I could use some help with a 50 year old Sona Amp. Has to be something simple.

[highlux]

Thanks for helping

[sluckey]

Actual measured voltages for all tube pins. Actual measured voltages on each power supply filter cap. It would be even better if you could add the measured voltages to the schematic you posted.

[highlux]

Thanks

[highlux]

Thanks

[Ed_Chambley]

Ok...so all the power turns to DC.   So I will be measuring volts correct?     While amp is on.   Black lead to ground.  One hand only on probe.   touch each tube pin while powered up and notate.   Correct?

Same on filter  caps?     

And never touch amp with both hands while probing live?

Am I close?

You will have AC on your heaters.  For example, a 12Ax7 pin 4,5 and 9 should measure across approx 6.3VAC.

[Willabe]

Ok...so all the power turns to DC.   So I will be measuring volts correct?     While amp is on.   Black lead to ground.  One hand only on probe.   touch each tube pin while powered up and notate.   Correct?

Same on filter  caps?     

And never touch amp with both hands while probing live?

Yes. Except like Ed said heaters will be acv.

You can also use the gator clip on the red meter lead too. With amp off clip to what you want to measure, set meter for dcv's, turn on amp, write down reading, turn of amp, repeat as needed.

[highlux]

Thanks

[sluckey]

Where do we start?

Logic says start with V1 pin 1. But your tubes are not labeled logically. Might be better to start in the upper left corner of the schematic and work your way across. Then drop down to the lower left corner and work your way across again. As I said earlier, if you can put the readings directly on the schematic that would be wonderful. Otherwise, try to make some kind of table.

[Ambugaton]

You are correct with how to get readings. You could go above and beyond and use clips to measure... power off... bleed caps... clip to the next pin... so on and so on. Be careful not to accidentally short from one to another with the probe. I have made that mistake in the past.

I had a similar problem (very low output but fully functional otherwise) with a JTM45 that I built last year... it ended up being a mistake I made on pin 6 and 7 of V2. I didn't have time to look at your schematic but just wanted to share in case it helped.

[highlux]

Thanks

[Ambugaton]

Heaters are connected to pin 4/5 and 9 on preamp tubes (V2-V5) and pin 4 and 5 on power tubes (V1, V6)

[Ed_Chambley]

Im going to print off schematic real quick and get my self ready out in the garage.  Ill check back here in a few.
With the print off....I can write down the values on the schematic as instructed.   

Ill snap a bunch of pics of the chassis and amp as well.

I am so glad I ran across you guys.
Maybe I can do a favor for you someday.  (I powder coat enclosures for a guy who makes pedals...maybe I can do something like that one day for you)

BRB

Dave

You do powder coating.  I don't believe I would have posted that.  Yeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeesssssssssssssssssssssssssssssss I could use a power coating contact.  Please PM me your contact info and BTW, I will pay for the service as needed.

[Willabe]

Im going to print off schematic real quick and get my self ready out in the garage.

Don't stand on a concrete floor.

If you slip and touch a live voltage in the amp that voltage will try to find ground through your feet/shoes to the floor. Stand on a piece of dry plywood with a piece of dry carpet or a rubber isolating mat on the ply wood.   

[Ed_Chambley]

Heaters are connected to pin 4/5 and 9 on preamp tubes (V2-V5) and pin 4 and 5 on power tubes (V1, V6)

If that is a question, you win the grand prize.

Yes, according to your schematic.

[highlux]

Thanks

[highlux]

Thanks

[Ambugaton]

Yes and they should be labeled on your tube sockets

[sluckey]

I urge you to tell the owner to take this amp to someone that is more knowledgeable.

[Paul1453]

I urge you to tell the owner to take this amp to someone that is more knowledgeable.

Oh come now Sluckey, we all had to start somewhere. 
He seems to maybe understand the dangers and wants to be safe.  Don't you remember the first time you actually fixed something, and how good that made you feel?   
Besides, He said he is a powder coater and would gladly return the favor for some of the guys.  Seems like he's already got some takers for that service.
If it is something simple I'm sure the guys will have him on it in no time.  If not, then I agree that someone more knowledgeable is needed.    

Seems odd to me that a 50 year old amp has a SS power supply instead of a voltage regulator tube.  My old Army training says to start with the power supply.  All voltages correct and no AC ripple?

[highlux]

Thanks

[highlux]

Thanks

[highlux]

Thanks

[Willabe]

Here's a link for our host Doug's tube library of information, it will help you get a lot of the basics down. 

There's a ton of great information in their. As you read let it sink in a little and if you need to read it again. Then if you have some more questions ask away. 

http://el34world.com/schematics.htm

[highlux]

Thanks

[highlux]

Thanks

[highlux]

Thanks

[Paul1453]

Looks like you already have a rubber mat on the floor.  +1 for safety.  How about a quick pic of the amp's guts.  Power problems tend to leave burnt/charred parts in their wake.  Also a quick smell test.  Do you smell anything burnt inside the amp?

[highlux]

Thanks

[Willabe]

Was tempted to spray it down with deoxit to clean it.

I don't think I'd do that. Just use air.

[Willabe]

The grill cloth is a little tattered at the bottom..but luckily they left 1/2 or better overlapped and I can cheat it down and recover it nicely.

Nice, I like that kind of grill cloth. 

[highlux]

Thanks

[highlux]

Thanks

[Paul1453]

Those are very basic troubleshooting tips, but you would be amazed at how often a quick sniff and a good inspection for burnt parts will point you in the right direction.   

[highlux]

Thanks

[highlux]

Thanks

[highlux]

Thanks

[highlux]

Thanks

[highlux]

Thanks

[Willabe]

I guess this is the filter cap?  since it has one channel...one cap?   the twist doodle seem to hold it to chassis.

Yes, that is a multi section cap can.

No on the 1 channel/1 cap.

Looks like the twist doodle holds it to the bracket and the bracket is riveted to the chassis? Sometimes their soldered in place and sometimes there's a clamp that bolts to the chassis.

    

[highlux]

Thanks

[Paul1453]

That cap can has 4 electrolytic caps in it and is your main PS filter cap.  High voltage lives here and shorting any of those cap leads to the twist locks or the chassis with a carelessly placed test probe will cause sparks and blown fuses or circuit breakers.  That second picture shows a questionable resistor.  It could just be dirty, or it may show signs of overheating.  That other fat blue cap is looking questionable to me also.

[Willabe]

Those are really good pictures.      

[highlux]

Thanks

[sluckey]

Where are the voltage readings?

[Paul1453]

That cap can looks new to me and has possibly already been replaced once.  Are you sure this is a 50 year old amp?  It looks extremely clean to me if it is.

[Ambugaton]

Have you booked it up to a light bulb limiter and powered it?

[Paul1453]

The amp smells vintage. Nothing burned. No traces of heat damage I can see so far. I have not eagle eyed it yet.

In this picture, this resistor looks burnt to me.

[Paul1453]

The amp smells vintage. Nothing burned. No traces of heat damage I can see so far. I have not eagle eyed it yet.

In this picture, this resistor looks burnt to me.

I'm thinking that burnt one is either R19 or R20.  If so that would explain the decreased output.   

[highlux]

Thanks

[Paul1453]

One step at a time.  You're not blowing fuses, right?  You say it powers up but lost most of it's output, that's the symptom, correct?  If so then you don't need a limiter at this time.  You said it's got to be something simple, and I think it is.