Feeding Audio into Valiant

[stevef]

I would like to feed the output of my audio processing rack into my Valiant.  WA1HZK indicated that pin 8 cathode of the 12AX7 speech amp will accomodate 600-ohm audio feed.  My question is how to best route audio from the jack to the 12AX7.  I have a balanced audio line to a balanced TRS jack on the chassis.  Should I isolate the shield from the chassis at the jack and leave it floating all the way to the 12AX7?  OR should I ground the shield to the chassis at the jack?

Steve KK7UV

[W3NP]

W3NP Does it again, bringing you the very best in Ham Radio advice to the AM BB!!! 

That was a joke!  Sound familiar??

Here is what I do with my modified Valiant when I run external audio to it (mostly I just use the D-104 tho).

The phone patch jack on the rear panel connects directly to the cathode of that 12AX7. I have had good success using a Radio Shack LO-Z balanced to HI-Z single ended transformer. They are built into an XLR connector body. There are two models with different gender ends. I just run a bal LO-Z cable from my audio rack to the RS xfmr and then a VERY short patch cable into that RCA jack for the patch, J3 I believe. Set the mic gain to a low setting and adjust your audio gear gain up for a good S/N ratio.

If you do go the TRS route, you may have to experiment with grounding. The 600 ohm feedpoint is NOT balanced...it is referenced to chassis ground.

 

[KL7OF]

I was just talking with John K7RLD and he was on his Valiant with the outboard audio processing into the phone patch jack,,,,,He used a 600 ohm to 600 ohm isolation transformer and a 30 MF electrolytic as a coupling cap and it sounds very good.He started out with a .1 coupling cap and it worked but sounded very restricted..   Keep in mind that most BC rigs that use audio processing gear require +10 db or more audio drive.  The phone patch input on the valiant was meant to be driven by the phone line which is probably =10 db so you will have to reduce the output gain from your audio driver considerably.  John used the output transformer from an old computer modem for his isolation transformer.....You will have to go to unbalanced into the phone patch jack... Good luck...Steve

[w3jn]

I replaced the crappy driver transformer with a line to P-P grid xformer, hugeassed thing.  Decent response from about 80 HZ-10K, I think the limiting factor is the mudulation xformer.

[W3NP]

W3NP Does it again, bringing you the very best in Ham Radio advice to the AM BB!!! 

That was a joke!  Sound familiar??

Here is what I do with my modified Valiant when I run external audio to it (mostly I just use the D-104 tho).

The phone patch jack on the rear panel connects directly to the cathode of that 12AX7. I have had good success using a Radio Shack LO-Z balanced to HI-Z single ended transformer. They are built into an XLR connector body. There are two models with different gender ends. I just run a bal LO-Z cable from my audio rack to the RS xfmr and then a VERY short patch cable into that RCA jack for the patch, J3 I believe. Set the mic gain to a low setting and adjust your audio gear gain up for a good S/N ratio.

If you do go the TRS route, you may have to experiment with grounding. The 600 ohm feedpoint is NOT balanced...it is referenced to chassis ground.

 

Actually now that I think about it, I may have changed that patch jack J3 over to feed the grid of the 12AX7 right before the mic gain control. At any rate, it works FB with the RS transformer. The mic gain control on the Valiant does need to be set to a very low level.

I did the W6BM audio mods to my xmtr and am quite pleased with the audio response and distortion level. As I said, I mostly just feed the mic input with a D-104.

[WA1HZK]

I'm confused. Your audio processor likely has a transformer isolated 600 ohm output that can be connected as a 600 ohm un-balanced output to drive these tube rigs once they are modified for 600 ohm input. I guess you could just jam this unbalanced input into the original 600 ohm phone patch input of the Valiant or you could consider using the mods that I have done to a dozen Johnsons with great success. Check This:
http://amfone.net/ECSound/Valiant%20Audio%20Mods%205-2003.jpg
Now you can set your processor for a decent amount of output and adjust the modulation on the valiant with the O.E.M. Mic. level control. This is a good thing if your going to have more than one transmitter in the shack that you will be switching PTT and TX audio into. Every transmitter in my shack is set up this way. Now I just set the audio processing stuff for maybe 0 dbm and adjust each transmitter with it's original control and it's happy. There is no need for another matching transformer before the input of the transmitters unless you are going to remote control the transmitter with 600 ohm audio cable from some distance away. If your processor has a RCA connector on it's output, it's already un-balanced and can be jacked right into the transmitters. I have always done it this way since I converted to the Berringer B1 & Symetrix processor. I have never had a trace of hum in the station due to converting the output of the processor to un-balanced. Please, avoid putting a frequency robbing piece of iron on the input if at all possible. Most junk boxes do not have quality "mic. input iron" sitting in them.
Keith
WA1HZK
WA1HZK

[stevef]

Sounds good Keith - I'll just run it unbalanced to the jack and onward to the 12AX7 cathode.

While I have your attention Keith...

I'm doing the mods from that link you just sent.  But I have some questions about it:

1.  With the interstage transformer gone, what kind of power rating do I need on those resistors (the 100k, 510, 15, etc.) surrounding the modulators???

2.  Is that an error, or is the aduio supposed to be feeding the grid of the modulators?  Or is it supposed to be on the screens as drawn???

3.  Your lash-up is for 1100v on the plates.  I'm going to try about 750v.  Will that require me to change any of those resistances?

Thanks for your help all...

Steve, kK7UV   

[WA1HZK]

I replied to your e-mail. My drawing was flawed about the grids. I must resend that to the site. All resistors are 1/2 watt except the 10K in the common cathode return of the Phase Splitter. Not doing the 1100 volt mod will just lower the peak audio possible to get with the stock iron. Remember I did the lamination mods and the higher voltage in order to make 100% audio. Also I highly recommend that you use a 12AU7 instead of the 12AX7 & make the component changes I used. A 12AX7 will have too much gain and be subject to hum and noise. You do not need it any longer because you are driving the rig a high level lo Z.
Keith