REF. Topic "External VFO for my BC 610" Dated 12/29/2014

[N5AEA]

I have applied 20 Vrms drive from Kenwood 480 to the BC 610 tuning unit Xtal socket.  However, I have modified the TU-52, grounding the L14 side of socket and adding a 1000pf cap from Xtal socket and grid.  I have found that the 20 V drive works and 10 V will not. 

With the transmitter tuned in the 40M band and in "CW", "Normal" modes, the 250TH output to 50 ohms load is 320 watts max.  However, the carrier is not clean and has 60 Hz hum.  The hum is coming from the exciter 6V6, 6L6, 807's.  This was found by looking at a local receiver (Flex 3000) with only the exciter powered up.

Also have found that "INT Amp Grid x1" meter is only 3 ma max.  I don't yet know if this is a problem.  I don't have the spec for that.
73
Ed, N5AEA

[N8ETQ]

   Hey Ed,

       Glad your making progress. I wonder if
you ever tried that TU in MO position? I recall
the MO provided similar readings as the Crystal.

      How Much can you get to the PA Grid?

/Dan

[WD5JKO]

Ed,

  If you go to your original thread on this topic you will see mention to isolate the RF drive to minimize hum pickup from a ground loop.

Jim
Wd5jko

[N5AEA]

Performed CW/Key-Down test transmit with station in New Mexico, Jim K3IAN.  Transmit RF carrier power of 320 watts was received at far end strong, clear and clean of any trash or AC hum.

Question:  Is it normal for the PA Anode to glow bright rose red?? 

Answer to Dan's question:  The PA Grid current is at 50 mA.

[N8ETQ]

   Hey Ed,

          It is normal although your tube is a little
"Brighter" than I like to see mine.  Wonder what
Ip is at that level? Also wonder if your using the
Military Issued Tank Coils?  My 610 was modified
to use B&W coils with an "Easily" adjustable Link.

          About the tube glow, Make sure when
you switch to "PHONE" that the meter on the BC-614
reads less than 40 ma. and the 100TH's just get
a little "Blush".  I've gotten into the habit of looking
through those vent slots on the left side wing and
use the tube plate color to adjust the MOD Bias.
When the tubes look right my Meter always seem to
about 40 ma. Use the "HV Protect" until you get
the hang of it. I have SS 866's.

oops,,Sorry, I think you have an "F" or "I". You'll have to
look through the side panel.

          I also went through Mine and made sure that
all the transformer taps are wired to the highest voltage
tap on the primary.  With AC line voltages consistently
10 - 15 % higher than they were during WWII you may
be surprised how high your B+, and Fil. voltages are.

         Sounds like your making fine progress with the
old Beast!

73

/Dan

[N5AEA]

Dan,
It is interesting that my camera (Sony Alpha 350) sees the color not the same as I see it.  I didn't see the white hot center as the Sony did, but my eyes are 76 years old. All my tank coils are Military Issue.

My transmit time was only 5 seconds long.
The load coil was adjusted  for max. power out to 50 ohm load.
Power out was 320 W (180 Vrms @ 50 ohms)
Power supply set for "Normal" "CW".
Ip dip to 250 mA.
Igrid at 50mA.
PA Grid Bias in standby mode (plate supply off) is -188 VDC.

Question:  What should the "INT Amp Grid x1" meter read?  I only get about 2mA.

Thanks much for all your valued input.
73
Ed

[AB2EZ]

Ed

RF Power=

V_peak x V_peak / (2 x R)

or (equivalently)

V_rms x V_rms / R

If the output is really 180V rms into 50 ohms, then the output power is:

180V x 180V / 50 ohms = 648 watts

Stu

[N5AEA]

Stu,
OK looks like I made an error.  Help me out here.

My DMM measured 180 VDC across a 50 ohm load through a diode.
180 V / 1.414 = 127.65
127.65 x 127.65 = 16294
16294 / 50 = 325 W

So I should have said 127.65 Vrms
Is that correct??
Thanks much
Ed

[AB2EZ]

Ed

Yes... that is correct!

I am assuming that the RF output connector of the transmitter was connected directly to a 50 ohm load; and that (separately) you measured the voltage across the RF output connector with a diode in series with a DMM.

The input capacitance of the DMM, in combination with the diode, would behave as a peak detector. So the DMM would read a DC voltage that is equal to the peak (amplitude) of the sinusoidal RF voltage waveform across the output connector.

Therefore, the rms value of the sinusoidal RF output waveform would be (as you stated above): the DC value measured by the DMM / 1.414

Best regards
Stu

[N8ETQ]

  Ha Ha Ha,


        I have to ask. Ed, Is the 20 V RMS you mentioned in
your original post really 20 V Peak too ?

        That would be about 4 W into the Crystal socket.
Which seems about right.

        Ed, I'm still trying to figure out what the "Int Amp grid"
position of the meter should read but if you have 50 mA
to the 250TH grid it's probably fine, or just a little low.
All my manuals don't even mention it. Other than to say the
scale is 0 - 15 mA..

73

/Dan

[N5AEA]

Dan,
Yes you are correct about the 20V Peak.  I was just thinking about going back to correct that statement for the record.  I was doing the math correctly, just put the wrong label on things.  Guess I have to accept a B- on that problem!!

I have also looked all through the manual for the Int Grid Current, but can not find.  I was hoping that someone with a BC-610-F could tell me what they are seeing.

73
Ed

[N8ETQ]

  Hey Ed,

        That's too funny, Well we all had a good time and
nobody got hurt, and I learned a bit as well!

         Yeah, I need to power mine up again, I got into a big
shack Cleaning, Reorganize, reconfigure thing back before
my Mom passed away in 2011.  That's a busy time and just
never got back to it.  Funny how things that were a part of
your daily life can slip away.

         Anyway that is one of new years resolutions.

73

/Dan

Dan,
Yes you are correct about the 20V Peak.  I was just thinking about going back to correct that statement for the record.  I was doing the math correctly, just put the wrong label on things.  Guess I have to accept a B- on that problem!!

I have also looked all through the manual for the Int Grid Current, but can not find.  I was hoping that someone with a BC-610-F could tell me what they are seeing.

73
Ed

[W2PFY]

I think that grid current is a bit low for 40 meters. I run mine at 80 mills. That might explain the bright color of the anode if that digital picture is true to what you are seeing? Digital cameras for a point and shoot  make these types of pictures sometimes brighter than how they look to the eye.  Each 807 has a 22 K screen resistor that goes high in value. Replace them with 1 watt or better resistors. Your drive current should improve. I get over 100 mills on 160 & 80. Another improvement is to make a solid state rectifier for the RF deck. You sill see and increase in voltage to the  plates of the 807's. If you are getting carrier shift or downward modulation it means that you either have insufficient grid drive or the 250TH is soft.   

[N5AEA]

Hello W2PFY,
Thanks for your input.
I measured the value of the screen resistors, pin to pin of the 807's.
Should be 22000 plus 22000 = 44000.
The total was 47.7 K so not too bad as long as they are both the same.
The control grid resistors are also OK. 
73
Ed

[W2PFY]

Hi Ed, another thing to look at is your grid leak resistor or absence of one which was the case on my D model 610. I was getting way too low  grid drive so I added a 1000 ohm 20 watt resistor in series with the grid leak supply for the 250TH. It should be connected just before the grid RFC. If there is one in your 610, check its value or increase the value to achieve approximately 1000 ohms. Be sure it is a 250TH and not a TL. A TL would probably work well with some bias adjustment but I never gave that any study.. I am told that the use of a grid leak resistor will give you better modulation response than just a strait hard voltage bias supply?

Terry