POW KW+ keying circuit

[Trainman 8274]

This is why i cant find the heart to work on these things. I think it's absolutely amazing that guys are out there keeping all these old amplifiers running, but I will say that it's definitely a labor of love.

Hi Linearone,

I feel your pain! Ive had a couple of radios really frustrating me here lately. Both are galaxies.. lol! A friend of mine encouraged me to mess with this amp. I've had it for around a year or so and its been a big paper weight, so with his help, I've gotten this far. Now, with help from all of you, hopefully it'll be back up and running. If I would have had to buy tubes for it, it would have been cheaper to buy another amp... As it is, I don't have a lot of money in it and I basically got it for free with the Browning.... So, its been a learning experience for sure and a little frustrating, but fun, too. I like old stuff and tubes are cool! Yes, I know to take precautions because I can get killed working on this stuff. It definitely scares me. Working on solid state radios doesn't bother me, I just have a lot to learn..

 

[wavrider]

well said.

 

[Shockwave]

Good morning Shockwave,

Thank you for all the good advice! I was wondering about the coax, also if you notice, there are red wires from the center pins of the 259 connectors to the relay. Shouldn't these be shielded or coax with shield grounded? In nomads post below he recommended replacing the diode and the inductor, so I'll be ordering more parts....

As for what happened to this one.. I don't know for sure. I bought it with a Browning Mk3 from the nephew of a silent key. The radio had a golden eagle mic, Pal VFO and I thought he was running this amp with it. The Mk3 dead keys at 4.5 watts and swings to around 12 on my meter. It needs some help, but does transmit and receive. I didn't know much about tube amps, but am learning. I haven't found much information about POW amps and those that I have asked just wanted to buy it.

The red wires coming off of the relay are short enough to not make much difference at 27 MHz. I would leave them alone. However, that coax being unshielded is way too long and it passes right by a very critical area on the input tuning for that final stage. That needs grounding at both ends.

I noticed that you have replaced one new tube in this amplifier. Assuming they are all the same type, I highly recommend putting the new tube in the driver stage, where it is not as likely to receive way too much drive and turn red on the anode.

 

[Trainman 8274]

The red wires coming off of the relay are short enough to not make much difference at 27 MHz. I would leave them alone. However, that coax being unshielded is way too long and it passes right by a very critical area on the input tuning for that final stage. That needs grounding at both ends.

I noticed that you have replaced one new tube in this amplifier. Assuming they are all the same type, I highly recommend putting the new tube in the driver stage, where is not as likely to receive way too much drive and turn red on the anode.

Hi Shockwave,

Thanks! I'll ground the shielding on the coax and put the new tube in the driver section. The tubes are all M2057, some are maco and some are GE, but it was that way when I got it.

 

[Shockwave]

Hi Shockwave,

Thanks! I'll ground the shielding on the coax and put the new tube in the driver section. The tubes are all M2057, some are maco and some are GE, but it was that way when I got it.

Cool. You'll probably notice the Maco tubes, look identical to the GE, because they were all made by GE. Someplace on each tube, you are likely to see the 188-5 code. That indicates manufacture at the GE, Owensboro Kentucky tube plant.

 

[nomadradio]

The burned board looks just like the one Maco used for their combined preamp/keying circuit. Gotta be the toastiest one of those I ever saw.

73

 

[Shockwave]

The burned board looks just like the one Maco used for their combined preamp/keying circuit. Gotta be the toastiest one of those I ever saw.

73

Looks very much like lightning damage to me. That board would normally only have low levels of RF drive on it.

However, in receive, a lightning strike works it way right back to that input connector with the fried choke. Looks like the keying board took most of the energy discharge first.

This damage typically requires at least several thousand volts or, several thousand watts. Neither should ever be present in this amplifier, under normal operating conditions.

 

[Trainman 8274]

Cool. You'll probably notice the Maco tubes, look identical to the GE, because they were all made by GE. Someplace on each tube, you are likely to see the 188-5 code. That indicates manufacture at the GE, Owensboro Kentucky tube plant.

Good morning!

I read that and thought it was pretty cool! Owensboro isn't real far from me. If only these tubes were still made.

 

[Trainman 8274]

The burned board looks just like the one Maco used for their combined preamp/keying circuit. Gotta be the toastiest one of those I ever saw.

73

Good morning!,

I read somewhere that these were made by a former Maco employee. It didn't list a name, but that would make since as to why they are similar to a Maco.

73

 

[Trainman 8274]

Looks very much like lightning damage to me. That board would normally only have low levels of RF drive on it.

However, in receive, a lightning strike works it way right back to that input connector with the fried choke. Looks like the keying board took most of the energy discharge first.

This damage typically requires at least several thousand volts or, several thousand watts. Neither should ever be present in this amplifier, under normal operating conditions.

Good morning!

That makes since. I didnt see anything that would have high enough drive to fry it when I picked it up. I had assumed he was running it with the Browning.

 

[Trainman 8274]

Just an update on the POW… After replacing the 1000uf cap and the diode, I have 12v and the amp keys now.. I still have the 220uf caps to replace and to ground the coax, but this one is back alive! Thanks for all the advice!

 

[nomadradio]

Rock on! Gotta love it when a plan comes together.

73

 

[Trainman 8274]

Rock on! Gotta love it when a plan comes together.

73

Thanks Nomad! Without your board, it would have been a lot more difficult! I appreciate all the help all of you have given with this project. It was a great learning experience! I definitely like getting help when I have questions instead of being told to send it to a tech..

Thanks everyone!

 

[linearone]

Thanks Nomad! Without your board, it would have been a lot more difficult! I appreciate all the help all of you have given with this project. It was a great learning experience! I definitely like getting help when I have questions instead of being told to send it to a tech..

Thanks everyone!

To be honest that's probably the neatest looking sweep toob box I've ever seen.. to my untrained eye it just looks fairly neat.

 

[Trainman 8274]

To be honest that's probably the neatest looking sweep toob box I've ever seen.. to my untrained eye it just looks fairly neat.

Howdy,

Yes, its easy to work on. This one is the first I've really messed with. I've looked in a Varmint and a Swinger 105 and neither of those look very easy to work on...