I find these from time to time in my travels, but largely ignore them, but after seeing how much they go for on ebay and only costing 5 bucks a pop, i decided i should nab them.
It appears a few have built amps with them, so could be tempting to build an amp someday with them, since i have all the gear to make the transformers, it also seems you can get away with running these in an amp without the need of the extremely high voltages other transmitter tubes require.
Is there any way to make an adapter to test these tubes on the likes of a TV7 or other similar tester?
I have 9 tubes in total and at least 4 have a good full area on the glass with getter and look new, another 2 look new but appear to have a smaller amount of getter on the glass, and one of them appears used and no getter visible on the glass, but not white.
Could be a fun project and they are pretty magnificent tubes to look at.
I would imagine they would need a beefy power supply to run at their maximum ratings, looks like these things could easily pull 100 watts out of a pair?
Doesnt seem to be an awful amount of designs published, but I would feel that running in class AB2 would be beneficial to reduce power consumption when idle.
It appears a few have built amps with them, so could be tempting to build an amp someday with them, since i have all the gear to make the transformers, it also seems you can get away with running these in an amp without the need of the extremely high voltages other transmitter tubes require.
Is there any way to make an adapter to test these tubes on the likes of a TV7 or other similar tester?
I have 9 tubes in total and at least 4 have a good full area on the glass with getter and look new, another 2 look new but appear to have a smaller amount of getter on the glass, and one of them appears used and no getter visible on the glass, but not white.
Could be a fun project and they are pretty magnificent tubes to look at.
I would imagine they would need a beefy power supply to run at their maximum ratings, looks like these things could easily pull 100 watts out of a pair?
Doesnt seem to be an awful amount of designs published, but I would feel that running in class AB2 would be beneficial to reduce power consumption when idle.
Easier to lash up several power supply's, bench or quick tfmr, bridge rectifier + caps to test. A bog standard valve tester won't test them properly. I have several ex Tek 500 series scope tfmr's that are great for testing valves like these & some big bench supplies EG a 500v/3A jobby; if your looking at building amps with unusual valve types you need some mad test gear as datasheets are scarce.
Have fun, Andy.
Have fun, Andy.
Looks interesting. I would be tempted to use a grid choke instead of a grid resistor to stabilize g1. Those are relatively simple to create and with split center tap, allow variable fixed bias to both tubes.
Douglas
Douglas
Here are some curve traces for a used Philips QE08-200
Triode: 100mA/div Vert., 50V/div Horiz., 5V steps
" B Tetrode": 100ma/div Vert., 50V/div Horiz., 2V steps, 205V Vg2
I don't see any "Beam Plates" in the tube. Looking sorta half way between a Beam Tetrode and a Tetrode with those kinks. Looks like kinks only at lower currents though.
3rd pic are some Valvo tubes on Ebay. And 4th pic is the Philips QE08-200 tube traced here. As you can see, no beam plate supports on any of them.
Triode: 100mA/div Vert., 50V/div Horiz., 5V steps
" B Tetrode": 100ma/div Vert., 50V/div Horiz., 2V steps, 205V Vg2
I don't see any "Beam Plates" in the tube. Looking sorta half way between a Beam Tetrode and a Tetrode with those kinks. Looks like kinks only at lower currents though.
3rd pic are some Valvo tubes on Ebay. And 4th pic is the Philips QE08-200 tube traced here. As you can see, no beam plate supports on any of them.
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The Tek 576 does up to 220 Watts max (plate V x current ) and about 1 Amp max. on the 400V setting ( 1/2 Amp avg. ) as built. I did increase the grid stepping V from +/-20V peak to +/- 170V peak. (and like 1/2 Amp). TV Sweep tubes are well covered now. This QE08-200 is like 2.5x 6LW6 tubes though. My Vg2 supply was max'd out on current here, otherwise I could have traced the QE08-200 up to an Amp plate current.
I tried to curve trace a 7242 tube last year, which turned out to be gassy. The heater current wouldn't come down to spec and my clip leads were melting. .
I tried to curve trace a 7242 tube last year, which turned out to be gassy. The heater current wouldn't come down to spec and my clip leads were melting. .
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Looking it up it's interesting to see that it's a semiconductor tester.
Also neat that the manual has a page on modding it for bringing out leads. "
". . . It has come to our attention that it is becoming increasingly common for our customers to
connect 576's and 577 1177's to devices or fixturing external to the instrument and thus external
to or outside of the safety features that are designed into the instruments. ·
We have provided a wide range of adapters that are designed to allow you to test your devices
while inside the plastic protective cover. However, if you feel it is necessary to connect the
collector supply to devices or fixturing outside of this protective cover, in effect defeating the
built-in safety features of the instrument, the following simple modification will at least allow
you to do so with the plastic protective cover still installed. This will reduce the chances of the
operator coming into contact with the collector supply voltage."
Spirit prevails over the legal department , nice. I can't imagine anything like that now.
Also neat that the manual has a page on modding it for bringing out leads. "
". . . It has come to our attention that it is becoming increasingly common for our customers to
connect 576's and 577 1177's to devices or fixturing external to the instrument and thus external
to or outside of the safety features that are designed into the instruments. ·
We have provided a wide range of adapters that are designed to allow you to test your devices
while inside the plastic protective cover. However, if you feel it is necessary to connect the
collector supply to devices or fixturing outside of this protective cover, in effect defeating the
built-in safety features of the instrument, the following simple modification will at least allow
you to do so with the plastic protective cover still installed. This will reduce the chances of the
operator coming into contact with the collector supply voltage."
Spirit prevails over the legal department , nice. I can't imagine anything like that now.
Safety? What's that?
I did mod the rectifier for the 1500V scale so it's "only" 750V now. Still, I wouldn't want to get across that. Most of the Tek 576 units on Ebay are missing the Plastic Safety Cover. And the one I fixed had a failed relay for the safety cover switching. A pencil had been pushed into the hole where the cover normally inserted a peg when closed. The relay must have chattered until it's contacts failed. Fortunately the relay just plugs into a socket.
All in all, it's a great curve tracer, easy to mod, SS but with no CPU/software. Weak point are the push-buttons going flaky (especially the Invert buttons for NPN to PNP or N and P). But easily fixed with some Centralab switches off Ebay. Just have to swap out the contact push rods, no un-soldering needed.
Biggest problem is shipping. 75 Lbs. Some places want a pallet and arranged truck delivery. Make sure the CRT and the HV for it are working. And most of them need fixing or have become ridiculously expensive if they still work. Got mine working for $600 like 20 years ago. Then a fixer upper spare for $400. Tube testers cost more! Tek's service manual is great and readily available. 2" thick. S/N's go up to near 400,000, so there were a lot of them made.
I did mod the rectifier for the 1500V scale so it's "only" 750V now. Still, I wouldn't want to get across that. Most of the Tek 576 units on Ebay are missing the Plastic Safety Cover. And the one I fixed had a failed relay for the safety cover switching. A pencil had been pushed into the hole where the cover normally inserted a peg when closed. The relay must have chattered until it's contacts failed. Fortunately the relay just plugs into a socket.
All in all, it's a great curve tracer, easy to mod, SS but with no CPU/software. Weak point are the push-buttons going flaky (especially the Invert buttons for NPN to PNP or N and P). But easily fixed with some Centralab switches off Ebay. Just have to swap out the contact push rods, no un-soldering needed.
Biggest problem is shipping. 75 Lbs. Some places want a pallet and arranged truck delivery. Make sure the CRT and the HV for it are working. And most of them need fixing or have become ridiculously expensive if they still work. Got mine working for $600 like 20 years ago. Then a fixer upper spare for $400. Tube testers cost more! Tek's service manual is great and readily available. 2" thick. S/N's go up to near 400,000, so there were a lot of them made.
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Quite an interesting read here.
Turns out my 200H model doesn't have a 6.3V heater.
These have a 26V heater which is a weird voltage to use.
But i can wind my own power transformer to suit.
I notice these require a low grid voltage of 250V from what I can make out of the datasheet, but utralinear should not matter right?
How many watts could I get out of a single ended one of these in class AB1 or 2?
I was thinking about building a test power supply for prototyping but not sure what route i should go.
I have a whopping big transformer here with many multiple secondary taps.
This could work well for a test rig, just need a selector to change output voltages and have a way to swap out different rectifier configurations etc.
Not too sure what most people do, but having multiple voltages available at the same time could be useful.
Oh, and speaking of curve tracers, I have a tektronix 561A scope, I wonder if any curve tracer plug-ins exist for that?
Turns out my 200H model doesn't have a 6.3V heater.
These have a 26V heater which is a weird voltage to use.
But i can wind my own power transformer to suit.
I notice these require a low grid voltage of 250V from what I can make out of the datasheet, but utralinear should not matter right?
How many watts could I get out of a single ended one of these in class AB1 or 2?
I was thinking about building a test power supply for prototyping but not sure what route i should go.
I have a whopping big transformer here with many multiple secondary taps.
This could work well for a test rig, just need a selector to change output voltages and have a way to swap out different rectifier configurations etc.
Not too sure what most people do, but having multiple voltages available at the same time could be useful.
Oh, and speaking of curve tracers, I have a tektronix 561A scope, I wonder if any curve tracer plug-ins exist for that?
Impressively linear triode curves with this tube! Also impressive it's construction: Three cathode-control grid-screen grid Arrangements in a line, two massive graphite plate blocks at the sides.
Best regards!
Best regards!
The design in the thread quoted earlier looks tempting to build and i have all the parts.
So if im not mistaken, that thing will provide close to 40W as a single ended triode in class A?
Thats some pretty impressive stuff.
Only thing that puts me off with my tubes is they are the 26V heater version, might be harder to find spares.
So if im not mistaken, that thing will provide close to 40W as a single ended triode in class A?
Thats some pretty impressive stuff.
Only thing that puts me off with my tubes is they are the 26V heater version, might be harder to find spares.
That's still not bad, what about running as a tetrode and/or class AB1, would that increase power much, albeit at the expense of linearity?
Ok, so single ended is class A only?
Would running as a tetrode instead process much more power?
I might implement a switch like some do to switch between triode and tetrode modes.
Its still tempting to build a push pull design, but it would be a hell of a beast, but I have the stuff to make the necessary transformers
Would running as a tetrode instead process much more power?
I might implement a switch like some do to switch between triode and tetrode modes.
Its still tempting to build a push pull design, but it would be a hell of a beast, but I have the stuff to make the necessary transformers
The 3D21A has a more traditional construction, but it has two independent cathodes. If you grab one end and the center only one will light with 6.3 across it. That wee pulse tube has current plotted to something like an amp( short time period ). They sound pretty fine too.
Douglas
Douglas
I dug out a bigger power supply for Vg2, a 1 KW Xantrex XHR, a little over kill, but now we can do the full 1 Amp curves for the QE08-200. Usually the 60 Watt linear Xantrex 250V supplies under it are sufficient for TV Sweep tubes, but the curve knees here eat up the max current for them.
The little black box with colored banana plugs is a 10X -200V capable amplifier for the grid1 steps. These were available on Ebay last year for Tek 576 curve tracers to do tubes without modding the 576.
Looks like they sold 20 of them and then discontinued the sales this year. I messaged with seller then and they were considering an upgrade version that could do positive voltages too, with some current for grid2 stepping. Works well. This Tek 576 doesn't have my Step Amplifier mods yet, like my other one, so is a quick fix.
1) the Precision test setup 😈
2) Xantrex XHR 300-3.5
3) Philips QE08-200 at 100mA/div, 50V/div Horiz., 5V Vg1 steps, 275 Vg2
I think it takes 350 Vg2 or positive Vg1 to get up above 1 Amp plate current.
The little black box with colored banana plugs is a 10X -200V capable amplifier for the grid1 steps. These were available on Ebay last year for Tek 576 curve tracers to do tubes without modding the 576.
Looks like they sold 20 of them and then discontinued the sales this year. I messaged with seller then and they were considering an upgrade version that could do positive voltages too, with some current for grid2 stepping. Works well. This Tek 576 doesn't have my Step Amplifier mods yet, like my other one, so is a quick fix.
1) the Precision test setup 😈
2) Xantrex XHR 300-3.5
3) Philips QE08-200 at 100mA/div, 50V/div Horiz., 5V Vg1 steps, 275 Vg2
I think it takes 350 Vg2 or positive Vg1 to get up above 1 Amp plate current.
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