Type 807 Tube RF amplifier with transistor a pre amp

Thread Starter

ashok.das81

Joined Jan 4, 2017
16
Hi all,

I have a 807 vacuum tube and I want to make a CW RF amplifier with it. I am thinking of using transistors in pre amplifier and 807 as final power amp. I have only one tube so I cannot make push pull amp. First of all I need to know if it will be possible to make such RF amplifier. If possible how difficult it going to be. I need the ideas to start planning a design. I do not have any experience in Vacuum tube designs, I have fundamental knowledge of electronics. Kindly help.
 

DickCappels

Joined Aug 21, 2008
7,742
1618672002774.png

Last century (mostly the first half if I remember correctly) 807-based transmitters were very popular among amateur radio operators. I think the wooden breadboard will give you an idea of how long ago they started being popular.

Just use a search engine with the term 807 transmitter and you will get a lot of ideas.
 

Thread Starter

ashok.das81

Joined Jan 4, 2017
16
Thanks, yes I found some popular designs, but all them are fully tube circuits. My challenge is to use transistor in driver stage and tube in final stage. Currently I am trying to do simulation to validate my design.
 

LesJones

Joined Jan 8, 2017
3,498
I think just using a tuned RF transformer is the easiest solution. I don't remember having any problem when I did this sort of thing in the 1970s when high power RF transistors where expensive. I remember doing this sort of thing driving a QQV06-40 on 144 Mhz, 4CX250s on 432 Mhz and 2C39s on 1296 Mhz. In some cases the RF transformers were tuned lines. Have you looked in the ARRL handbook or the RSGB handbook for ideas.

Les.
 

LesJones

Joined Jan 8, 2017
3,498
When I bought them a new issue came out every year. The last one I bought was 1990. You basically just need a low power transmitter design and feed it to a coupling coil close to the coil of a tuned circuit feeding the control grid on the 807.

Les.
 

Thread Starter

ashok.das81

Joined Jan 4, 2017
16
Ok, i have found a design that i think I can duplicate with modifications. See below V2 is 807. @LesJones, I think you wanted to say that I put another coil over L1 and that coil will be connected to my driver stage or the QRP transceiver output. Also the entire part within blue is not needed. Am I going in right direction ? Link to this circuit is here

807 CW transmitter.JPG
 

Irving

Joined Jan 30, 2016
2,104
That'll work, or just couple it in with C5 as shown there (careful about output impedance of pre-amp). What frequency are you planning for?

@LesJones I too built something similar around late-1970's. But then I got a job (1980) working at Plessey Avionics in NE London in the Electronic Warfare labs, mainly fighter ground-air comms & telemetry and suddenly I had access to mil-grade RF power transistors and the then new-fangled MOSFET thingies (at £100+ a pop, and they did go pop rather well and regularly - mind you we were always having lots of free samples thrust at us). Suffice to say (and with a big sigh of relief from my parents/girlfriends) I moved away from tubes to all solid-state stuff. Sadly I moved away from amateur radio to digital electronics during the late 80s/early 90s.
 

LesJones

Joined Jan 8, 2017
3,498
ashok.das81,
As the bottom end of L1 is grounded you could tap into L1 a few turns from the ground end to increase the RF voltage to the grid of the 807. (You would have to experiment to get the best match.
Irving, I never used 807s as I only had a G8 licence which at the time only allowed the use of frequencies above 144 Mhz.
I worked for Plessey crypto in Liverpool in the early 1970s

Les.
 

Irving

Joined Jan 30, 2016
2,104
Les, ditto G8IJV IIRC. But I built stuff for others too. Most of the stuff I did was transistor based for 144MHz. I did use 4CX250s a couple of times but as I recall they needed silly plate voltages >1500v and my nearest & dearest weren't at all happy...
 

LesJones

Joined Jan 8, 2017
3,498
I used 4CX250s in the K2RIW 70 cm 400 watt PEP amplifier. I was cautious as the power supply was about 2KV and probably capable of about 1 amp output. I used that for working through the Oscar satellites.

Les.
 
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