The AM Forum

Hello folks,
I'm new to this part of the hobby so please forgive my lack of knowledge in all things fire bottle related.  ::)

I'm working on a Heathkit DX-60 (not a DX-60a/b) and have a question of the output power I should expect from a single 6146A.

I have re-capped the radio and checked all the tubes, B+ is 308VDC, and solid (no drift)
I'm showing after tune up into a dummy load, approximately 70W on a standard watt meter.
Am I wrong in thinking this a bit high for a single 4164A?

Thanks es 73
Dan, N8IE

This may be of some help ...........  klc


http://www.amwindow.org/tech/htm/wc3kmods.htm

Yes

Sounds very high. Also, your measured plate voltage sounds very low.

The r.f. output power (if it is tuned up to maximum output) should be roughly

output power = electrical input power x 75% = B+  x  average plate current  x  75%

In typical operation (e.g., for a Johnson Ranger), with the B+ set at 550 volts and the average plate current set at .120 amps... the r.f. output power would be: 66 watts (electrical input power) x 75% ~ 50 watts.

Stu

The 308VDC is the B+ for the VFO not the plate voltage, sorry for the confusion.
I'll take a voltage reading on the HV side of the PS tonight.

I notice a big difference between the voltages listed in the manuals for the DX-60 and the DX-60B.
Math tells me I may not be too far off:
Plate V = 700
Current = 150mA
Power = 105W
At 75% that figures to +/- 78W

Hi Dan,

I have both a DX-60 and a DX-60B, and the max power output is about the same: 60 to 65 watts into a dummy load in the CW position. These were measured using 75 and 40 xtals on the fundamental frequency, with the recommended grid drive of 2 to 3 ma.

70 watts is a bit high, but probably within tolerance of meter accuracy. Make sure your SWR is 1:1 (as it should be with a pure resistive 50-ohm load).

Good luck,

Bob
W6REF

Hi Bob,
Thanks for the tips.

I just measured my plate voltage at 743VDC. This is high per the schematic. It shows 600VDC. The math bears out the results so I need to check out a few resisters.

Man this is fun and I'm learning something.
I feel a headache coming.  ;D

73
Dan, N8IE

743 Volts is fine for a 6146.      Assume 100ma as plate current, then your input would be 74.3 watts. Assume  65% efficiency, you output would be between 48 and 50 watts.   Normal.   Assuming plate current of 125 ma,  giving  an input of 92.9 W, and an output of 60W. Very normal.

tube circuits are forgiving. almost anything can be + or - 20% different from the "text" value without any trouble at all. Do not waste time making your B+ exactly whatever value. Unless whatever is wrong is + or - 50% from what it is supposed to be, the rig will work well enuff to figure out  what that thing is.

the 2 exceptions - bias voltages an filament voltage. They need to be held to lower tolerances. bias voltage will either cutoff conduction of your tubes over all or part of the operating cycle if hi, causing scrotelessness, and if low, will cause your tube to operate over the entire cycle in class A which will blow up the tube due to plate current being drawn all the time

At least, I think thats it. I may have reversed "hi" and "low", and someone can tell us if i did.

Of course, I cant fix G-G linear amps which are simple things and I sometimes set my radios on fire by spraying contact cleaner on the bandswitch with the power on, so take all the above with a grain of sea salt.

Derb,

I have enough of those stories to sell a lot of salt..........

Thanks for all the info folks.
I have it cleaned up, re-capped, a new 6146A in place, and all the wafers de-oxed!

It's putting out 60 watts +/- with good reports for audio and CW. What else could I ask for. Hope to catch one of you on the air soon!

73
Dan, N8IE
Happy DX-60 owner!  ;D

Here is a picture of it:
http://n8ie.com/images/DX60.JPG

73
Dan, N8IE

Very nice looking station Dan.  Looks so new too.

I've always like the looks and paint scheme of that pair but hoped for years that Heath would come out with sturdier knobs or at least have a brass insert.