The Novar socket was very uncommon in Europe, too. Instead, and beginning with the PL500 in 1960, we've got the Magnoval, which is of the same pin circle diameter, the same 36° pin spacing, but features thicker pins. Only power pentodes, HV rectifiers or booster/ballast diodes were made with Magnoval sockets.
Best regards!
Best regards!
Looks like RCA's Novar and GE's Compactron designs came out around 1961. The Compactron apparently caught on better for multi-function tubes with the more generous (12) pins.
Most of the TV "Sweep" tubes we use now are the 12 pin Compactron type, but there are a number of decent Novar Sweeps too. Novar sockets can be a problem to find however.
Novar bases and tubes:
9NZ/9RW: 6GT5 7868
9QD: 6GF7
9QK: 6GJ5
9QL: 6JB6, 6JE6, 6JF6, 6JU6, 6KM6, 6LQ6, 6MC6, 6ME6, 6LZ6
9QT; 6KY8, 6LR8, 15MX8, 17LD8
9QU: 6JG6, 6JR6, 6JT6, 6KV6
Most of the TV "Sweep" tubes we use now are the 12 pin Compactron type, but there are a number of decent Novar Sweeps too. Novar sockets can be a problem to find however.
Novar bases and tubes:
9NZ/9RW: 6GT5 7868
9QD: 6GF7
9QK: 6GJ5
9QL: 6JB6, 6JE6, 6JF6, 6JU6, 6KM6, 6LQ6, 6MC6, 6ME6, 6LZ6
9QT; 6KY8, 6LR8, 15MX8, 17LD8
9QU: 6JG6, 6JR6, 6JT6, 6KV6
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There is some Novar crossover to Compactron equivalents, and several that are close.
1st, I missed 6MJ6 under the Novar 9QL base. Pretty rare I think.
6LR8 = 6LU8 as Tony mentioned.
7868 = 7591A and 6GM5
6GF7 = 6EM7 and is close to 6FM7, 6EA7, 6GL7
6GJ5, 6GT5, 6JB6, 6JT6 = 6GW6 and are close to 6JN6, 6GE5, 6GV5, 6FW5
17LD8 is close to 6JZ8
6LQ6, 6ME6, 6MJ6 are close to 6JE6, 6JS6, 6LG6A
6JE6 is similar to 6JS6, 6LQ6
6MC6 is close to 6LX6, 6KD6, 26HU5, and later single section version of 6KN6, 42KN6
6KV6 is close to 6KM6, and similar to 6HB5 (Sylvania 6KV6 and Sylvania 6HB5 appear to be identical except for cooler fin on grid 1, RCA 6KV6 has a lower Rp)
6LZ6 is roughly similar to 6JE6, 6JS6
non Novar trivia:
The double section (old version) 42KN6 appears to be identical with two 38HE7 pentodes in parallel (were $0.35 tubes once, then $1 tubes) (Many 38HE7 tubes have the 21V pentode heater alone, across pins 10 and 12)
1st, I missed 6MJ6 under the Novar 9QL base. Pretty rare I think.
6LR8 = 6LU8 as Tony mentioned.
7868 = 7591A and 6GM5
6GF7 = 6EM7 and is close to 6FM7, 6EA7, 6GL7
6GJ5, 6GT5, 6JB6, 6JT6 = 6GW6 and are close to 6JN6, 6GE5, 6GV5, 6FW5
17LD8 is close to 6JZ8
6LQ6, 6ME6, 6MJ6 are close to 6JE6, 6JS6, 6LG6A
6JE6 is similar to 6JS6, 6LQ6
6MC6 is close to 6LX6, 6KD6, 26HU5, and later single section version of 6KN6, 42KN6
6KV6 is close to 6KM6, and similar to 6HB5 (Sylvania 6KV6 and Sylvania 6HB5 appear to be identical except for cooler fin on grid 1, RCA 6KV6 has a lower Rp)
6LZ6 is roughly similar to 6JE6, 6JS6
non Novar trivia:
The double section (old version) 42KN6 appears to be identical with two 38HE7 pentodes in parallel (were $0.35 tubes once, then $1 tubes) (Many 38HE7 tubes have the 21V pentode heater alone, across pins 10 and 12)
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Many know that I learned a lot about tubes by experimenting with parts that I removed from discarded consumer electronics in the local trash dump. This was in the 1960's when the most common item in the trash was a 1950's vintage TV set, or an older radio.
An hour in the dump with both pockets full of tools could yield a box full of tubes, a grocery bag full of components (caps, resistors and tube sockets), and as many transformers as I could carry.
The most common sweep tube was a 6BQ6 in GT or GA flavor, followed by a 6DQ6. Real audio tubes were extremely rare, I might find a 6V6 type occasionally and only found some 6L6GA's once in an old organ.
The 6BQ6 was my go-to tube for a SE guitar amp. I learned how to make that one rock early on. I would not conquer the 6DQ6 until high school electronics class where I learned things like bias, load lines and impedance matching.
What I have learned over the years is just how many tubes have identical guts, but different numbers or pinouts.
The 6AV5GT is a 6BQ6GT that lost it's plate cap and got a different pinout. Likewise the 6AV5GA is a 6BQ6GA.
The 6GE5 is a Compactron 6DQ6 without a plate cap, and the 6GF5 is the same tube with it's plate fins cut down to fit in a skinny bottle.
Many now know that the 6BG6 and 807 are 6L6GB's with plate caps. I never knew this as a kid or I would have collected 6BG6's, they were quite common in the trash, but usually in quite old TV sets that had been outdoors for years.
A few months ago I bought a bunch of "Magnoval" sockets from Antique Electronic supply.
"Novar" tubes fit them perfectly (they don't fall out of the socket when turned upside down). They are cheap too.
I also bought from ebay sockets listed as "Magnoval Novar B9D" which turned out to fit Novar.
I wouldn't go there.
The 7868 has a max G2 spec of 440 volts. The 6AU5 is a true TV sweep tube with a max G2 spec of 200 volts. I don't know the circuit of that particular Fisher, but I bet it runs the screens on B+. Each 6AU5 eats 1.2 amps of heater current, where the 7868 eats 800 mA, demanding more current from the transformer.
I haven't done much tinkering with the 6AU5 since the 6AV5 in GT and GA versions are more common and roughly the same tube, including the pinout. None of these will live with 400+ volts on the screen grid.
The similar 7591 was used in several guitar amps. Again there are mixed reviews on whether the new production tubes will live in these amps or not. Some users added screen grid resistors to prevent meltdown. Maybe that's all that's needed to make EH tubes live in your Fisher.
Excess G1 circuit resistance is a reason for tube runaway in amps with other EH tubes, particularly some batches of KT88's. The tubes run fine for a year or two, then meltdown suddenly.
I swapped 6L6GC's into some of those amps many years ago, but the lower Gm makes it a non exact replacement, especially if the user expects to drive it 20 dB beyond clipping. Tube diameter is another issue too, the 6L6WGB and 7581A versions are smaller as is the rare 6BD5GT (a 6L6GB stuffed into 6V6GT sized glass).
I found a schematic for the Fisher 400 and it has a fixed 365V on grid2 and 405V on the plates.
There are plenty of tubes with a 330V g2 rating, but Sweep tubes are usually more like 220V g2. The 7868 tube with 550V Plate and 440V g2 ratings is an oddball. Like a 6L6GC grid2 with a later Sweep tube grid 1 (highish gm at 10200).
Since the grid 2 voltage is fixed, one could drop that down to 150V for use with a Sweep tube. A Novar tube like 6JG6A could work then if it were not for taking twice the heater power (1.6A at 6.3V). (2.5" to 2.75" seated height, 1.5" diam.)
There are plenty of tubes with a 330V g2 rating, but Sweep tubes are usually more like 220V g2. The 7868 tube with 550V Plate and 440V g2 ratings is an oddball. Like a 6L6GC grid2 with a later Sweep tube grid 1 (highish gm at 10200).
Since the grid 2 voltage is fixed, one could drop that down to 150V for use with a Sweep tube. A Novar tube like 6JG6A could work then if it were not for taking twice the heater power (1.6A at 6.3V). (2.5" to 2.75" seated height, 1.5" diam.)
6GT5 seems to be a good specimen...https://frank.pocnet.net/sheets/049/6/6GT5.pdf
G2 supply adjusted to 150volts...
G2 supply adjusted to 150volts...
