Spud: what, again!?!

[squiffiness]

Parsing the Tubelab website and this forum, I see twinklings of a Tubelab Spud SE based on compactrons, dating back to 2008 and fizzling out around 2010 timeframe.

I also see a LOT of other activities in Tubelab's life/career as well as answering our various questions here in TubelabLand. With the Simple P-P taking up what looks like much time, certainly understand if the spud PCB is dormant. Heck, I can't even get around to building out my SSE board due to other commitments.

If Tubelab could look into their crystal ball, would a Tubelab SpudSE PCB be rekindled and available? A spud puffing out more than 3W/ch with a simple build and budget price tag would be suh-weet.

Danke

[tomchr]

I built a Spud which was heavily inspired by Tubelab's SpudSE. You can check it out here: 6LU8 Spud : Neurochrome.com : : Audio
I actually built my prototype Spud using point-to-point wiring. It's certainly possible if you want to go that route. I think the total cost of mine was around $250. That included about $40 worth of walnut for the chassis.

I think a lot of things fell on George at the time the SpudSE was conceived so I suspect it's one of those "too many projects, not enough time" kinds of issues.

~Tom

[squiffiness]

Originally Posted by tomchr

I built a Spud which was heavily inspired by Tubelab's SpudSE. You can check it out here: 6LU8 Spud : Neurochrome.com : : Audio...

Very nice work. Particularly like the 5AR4 in your P/S and the toroid up top for power. The chassis is very nice. I'd seen your website during my initial research and found your CV an interesting read.

Point-to-point is a little beyond my skill level. Modestly handy is about right. Your comment about your entry into tube gear as getting into the "kiddie pool" end is just how I feel. Since I'm a mechanical engineer, I received some university level power engineering for electrical transmission and distribution and did some tower design with Ontario Hydro (when it still existed), but that was many, many moons ago. Understanding 3 phase electricity is, for me, a lot easier than plotting load lines and reading tube datasheets. I've had a few "ah ha" moments in the last few months.

I've just really liked the look of Spuds and the minimalist philosophy of their design. I remember reading something about an ideal amplifier being a "straight wire with gain..." (might've been Bob Carver years ago in an ad for his TFM series transfer function mimic amps) so Spuds seem to approach this type of philosophy.

Hence, the question of Tubelab George. He's got the tools and he's got the talent. I just have to recognize my limitation and the need for a PCB to pull off a tube amp.

[tomchr]

Thank you, Sir...

Load lines are a lost art these days. I recall briefly seeing them in the textbook I used in college, but I don't think they were taught. If they were, then I certainly was asleep during those classes... I got a good amount of information from reading Morgan Jones, "Valve Amplifiers". Also, Electronics 27 is a good read. Jones is probably a bit more accessible, though.

Rather than waiting around for a Spud PCB, I suggest grabbing a SimpleSE board. It's the same circuit topology but with two tubes rather than a double-tube. You can go as simple or as complicated as you'd like. Or as inexpensive/expensive as you'd like. The 5842 can be a little hard to find, but the various tube places on-line (or eBay) should be able to source them.

I had a SimpleSE going in point-to-point wiring at some point. It's a pretty neat amp.

~Tom

[tubelab.com]

I think a lot of things fell on George at the time the SpudSE was conceived so I suspect it's one of those "too many projects, not enough time" kinds of issues.....I also see a LOT of other activities in Tubelab's life/career as well

There have been a lot of strange diversions that have come my way over the last 5 years, and indeed my soldering iron has not been turned on yet this YEAR! However there was a totally unique reason for the death of the spud.....tube sockets. The 6LU8 and the 6LR8 are the same tube except for the base. The 6LU8 has 12 pins and the 6LR8 has 9. I first met these twin brothers when I worked in a TV repair shop in 1968. I made a few guitar amps back then with 6LU8's and other parts from discarded TV sets. The spud amp concept is a similar design, so I made one with an SSE and about half a million clip leads. It worked and sounded reasonable.

Before considering any amp for possible production I investigate the long term supply of parts. Neither of the twins are very common outside the USA. The 6LR8 was in far better supply than the 6LU8 back when I considered making the spud, so that is the tube I chose. I made a PC board and an amp and played with it for a while. At the time PC board mount sockets were not being made yet, but I was assured that they were coming.....from China.

I was looking into a parts kit like the ones I now have for the Simple P-P, and even boiught most of the parts. When the first batch of Chinese tube sockets showed up they were crap. The terminals were too loose for a Noval (.040" pins) and too tight for a Magnoval (.050" pins). The tube socket fiasco went on for at least 2 years and I gave up.

I saw Stan (ESRC) at the Orlando hamfest and he handed me some new production Chinese 9 pin PCB tube sockets that actually fit! It took what 3 or 4 years??????

I have about 100 6LR8's, all the small parts, but never bought any PCB's. Is anyone else still interested in this thing? If so I will have to make a spreadsheet and run a cost analysis to figure out what it would cost.

Back to the not enough time issues......

Tubelab has only made money (and only a few hundred bucks at that) for one of its six years as a corporation. I have worked at the same Motorola plant for 39 years. They have been laying off engineers slowly but constantly over the last 10 years. I have beaten the odds, but sooner or later my number will come up. Tubelab Inc. must be making some money when my employment ends, or it will cease operations. We have been paying $2510 a year in warehouse rent. If that payment did not exist, Tubelab would have been in the black for 5 out of 6 years! So, the obvious must be done.....bye bye stuff.....lots of stuff. Sherri and I have a goal to be out of the warehouse by July even if it all goes to the trash dump.

I have been sorting, selling, tossing, and giving away tons of stuff. I have hit every local hamfest and swap meet selling my stuff, although last week I sold about 300 tubes for $1 each and a bunch of other stuff, but bought a guitar and amplifier......not cool but for $60 I couldn't say no.

The mother of all hamfests is in 34 days 11 hours 5 minutes and 34 seconds, so I will pack up one cubic Honda Element full of stuff and drive it 1200 miles to Dayton Ohio. Then on to West Virginia. Be back on Memorial day. Until then I won't have time for electronics stuff, and the soldering iron will likely stay cold and so will the tubes......After that?????

[squiffiness]

I guess we're getting a little off topic here, but we're still talking about tubes and the learning experience of building Tubelab equipment.

Originally Posted by tomchr

Load lines are a lost art these days.

And, I can tell you that it is not well explained in most places. Most of the authors seem to skip something vital in their treatment and a load line magically appears on the plate characteristic curves plot...so pick a quiescent point (uh, how?!?), and that gives you one point, then use a plate current value that is your load resistance (selected HOW) divided into the E-sub bb voltage (selection not quite clear).

Join the two mystery points and that's your load line. It wasn't until recently that I discovered (for the 6L6GC) that in the Vp verus Ip the tops of all the sweeps were a straightline that was a typical load line. Came from a vendor's site: Tube amplifiers for high-end audio by The David Berning Company

So, it wasn't until I started treating the output tube like a quarter turn ball valve that I understood that the tube is throttling the power supply (B+) through the load by modulating the grid that things have started dropping into place lately.

Originally Posted by tomchr

I got a good amount of information from reading Morgan Jones, "Valve Amplifiers".

Even Master Tube Man Jones didn't explain load lines to my understanding. He jumped into it like everyone will just "get it".

Originally Posted by tomchr

Rather than waiting around for a Spud PCB, I suggest grabbing a SimpleSE board.

Already have it. Just waiting for more spare time and some budget funds to start the build up.

Brad
-------------------------
Things are only impossible until they're not!

[squiffiness]

Originally Posted by tubelab.com

The spud amp concept is a similar design, so I made one with an SSE and about half a million clip leads. It worked and sounded reasonable.

Seeing that picture of squid-like art that produced a working amp is what caught my eye, George. So, I thought I'd just ask.

Originally Posted by tubelab.com

Before considering any amp for possible production I investigate the long term supply of parts.

I am involved (part of my time) in safety/reliability for petrochem clients and that's always part of the lifecycle cost/design. Understand completely.

Originally Posted by tubelab.com

Back to the not enough time issues...
They have been laying off engineers slowly but constantly over the last 10 years...Tubelab Inc. must be making some money when my employment ends, or it will cease operations.

I've lived that distress twice in the last three years with major employment losses in Ontario, Canada, including me, twice as one of the last to go both times.

Originally Posted by tubelab.com

After that?????

Understand that too. Clearly, however, there is quite a little community here at DIYAudio that thinks the world of your work, so I'm hoping it can continue, since I have just barely arrived at the ground floor.

[Alvis]

Has anybody looked into soldering the tubes in, could this be done without damage to the tube? My first thoughts are, you would be fine, I have never tried it though.

Sure tube rolling would be a pain, this could be offset by the ability to use uncommon tubes.

You could even drill the PCB to accept different tube basses, like they do with capacitors.

[tubelab.com]

Has anybody looked into soldering the tubes in, could this be done without damage to the tube? My first thoughts are, you would be fine, I have never tried it though.

It was commonly done with the tiny subminiature tubes used in military aircraft electronics and hearing aids. I met a guitar preamp about 20 years ago that had the 12AX7's soldered into a little PC board that plugged into the main board so it would fit into a 1U rack cabinet. The company wanted over $100 for a replacement board. I used a propane torch to unsolder the tubes. I cleaned up the board with solder wich and soldered in some new tubes.

I suspect that the bigger tubes with pins through the glass like the 6LU8 and the 6LR8 would get the pins hot enough to stress the solder joints causing them to become intermittent over time.

Load lines are a lost art these days......And, I can tell you that it is not well explained in most places.

I went to a technical high school where I was enrolled in a 3 year long 3 hour a day vocational electronics program. It was 1967 - 1970 and our books were old US Army training manuals, and some textbooks printed by Philco. All centered on repair and basic design of electronic equipment built with vacuum tubes! It was here that I learned how to melt them. We learned how to draw load lines. I also quickly learned how to ignore them and squeeze more power out of a tube than the text book says was possible. A2 and AB2 weren't in the text books. Neither was screen drive. It was then that I made the biggest audio amp that I have ever made. It was completed during the summer after high school graduation and made 1200 watts. A lot of audio power for 1970 and it was clean power used for a rock groups PA system. All silicon though (24 X 2N3773).

I was a teenager with no money and I wanted to make loud guitar amps with old TV parts. Who needs a load line when you are using a power transformer for an OPT, you have no idea what the impedance or turns ratio is, you connected 42 speakers together in whatever series - parallel combination made the most noise and distortion was an acceptable and even desirable attribute?

I still do it the same way. I connect a tube to a variable power supply using an oversized OPT. Then I test the power and distortion at every possible load impedance from way too little, to way too much. Then I pick what works the best for the job at hand. The curves in the tube manual seem to never be drawn at the operating point you want to use (especially screen voltage) any your "8 ohm" speaker isn't 8 ohms.

Seeing that picture of squid-like art that produced a working amp is what caught my eye

That one even amazed me. I thought it would be a full blown TV jammer, but it never tried to oscillate. I have built some very clean designs that oscillated themselves into meltdown. They usually involved mixing tubes and mosfets though.

[w5jag]

There have been a lot of strange diversions that have come my way over the last 5 years, and indeed my soldering iron has not been turned on yet this YEAR!

I don't think mine has been on this year either. I am BIG time backed up on projects: the DZ kit, the 6146 SSE Rev 2, a new crankshaft damper for a V12 Jag, and more. And, child number 3 is expected in September. This is on the heels of grandchild number 3 that arrived a month ago .

I have been sorting, selling, tossing, and giving away tons of stuff. I have hit every local hamfest and swap meet selling my stuff, although last week I sold about 300 tubes for $1 each and a bunch of other stuff ...

I only bought one tube at my last hamfest, a 6HS6 for $1, and sold about $300 worth. I even sold a bunch of 6AL5's. I would say there is hope, but at the hamfest before last I fell off the wagon and bought probably three dozen NOS TV sweeps. NOS 6BG6's for a buck, what can you do?

The mother of all hamfests is in 34 days 11 hours 5 minutes and 34 seconds, ...

It's now looking grim for me AGAIN this year. I had to involuntarily take back a property two weeks ago, and I've decided to gut and remodel the place. Since construction always seems to take twice as long as I think it should, I'll probably be in the big middle of it during Dayton week. I feel if I don't make it this year, it could be a long time before I get another chance .

Win W5JAG