Bare Bones Exciter For 813 or anything....

[W9ZSL]

   To all of you who don't know, I have a recording studio and am a Ham.  I'm 68 and getting serious.  I finished with a recording project and wires are about to fly.  I'm finally integrating my studio with Ham.  I have a DX-20, DX-60B and a Kenwood TS440 with auto-tuner.

My goal has always been building a 250-300 watt AM rig but I can toss together a test rig with a pair of 5933s modulated by another pair.

I've decided to build a single band crystal exciter tuned to 3885.  I have the crystal.  I'll probably turn the circuit into an VXO.

So here is my diagram.  Ignore the tuned circuit between the oscillator and the PA because it will be a direct plate to grid.  Classic MOPA but with a twist.  I'm putting a socket in the oscillator plate output in order to modify with coils and add the 100 pf variable cap. It's basically identical to the 1949 Radio Handbook.  All plug-in hand-made coils. For now it's 3885 +/- crystal.  This unit has one purpose and that is exciting either the 5933 amp (my test rig) or the 813 amp to follow.  I'm only looking at a max of 7 watts out.  Comments?

[W3GMS]

Looks like a good start!  Quickly looking at it, I noticed no RF bypass caps at the base of the plate RF chokes which I am sure is just an oversight.  Build it in stages and get it working piece by piece!

Joe, W3GMS   

[Opcom]

Have you considered a 6Y6GB instead of the 6V6? If it will make enough power, is a better tube in some ways than a 6V6 for RF. Both have the same basing. It is more like a sweep tube and required only a low screen voltage for full current which is higher than the 6V6's.

Where the 14.5W Pd 6V6 makes 5.5W @ 315V in class A, the 12W Pd 6Y6 makes 5W @ only 200V.

It is easier to drive/ more sensitive according to multipliers and drivers but by W5FRS Dennis Brady and he has tried a number of tubes in a similar circuit. The RCA book gives the 6Y6 only the 200V rating, but it has been used at 300V in RF circuits and 400V in modulators. Frank Jones also used the 6Y6G and GB up to 50MC. He favored the -GB and use a lot of that tube.

[W9ZSL]

Actually I considered either a 6F6 or 6Y6.  I did miss the plate bypasses.  I also have an alternative oscillator, again with the 6AG7 but provision to add a VFO.

[K1JJ]

I would also consider the more elegant CW grid block keying method.  Ground the cathodes during PTT transmit only.

When you hit the PTT transmit switch,  leave the VFO / xtal oscillator always running for stability and well shielded from the receiver if using full break-in.  The GB keying negative bias can be introduced into the second stage grid or any other succeeding stages.  


Grid block will isolate your telegraph key from shocks and also give you the chance to tailor the CW waveform for nice, rounded leading edge pulses vs: a hard lead that can produce key clicks.

If you plan to excite an 813 final, etc., you will need good exciter CW cleanliness.

T

[W9ZSL]

I don't plan on running CW with the 813, strictly AM phone at least for starters.

[W3GMS]

I don't plan on using CW...strictly AM phone.

If you did want to operate CW with it a FET inserted into the cathode keying line works very well.  Since the gate of the FET is very high impedance its very easy to control the rise and fall time of the keyed waveform.  If you use a steering diode going in and another one going out of the gate, then you can control the rise and fall time independently.  Simple and works quite well. 

I still enjoy CW so many of my OT rigs have that modification. 

Joe, W3GMS

[K1JJ]

A FET in the cathode sounds like a great idea, Joe.   The CW shaping would be a breeze.

I'll bet any of the common 11N90s or 260s lying around would work FB there.

T

[W3GMS]

Any FET that has adequate drain to source voltage along with the required drain current will do the job nicely.  Many available parts and dirt cheap!     

Joe, W3GMS

[W9ZSL]

OK guys.  Maybe I'll reconsider CW!  I'm nowhere near your schmartz when it comes to design.  I'm more a "if it looks right, I'll go with it" person.  It's like doing recording.  

Last November I recorded the Reformation (yeah, I'm Lutheran) Service at our church.  We have a massive two-chancel pipe organ with bass and some mid pipes left, short pipes and chimes right.  Isolated, permanent mics because we broadcast from the church.  Picture a 50-voice choir and a 5 piece brass choir all parked below the left chancel totally left of the altar.  Now make it stereo. I set up mics while the Broadcast Engineer set up levels on an 8-Track digital machine.  No chance to re-adjust mics for placement.  Point and shoot. Record. It wasn't a broadcast so the other engineer adapted for recording.  The church has capability as a recording venue.  Martin Luther's "A Mighty Fortress" finale gives me goosebumps.

Back to the point.  I know audio.  Recorded my first 45 disk in '65.  I got out of Ham around the same time.  No Ham until around 4 years ago.  Recovered from heart shit.  Studied, got ticket.

All my Ham projects from now on will combine the studio with Ham station. I worked over 38 years in radio broadcasting and production with over 4 as production manager at KSTP-AM in Minneapolis.

Here's my question (finally!!!):  I have a nice Kenyon 500 Ohm balanced Line to class B grids iron, NOS.  I'd have to check, but I think it's at least 10 watts.  I can switch outputs to various grids.  Just remember the limiter will feed the Kenyon.

I have an incredible limiter amp that I built back in the late 60's.  It uses a pair of 12AU7's operating in parallel push-pull parallel for the output.  It's a cool amp I pirated.  Each tube acts as a parallel triad. The two tubes (basically 4 triodes) is the driver.  That bugger was designed to drive a broadcast transmitter. Coolest thing I ever built, and I have a pair.  It's the big white unit in the pix in the rack  Old pix.

I'd like to mount the Kenyon so I can switch from my limiter/driver to any modulator using a chassis and rack panel with output assign switch.  The Kenyon has multi-matching out.  Perfect!  No problem.  

Now. Any ideas how I can hang a VU meter into either the input or output circuits and create a true modulation meter at that point?  My Broadcast experience is barking.   I'm assuming I can put a meter on one of the unused taps on the secondary, and then use a scope to match the meter with modulation percent through a separate meter driver?  Hanging it on the input side of the Kenyon doesn't make sense, or does it?

My goal is to control the Ham station from the studio.  The meter on the board will correspond with modulation.  Basically I'm merging the Ham with studio. What goes round comes round.  I gave up Hammin' when I started recording. One expensive hobby too many!  Merger time!

I'm including all this background just to give you an idea where I've come from in the hopes I can build my dream "combo".  My other major product is getting cataract surgery.  Gotta see to solder! Sigh.