TheRadioBoard

With my 40m regenerative receiver up and running, it’s time to build a matching CW transmitter! The receiver consists of crystal controlled down-converter built on PC material:

http://theradioboard.com/rb/viewtopic.p ... ight=ab8if

and a regenerative detector functioning as a tunable IF. This part of the receiver is built on a breadboard, 1930’s style:

http://theradioboard.com/rb/viewtopic.p ... ight=ab8if

The transmitter will push my construction skills to the next level. It will consist of three subassemblies built on aluminum chassis boxes… a power supply, a VFO-Buffer-Driver, and an 807 final. Yeah, I listened to the forum suggestions and decided to go with the VFO (instead of hard-to-get crystals), and the 807 RF classic (rather than an RF wannabe audio or sweep tube).
The first subassembly is finished. Here is a photo taken at the “fire in the hole” moment. The power supply works!



Instead of spending $20 on a NOS 5U4 rectifier, I spent it on four glow tube voltage regulators. These tubes provide a colorful and photogenic indication of circuit operation! A 1N4007-based full-wave rectifier provides +350v @ 100mA for an 807 plate. The glow tubes provide +255v for the 807 screen grid and 6AG7 driver, and +150v for the 6AG7 screen and VFO-Buffer. Three negative supplies provide biasing for various control grids and grid block keying of the 807.
Here is bottom view of the chassis showing the wiring of the power transformer and tube sockets.



Here a 4”x 8” phenolic panel has been mounted to standoffs within the chassis box. To this panel a turret board and barrier strip have been attached. The turret board contains most of the discrete components of the power supply. The barrier strip will provides access to the various DC output voltages and 6.3vac for filaments. A hole in the side wall adjacent to the barrier strip will carry these outputs to the other subassemblies.



One last look at the glow tubes in dim ambient lighting… The “orange emitting diodes” are VR75/0A3’s, the purple tube is a VR105/0A3, and the whitish glow comes from a VR150/0D3. I would have liked to have included a VR95/0B3 in this line-up, but its quiescent current demand and regulation performance is inferior to the other three types.



There is one change I will make to this power supply… the 120uF capacitor next to the two 7W power resistors is getting a little warm for comfort. It will be moved to a cooler location.

Roger AB8IF

Roger,

That's some nice fabrication you've done! I see you used a Hammond transformer in the supply. They are made about 60 miles from here and are top quality.

73, J.B.

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To be where I am, I had to leave where I was!

Man, I love the glow of those VR tubes! And they flicker when you key the transmitter. Happy memories!

73,

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http://kr1s.kearman.com/
http://qrp.kearman.com/

Are those 470K resistors across the silicon rectifiers?

I've done that in multi-KV strings, but for under a KV, I would just put two 1N4007 in series.

In large HV stacks, we also used a 0.005 pr 0.01 uF ceramic cap across each diode, but that, too is overkill in a low voltage circuit.

Rich

(Ex-Westinghouse Power Semiconductor Div.)

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Homebrew Radio ex-Silicon Valley

Thank you J.B. Hammond has an impressive line of transformers.

http://www.hammondmfg.com/5cindex.htm

Thank you Jim. This visual appeal applies to almost all tubes... the glowing cathode, the blue fluorescence of a glass envelope, mercury rectifiers, a touch of red on a hard working plate, etc...

Hi Rich,

Being my first high voltage project, I decided to play real conservative with the design. Had those diodes failed I risked damaging a rather expensive transformer.

Roger

It's conservative and a really beautiful job.

Congratulations!


Rich

PS: I didn't see a fuse on the primary side?

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Homebrew Radio ex-Silicon Valley

Hi Rich,

We're both on the same wavelength regarding circuit protection... there's a 2 amp slow blow fuse on the primary side hiding on the third photograph. It's a 5x20mm leaded part attached to the lower barrier strip. It is wired between the 4th and 7th terminals from the right. I figured the design was conservative enough that a socketed fuse would not be needed (fingers crossed).

Roger

good work

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BIZTEK

Thank you Ashley.