# '72 Traynor YGM-2 problem



## Edwardamp (Feb 14, 2015)

Good day gentlemen,

My name is Ed, new to this forum but not new to amps. I have taken to performing some amp repairs and a customer of mine turned me on to this forum. I have read some of the Traynor threads and found the information very useful so I have a new problem that some may be able to help with. Here is the diagram I am working from:

http://www.edwardamp.com/1972 Traynor YGM-2 modified.pdf

Many of the preamp section components have been changed to focus the tome for the customer (no desire to keep it stock). However, the problem is in the output... I was expecting around 15 to 20 Watts but am getting less than 6 W. The output tubes themselves are pulling about 25 and 21 mA which is not a match but certainly not in "cold" territory. At this point I am suspecting something may be amiss with the output tranny but I would be very happy to hear some ideas from some more experienced techs out there.

Many thanks.
Ed


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## greco (Jul 15, 2007)

I tried to rotate your .pdf and post it in a pic (or a link) ...didn't work. Sorry.

However, if anyone viewing it wants to rotate it, this can be done by right clicking on the image and rotating it twice.

Welcome to the forum.

Cheers

Dave


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## jb welder (Sep 14, 2010)

Are you getting good drive at the power tube grids?


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## Church-Audio (Sep 27, 2014)

Edwardamp said:


> Good day gentlemen,
> 
> My name is Ed, new to this forum but not new to amps. I have taken to performing some amp repairs and a customer of mine turned me on to this forum. I have read some of the Traynor threads and found the information very useful so I have a new problem that some may be able to help with. Here is the diagram I am working from:
> 
> ...


What's the plate voltage? Based on what your telling me it should be around 350 volts. If it is you have an issue in the preamp section or output transformer.these Hammond transformers should be about 6-8k with an 8 ohm load measured with an impedance meter.


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## jb welder (Sep 14, 2010)

jb welder said:


> Are you getting good drive at the power tube grids?


Never mind, I see you marked it on the schematic. But do you have a scope? It could be a very distorted signal at low amplitude and measure high RMS. But probably not that high anyway (24VRMS). Check that there are no shorts at the speaker jack, speaker cable, or speaker itself. Other than that, you may just have to try swapping in another OT, any small push-pull OT would probably be fine for test purposes, doesn't necessarily have to be for 6BQ5's.


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## Edwardamp (Feb 14, 2015)

Gentlemen, thanks for the suggestions. The problem was the OT -- I wired in another one and power is good. I learn something new every day and perhaps the best clue was the fact that the output tube plates were not swinging the full supply B+. Also, the fact that one tube was pulling about 4mA less given that they were an exact match was another indicator (they now draw 25mA each).

Regards,
Ed


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## Church-Audio (Sep 27, 2014)

That's why one of the first things I check with an amp is the opt measuring the impedance with a proper load eliminates any guess work. And saves hours of trouble shooting. I have a bk precision 879b and this one the DE-5000 I got in ebay that's actually more accurate than my $400 bk precision. Anyone that is into fixing amps should get one if these meters. They are very accurate and extremely useful. For measuring caps output transformers ect.


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## nonreverb (Sep 19, 2006)

I don't know about that....I've never had to resort to my LC meter to decide whether an output transformer is toast. A resistance check across the primaries to center tap gives you an accurate reading as to what's wrong plus the type of failure is usually pretty telling. Experience is your biggest asset.



Church-Audio said:


> That's why one of the first things I check with an amp is the opt measuring the impedance with a proper load eliminates any guess work. And saves hours of trouble shooting. I have a bk precision 879b and this one the DE-5000 I got in ebay that's actually more accurate than my $400 bk precision. Anyone that is into fixing amps should get one if these meters. They are very accurate and extremely useful. For measuring caps output transformers ect.


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## Church-Audio (Sep 27, 2014)

Ac resistance shows you if the transformer passes a signal and if the spec of the transformer is way off, you know right there you for sure have an issue with the transformer. Expireance has nothing to do with wanting to see if the output transformer is even remotely close to spec. Gets the amp fixed faster so you can move on to the next one. I guess different techs do things differently  also when you change the load on the opt you can see the primary stays pretty constant. Dc ohms does not show you that. Dc ohms does not show transfer function between the secondary and primary. Lots if reasons to use an lcr meter boy by the sounds of it you should sell me that nice Sencore you have sounds like I might get a lot more use out of it  I use everything at my disposal to fix an amp And I have all kinds of experience but for me I need to fix it fast and correctly cease there are always 20 lots more amps waiting for my attention.


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## jb welder (Sep 14, 2010)

I just got one of those DE-5000's too! I got it for the cap functions as my regular meter capacitance function doesn't check ESR. Very nice to have. I don't measure inductance much, but when you need it, you have it . Best if you have a good number to compare to, so keeping a log book of proper inductances for different brands and models is helpful.
But the worst thing about transformers is a shorted turn. Nothing I know of will find that aside from a simple neon bulb tester like RG Keen describes: http://www.geofex.com/FX_images/xform_test.gif


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## greco (Jul 15, 2007)

jb welder said:


> But the worst thing about transformers is a shorted turn. Nothing I know of will find that aside from a simple neon bulb tester like RG Keen describes: http://www.geofex.com/FX_images/xform_test.gif


Cool device....very simple and must be very useful if it is the only way of determining a shorted turn.

Cheers

Dave


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## nonreverb (Sep 19, 2006)

Not quite sure what you mean by a transformer is close to spec....it either does what it's supposed to or it doesn't. If the primary winding has a shorted winding, you'll know it. If one half the resistance is more than 15% off it's probably bad or a really shitty transformer. Transfer is a function of the windings. if the windings are bad they'll show themselves in ways that don't require any LC meters etc. 




Church-Audio said:


> Ac resistance shows you if the transformer passes a signal and if the spec of the transformer is way off, you know right there you for sure have an issue with the transformer. Expireance has nothing to do with wanting to see if the output transformer is even remotely close to spec. Gets the amp fixed faster so you can move on to the next one. I guess different techs do things differently  also when you change the load on the opt you can see the primary stays pretty constant. Dc ohms does not show you that. Dc ohms does not show transfer function between the secondary and primary. Lots if reasons to use an lcr meter boy by the sounds of it you should sell me that nice Sencore you have sounds like I might get a lot more use out of it  I use everything at my disposal to fix an amp And I have all kinds of experience but for me I need to fix it fast and correctly cease there are always 20 lots more amps waiting for my attention.


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## jb welder (Sep 14, 2010)

In most cases, a fried winding will be very obvious, and a resistance reading will find it. But a single shorted turn may only affect only a tiny percentage of the DC resistance, and the resistance check will not find it. Yet it can make the transformer overheat, or not work at all. The neon tester will find a shorted turn.
And with intermittent issues, you can have insulation breakdowns that only occur with high voltage. A resistance check will not find these either but the bulb tester will. Just as some caps will test ok resistance wise but breakdown under voltage. It's pretty rare, but I've seen OT's that only break down intermittently when putting out high power, yet measure fine resistance wise.







Ideally, the easiest way to test is just to sub in a known good one (same as with caps or tubes) :smile-new:.


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## nonreverb (Sep 19, 2006)

I understand your point and accept that it's one way of dealing with a troublesome transformer. An intermittent winding though, may not be detectable with a neon bulb if the threshold isn't high enough. I've had some where it's a combination of high voltage and current that cause the failure. The neon test simply wouldn't find it. Those are the ones you earn your living on as they're hard to detect if the conditions aren't met. Sometimes, I have to do a few tests to make sure I've found the problem. Fortunately, most output transformer issues are pretty obvious and due to the heavy workload they endure, they fail in ways that are obvious to those who are familiar with them. PS I have a few OT transformers lying around for that very purpose











jb welder said:


> In most cases, a fried winding will be very obvious, and a resistance reading will find it. But a single shorted turn may only affect only a tiny percentage of the DC resistance, and the resistance check will not find it. Yet it can make the transformer overheat, or not work at all. The neon tester will find a shorted turn.
> And with intermittent issues, you can have insulation breakdowns that only occur with high voltage. A resistance check will not find these either but the bulb tester will. Just as some caps will test ok resistance wise but breakdown under voltage. It's pretty rare, but I've seen OT's that only break down intermittently when putting out high power, yet measure fine resistance wise.
> View attachment 12222
> 
> Ideally, the easiest way to test is just to sub in a known good one (same as with caps or tubes) :smile-new:.


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## jb welder (Sep 14, 2010)

nonreverb said:


> I've had some where it's a combination of high voltage and current that cause the failure. The neon test simply wouldn't find it. Those are the ones you earn your living on as they're hard to detect if the conditions aren't met. Sometimes, I have to do a few tests to make sure I've found the problem.


For sure! An intermittent that needs heat (current) and high voltage will probably not be detected by the neon or any other piece of test gear. Probably the worst case scenario for a transformer, and can be a nightmare to find. If you can get it to act up in the first place, substitution is the only sure way to deal with it, but then you can't be sure if the fault is truly gone or just intermittent again :confusion:. Those ones you really want to burn in a long time to make sure they're really fixed!


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## Church-Audio (Sep 27, 2014)

Well most output transformers have an impedance spec. If it's an 8 k impedance and that's with an 8 ohm load you should see in most cases close to 8 k if you see 6k that indicates a problem. Shorted winding or not, this test tells you all you need to know. Has worked for me. If the amps not putting out and one side of the primary is much lower than the other it's a good indication. We all have our own way of doing things. I have had to replace very few output transformers. And if you have the meter why not use it?? You already have a load connected. If your like me you check voltages bias input ect with out power tubes until your sure all the voltages are at least in the ball park. Anyway to each his or her own. Many ways to skin a cat. I also look at frequency response of all the amps I test and I have saved files for comparison. Makes looking at an amp and seeing how sick it really is go very quickly. But for me the ultimate test is plugging a guitar in and playing it. Technology is great but the people that own these things make music with them not play with oscilloscopes  I guess that's why I could never understand how some techs that don't play could fix an amp properly imo they can't.


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## nonreverb (Sep 19, 2006)

I've had to replace dozens of them over the years and 90% of the time it's pretty obvious. Remember, the output transformer, like the power tubes and speaker, are the hardest working components in the amp. When they go, they usually go big. That being said, there are the odd instances where you get an intermittent transformer as discussed above that you really have to work on. These are the ones the test equipment don't pick up. As you state, to each his own. Personally I don't use my LC meter to diagnose bad output transformers as I've never needed to. It does come in handy though when I have a choke transformer with an unknown value. :smile-new:




Church-Audio said:


> Well most output transformers have an impedance spec. If it's an 8 k impedance and that's with an 8 ohm load you should see in most cases close to 8 k if you see 6k that indicates a problem. Shorted winding or not, this test tells you all you need to know. Has worked for me. If the amps not putting out and one side of the primary is much lower than the other it's a good indication. We all have our own way of doing things. I have had to replace very few output transformers. And if you have the meter why not use it?? You already have a load connected. If your like me you check voltages bias input ect with out power tubes until your sure all the voltages are at least in the ball park. Anyway to each his or her own. Many ways to skin a cat. I also look at frequency response of all the amps I test and I have saved files for comparison. Makes looking at an amp and seeing how sick it really is go very quickly. But for me the ultimate test is plugging a guitar in and playing it. Technology is great but the people that own these things make music with them not play with oscilloscopes  I guess that's why I could never understand how some techs that don't play could fix an amp properly imo they can't.


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