# I really wan to do it on my own (Traynor YBA-1a repair)



## PulienJier (Dec 5, 2014)

Ok... I just got my amp back from the tech. This is how it went:
Tech: "I changed everything you told me to change (Output tubes + rebias), your amp sounds good, but your caps are about to die and I think that's what caused your problem"
Me: "Does it works?"
"Yes it does, but the problem will probably come back really soon."
"Ok, I'll take it as it is and I'll come back when the caps are going to die"

And guess what... a couple hours later, the same problem happened. I called him back and he told me "I told you!"

So now, after a little conversation, he told me that I had to change my power supply capacitors (this is what I remember I heard) which I think are the filter caps!? The big brown things that look like a cigar.
And while I am in there, is there anything that might need to be replaced? 
And if you could point me toward some good components.

Here is the gut of the beast!








I know I should go to a tech, but I really want to learn! 
I know how to discharge an amp, I am solid with a soldering iron and I am a DIY aficionado! 
I just need to learn what to change and it will be done in a matter of minutes.

While we are on the subject, what is this thing?


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## WCGill (Mar 27, 2009)

What was the original problem? Was the amp buzzing and noisy? That would be filter caps. Hard to tell but I'd guess that's a bias pot that someone installed.


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## dtsaudio (Apr 15, 2009)

If you really want to DIY. A couple of things first. 1) Safety is everything. Double check that it is unplugged and drained off. If you're not sure ask, or read. 2) Invest in a reasonably good meter. You don't need to spend a lot. Under $50.00 at Home Depot will get you an adequate meter. Learn how to use it. 3) A decent soldering iron will make things easier.
Ok, now to the caps. The 3 brown tubular things are the main filter caps. The Tubestore should have something pretty close. Don't go much higher on capacitance, but higher voltage rating is fine (probably better). While you're at it, the 5 blue tubular things are also capacitors. While not necessarily bad, they are old and can dry out. Replace them as well.
That thing you don't know is a trim pot. Probably to set the output tube bias.


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## PulienJier (Dec 5, 2014)

Thanks! 
I already have a good meter and a decent soldering iron. 
I know how to drain an amplifier (watched on Youtube and tried with success).
I know the thing is a trim pot, but I don't know its use. Bias would be logical.
Thanks for the concern and the feedback.

The problem is that it just stopped making sound. All of a sudden.
The few seconds before that, it seemed like I had a "gate". I was playing and the sound was cutting straight as soon as my notes were under a certain level.
And it's not the cab nor any cable for they have all been tested on other amplifiers and they all worked just fine!


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## jb welder (Sep 14, 2010)

Did you ask the tech to repair a specific symptom, or did you ask him to replace some parts?
It doesn't sound like he did any troubleshooting.
Filter caps should not cause the kind of problems you are having. It could be something as simple as dirty pots or tube sockets, or something more serious, but doesn't really sound like a filter cap type symptom.


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## dtsaudio (Apr 15, 2009)

I agree with JB. There are a few things I can think of that would cause that problem. As mentioned above, dirty pots, jacks, tube sockets. Loss of high voltage is another. That would most likely mean a bad connection or open resistor. A bad coupling cap can also cause this type of failure. 
One thing I saw recently, was a bad standby switch. Amp would turn on sometimes, but not always. Turned out to be a switch with bad contacts.
Bad filter caps usually result in hum or buzzing. Sometimes quite loud.

When the amp fails, can you here anything at all through the speaker. Is there any hiss, or very mild hum.


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## PulienJier (Dec 5, 2014)

When I gave the amp to the tech, it decided to work and it worked just fine for two weeks until it failed again yesterday. So he changed what had to be changed (my output tubes which were going really bad after 4 years of abuse).

To answer your questions, the amp is dead quiet when it fails, not the slightest hum nor hiss. And when it works, it does not make unusual sounds so the caps are probably still working well.


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## jb welder (Sep 14, 2010)

When it cuts out, do all the heaters remain lit (one in each power tube and 2 in each preamp tube) ?
Also check the standby switch, as it could cause the problem like Dan mentioned. When it cuts out, check the voltage from the standby switch to ground. Check both sides of the switch.


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## PulienJier (Dec 5, 2014)

I just bring my amp to my apartment and, in fact, there is a slight hum. Very light, just like if it was stuck in Standby.
I'll check the voltage as soon as I get my multimeter back from my father (tomorrow).
Thanks a LOOOOOOOOOT for you help guys!


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## PulienJier (Dec 5, 2014)

And all the heaters are lit


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## PulienJier (Dec 5, 2014)

The standby switch measures -300v, the caps all seems to work properly, the tube sockets all seems to be conducting properly. All the pots are in perfect working orders. I didn't look for the coupling caps since I don't know where they are. 
At least this is not my only amp. I will take my small 15watt amplifier to my gig tomorrow.


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## dtsaudio (Apr 15, 2009)

When you flip the standby switch to operate. Does that voltage drop to zero (referenced to ground). If it does not. Then that's your problem.


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## PulienJier (Dec 5, 2014)

Yes it does.


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## dtsaudio (Apr 15, 2009)

Does this look like your amps schematic?


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## jb welder (Sep 14, 2010)

The voltage checks at the standby switch need to be done when the sound cuts out. When it cuts out, if you see any voltages at the switch, then the switch is bad.


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## dtsaudio (Apr 15, 2009)

Good point JB. 
Also just because there is voltage at the tube sockets doesn't mean the tube is working. The actual voltage is important to determine if that's where the trouble lies.


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## PulienJier (Dec 5, 2014)

Nope, this does not look like my amp schematic (even tho I can barely see since it is blurry).
Here it is http://www.toomanyhelicopters.com/schems/700912_YBA1_A_Mk2__rev13.gif
The amp stopped producing sound before I started this thread.

I don't think it is the standby switch since it goes to zero when I engage it (still no sound from the amp).

The voltage in V4 and V5 is over 500v for pins 3 and 4 and -50v for pin 5


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## jb welder (Sep 14, 2010)

How about voltages for pins 1,3,6, & 8 of V1, V2, & V3


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## PulienJier (Dec 5, 2014)

Problem solved!!!!!!
A friend of mine who happens to be a Hi Fi amplifier guru wanted to help me solve the problem. 
And it was only a resistor that someone added between pin 8 and 1 on v4 that literally roasted.
We changed it and voila! Alive again!

And then he went on adding a circuit that I don't understand which DRASTICALLY reduced the noise floor so that my amp now is SUPER silent.
Here is a picture of the thing.








And we also changed some of those old dried caps, which tightned the low end A LOT and, as soon as we receive the order from Mouser, we will proceed with the replacement of ALL the old caps (he didn't have the right values on him to do it right now).

I am now in the pocession of an amplifier I love even MORE than I used to!
And I found out that the previous tech lied to me. 
Anyway, problem solved, I learned a lot and I am super happy!


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## dtsaudio (Apr 15, 2009)

There shouldn't be a resistor between pin 1 and 8 on v4 OR v5. They should be tied together and going to ground.
Have your buddy draw out that little circuit of his. From the looks of it, it's not doing anything, but the picture make it too difficult to tell where the connections are going.


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## PulienJier (Dec 5, 2014)

Here is a picture of his schematic


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## jb welder (Sep 14, 2010)

Sounds like the burnt resistor was probably a current sense resistor for checking bias, more likely would have been between pins 1&8 and their ground connection (1&8 should be tied together).
The circuit he added is to reference the heater center tap to a DC voltage rather than ground. This often helps hum issues.
Don't be too hard on the previous tech, you did end up changing some caps anyway. :smile-new:
It's even remotely possible one of the new tubes has a fault that burnt the resistor.
In the attached photo, I've circled in blue some scraps that need to be removed.


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## PulienJier (Dec 5, 2014)

The little scraps have been removed, but thanks for the attention =P!

All this schematic reading and soldering made me want to build an amplifier on my own...
Maybe one day.

The resistor was roasted because of my previous output tubes. I remember opening my amp and thinking it was a weird looking resistor, but I was scared I would die if I put my hands in there! 
Learning process.
I now know a bit about troubleshooting and how to test components!


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## dtsaudio (Apr 15, 2009)

It was hard to tell from the photo, but now I see the schematic it's clear. That little circuit is used quite often in tube phono preamplifiers to reduce hum. It lifts the reference from ground to about 50V (depends on resistors) of the B+ supply. If you measure the filament voltage to ground each pin of the filament will have a DC voltage on it, but separated by 6.3VAC. Works much better with DC filaments, but does keep noise from floating around the ground circuit.


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