everything you need in PDFs to make your own converters.

My 1975 RCA Tube Data Book and my Tube Substitution Book was just too large to upload, however it is free to down load here.

http://www.tubebooks.org/tubedata/RC30.pdf

https://frank.pocnet.net/other/Sylvania/SylTubSubs...

Fix It Challenge

Second Prize in the
Fix It Challenge

Be the First to Share

    Recommendations

    • Eggs Challenge

      Eggs Challenge
    • First Time Author Contest

      First Time Author Contest
    • Build a Tool Contest

      Build a Tool Contest

    31 Comments

    0
    Docleolab
    Docleolab

    1 year ago

    UHAOOO,..Grazie, bellissimo!

    0
    tklompmaker3
    tklompmaker3

    1 year ago

    Brings back memories... Once upon a time in Europe, we had in a problem that a relative new tube the ELL 80, was suddenly phased out. This ELL80 was a double penthode power amplifier tube that was usually running much to hot and failed every year or so. This was fixed by a similar converter from ELL80 to 2 X EL95 tubes (which were much more reliable). So, 2 (smaller) tube sockets stacked upon a single tube connector. We home brew 2 versions with a 90 degree physical offset for the set of EL95 tubes since there were different model radio's with these tubes so, one of the 2 versions used to fit. 2 tubes are of course much "wider" than a single one... We sold quite a few of those... Like yours better since it is shielded, ours of course was not... but worked fine.

    0
    Josehf Murchison
    Josehf Murchison

    Reply 1 year ago

    Old timers tube hack.
    Don't worry about ziqfriq I'm sure he has never worked on vintage electronics.

    0
    ziqfriq.
    ziqfriq.

    Reply 1 year ago

    I can see where a double beam power pentode tube would have been a good idea in theory, but not in practice.

    0
    tklompmaker3
    tklompmaker3

    Reply 1 year ago

    IT was used in one of the first stereo radio's, Both power end stages on one socket. Smaller footprint.

    0
    ziqfriq.
    ziqfriq.

    Reply 1 year ago

    It could also have found use in push-pull stages, though not many table radios used P-P. Clearly, putting that much plate dissipation in a single envelope was a mistake they thought better of.

    0
    tklompmaker3
    tklompmaker3

    Reply 1 year ago

    Indeed, IT could Deliver 9 watt in push pull and was thought to be a more powerfull option to An EL84 single ended at 4.5 Watt.

    0
    ziqfriq.
    ziqfriq.

    1 year ago

    Interesting article. I think it is a little short on detail as to how you made the male part. Concentration was on the nontrivial task of finding a suitable replacement.

    You say you "simply" soldered steel pins, without any suggestion for a source. Also, you presumably used ceramic sockets since soldering inside a Bakelite one without melting it and putting the pins out of alignment would be challenging. Finally, since you are plugging the top of one socket (with added pins) to the top of another, the pin numbers (that usually are engraved on the socket) would be wrong, since it is flipped. I think that is an important point and worth mentioning.

    Out of curiosity I went on eBay, and found boatloads of NOS 6AN8's in the 8 dollar range. If you were intent on only using tubes in your collection, or into the technical challenge of creating this adapter and sharing it with others, that's fine. But the amount of skilled labor you put into it greatly exceeded 8 bucks worth. Also, someone interested in doing an "authentic" restoration of the 'scope would prefer that option, I would think.


    0
    Josehf Murchison
    Josehf Murchison

    Reply 1 year ago

    WOW you assume a lot; Bakelite doesn't melt when you solder, just like printed circuit boards don't melt when you solder on them ether. Bakelite not ceramic and it is that simple. Just solder pins in the male socket. and grind the socket so it fits inside the shield.
    There is a reason I said solder with care, and check your connections with a multimeter, even mapped it out in the picks.
    Cost me nothing but my time, I had everything from salvage.
    When I wrote this Instructable over 2 years ago I couldn't find any tube converters on line, and eBay wanted almost $200 for a used 6AN8.
    As for eBay, too many ripoff posts and eBay never reimbursed me for the last ripoff. The only time I got what I ordered it was from a Canadian retailer.
    https://www.universal-solder.ca/
    This is a new 6AN8 tube on eBay today.

    6AN8.png
    0
    jott_1
    jott_1

    1 year ago

    This is great!

    0
    horimag
    horimag

    1 year ago

    Nice job, mate!

    0
    ve6cmm
    ve6cmm

    1 year ago

    Nice Instructable and a great idea. Thanks. I am pretty sure I have done something like this in the distant past. Thanks for the idea and reminding me just how a simple idea can make things work again.

    0
    bpark1000
    bpark1000

    Tip 1 year ago

    Be careful when you substitute. Depending upon the circuit tube is in, there are other characteristics that must match (such as whether the triode is "high mu" or not) for proper circuit function. Fortunately, for "receiving" tube circuits, usually nothing will "blow up" if everything doesn't match the original, but circuit function may not be proper. I had a fit replacing a 6X9 tube in Philco Predicta TV. There was just nothing that even partially matched! I had no choice but to buy the exact replacement. We run into these games because TV manufacturers would swap pins on old tube type & declare a new tube type for their product (to force consumers to purchase their tubes).

    0
    Josehf Murchison
    Josehf Murchison

    Reply 1 year ago

    That is why I said check the data sheets on the tubes.
    6X9 is a triode pentode tube but it isn't the same when you look at the grids and plates. First it is a 10 pin not a 9 pin.
    Grid 3 is not connected to the cathode and there is no shield between the two valves.
    And the other parameters not even in the same ball park.

    0
    Olgorofi
    Olgorofi

    1 year ago on Step 10

    This idea took me to the past when I learned about valves at the Escola Tecnica Federal in Brazil. I like to live with nostalgic and enthusiastic people who value our past. Congratulations on the project. I still have valves (tubes) in my personal stock.