The AM Forum
March 29, 2024, 04:10:37 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: 1 [2] 3   Go Down
  Print  
Author Topic: Valiant Making Progress  (Read 30511 times)
0 Members and 1 Guest are viewing this topic.
ka4koe
Contributing
Member
*
Offline Offline

Posts: 1157


It's alive. IT'S ALIVE!!!


« Reply #25 on: May 14, 2013, 10:46:14 PM »

RF bias found at -40V. Set to -70V. See new tx waveform. The grass doesn't start now until about -55 dB. Looks cleaner. Still working on the clamper.


* cleaner.JPG (92.84 KB, 1010x678 - viewed 432 times.)
Logged

I'm outta control, plain and simple. Now I have a broadcast transmitter.
ka4koe
Contributing
Member
*
Offline Offline

Posts: 1157


It's alive. IT'S ALIVE!!!


« Reply #26 on: May 16, 2013, 02:01:58 PM »

Can only get clamper plate idle down to around 100mA with key UP in CW position. Will swap out 6AQ5s with a couple of spares laying around and see what happens. Adjusting the grid final bias to the specified value seems to have cleaned up the o/p waveform and reduced hum greatly, as stated in an earlier posting.
Logged

I'm outta control, plain and simple. Now I have a broadcast transmitter.
K1JJ
Contributing
Member
*
Offline Offline

Posts: 8893


"Let's go kayaking, Tommy!" - Yaz


« Reply #27 on: May 16, 2013, 02:20:35 PM »

Hi Phillip,

The single CW carrier looks pretty good.  It's hard to see much deeper without test artifacts creeping in unless you work at the test set up.

Now the real test...When you have the modulator working, put in a 1 KHZ audio tone and modulate to 98% negative.  You will now see the harmonic distortion created by the modulator.  If the second lower audio peak (2nd harmonic) is at least -25 dB down from the center carrier, you will generally be OK. (about 5.6% THD) The 3rd, 4th, etc audio peaks should diminish farther down (-30, -35 dB) as they go away from the center freq to maintain this figure. You can also hear these tones on a remote receiver and can use the S-meter as an indication. Look for  X2, X3 X4 multiples, etc., of the 1 KHZ audio tone running above and below the center freq..

Post the pic when you get to this point and we'll take a look.  This is a good indication of potential splatter and will teach you the optimum settings for the rig to produce the cleanest signal under modulation.

T
Logged

Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
ka4koe
Contributing
Member
*
Offline Offline

Posts: 1157


It's alive. IT'S ALIVE!!!


« Reply #28 on: May 16, 2013, 09:23:43 PM »

I will cautiously say that the Valiant is working. Still needs some more work before I button it up, but the big stuff seems to be okay for the moment. Remaining tasks include:

1. Calibrate the variable frequency oscillator (tuning).
2. Replace a power resistor in the VFO compartment that is prone to fail in these transmitters.
3. Clean 50 years of gunk off the chassis and front with a 50/50 mixture of ammonia and 409.

Modulating ok, no sparks, no carbonized wiring, and no glass shrapnel in my skin from exploding vacuum tubes.
In other news, not shorting out anything. Cannot get clamper idle current below 50 mils (tried three tubes). Listening on a companion receiver and its nothing to get excited about, quality wise. Sounds a little scratchy on voice peaks. May be overmodulation on my part. The manual says to run 330 mA plate, 8 mA grid, and modulate no more than 165 mA.
Logged

I'm outta control, plain and simple. Now I have a broadcast transmitter.
ka4koe
Contributing
Member
*
Offline Offline

Posts: 1157


It's alive. IT'S ALIVE!!!


« Reply #29 on: May 17, 2013, 01:40:35 PM »

OK, I'm not sure I can get a precise measurement of 98% negative. The best I can do is a smidgen before the bottom flattens out. All I have is a Tek465/DM43, HP5326 counter, and the bandscope on the Flex.

Doesn't one have to be careful injecting tones of this nature with respect to duty cycle? I don't want to burn up another set of 6146's and their associated spur suppression resistors.
Logged

I'm outta control, plain and simple. Now I have a broadcast transmitter.
KA2DZT
Member

Offline Offline

Posts: 2192


« Reply #30 on: May 17, 2013, 04:24:28 PM »

Yes, limit the time modulating with a sine wave.  Few seconds on and more off.
Logged
K1JJ
Contributing
Member
*
Offline Offline

Posts: 8893


"Let's go kayaking, Tommy!" - Yaz


« Reply #31 on: May 17, 2013, 09:07:35 PM »

OK, I'm not sure I can get a precise measurement of 98% negative. The best I can do is a smidgen before the bottom flattens out. All I have is a Tek465/DM43, HP5326 counter, and the bandscope on the Flex.

Doesn't one have to be careful injecting tones of this nature with respect to duty cycle? I don't want to burn up another set of 6146's and their associated spur suppression resistors.

I meant to get as close to -100% as possible, but not over. -98% is just a way of saying that. Anywhere from  -90 to -99% is fine.  Heavily modulated will produce worse THD performance than lower modulation, so it's an acid test, worst case.

I don't see why any plate modulated AM rig worth its salt can't take a modulated sine wave. I run them thru my rigs quite often.  Going over negative 100% can break things, but if everything is running right and we limit the modulation to under 100%, it should be fine. If anything, keep an eye on the tube color.  If the 6146's get excessively red, then maybe you need better cooling or need to load the rig a little lighter. (More C2 loading capacitance to produce less carrier output)

T
Logged

Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
ka4koe
Contributing
Member
*
Offline Offline

Posts: 1157


It's alive. IT'S ALIVE!!!


« Reply #32 on: May 18, 2013, 11:38:13 AM »

Measurements using Daiwa CN101L/50 ohm dummy load

Plate 460 mil
Grid 7.5 mil
PO ~ 170 watts CW

Power output rises after tx heats up to about 480 mils ~ 180 watts, grid @ 7.5 mils.
Wave clean on scope

On 160m cannot get VFO higher than 1980 khz when calibrating.


* cw wave 18 May.JPG (90.3 KB, 990x719 - viewed 419 times.)
Logged

I'm outta control, plain and simple. Now I have a broadcast transmitter.
KA2DZT
Member

Offline Offline

Posts: 2192


« Reply #33 on: May 18, 2013, 01:28:07 PM »

460ma?HuhHuh??  The rig has three 6146s in the final.  Don't think you should be loading the finals much above 300ma.  Check the manual for the correct amount.  I think most folks run the Valiant below 300ma final current.

Fred
Logged
KB2WIG
Contributing
Member
*
Offline Offline

Posts: 4484



« Reply #34 on: May 18, 2013, 03:07:19 PM »

 " I think most folks run the Valiant below 300ma final current. "

Johnson loads their VK2 to 300 mA........ Its got 2 - 6146(s).

I don't load my VK2 more than 200mA on phone.


klc

Logged

What? Me worry?
WA2OLZ
Contributing
Member
*
Offline Offline

Posts: 184


« Reply #35 on: May 18, 2013, 04:20:05 PM »

I think the manual calls for 450ma on CW, 330ma for AM.
Logged
Steve - K4HX
Administrator
Member

Offline Offline

Posts: 2722



« Reply #36 on: May 18, 2013, 05:52:14 PM »

300 mA on phone? You must be reading a different manual.   Grin



Johnson loads their VK2 to 300 mA........ Its got 2 - 6146(s).

I don't load my VK2 more than 200mA on phone.


klc


Logged
KB2WIG
Contributing
Member
*
Offline Offline

Posts: 4484



« Reply #37 on: May 18, 2013, 07:34:58 PM »

"  300 mA on phone?  :

Gack! It doesn't mean Clock Wise??.

Yeah, the manual says 300mA for CW and 230mA, max, for Phone (p12, Johnson Manual). I feel so cheep. But I still have value.

klc
Logged

What? Me worry?
Steve - K4HX
Administrator
Member

Offline Offline

Posts: 2722



« Reply #38 on: May 18, 2013, 07:48:19 PM »

OK. 300 for CW. This is the AM Forum. Why are we posting CW numbers?  Wink
Logged
ka4koe
Contributing
Member
*
Offline Offline

Posts: 1157


It's alive. IT'S ALIVE!!!


« Reply #39 on: May 18, 2013, 08:02:54 PM »

Have the cover off the VFO compartment. I can see why there is much wailing and gnashing of teeth with respect to R3, 18K large resistor. Its gonna be a booger to get at and replace.

Philip
Logged

I'm outta control, plain and simple. Now I have a broadcast transmitter.
Jim, W5JO
Member

Offline Offline

Posts: 2506


« Reply #40 on: May 18, 2013, 08:14:49 PM »

Have the cover off the VFO compartment. I can see why there is much wailing and gnashing of teeth with respect to R3, 18K large resistor. Its gonna be a booger to get at and replace.

Philip

Clip it out and put it under the chassis with wires connecting.  Use a 5 watt or, at very least, a 3 watt.
Logged
WA2OLZ
Contributing
Member
*
Offline Offline

Posts: 184


« Reply #41 on: May 18, 2013, 09:34:23 PM »

Very hard to read but try enlrging the page view

Logged
w8fax
Member

Offline Offline

Posts: 55


« Reply #42 on: May 18, 2013, 09:55:56 PM »

My manual for the Valiant sez 450 ma for CW and 330 for phone with 8 ma drive, modulator at rest is 60 to 80 ma, peak to about 165 ma.....Al/W8FAX
Logged
Steve - K4HX
Administrator
Member

Offline Offline

Posts: 2722



« Reply #43 on: May 18, 2013, 10:04:44 PM »

Here ya go.


* valiant_tuneup.png (337.29 KB, 833x764 - viewed 453 times.)
Logged
ka4koe
Contributing
Member
*
Offline Offline

Posts: 1157


It's alive. IT'S ALIVE!!!


« Reply #44 on: May 19, 2013, 10:46:32 AM »

We're cool on loading procedures. I have both a hard and digital copy. I find it is easier to pull up the PDF viewer than deal with my bound hard copy.

However, since this discussion seems to have morpherized to a log of my progress, and not one dealing with a specific problem, perhaps the Moderator(s), in their Profound Amplitude Modulated Full Carrier Wisdom (PAMFCW), may wish to move this chain of postings into the QSO section.
Logged

I'm outta control, plain and simple. Now I have a broadcast transmitter.
ka4koe
Contributing
Member
*
Offline Offline

Posts: 1157


It's alive. IT'S ALIVE!!!


« Reply #45 on: May 19, 2013, 12:36:36 PM »

Chernobyl resistor measures 9.5 Kohm out of circuit vs. 18Kohm specified. Working on its replacement now...this is truly hateful job.
Logged

I'm outta control, plain and simple. Now I have a broadcast transmitter.
ka4koe
Contributing
Member
*
Offline Offline

Posts: 1157


It's alive. IT'S ALIVE!!!


« Reply #46 on: May 20, 2013, 08:48:43 AM »

Replaced resistor. VFO working after a fashion. Will likely need to replace 0A2 regulator. However, getting some really severe backlash with the dial. Can someone tell me how to break this thingy down without breaking something?

Cannot get end points on 160 LO adjustment and HI adjustment to line up. This may be related to tube damage (0A2, 6AU6) as R3 was found to be only 9.4 Kohm. Also, the aforementioned backlash is not making things easy.
Logged

I'm outta control, plain and simple. Now I have a broadcast transmitter.
KB2WIG
Contributing
Member
*
Offline Offline

Posts: 4484



« Reply #47 on: May 20, 2013, 09:17:54 AM »

Before Natasha visits you, you may want to read this. I don't have a Val, and I don't know fer sure, but I think you should "Beware the flexible coupler" if you take the panel off.


http://amfone.net/Amforum/index.php?topic=15634.0


klc


* natasha.jpg (10.28 KB, 346x227 - viewed 391 times.)
Logged

What? Me worry?
N8ETQ
Member

Offline Offline

Posts: 795


Mort


« Reply #48 on: May 20, 2013, 09:55:59 AM »


Hey Phil,

    If you have that much Backlash, Chances are
it's already Broke...

GL

/Dan


Replaced resistor. VFO working after a fashion. Will likely need to replace 0A2 regulator. However, getting some really severe backlash with the dial. Can someone tell me how to break this thingy down without breaking something?

Logged
KA2DZT
Member

Offline Offline

Posts: 2192


« Reply #49 on: May 20, 2013, 11:44:53 AM »

Could be the phenelic shaft coupler is broke.  Take a close look at it while turning the dial.
Logged
Pages: 1 [2] 3   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone © 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.121 seconds with 18 queries.