Teaberry model "T"

[jammeejoe]

Anyone know how to lower the dead key watts on a 40 channel model "T" ? Maybe like the Browning by changing the value of a resistor in the power supply. It dead keys 4 watts now. I would like it to do 2 watts if possible. Any help would be appreciated. Thanks

["Doc"Hammer]

Use the load and plate adjustments on the back of the radio. Backing your load off slightly and re-peaking the plate adjustment- should give you what you want..
There is also a service manual available for it at CB Tricks:
www.cbtricks.com/radios/teaberry/model_t/index.htm

[jammeejoe]

Wouldn't adjusting it out of resonance cause it to heat? I know adjusting a linear like that will cause heat and tube failure. There is a 10 watt resistor in the power supply of a mark III that can be changed to a higher resistance and drop your wattage. Just wondering if the 40 channel model "T" had this set up also. Thanks

[Sandbagger]

Jun 25, 2012 23:01:18 GMT -5 jammeejoe said:

Wouldn't adjusting it out of resonance cause it to heat? I know adjusting a linear like that will cause heat and tube failure. There is a 10 watt resistor in the power supply of a mark III that can be changed to a higher resistance and drop your wattage. Just wondering if the 40 channel model "T" had this set up also. Thanks

Tuning the plate control out of resonance is BAD. It will cause the tube to draw more current and shorten its life. However, you can overcouple the load control slightly and this actually can make the transmitter run more cleanly, while not really increasing the strain on the tube. But if you need to drop power more than 1 or 2 watts, it's probably better to increase the value of the plate voltage dropping resistor (and make sure to use a 10 -50 uF cap to bypass the resistor to keep audio level high with the lower dead key).

[jammeejoe]

Do you know where the dropping resistor is located? The schematics I've found don't number the components or have a lay out picture to go by. I have other radios I can talk on but just like the old tube radios. I am driving a 2 pill and it doesn't like 4 watts, that's why I would like it to be 2 watts. Thanks

[Sandbagger]

Jun 26, 2012 15:19:06 GMT -5 jammeejoe said:

Do you know where the dropping resistor is located? The schematics I've found don't number the components or have a lay out picture to go by. I have other radios I can talk on but just like the old tube radios. I am driving a 2 pill and it doesn't like 4 watts, that's why I would like it to be 2 watts. Thanks

Here is a copy of a good schematic:

www.cbtricks.com/radios/teaberry/model_t/graphics/teaberry_model_t_sm_sch.pdf

The resisor you want to change is marked R79. It's currently at a 1K value. Changing it to around 2K would probablu get you what you want. Also, there is already an AC bypass cap across R79. You might want to up the value of that cap to a 10 uF, and up the voltage rating as well to be safe, since there will be more voltage dropping across the resistor once you change it. The cap will give you a little more forward swing, and allow you to keep a 10 or 11 watt PEP even with the lower dead key power.

[jammeejoe]

Thank you so much. I have a Sams Photofact coming for it to make it a little easier. Again thanks

[zman]

Supposedly there is a plate modulation mod out there for these radios. id love to see if i can find that and mod mine.

[Sandbagger]

Jun 30, 2012 17:17:12 GMT -5 zman said:

Supposedly there is a plate modulation mod out there for these radios. id love to see if i can find that and mod mine.

I'm not sure what that means. The radio is already plate modulated from the factory. But there are various mods that could be done to increase swing, or to clip negative peaks, or increase low frequency response.

[cbrown]

I wouldn't touch the audio stage at all, but it's your radio and your call.

[jammeejoe]

Mr Sandbagger do you know where any of these mods can be found? I have looked under everything and every possible name I can on the net and I can't find anything on the model "t". Plenty on transistor models but nothing on a tube type. But I am old and not very computer savvy. Thanks

[cbrown]

Nothing wrong with modding a radio, I've done it since the early days when I started and I still do to this day. What I meant was in my personal opinion I think there is no reason to modify the audio section of that radio. If he wants to, by all means have at it.

Heck I put a sweet modified digital Siltronix VFO on my Mark III.

[Sandbagger]

Jul 2, 2012 17:17:24 GMT -5 jammeejoe said:

Mr Sandbagger do you know where any of these mods can be found? I have looked under everything and every possible name I can on the net and I can't find anything on the model "t". Plenty on transistor models but nothing on a tube type. But I am old and not very computer savvy. Thanks

I can't point you to a specific place where there are step-by-step instructions on how to mod your specific radio. The mods are usually well-known to old-school radio techs, and they are more general in nature. But they may be out there somewhere buried in the bottom drawer of someone's file cabinet, written is pencil.

That's the problem with us old school analog guys, we're too busy playing with our radios to actually transpose all that accumulated knowledge into the digital realm. Someday, someday.......

[gator7]

I guess I will comment on this thread, I some cases doing audio mods will only cause one thing. Over modulation, bleed over, and poor quality audio. On tube type or solid state, it can cause flat topping which only adds to the poor audio.
I think that is what CB meant. I can't speak for him, but it is my opinion that if the radio is already doing 90-100% modulation, leave it alone and work on power output.
I am not against mods, I just am tired of people running the audio way to high. Between the distortion, bleed over and audio that sounds like crap.
Yes, I am on my soap box. And it is a issue here with the locals. But it is what it is.

Enough said.

[cbrown]

You basically covered it, gator. I'm also not a fan of trying to eek out every last watt on these old radios either. If you want more power, buy an amplifier. Preferably a Class AB.

This is just my opinion.

[Sandbagger]

Jul 9, 2012 7:28:12 GMT -5 gator7 said:

I guess I will comment on this thread, I some cases doing audio mods will only cause one thing. Over modulation, bleed over, and poor quality audio. On tube type or solid state, it can cause flat topping which only adds to the poor audio.
I think that is what CB meant. I can't speak for him, but it is my opinion that if the radio is already doing 90-100% modulation, leave it alone and work on power output.
I am not against mods, I just am tired of people running the audio way to high. Between the distortion, bleed over and audio that sounds like crap.
Yes, I am on my soap box. And it is a issue here with the locals. But it is what it is.

Enough said.

Well, my opinion on this....... There are "mods", and there are mods. Some mods are just what you've described, and can turn an otherwise clean sounding radio into a splatterbox. Yea, it might be louder, but what it gains in volume, it loses in clarity.

But there are also mods to improve audio quality, or broaden the fidelity. Increasing positive modulation peaks without clipping the negative. Usually these mods are a little more involved and you'll need good test equipment to set them up properly.

Bottom line: Not all mods are bad mods, it all depends on what you're trying to accomplish.

[gator7]

Sanbager,
I agree, not all mods are bad ones. The problem lies with the person doing it having a good understanding of what that mod does. To many of us have had a wire clipper do a mod, and it turned out not so good.
My area has lots of wire clippers, not so many good techs. Heck, I know how to clip wires, even pull a diode out of a circuit.
But that's about all I should do. Too bad other don't figure that out. LOL..

[Sandbagger]

Jul 14, 2012 8:53:28 GMT -5 gator7 said:

Sanbager,
I agree, not all mods are bad ones. The problem lies with the person doing it having a good understanding of what that mod does. To many of us have had a wire clipper do a mod, and it turned out not so good.
My area has lots of wire clippers, not so many good techs. Heck, I know how to clip wires, even pull a diode out of a circuit.
But that's about all I should do. Too bad other don't figure that out. LOL..

Well, yes you are exactly right. If you don't have a good underlying grasp of the theory behind what you are doing, you probably shouldn't be experimenting on radios. On the other hand, if someone who DOES have a good understanding, writes up a step-step procedure how to perform a good mod, then someone who's good at following and interpreting instructions could probably get away with it as well. And that goes back to my first point that a lot of the old school good mods are either buried in the cobwebs of the knowedgeable old timers' minds, or are scribbled on some yellowed piece of paper in the bottom of another old timer's file cabinet.

[gator7]

So ture, I lost many of those yellow papers in my day.

[cbrown]

My notebook on microphones that I wired since I was a youth now has the appearance of the dead sea scrolls. ;D I'd be afraid to try and scan it.

Besides, my handwriting isn't the neatest out there. I keep telling myself I'm going to do something with it before it falls completely apart.

[gator7]

I understand CB. LOL