Browning mk3 transmitter issues

I was able to get most of the radio transmitter working but still have some issues with the transmit. Im getting a 2w carrier on AM and 4W peak. Pretty sure that I should have a better carrier on AM than 2 watts. On SSB, I get 2 watts full whistle on both USB and LSB. The7558 is new and works properly in my other transmitter. Ive adjusted the aircap in the back tonprovide max output. I didnt try to adjust any cans yet. It may have been broadbanded somewhat. Who knows...I have the sams and what Ive found online. I cant see that in ssb that any can adjustment could cause this. I have removed the power mod that was strapped accross the 2k power resistor, and there were other mods like a switched mod that enabled the transmitter to transmit on all 40 channels with the exception of 26 and 36. I have the 90-3 siltronix for expanding that. Im not a mod guy unless its a clarifier mod because so many people are off freq I can compensate to speak to them. Anyhow, my issue is low AM carrier and horribly low output with a very good turner powered desk mike. Help would be appreciated. 73s

UPDATE: I spent a few hours going through the transmitter alignment prcedures. Made some headway. On my bench meter which is a CPI, I get about 2.5 wats dk, and now near 6 watts mod on AM, and the same on SSB. Cant figure out after the recap and even changing tubes why I just cant get at least 10 watts of SSB modulation. ALC is fully cranked up at this point. Sadly the sams isnt all that great when it comes to alignment. Ive seen better from sams. L5 from pin 9 of the 6gh8 gave me more of a boost. The aircap also brought up the power along with the can string alignment. This transmitter was a real basket case when I received it. I was able to get a USB crystal from Alan. Still would like to invest in the dial crystals that cant be brought into spec or are doa. I have 2 mk3 radio sets, and 1 mk4 set. Always loved these pioneers in the hobby. If anyone has some more insight on getting my ssb up to a reasonable power, please let me know.

tramd said:

Here's the Browning manual with alignment procedures. You may want to check voltages at the tubes to make sure they are correct.

Click to expand...

Thanks. Much appreciated. I will check voltages and trace the circuit.

nomadradio said:

How many of the 10 or 12 electrolytic capacitors have been replaced? If any of them are original, this is trouble in the making even if all of them still work today. Good chance at least one of them is contributing to reduced performance.

73

Click to expand...

I replaced all of them. Unless some are hidden, I got them all. I pretest all the new ones and test the pulls. All the pulls tested within spec then of course tossed. I replaced a few resistors that had signs of overheating. Some values were off. Main plate voltages all tested good. I might be looking at possible silver mica or disc caps as an issue. I'll scope each section with a tone on the input and look for drops. Still need a few crystals for it. Hopfully Alan can hook me up when he gets his Barkett buy done.

73s

vswr said:

I replaced all of them. Unless some are hidden, I got them all. I pretest all the new ones and test the pulls. All the pulls tested within spec then of course tossed. I replaced a few resistors that had signs of overheating. Some values were off. Main plate voltages all tested good. I might be looking at possible silver mica or disc caps as an issue. I'll scope each section with a tone on the input and look for drops. Still need a few crystals for it. Hopfully Alan can hook me up when he gets his Barkett buy done.

73s

Click to expand...

I wonder if the cans have caps inside like a lot of newer radios...

nomadradio said:

Cans? As in slug-tuned IF/RF transformers? Yeah, most of them. T1 doesn't. It relies on C11 to tune it to resonance. The rest of them have at least on internal disc cap.

73

Click to expand...

Yup. I call em cans. Not to be mistaken for the big old caps though. Yeah. A lot of these transformer cans have caps in them that fail. I know that in the newer radios the slug positioning can be a tell tale sign of a bad internal cap. Small pico value. Ive seen these go bad and spark in vintage table radios. Tear them down and in some they used mica sheets at the base. The silver would oxidize and arc through. Maybe these ones in the mk3 txer are weak but the slugs dont stick up or for the lower slugs in dual transformers push through the bottom. I need to do some more work on it to see if the disk caps could be causing the low output.

73s

nomadradio said:

Yep, those are called "K-Tran" IF/RF transformers. They tune with a cup core on the outside of the winding, rather than with a hollow core and a slug on the inside. It was a high-performance part back in the day. The cup core was also a magnetic shield. You could crowd them closer together without any magnetic interference between them. But I blame the "come and go" failures on the clear polystyrene frame inside them. It shrinks with age and the tension on the mica sheet/metal plate capacitors slacks off. Removing the old caps and soldering a silver-mica across the lugs works, but only if the plastic doesn't shatter or disintegrate. Not my favorite vintage component.

It really sounds as if one tuned circuit in there is not reaching a proper resonant peak. But which one? Only takes one to cripple it.

73

Click to expand...

Hey Nomad, firstly, I appreciate your support to the hobby in this forum. As for the coil cans I've worked with in the past, they had a disk shaped silver mica sheet that circled the base of the transformer inside the case. I often saw them in 5 tube AM brodcast desk type radios. The cans would spark from the inside and then the radio would die. Not sure if the spark would cause the coils to open up or just blow off the silver causing the coil to stop resonating. I've put the mk3 txer aside for now. Get a fresh start on it in a while. Im into a superbase now that has a bad vco. Im gonna see if I have a cybernet board with the same VCO.in it. With over 300 radios here, im sure I can find a suitable donor at least temporarily to rule out other problems in the superbase.