813 Rig Operating - The Good, Bad, and Ugly

[W7SOE]

The good:
I had it on the air and made contact with K6JEK in Novato CA, and another fellow in Carmel.

The Bad:
Signal report was strong carrier but bad audio, distortion and only low end, no highs.

The Ugly:
My neighbor four doors down gave me a favorable audio report as heard through his baby monitor (900 MHz).  (Most worrisome, luckily he is a nice guy, he was all smiles)

I am using the JVII as an exciter and speech amp (audio broken out as per the manual).  I notice "ripple" on the carrier when the audio line is connected.  I am only using a decoupling cap on the secondary of the JVII mod transformer, perhaps adding a VHF choke would help.

I am using a Drake LP filter.

I was running with 300mA plate current with 25mA on the grids (2 813's in parallel).  I am not sure of the plate voltage nor do I have a wattmeter (yet).  Perhaps I could reduce the power.

The modulation looked ok on the scope but perhaps I am not seeing the problem due to inexperience.  I have heard here that 811A's might have a hard time modulating 813's but wouldn't under-modulation reduce splatter?

While I am excited to have made contact with this thing I am most concerned about the local interference.  I like my neighbors.  I would appreciate any help.

Thanks

Rich

[WA1GFZ]

Let's start with the V2. Does it have stock audio?

[W7SOE]

Let's start with the V2. Does it have stock audio?

Yes, it has the stock (crappy) audio.  I have all the parts for the K6AD mods, so I have no excuse.   

Rich

[N3DRB The Derb]

gotta get that done first. Cant polish a turd and expect to come up with anything other than a shiny piece of a shit. 

the 6au6 speech amp and driver suck. The interstage xfmr sux. quickest change: triode connect a 6aq5 driver, change the mic amp 6au6 to a 6ah6, redo both sockets so it will pass some audio. Get a new driver transformer from www.tubesandmore.com p/n PT124E from hammond.

Even better driver tube is a 6B4, but it requires some metal work and may need a 6c4 with a volume control in between. It's a set and forget gain stage. If you are using a lower level mic, the extra stage comes in handy.

about 75% of how good a given TX sounds is the result of your speech amp and driver.

[KL7OF]

Congrats on getting the big rig on!!!  You get a big atta boy!!!  Let's hear it on 3870.....
For all the work and time that the Junkston Viker is gonna require to get audio out of it ....You could build a real speech amp that really sounds good,,,,.  and later when you build an RF driver you can modify the viker and have a nice 100 watt rig to set beside you big rig..I'd be happy to help you with the speech amp....My 2 cents,,,,,,   Steve

[W7SOE]

Congrats on getting the big rig on!!!  You get a big atta boy!!!  Let's hear it on 3870.....
For all the work and time that the Junkston Viker is gonna require to get audio out of it ....You could build a real speech amp that really sounds good,,,,.  and later when you build an RF driver you can modify the viker and have a nice 100 watt rig to set beside you big rig..I'd be happy to help you with the speech amp....My 2 cents,,,,,,   Steve

Thanks a lot Steve.  I like the idea of building my own speech amp.  That would still leave me with the VII for RF, I imagine an RF exciter project to much more involved so I would still be stuck with the VII for some time...

I am interested in your ideas for a speech amp though, I would be interested in your ideas.

I am very concerned about the interference with the neighbors baby monitor.  Perhaps cleaning up the audio would help.

Rich

[W7SOE]

Congrats on getting the big rig on!!!  You get a big atta boy!!!  Let's hear it on 3870.....
For all the work and time that the Junkston Viker is gonna require to get audio out of it ....You could build a real speech amp that really sounds good,,,,.  and later when you build an RF driver you can modify the viker and have a nice 100 watt rig to set beside you big rig..I'd be happy to help you with the speech amp....My 2 cents,,,,,,   Steve

Steve,
   How about copying the audio section in my SX-42, I have always loved the way that sounds.  A couple of P-P 6V6's.....

Rich

[KA7WOC]

Rich,
You will want more scrote than you can get from 6V6s.  Go for 6L6s or look at the backwards connected audio amp routine.  I use PP 6L6s feeding 813s for audio in the 4-400s rig and a 20 watt audio amp with a backwards connected audio output transformer, (8 ohms to 8 ohms) feeding the grids on my 811As x 811As rig.  Both work fine.  The former is more traditional while the latter was quick and easy.
Bob
ps  Do try to get to Winterfest.  You will meet several who can help you out with ideas and quite possibly material.  I did hear you the other night but band conditions sucked for me.
woc

[K9ACT]

Having just been there, I applaud your efforts.  My first contact on my big rig was just running the Ranger into it like it was a linear.  I didn't even have the modulator in yet but I was so excited that it made RF, I just had to talk to someone.  "Get it off the air" was the report I got.

Sounds to me like your report would not indicate that modifying the V2 is the solution.  My first question would be how does it sound barefoot?  Lousy audio with distortion is not what one would expect from a functioning V2.  I suspect you would be happy as a clam to get a typical V2 audio report out of the big rig.

I abandoned the Ranger for the simple reason that I wanted to do as much as possible without resorting to commercial equipment.

The first step was to eliminate the Ranger audio by building a speech amp and then used the Kenwood for RF because it was so convenient.  I eventually built an exciter too but that's another story.

If you want to do the speech amp with the least amount of hassle, you can get  15 W solid state audio amps from a number of places such as CanaKits for less than $20.  You can assembly from a bag of parts and call it homebrew or buy them assembled.  Add a backwards output tranny and you are in business.

This is what I did and the tube speech amp is still a someday project but the justification and motivation is hard to come by.

All this is described on my radio page if you want to see how I did it.

Jack

[W7SOE]

If you want to do the speech amp with the least amount of hassle, you can get  15 W solid state audio amps from a number of places such as CanaKits for less than $20.  You can assembly from a bag of parts and call it homebrew or buy them assembled.  Add a backwards output tranny and you are in business.

This is what I did and the tube speech amp is still a someday project but the justification and motivation is hard to come by.

Jack,
    I think you nailed it for me here.  While I would like to build a speech amp, there are SOOO many other things pending.  The Canakit is a good idea (ordered a 25W amp).  They are certainly devoid of any buzzardness, but ah well.  It also allows me to reconfigure the JVII audio back to normal so it can be used as a stand alone transmitter.  I started to mod the audio in it last night, I think that may be a new thread.

Any ideas on mod'n the Canakit amp to handle the D-104 impedance?

BTW, I am still using one of your Maltmills purchased many years ago.   


Rich

[K9ACT]

> The Canakit is a good idea (ordered a 25W amp).  They are certainly devoid of any buzzardness, but ah well.

Right-oh but if you mount it behind a panel, no one will know.  Mine is mounted directly on the rack panel in front of the modulator.  It is so small, the gain control is all that is holding it to the panel.

>Any ideas on mod'n the Canakit amp to handle the D-104 impedance?

Not sure which one you bought but they also have a mic preamp for about $10 that worked fine.  I have replaced that with a complete audio chain but it was a good first option.  There is no lack of signal from the D104 but I never got it to work right for some other reason.... humm I think.  Not being a classicist, I don't seem much point in building up a nice audio chain and then putting a D104 in front of it so I didn't try too hard.

I bought the 15 watt mono with two IC's wired in the bridged configuration.

I bought the transformer from Hammond 125E if you need a source.  In fact, I just  bought another one for the 811 rig so I can have two completely independent rigs.

>BTW, I am still using one of your Maltmills purchased many years ago.

That's pretty cool.  "Small World after all..."

   Jack

[Steve - WB3HUZ]

Any ideas on mod'n the Canakit amp to handle the D-104 impedance?

Many options but attached are a few. The first is a complete mic amp and compressor from K7DYY. I think you can buy this preassembled. But with the schematic you could build your own. Put it in the base of the D-104. Then you can use the D-104 with any rig. Same for the other preamps shown.

The second is a simple preamp that provides no gain but gives the D-104 a very high impedance to work into (best response obtained from the D-104). It also allows for flipping the phase or polarity of the output. This is a nice option to have when running AM.


There was also an article in the August 1999 issue of QST for a D-104 preamp.

[W3RSW]

Simple but pretty nice audio.

Obtain a Shack O Rack 25 to 30 watt PA amp with 3 slider EQ. (cheap used or new.)
Set the hi tone slider high to overcome the too large screen bypasses on your 813 amp.  This is one of the things that is sucking down your highs.

Come to think of it change out the plate and screen bypasses to 500pf. (3kv, scr and >10kv, plate.)

Obtain a surplus 20 to 30 watt tube amp audio output transformer cheap (Fair Radio) or new from Hammond.

Hook up 4,8,16,70volt output of this xfor. to the RS PA amp, whichever taps give you 1 to 4k ohms c.t. on the other side.

Hook up the erstwhile "PP outputs" to the grids of your 811's, CT the ground through a 5V Zerner to ground or through meter and control circuitry if desired. Bypass the zener diode by 100uf/25v and .01u/50v.

Use Steve's referenced Hi Z to ave. Z D-104 simple MPF102 follower circuit. You don't necessarily need the phase reversal switch. Just switch the 811 plate caps if necessary. You'll see that one way the audio will be so- so but the other way will give fantastic peaks. .... well, would you believe much larger ones...

On the mod scope make sure you have enough audio to hit the zero line occasionally.
Have fun,
 '3's Rick

[steve_qix]

Here's another MIC preamp.  This one has a PC board, no surface mount components, and includes bass and treble controls.  Provides power for an electret condenser mic ($3.00 from radio shack).

[W7SOE]

Here's another MIC preamp.  This one has a PC board,

Cool circuit, I could lay that out pretty quick on a PCB, might be cheaper if 2-3 others are interested...   

Rich

[David, K3TUE]

No need:

http://www.classeradio.com/parts.htm

[...]
# Other Boards:
    * Microphone Preamp / Equalizer / Compressor Board Only: $15.00
    * Microphone Preamp / Equalizer / Compressor Board with all board parts: $45.00
[...]

[W7SOE]

There it is!  Thanks