I noticed some white flakes inside my RCA tube. I'm guessing it's a loss of vacuum. Does anyone have recommendations for a suitable replacement? I'd prefer not to highly modify the circuit for a completely different tube. It's a single ended design
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Might be flakes of mica from the spacers. Usually the getter flash at the top turning white or disappearing altogether means vacuum has been lost. Does the amp still work with the tube in place? If you've lost vacuum it won't work.
Replacements: JJ EL84, any of the russian relabels, Sovtek as well.
S.
Replacements: JJ EL84, any of the russian relabels, Sovtek as well.
S.
Lots of old 6BQ5s still available, just get some more. Your tube looks like it's got a lot of hours on it.
jeff
WHY would you replace a perfectly working tube?
WHY OH WHY would you replace it with a DIFFERENT tube?
WHY OH WHY would you replace it with a DIFFERENT tube?
Thanx. Felt like drawing something. Please check for glitches. There are a couple places where it wa snot clear what was intended.
Update #1.
dave
Update #1.
dave
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I don't get the X Y 100 ohm resistors to pin 3 on the 6BQ5 ?
The X Y I'm guessing is from the heater supply.
What does this accompish?
-ICHI
Looks very nice. Is this drawn on paper, or do you have a drawing program?
You've changed the first stage cathode resistor, possibly because it looks too small, but the original value looks to have been chosen accounting for a lot of current from the 150K Ohm resistor. I'm not crazy about the 470K Ohm plate load though. Somewhere near half of that, maybe.
All good fortune,
Chris
Ignoring the cathode voltage the current through the 150K between B+ to V1 cathode resistor would generate ~3.5 volts of G-K bias. Seems high for a 12ax7. At 100 volts plate the data sheet specs 0.5 ma plate current at 1 volt G-K. The voltages shown across the plate resistor work out to 0.27 ma plate current.
The getter on that tube looks nice & silvery; I doubt that the vacuum has been lost, since the getter would assume a whitish-purplish hue if air got in there.
OK I almost feel like there are 2 different threads in this thread. 1. Is the tube OK? Replacements as in brand availability, and 2. Modify the amp and swap tube types. No idea what the original intent of the question was.
As was said, if the getter is still silver and the tube works (be great if you could check it on a tube tester), don't worry about it. It could be mica flakes from the spacers, it could be some random dust finally moved around from manufacture. But in my experience, it's almost always the heater/cathode assembly coming apart/wearing out. That usually happens pretty quickly and takes the tube out and blows chunks all through the tube. You'll hear this obviously in the amp and it's quite apparent. I think the Russians literally build tubes to do this on a set schedule, at least the ones they sell (sold?) to the USA. You may have a tube that has spit a few (would test a little low on tube tester but appear OK), but is still working and may stay working a good while. Or not. But why fix it if it's not broke?
Also as was said, if vacuum was lost, the getter turns to a white ghost of itself... there's no mistaking a tube with lost vacuum. That doesn't look like one.
On replacement types, literally almost any power tube you want to plan on buying and having some stock of. Nothing about that circuit above is demanding. Small TV sweep tubes, radio tubes and basically every modern made power tube ever could handle that circuit with some slight adjustments for bias.
As was mentioned, the easiest solution is leave alone if works, or swap with another EL84/6BQ5.
As was said, if the getter is still silver and the tube works (be great if you could check it on a tube tester), don't worry about it. It could be mica flakes from the spacers, it could be some random dust finally moved around from manufacture. But in my experience, it's almost always the heater/cathode assembly coming apart/wearing out. That usually happens pretty quickly and takes the tube out and blows chunks all through the tube. You'll hear this obviously in the amp and it's quite apparent. I think the Russians literally build tubes to do this on a set schedule, at least the ones they sell (sold?) to the USA. You may have a tube that has spit a few (would test a little low on tube tester but appear OK), but is still working and may stay working a good while. Or not. But why fix it if it's not broke?
Also as was said, if vacuum was lost, the getter turns to a white ghost of itself... there's no mistaking a tube with lost vacuum. That doesn't look like one.
On replacement types, literally almost any power tube you want to plan on buying and having some stock of. Nothing about that circuit above is demanding. Small TV sweep tubes, radio tubes and basically every modern made power tube ever could handle that circuit with some slight adjustments for bias.
As was mentioned, the easiest solution is leave alone if works, or swap with another EL84/6BQ5.