Small 75 Meter triode or tetrode lineear amp for 4SQRP Nouveau

[N4LTA]

I have a 4SQRP Nouveau kit that I plan to build  in the next few months and was thinking about a small single band tube type linear for it. I can think of many reasons to do something different line a SS amp  but doing something with a tube would be fun. I have looked at multiple 807s  or a single 811A  or even a Chinese 572 but nothing looks like a real good fit. I have many power supply transformers and components to build whatever might be needed. Is a small one band linear amp for AM just totally not a good idea?

The 4SQRP syas that is can output about 20 watts pep so a single or dual tube in  GG could do 10 dB or so and would seem to be feasable.

I realize doing something class C and modulating it would be a better option but was looking for something to go with the little class e transceiver.


Pat
N4LTA

[w8khk]

I was thinking more along the lines of one or two parallel 4D32 tetrodes, grounded cathode.  Should not even need to be neutralized for single band 75 meters.  Either build from scratch, or re-purpose an old linear. 

I have a Dentron Clipperton, and my brother W2WM has a Collins 30L1.  Eliminate the voltage doubler and run fixed grid bias.  At half the plate voltage and half the plate current of the original amplifier, the plate tank impedance and Q should be rather close with no mods.  Just have to add a regulated screen supply.  Not a lot of work even if it doesn't work out well. 

I will start assembling my 4SQRP rig next week.

[WU2D]

Two to four 6LW6's, 6LQ6's, 6KD6's, 6JS6's or my heavens 6DQ5s or 6146's! conventional grounded cathode and properly neutralized, would be compact. 

[WD5JKO]

When I was using my Retro75 on 80m phone, I too looked for a linear amplifier. Not far in my shack was a Central Electronics 600L linear amplifier. This was a grid driven 813 with regulated bias, and screen voltages, and used advanced broadband couplers on the input and output. I built up a PTT relay box, and tried it out. The drive was too much! I found that a 50 ohm load at the 600L input stabilized the impedance, and reduced the drive. With the Retro75 at 10v, I had a 70 watts carrier output, and with 14v I had a 100 watt carrier. The 813 was blushing a bit at 100 watts carrier. Amazingly, I could modulate fully at 100 watts out.

The 600L is not small or light....

Jim
Wd5JKO

[PA0NVD]

Hi Pat
I have a number of new Siemens RS1003 tubes. Small and a lot of power. If you really use them and do not just put them on the bench, I can find out what it cost to mail them to you.

[N4LTA]

That tube looks very interesting. Especially the 60 W anode dissipation for such a small tube.I am having a hard time finding any data on linear operation  though.

Thanks

Pat

[PA0NVD]

Hi Pat
The SRS551 is the same tube. In Radiomuseum.org you find a diagram of a linear amp with two of these tubes for 200W output
One tube can deliver 155W CW at 1200V, so 200 Watt ICAS for two tubes seems conservative to me. You may find more info looking for the SRS551

[w9jsw]

There is a NXP Amp Challenge going on. Jim Veatch, the Hardrock-50 guy has some interesting entries. There are others - google them.

Perhaps take that high efficiency exciter and drive high efficiency amp?

https://sites.google.com/site/rfpowertools/home

John

[N4LTA]

Nico

I ordered some sockets and have done some research on running those tubes as a linear am. Likely I'll use about 900-1000 volts on the plate and about 350 volts on the screen. I plan to use the same regulator MOSFET circuit that I used with my PWM with a higher voltage MOSFET.  I have ordered a power transformer and choke from Hammond. Plan to use a choke input filter and a couple o 330uF,  550 volt snap in electrolytics in series. I also ordered some sockets from EBAY (from China).  This will be a grid driven amp and I'll have to neutralize it which will be new for me.
Looking forward to building it.

My only concern is that the anode circuit will be close to the control grid circuit. I have never built a RF power amp except with tubes with the anode out the top. I'll have to be careful with layout.

Thanks again.

Pat
N4LTA

[KD6VXI]

4cx250.  Lots of power from such a small tube.  And last forever!

--Shane
KD6VXI