Trc 448. Low power out

[vswr]

Im working on a 448. Got the sams for it. Aligned it twice. Removed the c2020 driver. Tested the hfe. 135. Removed the final. Hfe 152. Very good set. Cant seem to get more than 2 watts on an and about 3 on ssb. The radio works with multiple final and driver combo. The c1306 and 1307. I bought a bunch of both sets from amazon. Surprisingly inexpensive. The base voltages are correct. +or- .02vdc. The collector voltages as per sams say 9.5vdc. I get 10.5. 1 extra volt. But still my output us no greater than 2 watts at full peak and tune. When the radio came into the shop the only bad transistor was the final. The coils and trim pots all turned. Off freq and overmodulating. Even the pots for the meter were messed with. I aligned it using my freq generator, my scope, my vtvm and ammeter. It tuned up spot on and Im amazed at the sensitivity. There is not much circuitry on the TX side. But something is keeping the power from getting 4 watts am and 11 watts pep ssb. I dont see any csos that would interfere with it. No electrolytics other than the power ones on it are anywhere close to the TX circuit. On key up, voltages are stable. Unkey and then they slowly climb higher and then start to drop if measured with a standard vm. Im thinking cheap transistors but how can they rig them so that the gain is exactly within the datasheet range. Could there be a bad tuning can? What feeds the driver and the final? I know the driver feeds the final but what feeds that driver? Im gonna have to really think this through. After all its RF. Something is either not amplifying or diverting the signal to ground but what?

[Sandbagger]

Aug 21, 2023 22:00:54 GMT -5 vswr said:

Im working on a 448. Got the sams for it. Aligned it twice. Removed the c2020 driver. Tested the hfe. 135. Removed the final. Hfe 152. Very good set. Cant seem to get more than 2 watts on an and about 3 on ssb. The radio works with multiple final and driver combo. The c1306 and 1307. I bought a bunch of both sets from amazon. Surprisingly inexpensive. The base voltages are correct. +or- .02vdc. The collector voltages as per sams say 9.5vdc. I get 10.5. 1 extra volt. But still my output us no greater than 2 watts at full peak and tune. When the radio came into the shop the only bad transistor was the final. The coils and trim pots all turned. Off freq and overmodulating. Even the pots for the meter were messed with. I aligned it using my freq generator, my scope, my vtvm and ammeter. It tuned up spot on and Im amazed at the sensitivity. There is not much circuitry on the TX side. But something is keeping the power from getting 4 watts am and 11 watts pep ssb. I dont see any csos that would interfere with it. No electrolytics other than the power ones on it are anywhere close to the TX circuit. On key up, voltages are stable. Unkey and then they slowly climb higher and then start to drop if measured with a standard vm. Im thinking cheap transistors but how can they rig them so that the gain is exactly within the datasheet range. Could there be a bad tuning can? What feeds the driver and the final? I know the driver feeds the final but what feeds that driver? Im gonna have to really think this through. After all its RF. Something is either not amplifying or diverting the signal to ground but what?

The first thing I would suspect are those "cheap" parts you got from Amazon. There are a lot of these parts out there, most of which are cheap Chinese knock-offs which can't seem to amplify RF (at least at 27 Mhz) worth a plug nickel. I would try to find a decent replacement part from a reputable place, such as RF Parts. If that doesn't fix it, a long shot, but something that happened to me with a radio I had which wouldn't do more than 1 watt. Turned out one of the ceramic disk caps in the final tuning section shorted. I found it by accident while I was poking my fingers around the area and noticed that the cap was hot to the touch. You might have a similar condition.

[vswr]

Hmmm...valuable info boss man. Appreciate the come back. I have a few extra ssb rigs kicking around the shop. Same finals. Known working radios. Im gonna swap out the good finals for the cheapies. BUT before I install the real ones on the 448, Ima test out these Chinese ones on the known good rig and see how stupid these sellers think we are. Thanks. I will post my findings asap.

73s!

[vswr]

Typical. Chinese crap was once again to blame. Found a good set in a donor rig and that was the answer. Man these cheap Chinese parts can really throw you off. Fixed, tuned, nice radio.

[oldgeezer]

Buy NIB TRC-483 in eBay for $50.

[cbrown]

Jan 1, 2024 10:05:36 GMT -5 vswr said:

Typical. Chinese crap was once again to blame. Found a good set in a donor rig and that was the answer. Man these cheap Chinese parts can really throw you off. Fixed, tuned, nice radio.

With the Chinese parts, you do (sometimes) get what you paid for. I tend to avoid them at all costs, if possible.