|
|
Post by 321 treeclimber on Jan 7, 2019 18:40:54 GMT -5
To boost modulation volume and audio strength in my yellowbird,my tech experimentally added a capacitor to the audio amp circuit. But we think by doing so, it overwhelms the overall audio system including rec'v so as the tubes warmed up,a distortion gradually built-up in the rec'v until it was equal to the actual radio signal rx. Tx was uneffected adversely. No distortion was transmitted and it is quite loud compared to without.so i think, unfortunately, it needs to go...sadly
|
|
Sandbagger
Administrator/The Boss 
Posts: 6,247 
|
Post by Sandbagger on Jan 7, 2019 20:33:48 GMT -5
To boost modulation volume and audio strength in my yellowbird,my tech experimentally added a capacitor to the audio amp circuit. But we think by doing so, it overwhelms the overall audio system including rec'v so as the tubes warmed up,a distortion gradually built-up in the rec'v until it was equal to the actual radio signal rx. Tx was uneffected adversely. No distortion was transmitted and it is quite loud compared to without.so i think, unfortunately, it needs to go...sadly Unfortunately, in many cases, modifications performed to increase one level of performance often results in degradation in another, or some form of instability or other undesirable behavior. It's rare that radios are made with oodles of extra performance (especially in the receiver) and then "detuned". Any time you modify a radio, you need to be careful of what you are doing, and watchful that what you are doing isn't going to make something else worse. |
|
|
|
Post by 321 treeclimber on Jan 7, 2019 21:44:55 GMT -5
Copy that. It really boosted output modulation but by the time the tubes were thoroughly warm i could barley hear incoming rx.so out with that modification! Sandbagger
|
|
Sandbagger
Administrator/The Boss
Posts: 6,247
|
Post by Sandbagger on Jan 7, 2019 22:02:26 GMT -5
Copy that. It really boosted output modulation but by the time the tubes were thoroughly warm i could barley hear incoming rx.so out with that modification! Sandbagger I'd be interested to know exactly what that mod was. One of our locals has a 40 channel Panasonic chassis tube rig which had a problem where the receive would get increasingly more distorted the longer it was on. I don't think the radio was modified, but there may be a cap/bias issue somewhere in there. The nature of your mod may offer a clue. |
|
|
|
Post by 2600 on Jan 7, 2019 23:01:28 GMT -5
Reminds me of a guy from about 40 years ago. He "discovered" a secret-sauce mod to the Tram D201 radio. It would boost the modulated power to nearly double the normal level.
Just one problem. The audio-modulator tube would "cherry", making the normally gray-colored plate in that tube glow red, then orange.
Just before it would go "POOF!".
I called it the "unlimited fueler" mod. Uses up half the parts in the engine for every quarter-mile run.
The guy figured this out and stopped setting up his friends' radios with this setup. About the time they figured out not to let him install it to begin with.
Secret sauce. Tastes good going down, but oh the heartburn the rest of the day.
73
|
|
|
|
Post by 321 treeclimber on Jan 8, 2019 5:11:30 GMT -5
Wow ! Ok I'll let you know exactly what he did if i can post a pic. Worth a thousand words,they say.
Stand by....
|
|
|
|
Post by 321 treeclimber on Jan 8, 2019 7:48:40 GMT -5
 pencil points out the added capacitor. I dont have its value on hand. Will add that info later. When removed, recieve went back to normal.the symptoms were exactly that of your local buddy's. 321 |
|
|
|
Post by tubefan on Jan 8, 2019 18:04:22 GMT -5
Im not big on golden mods like this but if you must have it on the TX audio why not hook up a relay to the keying circuit so that cap is connected when keying and transmitting and disconnected when in rx?
|
|
|
|
Post by 321 treeclimber on Jan 8, 2019 19:26:58 GMT -5
Because your right. I dont need it. Its out now and ive gotten good radio checks. I prefer the old tube jobs as close to stock as possible, but that relay would definitely work! Anyway im having enough exitment trying to learn how to tune the raider !!!
|
|
|
|
Post by 321 treeclimber on Jan 8, 2019 19:38:17 GMT -5
You guys were all right about tuning sequence, but i learned about the patience required for complete warm-up before tuning....woof.
|
|
Sandbagger
Administrator/The Boss
Posts: 6,247
|
Post by Sandbagger on Jan 9, 2019 18:53:19 GMT -5
View Attachment pencil points out the added capacitor. I dont have its value on hand. Will add that info later. When removed, recieve went back to normal.the symptoms were exactly that of your local buddy's. 321 Hmm..... That looks like he added a cathode bypass cap. There is one audio stage in the Panasonic chassis that lacks one. Adding that cap will boost the AC gain of that stage. I've played around with that before, but I never experience any distortion as a result. Based on what I can see of the pins, I'm guessing it's the 6BQ5 output. That cap should be across a 100 ohm resistor |
|
|
|
Post by 321 treeclimber on Jan 9, 2019 20:11:53 GMT -5
That makes it sound like he was on the right track....i will pass that insight on. Now that i removed it there is no more noise or distortion on receive. Less audio strength on tx but modulation reports say good and very clear. Im using an un-amplified d104 chicken choker. power mics dont seem to work well on these radios.
|
|
