Breadboarding didn't go as planned...

Ripthorn · February 18, 2009, 12:11:05 AM

Hey guys, I am working on a submini tube project and I tried breadboarding it, but it didn't go as I hoped. I put in a bridge rectifier and used two tubes (though what I am working on only takes one) because my transformer puts out 12.6vac. I wired the heaters in series (at least I think. I did ac to pin 3 of tube 1, then pin 6 of tube 1 to pin 3 of tube 2 and pin 6 of tube 2 to the other ac lead) and put all the other parts in. Once I got it all together, I fired it up, but got nothing. I audio probed and found that I am not getting any signal from the plate of the tube I am using. I also noticed that the voltage on the tube that is being used seemed to be the full 12.6 volts. Do I need to ground the cathodes of the tube not being used? I am feeding almost 18V dc to the plate, so that should be enough. I am welcoming any ideas. Be kind as this is my first tube project.

frequencycentral · February 18, 2009, 06:03:36 AM

Sorry to hear its not going as planned.

What tubes are you using?
What is the current draw of each tube?
What current is the 12.6v AC providing?
Are the tubes glowing orange? Are they warm to the touch?

The way you have the heaters connected in series is exactly how I do it when breadboarding with 6111's and 7327's - I have only ever used DC to do it though. From what I understand it should work with AC too. Maybe not (?). Can you try it with DC?

The unused tube's heater should be acting as a voltage drop resistor, you shouldn't have to connect anything else on it up.

A schematic (with voltages) would be good to see. You can also measure the ohmage across a tube's heater (when unconnected) and compare it to a known 'good' tube to test if the heater is burnt out. It should be around 20 ohms if I recall.

In my experience these submini tubes are pretty tough cookies - I've accidentally put 12 volts through a 6111 heater for a short time and the tube has survived. It glowed very bright though (and I may have shortened it's life).

Ripthorn · February 18, 2009, 09:36:12 AM

I am using 6111's and so the heaters should be drawing 300mA. My DMM only goes to 200mA, so I can't test that. They are not glowing orange and are not warm to the touch. The transformer is a 12.6Vac/2A transformer, so I don't think current should be an issue. If I read you right, I should be getting a 6.3V difference between pins 3 and 6 of my first tube, is that correct? Because I think I am measuring the full 12.6V. Maybe I will see if I can do it with DC, I will just have to pick the right resistors for the current draw and hopefully they have a high enough power rating.

As for a schematic with voltages, I will try to do that tonight (no time this morning with a one and a half year old running around

)

frequencycentral · February 18, 2009, 10:06:24 AM

Quote from: Ripthorn on February 18, 2009, 09:36:12 AM
I am using 6111's and so the heaters should be drawing 300mA. My DMM only goes to 200mA, so I can't test that. They are not glowing orange and are not warm to the touch. The transformer is a 12.6Vac/2A transformer, so I don't think current should be an issue. If I read you right, I should be getting a 6.3V difference between pins 3 and 6 of my first tube, is that correct? Because I think I am measuring the full 12.6V. Maybe I will see if I can do it with DC, I will just have to pick the right resistors for the current draw and hopefully they have a high enough power rating.

As for a schematic with voltages, I will try to do that tonight (no time this morning with a one and a half year old running around )

Yeah - if you measure the voltage between the two tubes' heaters it should be 6.3 volts.

Are you sure you have the tubes' pinouts correct?

This is how I do it:

Powering heaters with AC is outside my experience I'm afraid.

Instead of the second 6111 you could use a 18ohm/3 watt resistor. Or a 7806. Or hook something up with a LM317 like the Subcaster.

Ripthorn · February 18, 2009, 10:21:51 AM

I just took a quick measurement of the resistance, and all four of my tubes that I have are measuring about 3-4 ohms between pins 3 and 6, which is rather disconcerting, considering these are NOS Raytheon tubes. I hope they aren't all bad. I have checked the pinout and I have it correct. I guess when my 6021's get here I will be able to do a better comparison. It would suck if I wasted 25 bucks on these tubes.

frequencycentral · February 18, 2009, 10:49:58 AM

Quote from: Ripthorn on February 18, 2009, 10:21:51 AM
I just took a quick measurement of the resistance, and all four of my tubes that I have are measuring about 3-4 ohms between pins 3 and 6, which is rather disconcerting, considering these are NOS Raytheon tubes. I hope they aren't all bad. I have checked the pinout and I have it correct. I guess when my 6021's get here I will be able to do a better comparison. It would suck if I wasted 25 bucks on these tubes.

Sorry - my bad. I just checked three 6111 which I know to be working. They all measure 3 ohms across the heaters. So you're OK there. I was obviously misremembering (or thinking of a different tube)!

Ripthorn · February 18, 2009, 11:07:59 AM

Well, you had me scared there for a bit, though I figured that all four NOS tubes couldn't be bad. So they appear to be good. I will have to try some other things to make sure they work. So these ones will glow when they are up and going? Any other pointers before I go into battle with the vacuous ones?

frequencycentral · February 18, 2009, 11:18:45 AM

Quote from: Ripthorn on February 18, 2009, 11:07:59 AM
Well, you had me scared there for a bit, though I figured that all four NOS tubes couldn't be bad. So they appear to be good. I will have to try some other things to make sure they work. So these ones will glow when they are up and going? Any other pointers before I go into battle with the vacuous ones?

Sorry!

I just checked the data sheet and AC should be fine. I can't see any reason why running the two tubes' heaters in series from AC should not work either.

Maybe just to assure yourself that they are working (and to see what a nice orange glow to expect) you should first hook one up to a 6 volts DC / 300 ma supply (using whatever method to get 6v - drop resistor, 7806, LM317 etc.).

Ripthorn · February 18, 2009, 10:26:45 PM

Okay, I took a 317T and got myself a pretty solid 6.3Vdc and fed it to the heater of one tube. It gives me a nice little orange glow and the drop from one side of the heater to the other is 6.05 V, still within the +/- 5% tolerance. I then audio probed, but got nothing on the plate of the first section. I was only getting like 5V to the plate, so I put in a jumper as opposed to a large resistor and I got 11V to the plate. Even with this, all I got was a large hum on the plate, no signal at all. This really confuses me because it shouldn't be that difficult of a thing, should it? Maybe I should start even simpler...

Boogdish · February 18, 2009, 11:57:25 PM

Are you using a coupling cap or trying to tap the audio directly from the plate? A schematic of what you're working on would help us greatly to help you troubleshoot it.

If you haven't checked out the valve wizard site yet, I'd suggest you do:
http://www.freewebs.com/valvewizard/

It talks about math, but don't let it scare you off, he gives very good explanations of how valves in guitar circuits work.

Ripthorn · February 19, 2009, 12:06:51 AM

I have no problem with math, being a physics grad student. I have been to the site and it has some very good info.

A schematic of the basic thing I am doing is found in this thread http://www.diystompboxes.com/smfforum/index.php?topic=73648.0. Currently I am just working on the first stage. I tried tapping of the audio both with and without a coupling cap, same loud hum in each case.

The main thing that is really bugging me is that it seems like it should work. I know I have the pinout correct and I get the glow from the tubes, so it seems like something is happening that I just don't understand and that I don't understand. I wonder if maybe I am not feeding the plate enough voltage.

frequencycentral · February 19, 2009, 03:59:26 AM

Tubes will hum like MFs if no supplied with enough ma, or if the power supply if dirty. The LM317 is giving you a nice regulated voltage to the heater, but is your B+ voltage nice and clean? ie. Maybe it needs filtering/regulating? Most tube problems would appears to stem from power supply issues. The B+ doesn't need to have much ma, but it does need to be clean.

Ripthorn · February 19, 2009, 09:31:12 AM

I will have to check the current draw, because that seems like a very possible reason now that you mention it. Now that I think of it, after rectifying, I don't have any power supply filtering! Oh crap! Gonna have to stick myself a 470uF electrolytic in there to smooth it out. I am also thinking I might take the 1044 I have on hand and boost my plate voltage so that I get something. Thanks for the suggestion, I didn't know that and it makes more sense than what I was thinking might need fixing. Hopefully this will get up and running and then I can work on my power section. I still need those 5902's... Man tubes can be frustrating, but they seem like so much fun, despite the challenges.

frequencycentral · February 19, 2009, 11:16:02 AM

Quote from: Ripthorn on February 19, 2009, 09:31:12 AM
Man tubes can be frustrating, but they seem like so much fun, despite the challenges.

It's just like everything in life - once you bust your cherry it will seem easy the next time. I've not even reached the 1 year mark yet with tubes, but it was the first project that was the toughie - and that was power supply issues. Have fun - and consider the frustration learning experience.

Ripthorn · February 19, 2009, 11:38:09 AM

Thanks, we'll see if I can't get this all worked out this evening. If this thing ends up working the way I want, I will post about the project later. If I have more problems, this thread will probably be around for a while.

Ripthorn · February 19, 2009, 02:58:52 PM

I think I may have found my problem. I got a finger near my 317 chip and it was hotter than blazes. I am dropping about 11V on that thing, and at 300mA, I think my problem is that it is not dissipating enough power to keep up with current demand. So splitting this between the 317 and plates is not giving me enough juice. At least that is my theory. Data sheets won't tell me the max dissipation without a heatsink, however, so only one way to find out.

Ripthorn · February 19, 2009, 10:26:00 PM

Okay, some strangeness going on. I got the power supply stuff working, so now on the plate of the first stage I get a great chimey sound, very nice. I put the signal through the resistors and caps and get a signal on the grid of the second triode. But then strange things happen in tubeville. I get nothing on my plate on the second triode. Not with a coupling cap, not with nothing. I have no crossing leads, I have adequate voltage to the plate, I have resistor and cap to ground from cathode, but nothing on the plate. Any ideas what it could be? How do I know if I have a bad section or short in the tube?

Ripthorn · February 19, 2009, 11:54:45 PM

Sorry to keep bumping this thread, but I got the clean stage working and it has such a nice sound. The distortion stage is coming along well, I am just letting the LM317 cool down, since I am running .6A through it at a voltage drop of about 4V. But anyway, it looks like it should work. Let the tweaking begin!

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Breadboarding didn't go as planned...