I'm using a set of Svetlana and they are great... I got them for a great deal though so they were actually less than the JJ or EH.
rongon,
Most pictures are not quite clear enough to see for sure what they are.
I rotate the tube to get a scale of the dimensions and spacings of the elements and connections to them, as they are spaced away from the center.
Look for items that penetrate the top and the bottom insulating mica supports (above the top mica, and below the bottom mica).
You will see one of the two following structures:
The filament inside the cathode.
Then pairs spaced equally on both sides away from the cathode.
A pair of vertical support rods (control grid)
A second pair of vertical support rods (screen grid)
A third pair of vertical support rods (suppressor grid)
This is a Pentode tube.
The filament inside the cathode.
Then pairs spaced equally on both sides away from the cathode.
A pair of vertical support rods
A second pair of vertical support rods
A pair of small sheet metal tabs
This is a Beam Power tube.
Most Beam Formers have the largest openings facing the plates at right angles to the holes that are in the plates. The small holes in the beam formers that you see through the holes in the plates are not the main beam former openings. You usually can not see the large openings of the beam formers, unless you deconstruct the tube.
I have some tubes with the following structures:
Beam Power tubes:
JJ: KT88, KT66, 6L6GC, and 7591 with holes in the plates and the beam formers
JJ: KT77 with no holes in the plates
CBS and Tesla 6L6GB with no holes in the plates
All of these have sheet metal beam formers that are connected to the cathodes
Pentode tubes:
JJ E34L
These have a suppressor grid, with a separate connection to pin 1.
Post 14 is hard to tell.
Post 15 appears to be a Beam Power tube
Post 16 appears to be a Pentode tube
Post 17 appears to be a Beam Power tube
Post 18 is hard to tell.
Post 19 is hard to tell.
Post 20 appears to be a Beam Power tube
Most pictures are not quite clear enough to see for sure what they are.
I rotate the tube to get a scale of the dimensions and spacings of the elements and connections to them, as they are spaced away from the center.
Look for items that penetrate the top and the bottom insulating mica supports (above the top mica, and below the bottom mica).
You will see one of the two following structures:
The filament inside the cathode.
Then pairs spaced equally on both sides away from the cathode.
A pair of vertical support rods (control grid)
A second pair of vertical support rods (screen grid)
A third pair of vertical support rods (suppressor grid)
This is a Pentode tube.
The filament inside the cathode.
Then pairs spaced equally on both sides away from the cathode.
A pair of vertical support rods
A second pair of vertical support rods
A pair of small sheet metal tabs
This is a Beam Power tube.
Most Beam Formers have the largest openings facing the plates at right angles to the holes that are in the plates. The small holes in the beam formers that you see through the holes in the plates are not the main beam former openings. You usually can not see the large openings of the beam formers, unless you deconstruct the tube.
I have some tubes with the following structures:
Beam Power tubes:
JJ: KT88, KT66, 6L6GC, and 7591 with holes in the plates and the beam formers
JJ: KT77 with no holes in the plates
CBS and Tesla 6L6GB with no holes in the plates
All of these have sheet metal beam formers that are connected to the cathodes
Pentode tubes:
JJ E34L
These have a suppressor grid, with a separate connection to pin 1.
Post 14 is hard to tell.
Post 15 appears to be a Beam Power tube
Post 16 appears to be a Pentode tube
Post 17 appears to be a Beam Power tube
Post 18 is hard to tell.
Post 19 is hard to tell.
Post 20 appears to be a Beam Power tube
OK, I see. It is hard to know for sure without dissecting the tube in question.
- The tube in post 15 that appears to be a beam power tube is an RCA 6L6GC.
- The tube in post 16 that appears to be a pentode is a Tesla EL34.
- The tube in post 17 that appears to be a beam power tube is a GE 6CA7. Post 18 has more photos of that same tube.
--
Thanks all for the recommendations, links to similar discussion, and sharing your experiences with these. I'll look hard at the top 2-3 and take a shot. JJ or Mullard look promising.
RFT EL34 are good. Most of them appear under other brand labels (including Mullard), but some are actually labelled RFT.
Second on the RFT and the Winged-C EL34, those are the "they don't make it like this anymore" quality tubes at the most reasonable price. Another good one is the Tesla EL34.
Yes, the RFTs are quite good, bought tons of them sold as Mullards in the late 1980s and early 1990s - not one failed and they sounded just fine in the modified ST-70s where they all ended up.
just be careful with the heating voltage for the JJ tubes.
it must be a little below the recommended voltage or just at the recommended voltage but not more
it must be a little below the recommended voltage or just at the recommended voltage but not more
rongon,
See if you can get a couple of bad/dead output tubes, a beam power tube, and a pentode.
Maybe a repair shop can let you have a couple they were going to throw in the garbage.
Then you can carefully break off the glass envelope and dis-assemble the tubes.
You are going to look at the parts with stereoscopic and 3D with both eyes, not the single lens of a camera.
After that, you will be better able to look at good tubes and determine whether they are beam power or pentode tubes without breaking them.
See if you can get a couple of bad/dead output tubes, a beam power tube, and a pentode.
Maybe a repair shop can let you have a couple they were going to throw in the garbage.
Then you can carefully break off the glass envelope and dis-assemble the tubes.
You are going to look at the parts with stereoscopic and 3D with both eyes, not the single lens of a camera.
After that, you will be better able to look at good tubes and determine whether they are beam power or pentode tubes without breaking them.
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