A simple tube adaptor for solderless breadboards

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A few days I had an idea that might be useful to other tube-tinkerers, so I thought I'd share it here.

Solderless breadboards make tinkering with solid-state circuitry so much easier than the days when we had to solder everything. I wanted to see if I could make it just as easy to tinker with tubes - at least, small, small-signal tubes run on relatively low B+ voltages.

So I came up with the adaptors shown in the attached photos. The basic adaptor is a 90-degree straight pin header cut to appropriate length, and soldered into a square of stripboard. Since tubes run on much higher voltages than stripboards were ever designed to accommodate, I snipped off every other pin, creating a little more room between adjacent pins at different voltages.

To strengthen the little 2"x2" squares of stripboard, I epoxied a same-size square of thin plywood to each one.

The final step is to decide where pin 1 is on the adaptor, and then wire the socket to the appropriate copper strips.

The photos show one adaptor with a 9-pin socket, and one with a smaller 7-pin socket.

I haven't yet used either of these with an actual tube in them, but the first tube I plan to tinker with is a 6JW8 (9-pin base). It is a triode-pentode, so there are three grids that need grid-stoppers (one screen grid and two control grids). You can see two of them in one of the pictures. I forgot to solder in the 3rd grid stopper, an omission I will correct before using the adaptor.

Both the triode and the pentode in a 6JW8 will run pretty happily at B+ voltages from maybe 120V up to 250V or so. I guess I'll soon find out if a typical solderless breadboard will cope with that range of voltages.

These tube adaptors are pretty cheap and simple to make, so anyone who plans to do a lot of tube tinkering might want to make up several, pre-wired for specific tubes, so you don't have to add and remove grid-stoppers, etc.

-Gnobuddy
 

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Solder less bread boards are rated at a maximum voltage of 50volts as the insulation is pretty poor.
All true. However, there are a few diyAudio stalwarts who have been putting tube voltages on solderless breadboards for years, and I've taken the additional step of doubling the distance between pins, so you get double the insulation thickness.

The breadboard I dissected had about 1.5 mm of plastic insulation between adjacent metal bus-bars. By skipping alternate bars, there is about 3 mm of insulation. I think this will cope with the B+ voltages I have in mind. (And I will report here if I turn out to be incorrect.)

The exposed underside of the tube adaptor is by far the biggest safety issue, and should be treated with the same extreme respect you would give any other tube circuit that's been powered on.

-Gnobuddy
 
I've used IC sockets for sub-miniature tubes, specifically 6122 and 5902, without issues. These run about 170V.
Thanks for your input! I've seen that trick done a few times on various tube forums.

I myself have a few 5902 beam tetrodes squirreled away for a someday project, along with a couple of other less popular subminis. I will confess that the thought of cutting those irreplaceable wire leads short is one of the things that's kept me from using these little subminiatures.

For the moment, I'm tinkering with 6JW8s and 6AQ6s. The beam tetrode in the 6JW8 is easy to operate with as little as 100 volts B+, and the anode will saturate down to 10-20 volts, so it will probably work fairly well even with a 60V B+.

The triode in the 6JW8 triode can work with a 100V B+, but you can use more of its characteristic curves, and it works more like a half-12AX7 (with usable curves to Vgk=-4V) with 200 volts B+.

There are some other 7-pin tubes I plan to take well north of 300V B+, but I have no plans to ever plug those into a solderless breadboard.

-Gnobuddy
 
mnimum Distance between PCB-Traces in relation to Voltage

Volts Gruppe B2 Gruppe B4
unbeschichtet beschichtet (polymer)
non coated coated (polymer)


0-30 0,1mm 0,05mm
31-100 0,6mm 0,13mm
101-150 0,6mm 0,40mm
151-300 1,25mm 0,40mm
301-500 2,50mm 0,80mm

>500 0,005mm/V 0,00305mm/V
 
I have used breadboards a number of times up to 300V but I had the pins of the sockets come out to the board with solid wire. I spaced the components with the relative voltages in mind. A cathode biased preamp tube might be an adjacent strip while a plate circuit loop might get two or three strips between them. I have my 6AK6 thread circuit partly breadboarded but have been finding it hard to get back down to play with it. I have used the same board with 6AQ5's at 300V with no problem.
 
I'll soon find out if a typical solderless breadboard will cope with that range of voltages.

I have had mine up to 400 volts, the limit of my small power supply. This has been used for preamp duty only so far. I went off the deep end with this one by wiring an Arduino compatible board up to some 12AX7's in an attempt to recreate my ADA MP1 which has become too intermittent to be useful anymore. It's kinda hard to smack it when it's buried in the middle of a rack full of goodies.

I made some socket adapters for the typical tubes used in guitar preamps. like the 12AX7. I pre-wired them such that the plate was spaced with two rows in between it and the grid, and one row between the grid and cathode. I kept the tubes vertical for several reasons. My first attempt was horizontal and looked a bit like yours but I kept breaking a pin or two off the board while attempting to change parts, eventually deciding that the space underneath the tube was wasted anyway, so I would switch to mounting the tube vertically.

I made some new adapters with the tube vertical. These sucked up much of the breadboard space, so I simply straddled the adapter across two breadboard sockets. This worked but I decided to start over and make the socket adapters smaller. This time they will be much smaller, maybe 10 X 12 or 12 X 12 holes, just large enough for the sockets.

The breadboards themselves were not mounted, just lying on the workbench. This was a contributor to the broken pins since it's too easy to knock stuff over.

I am using super cheap Chinese breadboard sockets from Amazon (3 for $10). They do not have mounting holes so I stuck two of them to a piece of plywood using the double sided tape that comes on the board.....big mistake. I destroyed the breadboard trying to remove it because I stuck one on a bit crooked.

If the voltage turns out to be an issue I can always reassemble one of these with some of the metal strips removed.

I have parts coming from Amazon tomorrow to rebuild the breadboarding system again for a third time tomorrow.

Back in the 1960's I had an electronics kit that used little spring connectors to make connection to leaded parts. I made adapters to use vacuum tubes on this board since the pegboard base was quite large, about 18 X 24 inches with holes on 1 inch centers. I used it well into the 70's when it just finally fell apart. I have searched in vain for those little spring connectors for years, finally finding something similar at Sparkfun. I bought a bunch of them and started designing a new breadboard that's more high voltage friendly. It got packed up in a partly finished state when I left Florida 4 years ago. It still sits in its box, untouched for years. Sparkfun has since discontinued the little spring thingies, but they are still available on the web under the old Sparkfun part number (PRT-11822). I'm going to get some more while I can for the next generation Tubelab vacuum tube breadboard since I know that the little white breadboards DO have a voltage limitation, and it's only a matter of time before I find it. Here is a video that shows the little springies.

YouTube
 

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...little spring connectors...
Great idea! I have seen those pictured on the outside of some beginner electronics kit decades ago, but forgot about them long ago. I might get a few to try.

Some of the first electronics books I read when I was about 8 years old mentioned Fahnestock clips, used to assemble a crystal radio. I've never seen one of these clips, but to my surprise, they are still available on Amazon: Amazon.com : Pack of 10 Fahnestock Clips Electrical Brass with Nickel Plating : Other Products : Everything Else

-Gnobuddy
 
I spaced the components with the relative voltages in mind.
That is exactly my plan, also.

I have my 6AK6 thread circuit partly breadboarded
I'm hoping to find out if a 25k reverb transformer and a one-buck 6JW8 might come together to make a sort of micro-Champ / guitar amp in a pedal. :)

If I get any good results, I will post them to your mini-amp thread.

-Gnobuddy
 
Some of the first electronics books I read when I was about 8 years old mentioned Fahnestock clips, used to assemble a crystal radio. I've never seen one of these clips, but to my surprise, they are still available on Amazon: Amazon.com : Pack of 10 Fahnestock Clips Electrical Brass with Nickel Plating : Other Products : Everything Else

-Gnobuddy

I used to use the Fahnestock clips when I was a wee lad in the 70's. I think I bought them at Radio Shack. I also bought all of the Engineer's Mini-Notebook by Forrest M. Mims III (attached) from the Shack too. It's what turned me on to electronics.

A couple of years ago I bought more Fahnestock clips on eBay. I like 'em :)
 

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Fahnestock clips...but to my surprise, they are still available on Amazon

My first Tubelab prototyping system (the source of the Tubelab name) used Fahnestock clips, I got them at Mouser maybe 15 years ago. They are no longer stocked there or at Digikey. I still have half the box......somewhere.

My grandfather played with early radio in the 1920's after leaving the US Army signal corps when WW 1 ended. He had some big Fahnestock clips that held the wires for the 6 volt lead acid storage batteries that lit the filaments on the old battery radios.
 
I am in the middle of a building project. This is the wooden laptop project that I talked about in the "what did we buy today" thread several months ago. Made with desktop components, it's not going to be a traditional laptop, but a full blown Core i7 powerhouse with 5 TB of disk space, 10 WPC audio, semi-decent speakers and a 4K screen in a portable form factor small enough for use almost anywhere.

I have a large plastic tote bin labeled "connectors" that I dragged out to find suitable interconects for building the computer. Could the remains of the box of Fahnestock clips from a 15 year old project be in that tote? The odds were against it, and sure enough they weren't there, but there was another box of 100 Fahnestock clips that had never been opened. They were still in the original Mouser bag with a stock number and an invoice number, but no date. They are obviously old since the "country of origin" is UNITED STATES.

Neither the stock number or the invoice number can be found via Mouser's web site.
 

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I'm hoping to find out if a 25k reverb transformer and a one-buck 6JW8 might come together to make a sort of micro-Champ

I'm still digging through old boxes looking for parts to build my portable PC......like how do you lose some long piano hinges?

In my digging I found a box full of leftovers from the original Hundred Buck Amp Challenge build. I found a few transformers that were successfully used as OPT's. There were two Mouser 41FW300 multi tapped power transfomers that I never mentioned in the original HBAC thread since I was planning to use them in an amp which never got finished. They made nice push pull OPT's for small low powered tubes that liked a highish load impedance. 6AK6's, 6AH6's and a bunch of high Gm tubes that were on the dollar menu all worked with this OPT in the 1 to 2 watt zone......Unfortunately Mouser has chosen to discontinue it and I can't find anything like it today.
 

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Unfortunately Mouser has chosen to discontinue it and I can't find anything like it today.
With all the advantages of small switching power supplies, I think we are on borrowed time when it comes to the availability of small power transformers. :(

Even small 70V audio line transformers might be endangered. A couple of years ago, someone told me that he'd just installed new speakers in his pickup truck, and each speaker came with a small class D audio power amplifier module mounted right on the speaker frame. Hook up +12V DC, ground, and a line-level audio signal, and you're done.

The advantages for aftermarket auto speakers are obvious - you can add more speakers or more power without needing to tear into the factory audio equipment, which these days tends to be heavily integrated into the vehicle's electrical and electronic sub-systems.

I can see the same idea catching on for public-address / paging speaker systems, just as soon as the class-D amplifier module becomes cheaper to manufacture than a 70V audio line transformer. Put an audio trimpot on each speaker, and you can set it's volume to taste. No need for a multitapped audio line transformer any more.

-Gnobuddy
 
Even small 70V audio line transformers might be endangered.

The real reason these things still exist are the regulations in place in places like the USA.

In a factory like the Motorola plant where I worked ALL wiring over 75 volts must be routed in conduit. No Romex running through walls and ceilings is allowed. I believe that the same rules apply in all commercial buildings over a certain size. Australia allows a higher voltage without conduit. That's why they have the 100 and 140 volt transformers that we can't get.

There must have been 10 miles of fat twisted pair running loose through the ceilings fed by a 70 volt audio distribution system.

There was the in house PA system that played crappy music, and a 250 WPC solid state McIntosh that fed two channels of audio, a 1KHz tone, and a standardized voice loop. Both went to every test station in the factory for use in testing the two way radios we built. For almost 10 years the maintenance of the McIntosh based system was part of my responsibility. Other than adding or deleting users and changing the tape loop, it never needed fixing, because it never broke. Adding a new output just required a pair of wire cutters and some wire nuts. Idiots like me would splice into it live. 70 volts will get your attention and is best not messed with while you are standing on a ladder 15 feet in the air, I managed to get the use of a scissor lift for ceiling climbing.

We also had a few miles of coaxial cable for the 1 MHz and 10 MHz standard clock signals for all the test equipment in the place......unfortunately, that stuff broke all the time.

When the factory shrank from over half a million sq feet to just a few test stations the audio distribution system was shut down. It was far cheaper to burn a CD and put a CD player in every test station.

That class D amp still needs power and signal routed to it, so in most places the status quo will remain for a while. Nobody in charge of a big facility likes anything new, particularly if the old stuff just works and doesn't need much maintenance.
 
I was hunting online for some new tube sockets, and I found a vendor listing "New old stock Elco special 7 pin PCB mount miniature (B7G) tube socket". Take a look at the attached image - it looks a lot like my solderless breadboard adaptor!


-Gnobuddy
 

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