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 on: Today at 07:29:36 PM 
Started by k7mdo - Last post by N1BCG
The resistance to use will depend on the class of amplifier. In the case of Class C I've seen some formulas use a 0.6 multiplier (although others have used 2.0 as you mentioned). My experiments have yielded results closer to what the 0.6 multiplier would produce so I've stuck with that. The formula would then be Plate Volts / Plate Amps * 0.6.

For the Gates BC1-G, that would be 1250 / 0.27 * 0.6 = 2778 Ohms so a common 2.7k resistor would be fine.

 on: Today at 07:28:44 PM 
Started by W2PFY - Last post by WD4DMZ
I have a Ramsey FM100B that came as a kit in 2009. 100MW but with a 1/4 vertical good stereo reception about 1/2 mile. At 100MW it meets the part 15 rule as I read it.

I used it at the HS where I taught physics and let the students broadcast with it. Dual channel plus mic input with level adjustments and LED bar displays.

Search for local stations and you will likely find an open channel. Mine is set at 90.9.

Ramsey no longer makes these but they are likely on EBAY.


 on: Today at 07:00:17 PM 
Started by k7mdo - Last post by k7mdo
OK, I thought I read somewhere that the RF resistance was represented at twice the plate current whereas the modulator current was at the DC plate current....  I can try both ways of course but leaving the tubes in was not yet on the agenda.  More to do!  The tubes are not in right now!  Thanks, Tom

 on: Today at 06:48:33 PM 
Started by k7mdo - Last post by N1BCG
If you "back feed" the output circuit with an antenna analyzer or impedance bridge to check the tuning then the resistor would be Plate Volts / Plate Amps. The tubes need to remain connected since their interelectrode capacitance will affect the tuning.

 on: Today at 06:42:36 PM 
Started by k7mdo - Last post by k7mdo
Plate resistance question:

I want to use my "rig expert" to tune the tank circuit and the method I want to use is to remove the finals (833A) and replace them with a resistor representing their total RF plate resistance. Then measure the tank circuit by "looking back" into the antenna line".

From reading the forums I think that the value should be around 2400 ohms.  Arrived at by multiplying the plate current by 2 and dividing it into the plate voltage.

At 250 watts the plate will be 1250 VDC and the current estimated at 270 milliamps. Or, at 1000 watts the plate voltage (per manual) will be 2525 VDC with a current of 525 milliamps.

Are there any arguments to this? Huh

Thanks, Tom

 on: Today at 06:38:34 PM 
Started by W2PFY - Last post by N1BCG
There's nothing illegal about owning or operating an FM transmitter of any power level as long as you take precautions against excessive radiation as outlined under Part 15. Since that's in the plan, you're all set.

As you've noticed, there are numerous FM transmitters out there ranging from true Part 15 to pro-broadcast to Chinese imports with the latter being the most common. Of those, look for the lowest power output so that it's easier to control using simple methods.

One possibility is the V6000 model from https://mobileblackbox.com

That model is relatively inexpensive, low power, but monaural, if that matters.

 on: Today at 04:49:01 PM 
Started by W2PFY - Last post by W2PFY
I want to be able to run a legal FM transmitter for my own use in my own house, I thought I would get a cheap five watt chinese FM stereo transmitter so I could turn it down to one watt.

I would be running that 1 watt into a 50 ohm resistor with about a 1 foot pigtail coming off the hot end of the resistor acting as the antenna. The antenna will be located in the cellar about 5 or 6 feet below street level so I am not too worried about getting some DX with the transmitter.

The question I have is if anyone is using a transmitter out there for this purpose, would you please let me know the model and make of your transmitter. There are a ton of them out there and I don't know what is a good pick?

If you don't want to talk about it here, PM me please.

Thanks Terry   

 on: Today at 04:36:37 PM 
Started by KJ6EFH - Last post by W2PFY
Hello Gary, do you have a couple pictures of how that 2.5 K resistor is hooked up? I have a BC-610D and before that I had a C model. Been playing with them for about 30 years and have been on the air more regularly almost exclusively on 610's since about 1989?   They are simple transmitters to work on abit heavy. I have had a number of problems through the years but once gone thru, they are very reliable. 

Sounds like that 2.5 K resistor may have been in a feedback circuit?

Yes, we must Bear with Bear Grin Grin  Did someone say Beer?

 on: Today at 02:44:08 PM 
Started by wa2pjp - Last post by WA2SQQ
13.jpg looks like it has a photo of it. Not the best image.

 on: Today at 01:13:04 PM 
Started by KJ6EFH - Last post by w4bfs
as stated before in other threads .... the windings have different resistances since one of them will be closer to the center of the core and will therefore have less wire per turn and with less wire, less resistance .... Bear's test will likely bear this out .... (i've been wanting to say this for a while) ... Smiley Smiley

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