TheRadioBoard

Thank you Peter,

I am not familiar with the Ham Tips VFO, but I will go check it out on the Internet. My VFO is mostly designed around parts found at hamfests, etc.

Here is the schematic...



73, Roger

I'm going with a very similar solution after finding a metal can with a twist-off lid at the local crafts store (Michaels). It is sold as a "bath salts" container. The can already has a hole in the lid (after removing a plastic window) and it should fit nicely over the 807 socket.



I'll use a hole saw to open the bottom of the can to a diameter of 2-1/8"... just enough to clear the envelope of the 807. The finished assembly will reach the base of the shield that is internal to the 807.

73, Roger

Looks like an RFC tied directly to the 807 plate terminal. I assume you did not find it necessary to add a stopper for parasitic oscillations in the 807.

73, Roger

yes Roger, that's a parasitic suppressor put in to stabilize the 807 when I first built the exciter. Since then I've changed the circuit drastically (I'll put up a schematic) and the suppressor is a "legacy" part...I'll try taking it out to see if it is really needed now that the actual circuit has changed. What you see works great on 160-80-40 with xtal or vfo (I have adapted a heathkit vf-1) but I have problems with hum on the carrier on the higher bands. SO it's not ready for prime time yet.

Your build looks great. On to the 807 !

Peter

In edit: Looking at your vfo circuit I wonder why you called it a Colpitts type. I've only seen feedback to the plate in the Vackar vfo.

Hi Peter,

I'll keep an eye out for your exciter schematic!

Meantime on VFO topologies, I can't say I'm an expert, but I believe Colpitts means a single inductor and a capacitive divider in the feedback path. This link shows a common emitter transistor circuit analogous to the common cathode configuration that I have used.

http://www.electronics-tutorials.ws/osc ... pitts.html

The "single inductor" in my VFO is effectively L1 in series with C11. The capacitive divider is formed by C1 in series with C2//C3, and C6. Without a computer I'd just call it quits on calculating this stuff!!

73, Roger

Here is the Ham Tips VFO article that Peter referenced...

http://n4trb.com/AmateurRadio/RCA_Ham_T ... ps1304.pdf

Roger

Here is the end result... a $0.95 shield for an 807!

[img][img]http://i1142.photobucket.com/albums/n612/126gliderpilot/Final%20Amplifier/807Shield3.jpg[/img][/img]

I'd like to see that shield extending to at least the bottom of the anode, for best shielding. You could recess the socket with spacers and keep this shield.

73,

_________________

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Jim, I agree. But to drop the 807 base below the chassis, I'd need either another size hole saw (not the prettiest way to cut metal), or another knockout punch (BIG bucks even on eBay!).

The No.19 Wireless Set got away with a 1-1/4" chassis-to-socket offset (see pic). Soooo... I'm hoping I might get away with the 1-3/4" height of my shield.

73, Roger

[img][img]http://i1142.photobucket.com/albums/n612/126gliderpilot/Final%20Amplifier/No19Set.jpg[/img][/img]

I would also suggest raising the shield to cover the bottom 3/4 (at least) of the plate area.

Here's my schematic...it's missing some component values, I will edit it when I open up the exciter again (didn't keep notes when I was putting it together).


Peter

It sounds like I'd better have a Plan B in my back pocket! What are the operating symptoms of an 807 with inadequate shielding?

For reference I have attached a schematic of the (as yet) unbuilt final amplifier.

73, Roger

[img][img]http://i1142.photobucket.com/albums/n612/126gliderpilot/Final%20Amplifier/FinalSchematic.jpg[/img][/img]

Just built a stand alone RF PA for my AM RX TX. It is also a beam power tube. About a 1/2 dozen parts and no trouble . Will idle nicley when not driven and gives good amplification for my flea power AM tx.Got its first successful QSO yesterday. It is currently a 6V6 and becoming a 6L6. I have also used it with 50L6 and a 50c6 but like this the best so far. While no cap on these tubes the tube design is not particularily different and it is also 40M. Tunes very sharpely on the tank.

You by the way do very neat work. Nice job.
Don VE3LYX