Weird cobra 1000 problem.

[King Mudduck]

I just got a nice 250 maverick base amp today and it works great. Also got a nice Cobra 1000 with echo and a channel kit installed that works great as well. Now the weird thing. I can tune my Yaesu FT 101EE ( this is the radio i use most ) down to a 3 watt key swinging to 20 watts pep and it drives the amp just fine, seeing a little over 600 watts. But the Cobra 1000 with a 3 watt key swinging to a little past 20 watts will not make the amp swing forward at all! I'm using the same jumpers, meter and everything but the amp just will not work with the Cobra. It will key up and show a 150 to 200 watt dead key but has forward swing at all, and that makes no since to me!!! The amp works fine with 5 other radios that i have here but it wont with the Cobra,

Someone help me out here. I have never seen anything like this before and it's got me stumped:?

 

[DTB Radio]

That has me stumped, too. My best guess is some kind of goofy interaction between the amp's input circuit and the tank circuit of the 1000. Have you put a meter between the amp and radio when trying to run the amp?

 

[fnkycoldmedina]

try different jumpers between radio and amp.what works with one radio doesnt always work with another radio.thats where i would start.

 

[King Mudduck]

No. But i did find something just now that im going to try and repair since i dont have anything like it here with me. someone has cut what looks to be some kind of resistor located at C36 or R93.One number is over the resistor and the other is under it, not sure which one is correct, will let you know what happens.

 

[King Mudduck]

No change. I'm going to have to throw in the towel on this one. If i could find something on the net that walked you threw tuning step by step like you can find for just about any radio on cbtricks then maybe. But since i have looked ( even goggled it )and still can find nothing like that i'm just going to have to suck it up and send it to my tech.

I bet it's something very simple to!

 

[AudioShockwav]

I think that the 1000 just don`t like what it is seeing at the input of the amp for some reason or another. Do you have a antenna tuner that you can stick in between the radio and the amp?
Some of the old sweep tube amps have a "trimmer" on the back of them to allow you to adjust the input a little.
The bad thing there is that it seems that everything else has no problem with it.
I can understand that the Yaesu has no problem working into the maverick....the output section of a rice burner will work into less than a perfect load with ease.
I do think if you could put some kind of a matching device (tuner) behind the radio/in front of the amp, you could solve the problem.

73
Jeff

 

[King Mudduck]

OK, i will gave that a try. Also. I switched the meter from pep to ave and noticed that when using just my normal speaking voice the radio just would just barley swing forward,not even a half a watt. If i raised my voice and spoke into the mike then it would only swing forward about 1 watt and i cant see that being enough to kick any amp. I'm just wondering if the thing may have a bad driver final.

 

[557]

Here's the thing: I don't know the extent of what all has been done with your Maverick 250, but if the tube configuration inside is stock, better keep that Yeasu away from it. The Maverick 250 was made at a time which most radios only put out around 15-20 watts. The high powered radios such as Galaxy, Connex, Yeasu and such will seem to work fine for a while, but you are over driving the amp BAD! Keep a close eye on your plate choke on the driver plate. If it starts to turn color, it's a sure sign that your tubes a taking a beating. I think they use a Z14 or Z15 something like that. Anyhow, those tubes will go out very soon using that Yeasu radio. If your meters are showin about 20 watts peak, more than likely your RMS is only a 3 watt carrier swinging to 5 or 6. Here is what I have down for proper tuning on this amp:
ONLY LOAD THE AMP IN HIGH POWER POSITION

1) Adjust grid tune control on back of amp to max on the meter
2) Adjust tune control top right knob to max the meter
3) Adjust load control top left knob to max on the meter
4) Adjust drive tune control bottom left knob to max on meter
5) Adjust driver load control bottom right knob to max on meter
6) Go back to grid tune control re-adjust for max on meter
7) Adjust top left load control clockwise so the meter drops back 3 to 4 divisions. This is called over-coupleing.

You don't have to re-adjust for low side of amp

A Cobra 1000 GTL is generally laid out like a Cobra 29 with a power supply inside. You can perform a power mod, change the final and driver and even upgrade your swing kit to make it do more, but generally will only get 7-10 watts RMS. Get some field reports though, because it is not abnormal for these old amps to not show a lot of forward swing on your meter. Generally, an original stock D&A Mav. 250 will do around 300-500 pep (150-250 RMS). If the 1000 GTL is showing slight forward swing or straight up, you should be o.k. You will find that compared to a 2-pill Class C amp, you will give better results on the other person's S-meter! Hope this helps!