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Home made amp trouble

Discussion in 'Home Brew' started by mrmagoolew, Sep 13, 2008.

  1. mrmagoolew

    mrmagoolew Member

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    Hi, guys,



    I picked up a homebrewed amp at the flea market last weekend. It's a 2 tube sweep tube amp with 6JS6C tubes in it. It uses a 6BQ5 tube as the keying circuit. It has the regular 110V power cord on it, but also has another cord coming out the back. That cord had about 24V on standby, and about 142V on operate. It is hooked to the operate/standby switch on one wire, and the transformer on the other wire. I hooked the amp up, and keyed my mic, but the relay does not close. The tubes are lit, and they all test OK, but nothing is happening. Does anyone have any ideas as to what the extra wires are for, and why the amp doesn't key up? Could it be a burned up relay coil? The amp is crammed into a 6" X 6" X 8" cabinet, and it's almost impossible to see what is going on down inside. I can only pull the bottom of the cabinet down about an inch, and can only see a limited amount of components. If I can get the amp working, I'm going to put it in a different cabinet, but I don't want to tear the thing apart right now. Any ideas? Lew
     

  2. W5LZ

    W5LZ Crotchety Old Bastard

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    It's just a guess so take it that way. It sounds like that 'extra' line is a keying line. Does 'hard' keying and not RF keying. One way to find out is to short the connections. If the relay throws, then it's a keying line. With that much voltage, I sort of doubt if I'd use it with a contact in the mic to do that keying. Again, this is just a guess!
    - 'Doc
     
  3. mrmagoolew

    mrmagoolew Member

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    the amp

    Hi, Doc,

    Thanks for your answer. I did give that some thought, but the amp doesn't have a fuse or fuseholder in it at the moment. I'd be afraid of what might happen if I just shorted them. About the only thing that I can do for the moment is try to make up some kind of schematic, and take the thing out of it's case so that I can see the connections better. It's jammed so tightly in the case, that I wonder how the thing was even built. I think it was built right inside the case, and I tried to get the outside of the case off, but it's in there so tight that I'm unable to get it up past the transformer. I don't remember the exact dimensions, but I think it's built in a case that is about 6 X 6 X 8 or something close to that. The transformer takes up half of that, and the tubes and relay take up the other half.
     
  4. W5LZ

    W5LZ Crotchety Old Bastard

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    I think you're wise NOT trying that shorting thingy. At least as things stand. Taking it slow isn't a bad idea at all. Safe too, since tube type amplifiers deal with voltages that can really bite you.
    - 'Doc
     
  5. mrmagoolew

    mrmagoolew Member

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    amp

    I found a schematic for a Browning 180 amp at CB Tricks(?) that closely resembles my amp. The sweep tubes are of a different type, but it uses the same number keying tube. I'll be using that as a guide to see what differences there are between the two. It uses a DC powered relay from what the schematic shows. I guess I'll test the relay for continuity first. Of course, I'm gonna look on the relay for any markings before I do anything. I'll check out the wiring to and from the keying tube, a 6BQ5 and see if there are any broken/wrong connections, and then go from there.
     
  6. TonyV225

    TonyV225 W9WDX Amateur Radio Club Member

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    Ive never seen that number tube before. What is the rating on them?
     
  7. mrmagoolew

    mrmagoolew Member

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    Ratings

    I'm not sure what you mean by ratings, but if it's watts that you're wondering about, I was told that this amp and one that is similar to it will put out about 180 watts with 2 tubes. Actually, I was told that they can each put out about 100 watts. I don't know if it's that's true but that's what I was told. These are horizontal sweep tubes from old TVs. They were not really intended to be used as a power amplifier tube. It's just that someone discovered that they could be used like that, and that's what they are used for now. At least for the most part. I would suppose that there are collectors of old TV sets that actually use them for restoring TVs. If you were looking for something else as far as ratings go, let me know. Lew
     
  8. mrmagoolew

    mrmagoolew Member

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    New developments

    I finally got the amp out of it's case after a lot of diagrams and unsoldering. I found out that a wire was off the relay. I attached it back to where I THOUGHT it should be. I went to the local electronics shop today and got 2 new electrolytic caps and a fuse holder. I'll probably get those put in this evening. I was told that the 2 extra brown wires are probably just part of the standby side of the relay, and that they may need to be tied together to make the relay work. I'll be trying that AFTER I get the fuse holder installed, and the amp put back in it's case. I'll also be wiring a 3 prong plug up this evening.I'll try the amp out ASAP, and see how things go. Lew
     
  9. mrmagoolew

    mrmagoolew Member

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    Tube amp trouble

    Hi, guys,

    I got the amp back together, hooked it up, keyed the mic, and nothing. The relay is not keying. I twisted the brown wires together, but all that did was poof the fuse. It was a 3 Amp fuse. Now I have to decide whether to take the amp to the CB shop or, totally rebuild the amp to the schematic from the Browning 180. Any other thoughts?
     

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