# Help me diagnose my YGM



## hollowbody (Jan 15, 2008)

My 67 YGM is starting to show signs of its age. I'm currently experiencing an intermittent "sag" in volume when playing. It's like someone turns the amp down a bit and then back up to where it was. I'm using my YGM in conjuction with a Ultimate Attenuator with the Traynor's volume at 7. The tubes are brand-spanking-new (like <30 mins on them new )

I've used the UA extensively with my JTM and I don't have the same issue, so I'm almost 100% positive that it's not the attenuator, but I'm not able to run my Traynor at 7 without an attenuator in my apartment, so I have to rely on my findings using the UA.

Hell, the amp's 43 years old and almost entirely original other than a 3-pronger, so it's to be expected, but I'm wondering more exactly what in the amp it is that would need to be replaced to fix this particular problem.


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## Rugburn (Jan 14, 2009)

Could very well be your tubes. Check them first, because if it's a bad resistor or there's high frequency oscillation you'll need a tech. Is your output tansformer heating up when your running it at 7? 

Cheers,
Shawn


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## Wild Bill (May 3, 2006)

hollowbody said:


> My 67 YGM is starting to show signs of its age. I'm currently experiencing an intermittent "sag" in volume when playing. It's like someone turns the amp down a bit and then back up to where it was. I'm using my YGM in conjuction with a Ultimate Attenuator with the Traynor's volume at 7. The tubes are brand-spanking-new (like <30 mins on them new )
> 
> I've used the UA extensively with my JTM and I don't have the same issue, so I'm almost 100% positive that it's not the attenuator, but I'm not able to run my Traynor at 7 without an attenuator in my apartment, so I have to rely on my findings using the UA.
> 
> Hell, the amp's 43 years old and almost entirely original other than a 3-pronger, so it's to be expected, but I'm wondering more exactly what in the amp it is that would need to be replaced to fix this particular problem.


One of the more likely culprits will be filter caps. They dry up over the years. Filter caps smooth out the hum in the power supply by storing up energy during rectified pulses and releasing it between the pulses. As they dry up their storage capacity becomes less and less. Before they get so bad that you start hearing a bad hum they may show other effects, like running out of steam when you're really wailing the amp. That's what causes the "brown outs". Or you may start hearing "ghost notes" under the note you're actually playing.

The bad news is that the only way to be sure is to have a cap job done. It will likely fix the problem but if it doesn't you'll have to keep looking. The good news is that an amp as old as yours needs a cap job anyway! Filters were only expected to last 10-15 years. You've been on borrowed time for decades now, like original tires on a 57 Chevy. Those filters don't owe you anything!

WB


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## hollowbody (Jan 15, 2008)

Rugburn said:


> Could very well be your tubes. Check them first, because if it's a bad resistor or there's high frequency oscillation you'll need a tech. Is your output tansformer heating up when your running it at 7?
> 
> Cheers,
> Shawn


I haven't checked the OT for heat, but the tubes in it now are new and the ones that were previously in it all tested strong (except for one el84 which was starting to go). I was hoping a new set of tubes would take care of the problem, but it hasn't



Wild Bill said:


> One of the more likely culprits will be filter caps. They dry up over the years. Filter caps smooth out the hum in the power supply by storing up energy during rectified pulses and releasing it between the pulses. As they dry up their storage capacity becomes less and less. Before they get so bad that you start hearing a bad hum they may show other effects, like running out of steam when you're really wailing the amp. That's what causes the "brown outs". Or you may start hearing "ghost notes" under the note you're actually playing.
> 
> The bad news is that the only way to be sure is to have a cap job done. It will likely fix the problem but if it doesn't you'll have to keep looking. The good news is that an amp as old as yours needs a cap job anyway! Filters were only expected to last 10-15 years. You've been on borrowed time for decades now, like original tires on a 57 Chevy. Those filters don't owe you anything!
> 
> WB


Haha, yeah, they've done their job. I'll take it in for a cap job when my next paycheque comes in.


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## stratele52 (Oct 25, 2010)

You have to check your power tubes first.
Do you check bias ( and adjust ) when you put a new set of tube ? That's a must.

How do you check the tubes that was there previously ? tube tester ? witch one ?


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