The non-alignment of the g1 grid wires with the g2 grid wires makes for fairly substantial screen grid current compared with typical grid aligned beam/pentode output tubes. Output power efficiency gets lowered, and g2 overheating may be an issue. Note the 8417, which used a frame grid like the video tubes, also had reliability problems. Very close g1 spacing to the cathode for the high gm. Overheating makes grids warp. And any positive g1 grid current is likely to melt the tiny g1 framed grid wires. In a TV, the video amp has a nice stable signal, while an external sourced audio signal could overload the g1 and fry the tube.
Should make a great driver tube though, if run at reduced power (below rating) for safety.
Should make a great driver tube though, if run at reduced power (below rating) for safety.
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I am thinking seriously about paralleling of 5-10 tubes 6J52P in triode mode, for 20-50W of total dissipation. But I would not consider to run them on 10W per tube, it is too hard, though in specs. They are similar to 12GN7, and are specified for 10W dissipation as well, but used to live short lives in Soviet TV sets in such regimes.
It is very odd. They made the same claim for the 6AG7 right there in the spec sheet: that it could be used as a Class A1 audio final producing 3W at 7% THD. They also give an rp= 130K. That's way, way, way too much plate resistance for an audio final. The Zo will be enormous. These won't sound good, but I suppose the manufacturer wanted to sell as many as possible, and TV manufacturers wanted to use as few types as possible.
Types like this have such large plate dissipation ratings since the purpose is to produce decent gains while keeping the Rp under 10K for wideband operation, and to slam current into CRT cathodes to charge up internal device capacitance at 4.0MHz rates.
You can find much more suitable audio finals in the same power class.
Rp is plate resistance, not load resistance. Any pentode, audio or video, will have high Rp. A video pentode has high gm and current, so can work into a low load resistance for wideband operation. It is true that a video pentode will give high Zout, but so will any audio pentode. That is why feedback is used, to reduce Zout.
Yup...One thing for sure, the 12BY7 & 12GN7 configured as normal signal pentodes are unscreened and expect microphony. There is alot of "twang" when tapped. These tubes were designed for the mass TV market when large screen tube colour was fashionable before SS stole the show.. My favourite gape for the 12GN7, 12BY7 and host of others is configured as triodes for Williamson drivers with very respectable 25dB gain and is a very versatile tube. Configured as triodes, makes'em them far more usable.
For conventional use the low Vg-K makes it biassable using a couple of red series LED's as CCS's but drive these tubes at least 7-15mA anode current which have B/W into MHz. As the curves are pretty linear I use'm as the ultimate, cheap audio tube workhorses. Biassing read Morgan Jone Valve amps 3rd edit page 126,175.
With the fanstastic MHz b/w coupled with very high gm; beware to avoid lanky wiring and NOT using a CCS as the anode load as the tube can self oscillate.
Otherwise a darned good tube, like the 12BY7 which is a bit tamer but just as equally ideal. strangely, my GE versions of these tubes have same sized anodes and yet have different dissipation figures.
The 6CL6......this tube troubles me somewhat. Some vendors quote it as an EL84 substitute...NO!....it has a different spec...I find it flighty and snappy at anything approaching Vg-K cutoff and will oscillate when given half the chance. It's quoted also as a MiL RF pentode which it is.....probably due to it's robust construction. Good luck !
richy
Thanks for the information Richy! Have you experimented with the 5763's or 7551's and their 12 volt equivalents? I have lots of these tubes and would like to do something with them.
http://tubedata.milbert.com/sheets/049/7/7551.pdf
http://tubedata.milbert.com/sheets/049/5/5763.pdf
Thanks,
Ray
http://tubedata.milbert.com/sheets/049/7/7551.pdf
http://tubedata.milbert.com/sheets/049/5/5763.pdf
Thanks,
Ray
Gain is a factor, but so is frequency. 6CL6 is intended for video, although it will work OK at higher frequencies. 5763 is intended for VHF. I'm not sure what this means for the internal construction, but I guess it would mean that any circuit involving a 5763 needs to be built to VHF standards to keep it stable. (and/or use stoppers, possibly on anode as well as grid)
Hi Rich,
Wondering whether you are confusing the 12BH7 with something else.. The 12BH7 is a dual triode with fairly high rp, fairly low gm and is quite similar to the 12AU7A/ECC82 and in many applications is interchangeable with that tube. (Watch out for filament power)
I have triode data for some high-gm pentodes:
High Gm driver pentodes
...as does Tom Schlangen:
Tom Schlangen's Homepage - Tube DIY Pages
Never used them as output tubes, but I like them as drivers both triode and pentode connected. As a driver with a resistive load, the gm is so high you can use a prettly low load resistance (4-10k) and still get lots of gain.
Pete
Hence with lowish anode Z in triode config, Miller effect is nicely dealt with too.The penalty is a bit of current.
I've tried a few and they make excellent triodes.
Re for instance, 6AG7 as a class A1 amp, IIRC the Rl is specified as 10k, which is a rather tall order but not impossible. The sensitivity is very high, you can make a single tube amp.
Using the tubes RC coupled (which is the general way they were used as video amps) also works great - very good linearity, lots of gain and voltage and current swing. They work great connected in an anode follower configuration to reduce gain and output impedance.
Using these tubes in PP can be a problem. They work fine in class A but class AB is more like, in tube terms, class B. These tubes are made to be linear in SE, so curves only show compression at quite low currents so it's difficult to overlap the opposing tube's curves to get a nice crossover area, not so much because it's difficult to find the right bias point, but because there is a lot of variation between tubes. Auto-bias will not work right here due to low quiescent current class-B-like operation, and simple fixed bias is generally a no-no with high gm tubes.
I've only done a few simple experiments with this, but some experience with sweep tubes shows that setting the bias point is better done with Vg2 for high gm tubes, although this complicates things (sand is almost a requirement in form of Vg2 regulators for each tube).
Re for instance, 6AG7 as a class A1 amp, IIRC the Rl is specified as 10k, which is a rather tall order but not impossible. The sensitivity is very high, you can make a single tube amp.
Using the tubes RC coupled (which is the general way they were used as video amps) also works great - very good linearity, lots of gain and voltage and current swing. They work great connected in an anode follower configuration to reduce gain and output impedance.
Using these tubes in PP can be a problem. They work fine in class A but class AB is more like, in tube terms, class B. These tubes are made to be linear in SE, so curves only show compression at quite low currents so it's difficult to overlap the opposing tube's curves to get a nice crossover area, not so much because it's difficult to find the right bias point, but because there is a lot of variation between tubes. Auto-bias will not work right here due to low quiescent current class-B-like operation, and simple fixed bias is generally a no-no with high gm tubes.
I've only done a few simple experiments with this, but some experience with sweep tubes shows that setting the bias point is better done with Vg2 for high gm tubes, although this complicates things (sand is almost a requirement in form of Vg2 regulators for each tube).
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