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 1 
 on: Today at 10:53:32 AM 
Started by wa4nlw - Last post by WD5JKO
I like the simplicity of the original link. Looks like a bare bones project to be built at low cost.

The filament choke gives way to modern replacements that are readily available.

The output tank with a tapped coil will work fine so long as the tap point is adjustable. The Central Electronics 20A does the same thing with a fixed tap. Going to a Pi-Net would work except those variable caps these days new are getting pricey. As stated earlier by another, a 3 gang Broadcast Receiver variable (0-1000pf total) would do fine. If cost and room are constraints, the fixed tap works.

As to gain, an amplifier like this with an untuned input will have around 10db gain. A few db more if the input is tuned. So 9W in gives about 90w out. As stated earlier, this is a little hot for two 811's running AM linear.

If it were my project, I'd tune the input to increase the gain a little, and more importantly improve the linearity. Then I'd move the bias upward close to cutoff. At 1500v B+, that would be around -12v. This will reduce the gain, and increase the resting carrier efficiency. Some call this Class BC AM Linear Amplification. I do this here with a Gonset GSB-201 using a quad of 811A's built by the Ruskies. I can run 200W out AM with headroom for 100% modulation, or about 150w out for AM with enhanced positive peak headroom. The 811 plates show some color, but not full red. If I go back to -4.5v bias, and reduce the drive for the same RF carrier output, then the 811's are full red, and positive peak ability is diminished.

So IMHO, class BC AM Linear, an 811A is good for at least 40 watts RF output per tube. I can get up to 50 watts per tube here with my 20+ year old Russian 811A's.

Should be said though, not all 811A's out there are created equal. Some of the Chicon tubes I've tried worked great at first, and then had a steady decline.

I added two attachments describing Class BC.

Jim
Wd5JKO

 2 
 on: Today at 08:43:56 AM 
Started by W2JBL - Last post by WU2D
My Friend Spencer KW2S's Dad designed some of the circuits in those when he worked for Sonar in the 50-60's. Amazing combination of low cost COTS (Commercial off the shelf) parts, with no silly rules - Use what works and keep it cheap!

Mike WU2D

 3 
 on: Today at 08:38:03 AM 
Started by Detroit47 - Last post by WU2D
Druuuuul.

 4 
 on: Today at 12:15:32 AM 
Started by WU2D - Last post by K4RT
Thanks, Joe. Your transmitter and Mike's transmitter are awesome!

 5 
 on: Yesterday at 10:53:17 PM 
Started by wa4nlw - Last post by Steve - K4HX
Run the 813s as triode and you can run that zero bias up to 2kV. Grab the schematic of the B&W 1000 linear. It should give you all the details.

 6 
 on: Yesterday at 09:33:35 PM 
Started by wa4nlw - Last post by WBear2GCR
Pair of 813s in Linear service?

If you search here, there's a mod to a Heathkit SB-230(?) the one that used the conduction
cooled tube. Don KK4YY put a pair of 813s into that linear, replacing the ceramic conduction
cooled tube.

An approach like that might be a good "get ur feet wet" way to go with Linears?

You get to start with a complete linear, power supply, output tuned circuit & chassis with
switches and metering. These particular Heathkits do not command a high price, since
nobody wants the not-so-great and hyper expensive conduction cooled tube. (btw, others
have switched it out for a huskier Ruskie conduction cooled tube - but that's another
thing entirely)

                 _-_-bear

PS. At first glance this seems, appears, to be a very simple amp. But not shown
are the power supply and some means to key the linear. Also, there is no
tuned input, which may be advisable from a variety of reasons. So, keep these
things in mind. Also this old design does not show a shielded, enclosed RF & HV
chassis. That's something that is pretty much mandatory.

 7 
 on: Yesterday at 06:02:52 PM 
Started by W9ZSL - Last post by Steve - K4HX
How many spacers to you plan to use. Those ceramic spacers are quite a bit heavier than plastic ones.

 8 
 on: Yesterday at 10:44:36 AM 
Started by W1ITT - Last post by w8khk
I've only seen photographs, but the new unit, the NanoVNA-F appears to be fully enclosed, not the club-sandwich stacked construction of the original Nano.  For a case to protect it, something like a  large change purse would probably suffice if you could find one that wasn't too girly-looking.  Given that you'll probably want to carry a couple short RF cables, a USB charging cable,  and adapters to different coax formats, the imitation Pelican cases sold by Harbor Freight are very solid and protective with their pick and pull foam insert.  They have a little one that often goes on sale for about $10 that's very cool.  I have a couple of their medium sized cases for other test equipment that bounce along nicely on job sites.
de Norm W1ITT

I just received my Nano-VNA-F.  It took six weeks to arrive from AliExpress, but was well worth the wait!  Somewhat larger display, but instead of just a couple PC boards, it is very professionally packaged in an extruded aluminum enclosure, with ENGRAVED legends that are filled with white lettering and graphics, a very nice package indeed.  The enclosure provides shielding, which will likely improved the S/N when on the edge of performance with the original Nano-VNA offering. 

Thanks so much for the information, Norm!

 9 
 on: Yesterday at 08:03:29 AM 
Started by W1ITT - Last post by W1ITT
https://www.youtube.com/watch?v=mKi6s3WvBAM

If you have an hour, here's a pretty good YouTube video tutorial on the use of the NanoVNA.  The fellow starts off with a technical explanation then quickly moves to the test bench for some good  examples demonstrating the use of the Nano in practical radio situations.  Later on he even gets out a Millen grid dip meter and ties things all together.
By the way, don't worry if you don't have one of his cute little torque wrenches for coaxial connectors.  In a metrology lab those get used a bit.  In the field or on the test bench, I haven't used one in twenty years, just calibrated fingers. 

73 de Norm W1ITT

 10 
 on: November 15, 2019, 10:38:12 PM 
Started by KA3EKH - Last post by Opcom
The wide band nature of the radios donít help. Every year out in Dayton we do a net with about two dozen or so military radios on 51.0 and often someone may try to check in with a modern Ham radio and they have a hard time copying the 15+ KHz military stuff. The really old stuff like PRC-6 and 10 sets are wider still and think the worst is the stuff from back in the dinosaur days like the BC-1000 that deviate around 40 KHz.
We also do a net up in Gilbert PA at the MRCA event on 51.0 but most of us run in the old squelch mode so you donít need the tone.



Indeed! One quickly learns that one can narrow the transmitter easy as pie, but narrowing the receiver is an entirely different problem.

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