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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Ill advised Champ 600 project

Discussion in 'Glowing Bottle Tube Amp Forum' started by Prophetsnake, Jul 15, 2017.

  1. Prophetsnake

    Prophetsnake Tele-Meister

    134
    Aug 2, 2016
    ireland
    Hi all,
    New here and this is my first post in anger. I'll state up front that I am new to this and my understanding of how these contraptions work is on the rudimentary side. I would realy appreciate a little advice if anyone feels up to it!
    I bought one of those Chinese Champ 600 PC innards on eBay - cheap - and have been attempting to make it into a playable contraption.
    I ditched the stock PT because it was 120V and I need a 240 V unit. I have attempted to replace it with one of these:

    http://www.antekinc.com/content/AS-1T275.pdf

    - A dual-voltage (240/120 toroidal transformer. I replaced the original 1 amp fuse with a .5 amp item, before I forget to mention it.
    I believe I have wired the transformer correctly. The primary is wired in series, (black 1 to red 2) and continuity checks out. The secondaries exceed the amp's requirement by a good margin, so I have used only one winding of each and secured the other wires out of the way, their circuits open. The purple static shield is earthed to the chassis.
    The chassis is earthed to the mains.
    The chassis is mild steel - homemade.
    All input and output jacks check for continuity to the earth pin on the plug.
    I've also replaced the cheap and nasty LED pilot with a jewel unit.

    Right. Now when I powered it up, I got nothing. No noises, no hum. I checked the power at the switch, and nothing. The 3A fuse in the plug was gone.
    I didn't have another 3A, so I used a 13A and cautiously tried again. Nothing, no sound, but there was ,at least power to the switch. The pilot light didn't light. No smoke, no smells. After about a minute I tried cycling the power switch off, then on. That blew the onboard 500mA fuse.

    I'm reluctant to go any further without some sort of plan. Any suggestions gratefully received!


    Jeff
     

  2. dsutton24

    dsutton24 Poster Extraordinaire Gold Supporter

    Dec 29, 2010
    Illinois
    Oof! There's nothing 'cautious' about replacing a fuse with one that's four point something times as big as the right one. Oversized fuses are a prime source of dead amps.

    First things first, check your power supply to see if it survived. Put the right fuses in it, pull the tubes, and check your filament voltage and the plate voltages on the empty tube sockets.
     
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  3. dan40

    dan40 Tele-Holic

    628
    Aug 19, 2015
    Richmond Va
    Are you comfortable taking high voltage measurements? At this point you will probably need to to take a few readings to determine whats going on.
     
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  4. Prophetsnake

    Prophetsnake Tele-Meister

    134
    Aug 2, 2016
    ireland
    Thanks DSutton and Dan. You both seem to be pointing in the same direction.
    The 13 Amp fuse was just the fuse in the plug. The fuse on the board is after the switch, but stil before the primary winding.
    I haven't got a problem trying the readings further downstream, but it seems to me that I might have a more fundamental issue that needs to be looked at first. For starters, I'm wondering if I have seriously mismatched the amp and transformer. I get a calculated filament of .78, and with two windings there is 3A available, so I simple set one aside. The current is 35 mA, and 180 is available with both winding, so again, I just used one winding. Is it possible the transformer itself might be causing the problem?
     
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  5. Prophetsnake

    Prophetsnake Tele-Meister

    134
    Aug 2, 2016
    ireland
    Right. I powered it up and had a rummage around. I'm not really sure what I'm looking for here, but this is what I found:
    236V at the primary
    353 at the secondary. It's supposed to be 275.
    the 6.3V secondary is reading 2V
    The lead to the OT, the one opposite the 6V6, is reading 824AC, but 0 DC
    The 12AX7 plate is 403
    The 6v6 plate is 724


    None of that looks right to me.

    There were no funny smells. The speaker was completely silent.
     

  6. Bendyha

    Bendyha Tele-Afflicted Ad Free Member

    Mar 26, 2014
    Northern Germany
    Well....take the tubes out......one should do all preliminary checks relating to the supply voltages first.
    There should be no AC at Test Point 12. If there is, we must solve this problem first. as the problem lies infrount of this test point.


    upload_2017-7-16_10-15-51.png

    Across TP14 there is 353AC ..yes? and 0VDC?... Oh, I have two schems...no matter!...and across J9- J10 only 2VAC..Yes?
    upload_2017-7-16_10-21-39.png upload_2017-7-16_10-21-39.png
     
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  7. VintageSG

    VintageSG Tele-Afflicted Ad Free Member

    Mar 31, 2016
    Huddersfield, UK
    Remove the secondaries and heaters from whatever they're connected to.
    Measure the voltage across the white and yellow pairs.
    Twist the inner yellow and white together and measure the outer yellow and white.
    Do the same for the green heater wires.
    Don't blow yourself up in the process. Post the results.
     
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  8. Bendyha

    Bendyha Tele-Afflicted Ad Free Member

    Mar 26, 2014
    Northern Germany
    I think you meant green & blue, one from each pair, for the twisting/conecting together for the test....?


    upload_2017-7-16_13-26-54.png
     
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  9. VintageSG

    VintageSG Tele-Afflicted Ad Free Member

    Mar 31, 2016
    Huddersfield, UK
    Yes, blue + green. Quite where I got all green from is a mystery that even Scooby + Shaggy would struggle to solve.
    I'm just wondering if the odd voltages are a product of a simple wind and restoring the relevant turn ratios will solve it, or at least eliminate a few questions.
    Still, there are some crazy voltages being reported and at least we can eliminate any transformer issues.
     
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  10. Prophetsnake

    Prophetsnake Tele-Meister

    134
    Aug 2, 2016
    ireland
    Oh dear. I was entirely wrong in the way I was doing the measurements. For starters, I didn't realise that TP meant 'test point' and all of the measurements I posted before were from earth.

    So, all done with tubes out-

    Across TP 14 is 274v AC and 0 dc - Yay!
    And across the filament supply I got 5.9 DC. Better than 2, but not 6.3. The tubes do get hot.
    At TP12 it's 381 DC and 838 AC
    At the preamp tube it's 345 DC and 875 AC
    At the 6V6 it's 383 DC and 838 AC

    These make a bit more sense to me.

    Incidentally, I've powered it up three times today and on one of those it blew the 500mA fuse.

    Just to clarify, I am using only one coil from each of the secondaries. The amperage available from just one is more than 150% of requirement in each case. The spare leads are stowed and open.

    Thanks so much for the help, guys. At least I don't feel like tossing the damned thing in the bin now!
     

  11. dsutton24

    dsutton24 Poster Extraordinaire Gold Supporter

    Dec 29, 2010
    Illinois
    You've got plenty of transformer, so there's no worry there. If the unused secondaries are insulated they're not going to effect anything adversely.

    The fuse blowing...

    You've mentioned the 500 ma fuse a couple of times, is that the fuse in the primary of the transformer? Is it a slow blow fuse? Here's what I'm wondering about... You can blow a fuse just from the inrush of current when the transformer is powered up. You're supplying 240 instead of 120 to the primary, so logically you should use a smaller fuse. But, since your transformer is, comparatively speaking, huge, you may need to up the fuse a size or two to keep the inrush from hammering the fuse. The fact that you've blown a three amp fuse worries me, though.

    What meter are you using for your voltage measurements? Some meters do odd things if you put high d.c. voltages to them when they're in an a.c. range. Your filament voltage is a little low, but it's probably okay. Your d.c. voltages look good, but the a.c. componenet is puzzling. I'm wondering if that's just some kind of meter artifact.


    Where'd you find those drawings? I looked for schematics last night, and the ones I found were awful. Those are great!
     

  12. Prophetsnake

    Prophetsnake Tele-Meister

    134
    Aug 2, 2016
    ireland
    The meter is a Mastercraft 052-0060-2. I think it might be a shop brand from Canadian tyre.

    The circuit would have originally used a 120V supply and had a 1A fuse, but I installed a .5 because of the doubled voltage. In fact, I'm not 100% certain about the 3A fuse. That was in the plug itself and may have been gone before I plugged it in. I think I tested the pin to the switch, but I may not have. Anyhow, it hasn't blown the new 3A fuse since, just two of the 500mA fuses. There are lots of pretty crazy looking AC voltages everywhere. If it matters, they all appear to be stable - that is not jumping all over the place.
    I'll get a loan of a different multimeter and see what it has to say.

    Thank you!
     

  13. Prophetsnake

    Prophetsnake Tele-Meister

    134
    Aug 2, 2016
    ireland
    Oh, and I replaced the LED pilot with a filament jewel. It doesn't light up. Could this substitution be part of the problem? And would jumping R24 get it to work, maybe?
     

  14. Bendyha

    Bendyha Tele-Afflicted Ad Free Member

    Mar 26, 2014
    Northern Germany

  15. Bendyha

    Bendyha Tele-Afflicted Ad Free Member

    Mar 26, 2014
    Northern Germany
    I wouldn't jump R24, this would be putting the diode D5 straight across the heater supply, which you don't want. I would take the light supply from the two jumpers J9 & J10. This does place it infrount of the fuse, but it is the easiest way....Or leave the wire coming from WJ 1 where it is, and move the one from WJ 12 to J 9.
     
    Last edited: Jul 16, 2017

  16. dsutton24

    dsutton24 Poster Extraordinaire Gold Supporter

    Dec 29, 2010
    Illinois
    No. it's not causing the problem. If you just pulled the LED out and put the lamp in it's place, that's why it's not lighting up. The LED had a resistor in series with it to limit the current (R24, as you suggest) to the LED, the lamp doesn't need that resistor. Look at Bendyha's drawing above. You want to remove D5, and put a jumper across R24. What you're doing is essentially wiring your new pilot lamp across the filament supply.

    I'm not familiar with that meter. It would be interesting to borrow another one and see what that tells you.
     

  17. dsutton24

    dsutton24 Poster Extraordinaire Gold Supporter

    Dec 29, 2010
    Illinois
    Your reasoning is sound, but you also have to take the inrush current of your relatively huge transformer into account when choosing a fuse. The fuse should also be a slow-blow type.

    Primarily, the fuse is there to keep you from burning down your house. Secondarily, it's there to protect the transformer should something fail in the amp, say a shorted filter cap or PA tube. If you have to go to an absurdly large fuse on the primary side of the transformer to combat nuisance blowing from inrush, you can always install another small fuse in the secondary of the high voltage winding to protect the transformer.

    You're on the right track, it's just going to take some patience to get there.
     

  18. Prophetsnake

    Prophetsnake Tele-Meister

    134
    Aug 2, 2016
    ireland
    Thank you. The light is a minor issue I'll deal with after I figure out the bigger problem.
    I can't imagine where those mad voltages are coming from, and they are there with the tubes out, so the jury is out until I get another multimeter on it.
    There are quite a few test points that are completely dead.

    TP1
    TP6
    TP9
    TP3
    TP7
    TP8
    TP4
    TP13
    TP15

    Several of those are supposed to have voltages of 180 mVAC, so perhaps my meter isn't sensitive enough. It only has settings for 750 and 200 V, but others should have quite high voltages and absolutely nothing.
     

  19. Bendyha

    Bendyha Tele-Afflicted Ad Free Member

    Mar 26, 2014
    Northern Germany
    TP1 is where you inject the input signal of 25mV AC, all the following AC test point are there to show by how much this original 25mV has been amplified by at TP2, 3, 4, 5, 6, 9 & 13 if the amp is runnuing properly, otherwise there shouldn't be any AC there at all. (but there might be a touch of hum signal)

    TP6,7 & 8 should have the DC voltage stated there, but this will only be present when the tubes are in place , and current is being drawn through them and the resistors under the Test Points.

    TP2, 7, 9 will have DC voltages, but we don't know off the schem as to what they should be. Without the tubes in place, there is no current draw, and the voltages at TP 10, 11 & 12 should all be higher than stated, and quite similar to each other. The voltage should be DC only (maybe a very small AC component of a copple of volts)

    The ones that conscern us at the moment are TP 14, 15 & 16, that should all have AC voltages, but without current draw these will be about 10 - 20% higher than the what the transformer specs are telling you are the loaded voltages.
     

  20. Prophetsnake

    Prophetsnake Tele-Meister

    134
    Aug 2, 2016
    ireland
    Thanks Bendyha,

    I do have the correct voltages at 14 and 16, ( 235 and 274) but nothing at 15 at all. It might just be me, or perhaps there is some varnish or silicon on the contacts around there (the neighbouring can cap has some of that goo that supports the cap underneath of it)
    However, B+ seems to be powered. TP12 has 390V, and TP11 382, so I am guessing that if there was nothing coming from the rectifier, there would be nothing there either.
     

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