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Thread: Gallien Krueger 800rb repair - No power

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    Gallien Krueger 800rb repair - No power

    I wanted to know how to go about troubleshooting this amp. It won't power on. How can I test the power transformer to see if that is the issue?

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    Stray Cap DrGonz78's Avatar
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    A simple blown fuse will render an amp unable to power on, is it blown? Many suspects to investigate before jumping right into testing for bad power transformer. If fuse is blown then transistors or a bridge rectifiers top the list of suspects right off the bat. You got a schematic for this exact amp? Sure we can test the power transformer but first just have to ask if the fuse is intact. A bad transformer will surely take out fuses but many other things to consider first. If no fuse blown then it might a problem that deals with simple power connections or switches.

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    Lifetime Member Enzo's Avatar
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    It is the last thing on the list of possible failures, they are VERY reliable, transformers are.

    However, transformers can;t function if they get no power, so is mains voltage appearing right at the transformer primary wires? Is there continuity through the mains wiring? In other words, unplug the amp from the wall, turn its power switch ON, and measure resistance between the two main prongs of the power plug. You SHOULD see the resistance of the transformer primary, not open. Also measure for continuity through the primary winding right at the transformer wires. If there is any issue, then go individually through teh fuse holder, the power switch, etc.

    If all seems OK on the primary side, then see that proper voltages come out the secondaries, and no fuses open.

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Schematics

    Volume_1 - see page 14 for PSU. If the fuse is OK check for specified voltages on points A-G. If the fuse is blown, disconnect the PSU, replace fuse and use a lamp limiter before re-powering, then check those voltages again.

    Volume_2

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    Last edited by nickb; 10-16-2016 at 06:08 PM.
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    So I picked up the amp today. Got it for $30.

    The guy included an additional transformer with it. The one in the bad seems to be the original. There seems to be a new one in the amp.

    The fuses included are 15A 250V. Are those right.

    Upon opening the amp, the red wire from the transformer was disconnected.

    The fuse holder only has only wire going to it - coming from the power switch. The Brown wire from the transformer went to the power jack (AC cord jack). The other end of the power switch went to the other lug on the power jack. And the 3rd lug on the power jack is connected to ground.

    The rest of the wires from the transformer are wired to the main board - see last picture.





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    I tested the resistance of the Red and Brown wires on the transformer and got 7ohm.

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    Stray Cap DrGonz78's Avatar
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    Quote Originally Posted by beedoola View Post
    I tested the resistance of the Red and Brown wires on the transformer and got 7ohm.
    Well that's a positive sign there indeed. It is not open (OL) so the thermal fuse in the primary is intact too. The red primary wire not connected would appear to connect to the fuse but that is an assumption. However, 15 amp fuse is overkill and looking at the schematic it says 8 amp fuse. Have you built a light bulb limiter or have variac with ammeter? You are not going to simply plug straight into the wall to power up for the first time. Also, do some ohms tests on the "supposedly" damaged original power transformer, what is the resistance on it's primary winding?

    Edit: BTW is that fuse holder just unscrewed or is it busted loose?

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    I'll measure the other transformer.

    I haven't built a limiter but I think I have everything at home to build one so I will.

    I loosened the fuse holder to pull the transformer up to get a better look at how the AC connector was wired. The fuse holder is intact. I went and got some 7amp 250v fuses at Radioshack.

    EDIT** I tested the other transformer - the one NOT in the chassis and it read 1.1 ohms.

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    Last edited by beedoola; 10-16-2016 at 10:57 PM.

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    Senior Member mozwell's Avatar
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    If this is a replacement transformer, there is a chance the output voltages may be wrong. Who knows what was used to replace the original one.
    When you power it up, FIRST disconnect the secondaries from the amp & leave them floating. Maybe connect each one them into a separate pole of one of those 12 way screw terminal strips so you can be 100% sure they don't touch anything or short together.
    Power the amp up through a light bulb limiter & measure the AC volts of each secondary and the primary. You can then check these voltages are correct before reconnecting them to the amp.
    It would be a pity to damage something else in the amp because the transformer was replaced with the wrong type, when 10 minutes & a quick check can verify all is ok first.
    To quote Enzo, never think of a reason NOT to check something.

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    Stray Cap DrGonz78's Avatar
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    Also to mention that while you are checking the voltages of the replacement transformer that perhaps it would be wise to check original transformer too. You might get a surprise when it works just fine without a fault. Either that or just a very bright light bulb in your limiter. I bet that it is possible that someone thought just replacing the power transformer will get the amp to stop blowing fuses. If it ends up that way then what a score for $30!! Now if the old tranny is dead and the new one is not the correct one then that would be a shame. Either way you'll know soon enough.

    Edit: BTW the readings of 1.1 ohms across the primary of the old tranny made me wonder if it is still good. At least the primary thermal fuse is not blown. Also, the new toroidal looks like it has two other black primary wires is that true? Or I am seeing other wires that lead up to front of the chassis power on switch.

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    Senior Member mozwell's Avatar
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    Ive never worked on one of these, but from the pictures The green wires seem to attach to the board through a hole in the metal bracket. It is VERY important that these green wires do NOT touch the bracket, and that the 4 leads from the bridge rectifier next to the green wires do NOT touch the bracket. If one of these is shorting to the bracket, this could be the only problem with the amp

    OK
    Use a light bulb limiter for all these tests.

    Secondaries
    green - black - green, these power the 100W amp with +/-60V rails, & provide the +/-15V power. I would expect 42VAC or so between either green & black, and 84VAC between the two green wires.
    blue- black - blue, these power the 300W amp with +/-85V rails. I would expect 61VAC or so between either blue & black, and 170VAC between the two blue wires

    Also, there are some diagrams for the power supply that show different primaries for 115V and for 230V mains
    Page 20 shows wire colours for this, Brown, Red, Orange, Yellow
    For 115V connect Brown & Orange together, these go to the mains switch. Connect Red & Yellow together, these go to the IEC inlet Neutral
    For 230V connect Brown to the power switch, connect Yellow to the IEC inlet Neutral, and connect Red & Orange together (but don't connect them to anything). Insulate this connection so it cannot touch anything

    It may be that the transformer primary has not been connected correctly, so "it wont power on", and someone thought to replace it to fix it.
    Once we verify the transformer is correct, we can reconnect the secondaries to the amplifier & go from there.

    Mains fuse is 8A for 115V supply & 4A for 230V supply

    Before you reconnect the transformer secondaries, with a multimeter set to diode range, check BOTH the bridge rectifiers to see all the diodes are ok
    If you can, measure the power transistors for both amps. We are looking for shorts between C and E on the power transistors. An easy way to do this is to measure from +85V to the 300W speaker positive terminal, and from -85V to the 300W speaker positive terminal. Also measure from +60V to the 100W speaker output terminal & from -60V to the speaker output terminal. You can use diode range, you should measure open one way & 0.6V the other way.

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    Last edited by mozwell; 10-17-2016 at 08:26 AM.

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    The transformer is a Keen Ocean model TTO-17005-00.

    Do I need to remove all the secondary wires to test them?

    I saw the differences on the specs for the 115 and 220v power supplies.

    This new transformer has a brown and red input wires.

    When I wire the thing up to test it, the Red should go to one of the IEC pins and the Brown should be on the other side of the power switch - like in the diagram for the 115v wiring diagram.

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    Stray Cap DrGonz78's Avatar
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    Quote Originally Posted by beedoola View Post
    Do I need to remove all the secondary wires to test them?
    Yes you need to remove all the secondary wires to test AC voltages. You do not want any voltages entering the circuits to the amp yet. Testing the other power tranny will be done in the same fashion and use a light bulb limiter at first just in case, at least on the questionable tranny.

    Quote Originally Posted by mozwell View Post
    Ive never worked on one of these, but from the pictures The green wires seem to attach to the board through a hole in the metal bracket. It is VERY important that these green wires do NOT touch the bracket, and that the 4 leads from the bridge rectifier next to the green wires do NOT touch the bracket. If one of these is shorting to the bracket, this could be the only problem with the amp
    Yeah good eyes!! Yeah those green wires need to be installed much better than they are and definitely not touching the chassis. I did find a picture online of GK 800rb that has some sort of insulators in those holes too.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	GK800rb.jpg 
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    Old Timer J M Fahey's Avatar
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    I chimed in to answer bedoola but see he has not indicated where he lives, so I canīt.
    Sorry.

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    Dr. Gonz

    That black wire you see in that pic isn't part of the primary. Just the red and brown. That black wire is from the power switch.

    The transformer that is in her appears to be the original or the original type. The one that came with it looks older but has a different mounting/bolt pattern which isn't reflected in the chassis. Perhaps someone got one from another older 800rb thinking that it could be put in the current transformer's place.

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    Old Timer J M Fahey's Avatar
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    Being a 400W amplifier, and 120V mains voltage (thanks beedoola) , 7 ohms DC resistance for primary winding looks too high; although it might be reasonable for a 220/240V European one (thatīs why I asked where is the amp today )
    FWIW I just checked one of my own 300W Bass amplifier 220V mains power transformers and I have a 3 ohms DC primary.
    I design for low DCR for better regulation, but a standard one would be around 4 ohms, still in 220/240V, so somewhat above 1 ohm DCR at 120V should be normal.
    Can anybody measure a 120V primary transformer and post resistance (and estimated VA/power)?
    This would give us a reference about that power transformer health.
    Of course, how it behaves with a lamp bulb limiter is the definitive test.

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    Ok.

    54v AC between the Black and Blue (Black to each Blue) wires on the secondary
    109v AC between the Blue and Blue
    50v AC between Green and Black
    100V AC between Green and Green.

    The other included transformer that came with it is shorting - making the light on my limiter go off. Thanks for suggesting this BTW, guys. I've been a fool for not using one for the years I've tinkered with amps.

    Also. I'm getting continuity on these points on U1 and U2. Is that supposed to be the case? And I'm getting continuity across the three blue 1000uf caps and two of the 470uf caps as well.




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    Last edited by beedoola; 10-18-2016 at 02:22 AM.

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    Stray Cap DrGonz78's Avatar
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    Quote Originally Posted by beedoola View Post
    The other included transformer that came with it is shorting - making the light on my limiter go off.
    Got to clarify what you are saying here... "Making the light on my limiter go off" = Bright light or Dim Light?? If the light is going "Off" (Dim) then that is good. Bright bulb means something is drawing current on the tested piece of equipment.

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    Ha. I can see how that is confusing. It is making the bulb illuminate.

    The transformer in the chassis powered up and didn't cause the light to illuminate at all.

    I also tried measure the voltage on the secondary of the supposedly bad transformer and didn't seem to get a voltage.

    EDIT** I found another thread on this forum regarding an 800rb not powering and found a picture of the PS. I took the sheilding tape off the one that seemed to test bad and found the internal fuse and that it seems to be separated. Might this have cause the PS to fail?

    Here is the other thread with a picture of the poster's PS and below is a picture of my PS:

    http://music-electronics-forum.com/t41383/


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    Last edited by beedoola; 10-18-2016 at 07:28 AM.

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    Don't forget the joker g1's Avatar
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    The thermal fuse could not have made the old transformer fail. If it lights up the limiter lamp, it is definitely shot.
    Continuity is a bit of a vague term. Please provide resistance readings in ohms where you said there was continuity.

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    Old Timer J M Fahey's Avatar
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    Your posts are confusing and contradicting (like calling "off" a brightly lit bulb)
    And measuring 7 ohms resistance on a transformer with an *open* internal fuse.

    So, what will it be?

    Please:
    1)measure and post resistance of both transformer primaries
    2) retest both connected to lightbulb:
    a) does light bulb blink/stay bright/stay dull/not even blink nor show any light Pick one for each transformer
    b) what DC resistance do you measure across primaries
    c) what voltage do you read across secondaries.
    even "0" is a reading and must be postd as such; "no reading" means nothing
    d) I see the amp now has a toroid transformer, yet you show a square EI one ... which is the original one? (check mounting holes).

    Thanks .

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    Supporting Member gbono's Avatar
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    I assume you bought the one off CL missing half the original knobs?
    This one is listed for $100 but has a issue with the PA board Gallien Krueger 800RB Bass Amp

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    Quote Originally Posted by gbono View Post
    I assume you bought the one off CL missing half the original knobs?
    This one is listed for $100 but has a issue with the PA board Gallien Krueger 800RB Bass Amp
    Yeah, I got it for $30. I don't know if what the guy is said true - whether he or who he brought it from knew that was the issue. When I opened it up, the brown wire from the primary was disconnected.

    I didn't realize there are mounting holes in the chassis for both the current transformer and the one that came in the bag with it - the square type.

    So it looks like the current on in the chassis was the replacement, but I'm not even sure if they wired it correctly.

    Quote Originally Posted by J M Fahey View Post
    Your posts are confusing and contradicting (like calling "off" a brightly lit bulb)
    And measuring 7 ohms resistance on a transformer with an *open* internal fuse.

    So, what will it be?

    Please:
    1)measure and post resistance of both transformer primaries
    2) retest both connected to lightbulb:
    a) does light bulb blink/stay bright/stay dull/not even blink nor show any light Pick one for each transformer
    b) what DC resistance do you measure across primaries
    c) what voltage do you read across secondaries.
    even "0" is a reading and must be postd as such; "no reading" means nothing
    d) I see the amp now has a toroid transformer, yet you show a square EI one ... which is the original one? (check mounting holes).

    Thanks .
    See all prior posts.

    Quote Originally Posted by g1 View Post
    The thermal fuse could not have made the old transformer fail. If it lights up the limiter lamp, it is definitely shot.
    Continuity is a bit of a vague term. Please provide resistance readings in ohms where you said there was continuity.
    On my continuity test mode on my DMM I'm getting 4ohms across some of those electros.

    EDIT** I disconnected the wires from the Supply Board to the Power Amp board. I was getting continuity between Ground and the Orange and Brown wires - the 60+ and 85+ taps.

    Unsoldering this I stopped getting continuity on the Supply board in the areas I mentioned.

    I see that the large transistors on the PA board are tied to the grounding plate, so it's expected I'll get continuity in those areas, yes?

    Is it alright to disconnect the PA board and test the voltages with the transformer connected to the PS board?

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    Last edited by beedoola; 10-18-2016 at 11:27 PM.

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    Ok, so I got it running. All the screws that attach the transistors to the grounding plate were very loose. I mentioned I had continuity between ground and the Brown and Orange wires coming off the Supply board. Once I tightened those screws - and the rest of the other screws - the continuity went away.

    Thing is: I'm only getting 75v coming out of what is supposed to be 85v. I'm getting 66v out of the other taps.

    Is this an issue/going to cause an issue?

    This appears to be the transformer that is inside the amp and why it had the mounting hole on the bottom to work with this transformer:

    http://www.fullcompass.com/prod/2624...ger-350-0004-0

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    Last edited by beedoola; 10-20-2016 at 01:11 AM.

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    Senior Member mozwell's Avatar
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    If you are getting +/- 66VDC rails on the 100W amp, and +/-75V rails on the 300W power amp, the amp will work fine. You may just have slightly less power on the 300W amp output, but it wont make a huge difference in volume, so i say just run with it, especially for a $30 amp

    A few final checks, after the amp is on & warmed up for a while (no load, no input signal), measure and set the bias on each of the two power amps. This is measured across two resistors for each amp, and the Power Supply & Power Amp Test (page 6) in the test procedure tells you how to do this.
    Also, check there is no DC Volts on the speaker output on both the 100W and 300W amps

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    Stray Cap DrGonz78's Avatar
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    Quote Originally Posted by beedoola View Post
    Thing is: I'm only getting 75v coming out of what is supposed to be 85v. I'm getting 66v out of the other taps. Is this an issue/going to cause an issue?
    So I had calculated this for the rails while reading along a few days ago but I forgot to post it... 54vac * 1.414 = 76.34 VDC and 50vac * 1.414 = 70VDC, which is approximate values after rectifying AC to DC voltages. So the first rail being 75vdc is pretty close to 76vdc and 70vdc is pretty close to 66vdc. However, the rating on those caps (C5-C8) have a voltage rating of 63v. So right off the bat this is not ideal and is a bad idea. The original voltages had 60vdc which is cutting as close as you want with 63v rated caps. Obviously, to me I think the 75v is too low and 66v is too high. (Edit: Mozwell said it best as it will work but those 63v caps still have me worried.)

    Quote Originally Posted by beedoola View Post
    This appears to be the transformer that is inside the amp and why it had the mounting hole on the bottom to work with this transformer:
    I don't think they are the same transformers. That one says Gallien-Krueger 350-0004-0 and the other one you said is "Keen Ocean model TTO-17005-00." They are both toroidal types but I think the secondary voltages on the 350-0004-0 will be the right ones.

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    Stray Cap DrGonz78's Avatar
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    Looking at the schematic it says 41vdc NO LOAD. So is this a case where it has a zobel network on each output and a cap has to charge? I may have that wrong so that is why it is in the form of a question, but one that needs to be addressed. Also, I am still worried about 66vdc on rails that have 63v rated caps. So there are a few things that need to be worked out here before that amp gets a stamp of approval. Is there a way to reduce the voltage from 66v to 60 or so? I state all this to proceed with caution and wait for some feedback from some veterans on the site. I am curious how to proceed and if it was my project amp I would be asking these questions to get feedback too.

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    Quote Originally Posted by DrGonz78 View Post
    So I had calculated this for the rails while reading along a few days ago but I forgot to post it... 54vac * 1.414 = 76.34 VDC and 50vac * 1.414 = 70VDC, which is approximate values after rectifying AC to DC voltages. So the first rail being 75vdc is pretty close to 76vdc and 70vdc is pretty close to 66vdc. However, the rating on those caps (C5-C8) have a voltage rating of 63v. So right off the bat this is not ideal and is a bad idea. The original voltages had 60vdc which is cutting as close as you want with 63v rated caps. Obviously, to me I think the 75v is too low and 66v is too high. (Edit: Mozwell said it best as it will work but those 63v caps still have me worried.)



    I don't think they are the same transformers. That one says Gallien-Krueger 350-0004-0 and the other one you said is "Keen Ocean model TTO-17005-00." They are both toroidal types but I think the secondary voltages on the 350-0004-0 will be the right ones.
    Thanks for point that out about those 63v caps.

    Regarding the transformer. Are you sure the transformer on the site I linked is made by GK? Or the site is just selling it as a replacement for a GK 800rb? The "350-0004-0" - I'm not sure if that is just a reference number for the website.

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    The original transformer was CTM 24493-080-0004-0-9413 and we concentrate on the 080-0004 part of it as it is displayed on the schematic. 350-0004 seems to me to be a clue or indicator that it was specifically made with the correct specs for GK 800rb. I could be wrong but that was my take on it after finding that page a few days ago. For $160 or so dollars it does NOT seem like a good deal and is a bit higher than I would be willing to pay. However if you can sell that other transformer and get some money to throw into another one. There might be a way to drop a few volts on the +/-66v rail with a modification. Like Mozwell said the 300w part of the amp won't have as much power but it would work. Just depends on what you want to do.

    Edit: Another thought is that this transformer is the 350-0004-0 and it is the "best" suitable for replacement. I guess you could always call the guy who sold it to you and ask where he bought the replacement transformer to check.

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    Last edited by DrGonz78; 10-20-2016 at 09:36 AM.
    When the going gets weird... The weird turn pro!

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    For what it's worth, I had a GK400RB with a blown output transformer and GK sold me a kit very similar to yours but small
    Also, now I have an 800RB with what appears to be exactly the same kit(which includes bottom panel and bolt attaching the transformer) that full compass sells. Although I haven't gotten around to the repair.

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    Quote Originally Posted by pontiacpete View Post
    For what it's worth, I had a GK400RB with a blown output transformer and GK sold me a kit very similar to yours but small
    Also, now I have an 800RB with what appears to be exactly the same kit(which includes bottom panel and bolt attaching the transformer) that full compass sells. Although I haven't gotten around to the repair.
    Quite a few years ago GK switched all of their transformers to torroidal types. In fact for a few years they had no replacements for the old style transformers, so a lot of amps went unrepaired unless you could source a replacement from Hammond or Plitron. These new kits include new bottom panels for bolt mounting the new transformers.

    As for the low voltage readings, are you using a lamp limiter?

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    52 Bill - I'm not using the limiter during the voltage readings.

    I opened it up again just to check and I'm actually getting more like 68v on the 100w section. Still around 76v for the 300w section - measuring at the Power Supply board outputs to the PA board.

    Also. I measured the AC voltage of the secondaries against and they are now measuring about the same voltage - 50V going into rectifier bridge.

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    Senior Member mozwell's Avatar
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    I stand to be corrected, but here is what i would do.
    The issue is we have 66V on the 63V capacitors. This definitely needs to be corrected. We could do things to drop the DC voltage, but this would severely impact the performance of the 100W amp

    Both power amps use the same transistors, the 300W amp uses 2 parallel transistors for each rail, whereas the 100W amp uses one transistor for each rail only. So we have no problem with the voltage rating of the transistor with a high rail voltage on the 100W amp.
    The 15V power supply is fed from the 66V rails. TIP29C is rated for 100V so we have no problems here. As the rail is higher, we will dissipate a bit more power on the transistor, but as we are only up 6V this should be ok.
    This leaves us with the voltage rating of the 470uF capacitors.
    I would just change the four capacitors to 100V types, making sure you get the polarity correct when you change each one.

    Set / check bias current for both power amps, check there is no DC offset on the output of each power amp & we are done.

    Note, as we have higher than normal rail voltage on the 100W power amp, we will get more power out of it. This will heat up the single transistor on each rail more, so you need to be aware of this. We dont want to blow up the 100W when you crank the amp up.
    I would only use an 8 ohm or 16 ohm load on the 100W amp output.

    If you only have one speaker, then plug it into the 300W amp only.

    DrGonz
    41V in a rectangular box, according to the sch, means RMS voltage, refer note 4, bottom of the power amp sch page. It would be easier to write 41VAC or V~ or Vrms.....

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    Old Timer J M Fahey's Avatar
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    Short answer without the usual half page of babble, just woke up early (4 am here) to finish a rush job:

    1) put higher rated caps there, 70/80/100V ones, whatever you can find fresh and new at Mouser or some reputed supplier

    2) Iīm not happy with a +/-65V rails amp and just 2 power transistors being loaded with 8 ohms.
    For "100W into 8" outputs such rails should be around +/- 45V or thereabouts, +/-65V is murder.
    It would be fine into 16 ohms and provide rated 100 W

    I *guess* that was acceptable if used as a HF section in a biamped setup because HF would be intermittent (think a slapper Bass player) but I imagine a regular player plugging an 8 ohm full range extension cabinet there and driving it hard ..... it *will* work, no doubt, but too close to the edge of the cliff.

    On the contrary, the 300W side is fine.
    +/- 85V rails is still overkill but at least they use *three* pairs of transistors there.

    Such high voltages are fine if PT drops under load, and was probably the case with the first EI lamination ones, but toroids are stiff buggers; idle voltage should have been lowered by 5% or 10% .

    Iīd *love* to see actual measured output power at clipping using this transformer: the 300W section into 4 ohms, and the 100W one into 8 and 16 ohms.

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    Juan Manuel Fahey

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    bumping this as it died again.

    I had tightened the screws holding the power transistors casings to the chassis/heat sink and that solved the issue.

    It would for a week or so and then died.

    I checked the bridge rectifier and it tests good. Having the amp plugged into my light bulb limiter I'm getting a short.

    How do I go about testing the power transistors - the MJ15023 and MJ15022s?

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