High perveance, low screen voltage rating, decent plate dissipation- I'd say you've got a good candidate output tube for screen drive.
Anyone else playing with 7984's? I bought some from eBay and have been doing some experimenting. I'm using 500V on the plate and 225V on the screen. I set idle plate current to 37.5ma/tube. Screen current doesn't seem to vary and stays at 1ma. I'm using a 3300 P-P Edcor. Grid 1 voltage is -40.4V for 37.5ma. I'm feeding with the board from a Dynaco Mark III with feedback hooked up. First impressions are really positive.
How are the 7984's working out for you?
I ran across a sleeve of 8156's in my stash, and that got me thinking of 7984's. I'm wanting something 2E26 or 6146 like, and compact, without the inconvenience of plate caps.
I'll probably use them single ended, though.
win W5JAG
I ran across a sleeve of 8156's in my stash, and that got me thinking of 7984's. I'm wanting something 2E26 or 6146 like, and compact, without the inconvenience of plate caps.
I'll probably use them single ended, though.
win W5JAG
Very strange pinout on that 7984. The plate pins are doubly surrounded by cathode pins. What were they thinking? A recipe for disaster!
Curve and specs look close to a 12JN6, I think I'll stick to the $1 versions. (the 35 Watt spec is for ICAS, ie intermittant usage, only 20 Watt continous, which the 12JN6 easily matches in audio rating 17.5 x 1.2 => 21 Watt)
Curve and specs look close to a 12JN6, I think I'll stick to the $1 versions. (the 35 Watt spec is for ICAS, ie intermittant usage, only 20 Watt continous, which the 12JN6 easily matches in audio rating 17.5 x 1.2 => 21 Watt)
Actually it's a recipe for success.....in the tubes target use, a class C RF amp.
The cathode is RF ground, the plate uses 3 pins to reduce parasitic inductance, and the grids are on the opposite side of the tube. A tube, especially a pentode does not exhibit a 180 degree phase shift between grid and plate at VHF. Oscillation and instability is the prime concern here.
The tube was designed for VHF land mobile radio use where all the incumbent tubes were push pull. It was succesfully used in GE and Motorola VHF (136 to 174 MHz) mobile radios for several years.
I have a box full of these but never tried them. There is just too many cheap sweep tubes that look more appealing.
That's fine for RF stability, but according to the 750 V B+ spec for the 7984 there could be 1500 V across the 1/8 inch gap occuring in two different places on the socket. The 6L6GC is only rated for 500 V B+ and has almost a 50% larger gap between octal pins with only one such adjacent pin threat. Yet they still manage to burn up sockets regularly.
The 8150/8149 tubes look to be a remake of the 7984. Note the improved pin layout for safety.
The 8150/8149 tubes look to be a remake of the 7984. Note the improved pin layout for safety.
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Discussion
Hi gentlemen, this discussion is interesting... I've a few of these tubes, and I would like to realize an FM trasmitter with this tube. I red in his datasheet that it can be used for 175 MHz trasmissions, so it can be used also for 88-108 Mhz trasmitter. Can someone helps me? Some suggestions?
Thank to all!
See you
Hi gentlemen, this discussion is interesting... I've a few of these tubes, and I would like to realize an FM trasmitter with this tube. I red in his datasheet that it can be used for 175 MHz trasmissions, so it can be used also for 88-108 Mhz trasmitter. Can someone helps me? Some suggestions?
Thank to all!
See you
You will first reassure us that you, or the end-user, has an appropriate licence for this transmitter in the jurisdiction in which it will be used? And that you have the necessary RF experience to avoid personal injury or death during the debugging phase?
Good morning everyone,
I have used 7984's in PP with 500vdc on the plate, forget what I had on the screen with a 3.3K P-P transformer and a 4.2K P-P transformer. It sounded great in both instances. I used a driver board from a Dynaco Mk III.
Ray
I have used 7984's in PP with 500vdc on the plate, forget what I had on the screen with a 3.3K P-P transformer and a 4.2K P-P transformer. It sounded great in both instances. I used a driver board from a Dynaco Mk III.
Ray
Dear DF96, I've have all requirements for build a FM trasmitter. I've the knowledge of working with tubes (I drew and built more LF amplifiers) and in my country, law about transimissions says it is legal transimt in FM band (88-108 Mhz) but NOT cover other occupied frequencies (like Radio stations). Of course I will not trasmit over already occupied frequencies. Anyway, the output power can gives this tubes is little, it's no danger, I'm sure!
You can do some damage to yourself with 600VDC or 40W of RF. You will, of course, be aware of the danger of RF burns. As it operates in Class C it will need good filtering so you don't annoy people using harmonic frequencies.
Well the first image w9gr.com lead to an interesting diversion . Must have misunderstood the reference to the red base one.
You mean can I design for you a 100MHz Class C RF PA using the 7984? The quick answer is no. It is not a valve or a frequency I have any experience of.johnnybgoode58 said:
I did see somewhere that it is similar to the 6146, so look for VHF PAs using that and adapt them as necessary.
Try and hunt down an older (from the 1960's or earlier) copy of the ARRL handbook. That will help you get well on your way to getting what you want to do. I doubt that you will find direct schematics for what you are looking to do (fm transmitter) but you can use the equations and modify the designs to do what you want. Just a thought.
Thanks for all! I'll tray all solutions suggested by you, and of course, I'll make you know! Thanks again folks!
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