troubleshooting a Sonar br-21

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I purchased a vintage Sonar br-21. I have a little problem with it. I get Plate amps of 50 to 70 at idle and 300 to 500 while keying down. The 300 to 500 change with tuning.
My problem is I get no RF output though the meter on the amp or my watt meter. Well as I key for a split second the needle will move up a little, about .5 watt on my watt meter and then goes back down. The tubes are all aglow but no change when I key. I am thinking the Capacitors. I am not sure. I am changing all capacitors and tube anyway. I am trying to figure if that is what it is. Any ideas would be thankful. Please let me know what you think.
I found these capacitors. Do you think these will work well and if you know of better let me know.

http://www.galco.com/scripts/ ... =TC78-MALY

Thanks in advance for any help thanks Ron

[Nagant]

1. Check the high voltage to the tubes. Be careful, IIRC those 6JB6's will have around 900 to 1100 volts DC to the plates.

2. Check the tubes on a quality tube tester such a mutual conductance type like the B&K 707 DyNa Jet among others.

3. Clean the contacts on your relay (make sure the high voltage has been drained from the power supply first). This is a common problem with relay points in general but especially tube device relays. Sounds like it's loading and thus amplifying. With no output I'd clean and test those points with a VOM for continuity.

If your electrolytic capacitors were bad you would know it because they will either blow or dead short. However if they have bulges, and or leaking then they need to be replaced. But even it that state they won't cause you to get no wattage output.

Those capacitors are good quality but way overpriced in my opinion. I'd look at the 100ufd 450V axials here http://www.tubesandmore.com/

They have them in a couple of different brands and I've used all their varieties in many tube amps through the past 15 years or so with no issues.

If none of the above works let me know as there are some more not so easy to check items left.

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I clean the amp with contact cleaner. I clean the relays and sometime the relay will chatter and I have some power output. Then I took it apart again and though I was cleaning the relay better and now it will do just like before. When I first key a little power then none. I may not be cleaning the contacts on the relay right. What is the best way to clean them, or maybe there is something going out that controls the relay. I have never learned electonics. What I know is self learn and sometime that is just enough to get in trouble. I like to learn and I learn best by doing. So what ever help I am thankful.
Ron

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I found the problem. There are two relays or maybe it is part of the one relay. There are contacts on the underside of the amp. The side with the Capacitors and there are like three contacts that make contact when energized. This one works. The relay with one contact area on the tube side which I think is called ry2. It will not energized, so I took a good screw driver that is non conductive and touched the contact down and I have wattage. It is not tuned are anything, but I got 50 watts out of it. Maybe someone can give me more help now I know the problem.

http://www.cbtricks.com/Amp/s ... 21_sch.jpg

The link above is the schematics for the sonar br21. If you can help me by telling me what energizes the relay.

Thanks for the help Ron

[Nagant]

No problem. There aren't to many people left that even know how or want to work on tube amps.

On relays in tube type amplifiers don't use contact cleaner on them. Bad mix with high voltage plus it won't do much if anything to clean the points. Take a small non aggressive file and clean the black tarnish off of the points (make sure all voltage is drained from the pwr. supply 1st). In many instances you'll have to remove the rear spring and retainer clip, then slide the movable upper portion out. Makes cleaning both sides with the file easier. Another option is they use to make specialty flat files for cleaning relays. Not sure of they're still available or not. They are basically nothing but a thin flat piece of metal with some abrasive adhered to them. You seldom have to disassemble a relay with them since they are so skinny you can usually clean both sides with the relay together in the unit.

I can't really tell by that schematic where that relay gets it's voltage supple as it's a JPG and the scrolling back and forth is rough. There should be some coil tabs on each side of the relay. Trace them back and you should be able to see where it gets it's voltage from. A VOM will help. If there are two relays and both get there working voltage from the same source and if there is voltage on the one that's not working it could bee the coil in that relay has opened up. In that case it will need to be replaced. All that's needed to operate the relay is voltage to the coil and a means to take one side to ground in order to activate it to the closed position.

I'll see if I can find an easier to read schematic or some pics of the inside of one in order to give you some more specific information. I haven't repaired one of the Sonar amps in over 12 years and thus I honestly don't remember much of the internal layout anymore.

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I am 90 % sure that the relay is bad. Does anyone know where to get a replacement for a potter & brumfield relay. The numbers I can get off of it is KR 3004 and 110v DC. I can push down on the relay and I get wattage. So I feel the coil on the relay is bad. If you know where to get a relay please let me know.
Thanks Ron

[Night Crawler]

maybe there is something going out that controls the relay.

According to the schematic there's a small tube a 12AT7 that's used for the RF Sensing Circuit to switch the relay.
Try replacing the tube that might be the problem if not here's the relay.

Potter and Brumfield Relays http://relays.tycoelectronics.com/pnb.asp

Look for
Plug In/Panel Mount General Purpose Relays

[Nagant]

Sorry took me so long to reply. I see Night Crawler beat me to it. Found the PDF version of the schematic for the little Sonar and as he said check the 12AT7.

Likely either:

1. the 12AT7 has an issue
2. Relay is bad
3. or a supply voltage problem to the 12AT7

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Thanks for the replies. I have ordered a new relay and I should be in business again. Thanks

[Night Crawler]

Are you sure it was the relay?

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I used my vom to check the coil and I get nothing. I check the other relay that works and get like .457 ohms. I sprayed contact clean and the material around the coil was wet with contact cleaner and the relay would clatter. If I take a screw driver not conductive and make the relay make contact I get wattage out the sonar driver. I don't have the load and tune set right at the time, but I get 50 watt. I purchased another 12at7 tube, but it was weaker than the one I have. It had a hard time to flip the first set of relays. So I replaced with the old one and the first relay is opening and closing well. I feel it is the relay. Night crawler sent me to the website I needed to get the open relay as I have now. I just need to call them and order a spdt 110v DC. I don't need the SPDT, but that is what is on the amp. I can use the spst, but is will put the same thing back in.
Please if you can give me any help give me a replay and thanks a bunch,

[Night Crawler]

What I used to do when those relays that are switched with a tube went bad or the tube itself was to replace it with one with a 12vdc coil.

Tap off the filament voltage then rectify it to use for the supply voltage for the relay and build a sensing circuit with a transistor to switch it to ground.

I repaired a br-21 some years ago that way which had the same problem your having.

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if I can get the relay would that not be the way to go. I like to keep it original. I can also get a closed relay. I think I will try and keep it original. What benefits would I get by changing it to a 12 vdc coil. Thanks Ron

[Night Crawler]

If you can get the original one do it that way.

The reason I used a 12vdc relay i had it in a junk box and used a 49 cent transistor to switch it also a 12v relay cost less and is easier to get even RS has them and the 12AT7 can be eliminated.

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I can understand the saving money. I will have to purchase something so I think I will keep it real. Thanks for the help. Hard to find good help.HAHA

[Night Crawler]

I can understand the saving money.

I'm use to homebrewing and build a lot of my own equipment so I'm always looking to save a buck. I put together a number of receivers,transmitters and amplifiers over the years using parts from old radios and tv's.

[Conspiracy]

I just got a BR-21 and it worked for about an hour, then quit keying up. A tech friend replaced the tube in the keying circuit and both germanium diodes, like the manual recommended. He could not get it to key up. He left it in the garage over night and the next day it started working. He was able to talk on it for about a week but as soon as I got it home, you guessed it, dead. The unit will key up if you force the contacts with a non conductive stick. The thing would swing about 100w when it worked, so I'd like to get her going. I'm driving it with a stock FS-23. I'm only about $20 into this box so no big loss if she don't want to talk.