Gallien Krueger 800rb repair - No power

[J M Fahey]

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.

[beedoola]

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.

[DrGonz78]

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.

[beedoola]

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/

[g1]

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.

[J M Fahey]

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 .

[gbono]

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

[beedoola]

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.

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.

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?

[beedoola]

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

[mozwell]

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

[DrGonz78]

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.)

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.

[DrGonz78]

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.

[beedoola]

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.

[DrGonz78]

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.

[pontiacpete]

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.