The PL802 substitute was mostly a issue of some popular Philips hybrid color TV chassis such as K70. The solid state replacement was issued by Philips (and third party spare suppliers) in the '80 due to the subpar reliability of the PL802 tube in that chassis: the stock of spare PL802 tubes was out. The replacement was only meant to work on that chassis, it is not a general purpose substitute for PL802. It was possible to use the PFL200 tube with a socket adapter, but this decal tube was even more expensive back then. By the way, the end pentode of PFL200 / EFL200 tube is very good for audio when triode wired. I use it on my headphone amplifier.
That's a given, the 6CK4 singleton power triode was developed for one manufacturer of TV sets for use as a vertical deflection amp. You also had ESSSS-loads of other specialty types used for RF front ends, like the 6BQ7, or IF duty, such as the 6CB6. Both types also work very well for audio. 6BQ7s are quite useful as audio cascode gain stages, the type I used as cascodes in an LTP configuration that not only has excellent sonic performance, but eliminated a second gain stage. 6CB6s also work quite well as small signal gain stages, and good loadlines aren't that hard to find.
No B-grade innards for the non-standard heater voltages, types developed for "daisy chaining" when the DC was derived straight from the mains with no PTX. That's pretty much a good thing as this makes available types like the 6LW6 that are pretty much unobtainium available. I have some 36LW6s that I got for cheap. With this type, you can get well north of 100W with a very reasonable VPP= 350V. The nice thing about these horizontal deflection power amps is that you can spec bust without compromising life since audio amplification is a good deal less demanding than HD duty.
"PL802 = 16V heater, an annoying voltage, hence who wants it for audio work? (I don´t)". That's NBD, at least for me. Just wind up a heater PTX. As I said, I'll take those 36LW6s. Better than not having them at all since the 6.3V heater version has gone unobtainium. I have other types that feature these weird heater voltages.
Lol, I have the opposite theory.
That quite a few tubes were just relabeled and made "extra special" by the marketing departement.
Especially certain tubes in the later years seem so extremely similar.
Makes you wonder if binning was also a thing back than.
Unfortunately there seems to be many stories and history there that is just lost forever.
But I would be absolute thrilled to know the ins- and outs as well as the thought process from way back.
That whole ECL range of products is kinda interesting.
For example, the ECL82 and ECL85/805 are basically identical.
A ECL80 is basically a EL91 with a (poor) triode combined.
There are some PCL types that are not 12-15V anymore, but totally different heater voltage.
etc etc etc
Even the pinout of certain ECL tubes can be a little odd sometimes.
Fascinating what happened there?
I think the only criteria for the heater of 'P' tubes is that they are 300mA, so can be wired in series. Likewise 'U' tubes are all 100mA, so can be heated directly from the mains when in series in a standard configuration.
Ah yeah that is true
These days I sometimes just use them to connect in series with a DC PSU as well.
Works great with a little constant current source.
Anyone got a more detailed set of triode curves for the 6LF8 in the low current region? This is the best I could find, and considering this for an input stage, with the pentode as a current source for the LTP splitter. My usual go-to 6JW8 pentode doesn’t like 12 mA of static plate current - it wants to overdissipate the screen. The other alternative is the 6KV8, but it’s pentode is overkill, and I prefer to hang on to them for when I NEED a power pentode. I’d like to compare triode curves, but theres nothing on Frank’s any more detailed below 10 mA than this. Anyone by chance measure it, or have a better data sheet? Looks kinda similar to the 12AT7-oid in the KV8, with a bit less perveance. I’m down for the count for a while due to injury, and my shop is all packed away for the moment and the bench is inaccessible. So the design wheels are spinning up a storm.
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Been looking into the 17-18 watt class of tubes lately, gathering victims for Experiments That May Not End Well, as the Big Stuff is in development. Somebody’s been sandbagging here.
From left to right:
1. 6JN6 (Amphenol), 17.5W
2. 22JU6 (Japan), 17W
3. 6GY5 (GE), 18W
4. 6GY5 (RCA), 18W
5. 21LG6 (RCA), 28W
6. 21LG6 (GE), 28W
7 26LW6 (GE), 40W
Cathode current capacity (not listed here) follows heater power. In anything Id be using them in, they wouldn not be run up against cathode current/screen voltage limits. I’m only looking for half an amp, maybe 600mA or so apiece. What was interesting is that all 5 devices in the middle are the same size. And plate dissipation capacity should follow that. Maybe earlier versions of the 18 watters had the shrunk plates of the stubby JN6, I dont know. But I’m figuring the GY5s to probably take the same wattage as the LG6’s - at least on stuff I have. I have since ordered more. There are even two basic versions of the LG6 and GY5 (RCA and the GE that may be marked anything). You get both types in both places even. And the Made In Japan JU6 uses the same GE style ”28 watt” plate.
I also bought a whole box of the little 11 watt 17BQ6GTs. STILL on the dollar (75 cent) list. Those little things are cute - I thought they’d be bigger. It will be kind of fun making 100 watts out of a quad of tubes about the same size as EL84’s. Math says it stays within ratings.
From left to right:
1. 6JN6 (Amphenol), 17.5W
2. 22JU6 (Japan), 17W
3. 6GY5 (GE), 18W
4. 6GY5 (RCA), 18W
5. 21LG6 (RCA), 28W
6. 21LG6 (GE), 28W
7 26LW6 (GE), 40W
Cathode current capacity (not listed here) follows heater power. In anything Id be using them in, they wouldn not be run up against cathode current/screen voltage limits. I’m only looking for half an amp, maybe 600mA or so apiece. What was interesting is that all 5 devices in the middle are the same size. And plate dissipation capacity should follow that. Maybe earlier versions of the 18 watters had the shrunk plates of the stubby JN6, I dont know. But I’m figuring the GY5s to probably take the same wattage as the LG6’s - at least on stuff I have. I have since ordered more. There are even two basic versions of the LG6 and GY5 (RCA and the GE that may be marked anything). You get both types in both places even. And the Made In Japan JU6 uses the same GE style ”28 watt” plate.
I also bought a whole box of the little 11 watt 17BQ6GTs. STILL on the dollar (75 cent) list. Those little things are cute - I thought they’d be bigger. It will be kind of fun making 100 watts out of a quad of tubes about the same size as EL84’s. Math says it stays within ratings.
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I also would have thought the same, until I compared 6CB5A (heater power 15.15 W, cathode current rating 240 mA) and 6KG6A (heater power 12.6 W, current 500 mA).
Best regards!
The 26LW6 for me means business. The small caveat is to fudge an appropriate heater supply but silicon is cheap. These tubes are capable of being slam driven. I find these hardy sweep tubes deliver the goods. Generally ex TV tubes have larger cathodes, and can take more current. I prefer them. A 12HG7 12BY7 group though 12V heater for me is a darned good start for a long life setup.
Got ”big plans” for the biggest ones on hand (26LW6, 21LG6, and 6HJ5). A few more of the two biggest are on their way, to ensure I have enough of the various variants not to resort to mixing within a given amp, to be able to build and retube, and spares when we get a dud. But probably not enough to waste a batch of 8 or 12 too, when something goes sideways in development. I struck out trying to get enough 26DQ5’s to work with - have enough to retube my bass guitar amp but that’s about it. Enough 21EX6 to get started, but a bit thin on quantity and they’d need to be pushed all the way to screen rating to get half an amp a pop. So in started going down the list of 18 watt tubes and found some that look just like the 21LG6 inside. Better cathodes than the EX6 (more Ip with less Ih) to boot. I think we found our Guinea pigs. Might give me a feel for how different those two LG6 variants are to one another, too.
The “appropriate heater supply” for the LW6’s isn’t that hard. I need about 900 volts. Got 480 volt industrial control transformers. Those give a little under 700 rectified. So where to get 200 more volts? A 75-0-75 toroid from Antek! Gives me 110 and 220V taps for screen voltages - 110 for direct and 220 for a regulator so either can be supported. About 26 turns of #12 THHN around the outside, and presto! Heater supply solved. Something similar for the LG6’s - but the extra winding is already there. I can cut 24V down to 21.5.
I did that “two transformer trick” on that bass guitar amp, but it was just a single with a custom wind. separate 120 and 220 windings to make 170 and 475 volts, plus 26 and 12 volt heaters. I even put a 21.5 volt tap on the 26 volt winding because I was also considering 21LG6 for that too. That ended up being based on the “retro look” of octals. And at the time I was having a bit of trouble finding compactrons (only had 7 on hand).