Discussion in 'Amateur Radio Amplifiers' started by PS7PC, Jul 9, 2019.
Someone in the group has already used 6JM6A vintage tubes in linear amplifiers?
6JM6 replaces the 6LQ6.
6jm6 or 6mj6?
Which one is the correct substitute for a 6LQ6 sweep tube? What is the difference between a 6mj6 and a 6jm6? I think I have one but not the the other.
I think the ones I have are the jm's but not the mj's and whatever it is that I actually have isn't compatible in the sweep tube PA that I have on hand .
The Dentron GLA 1000 is such a type of sweep tube amp. This would be a good circuit to base a sweep tube design or to build upon.
Sorry, meant 6MJ6.
Unless you have a pretty big stash of "sweep type" tubes, it seems rather pointless to build anything around them. It has been many years since any commercial amp manufacturer has built around a sweep tube. I'd also think if you had that stash, now would be the time to sell those tubes at the current inflated market price they get for them to those who need them for replacement.
There are a couple of problems with building a high power amplifier using these kinds of valves . . .
They're fine for an Amp with just a Pair (like for the PA in many commercial SSB rigs) . . . but when you start paralleling 4 or 5 to get high power, the impedance is quite low, so you need quite large value Tune and Load variable capacitors in the Pi Tank.
But more of an issue is that often ONE valve will fail, so then you're running on 4 . . . which are working harder, so another fails, and so on !
This is why Yaesu's FL2500 amp (using five 6KD6s) had quite a short production run. It ran 1500W input, and was one of the first Amps to cover 160m. In the right hands it worked well . . . but when abused it eat 6KD6s !
6JM6A and 6MJ6 are different types. The first is a 12-pin compactron tube and the second is a novar-based tube, with higher anode dissipation. Ameritron AL84 uses four 6MJ6 for 400 Watts PEP output, in a grounded grid configuration. I have four 6JM6a and I intend to use them on a linear amplifier with my homebrew SSB and CW QRP 40 meters transceiver.
Only 17.5W anode dissipation max rating for the 6JM6A, so I'd guess ~35W output per tube.
Sounds like a nice project, since you have them anyway. Let us know how it works out.
I don't recall any amateur radio transmitter or amplifier using this tube.
Like I posted- typo. 6MJ6 is tube of discussion here.