amp builders or diy guys ?

[seti]

The story is too long for me to type. I sent two amps for someone to rebuild NOT by a forum member. I think it was damaged in shipping also it has a 60hz ground hum. I'm not sending it to the tech that did the work because it took me a year to get one amp back. First of all I am not even a wanna be diy guy. It has only been turned on twice for a total of 5 minutes max. However, I did notice a couple strange things and took some pictures.

Comments and opinions much appreciated.

What is this? It looks bad whatever it is.

 I do not know if this is bad or not but it appears these two resistors have sort of fused or look slightly melted  together a little at the edge. Is this bad?

 

Here are some more photos the rebuild pictures are named rebuilt# and are closer to the bottom of the page. I know it is not that easy to give advice based on pics but any impressions and opinions appreciated.

http://picasaweb.google.com/iain42/WEBSTERPARTS

 

THANKS

SETi 

 

[Guest " "]

the hum issue...try a cheater plug...test with nothing conected on the amp input.

the resistors....if they are too hot to touch then there is an issue...call the person who did the work.

[seti]

the hum issue...try a cheater plug...test with nothing conected on the amp input.

the resistors....if they are too hot to touch then there is an issue...call the person who did the work.

I did try a cheater plug. I will test with nothing connected. Thanks.

[Guest " "]

"I will test with nothing connected."

I had a strange tube amp hum once...amp did not hum with nothing connected on the input....but did hum once a pre-amp was connected....the pre-amp was quiet on other amps.....I needed a cheater plug on the pre-amp for this amp....even if the pre-amp was off

[seti]

"I will test with nothing connected."

I had a strange tube amp hum once...amp did not hum with nothing connected on the input....but did hum once a pre-amp was connected....the pre-amp was quiet on other amps.....I needed a cheater plug on the pre-amp for this amp....even if the pre-amp was off

That must have been fun to troubleshoot! Wow.

The amplifier is an 65 watt per block webster electric/allen 90 organ amp. It has a volume control on the unit itself which was using to keep as many components out of the oop as possible. That resistor in the first pic looks very strange to me. I wonder what happened to it?

[mikebse2a3]

That resistor in the first pic looks very strange to me. I wonder what happened to it?

Hey seti

If your talking about the part with the blue paint on the end that is a (small capacitor most likely) and looks OK.

I haven't seen anything in your pictures so far that are obviousely bad and often that is the case when electronic parts fail.

The suggestion to just hook the amp up and proceed from there is the best advice to start trouble shooting your hum problem.

mike tn[]

[seti]

That resistor in the first pic looks very strange to me. I wonder what happened to it?

 

Hey seti

If your talking about the part with the blue paint on the end that is a (small capacitor most likely) and looks OK.

I haven't seen anything in your pictures so far that are obviousely bad and often that is the case when electronic parts fail.

 

The suggestion to just hook the amp up and proceed from there is the best advice to start trouble shooting your hum problem.

 

mie tn[]

Thanks mike tn this shows what I know I would have bet good money that was a bad resistor. I have never seen a cap like that lol 

Have rolled tubes, cdp, speakers cables. I wish there was a really good tech in town. Shipping amps gives me the willies.

[mike stehr]

"I wish there was a really good tech in town. Shipping amps gives me the willies."

Your best bet is to call or email the guy who did the work, since he is the one that is most familiar with it.

See if you can't troubleshoot the problem/problems over the phone/emails.

I'm thinking that is some sort of ceramic tubular capacitor, like mike tn mentioned. Possibly used for some sort of HF compensation, or supression. If you knew the value of that cap, you could replace it with a silver mica or polystyrene.

[Erik Mandaville]

I wouldn't touch it at all until an experienced technician goes through all aspects of that amp -- from the output stage, preamp/driver section, power supply. Some of those old organ amps, as well as 'some' hi-fi' amps weren't fused. They can be dangerous, and if you've got melting resistors, there is likely excessive current draw somewhere.

My opinion is to NOT start trouble shooting on your own, even to find the hum, which may or may not be related to ground loops.

Good luck,

Erik

[seti]

The amp was just completely gone through and rebuilt for home hi-fi use..... It took me a year to get this amp back into my hands. This experience was so frustrating that I was about to sell it all on ebay. I just found a tech in Mississippi that I will send the amp to also I just won another on ebay. My new philosophy is that I am not sending an amp any further for repairs than I am willing to drive.

I have enough respect for electronics not to go diving in underneath this puppy.

thanks

[Erik Mandaville]

Is the hum very loud -- the sort that makes you want to dive for the power switch to turn it off, or is it just a slight but bothersome background hum?

[seti]

Is the hum very loud -- the sort that makes you want to dive for the power switch to turn it off, or is it just a slight but bothersome background hum?

It is a constant steady hum. If music is playing you can still hear the music and you can tell it could sound nice. It is a generic 60hz ground hum. Just enough to make you not keep it on for long

I just received my other one off of ebay. It has that some funky looking little cap that I thought was a bad resistor.

[mikebse2a3]

The suggestion to just hook the amp up and proceed from there is the best advice to start trouble shooting your hum problem.

Hey seti

Just to be clear when I made the above suggetstion I was meaning that it is best to start very simple and make sure that the Hum is due to internal problems and not from ground loop problems from system issues.

The best way to do that is to short the input(so that no signal is seen by the input circuit and by doing this the Amp should exhibit only noise created by the amplifier) with some RCA Plugs made up to do that.

Hum problems due to actual amplifier problems are often due to bad filters in the power supply but can be caused from bad internal ground connections, badly matched output tubes(in push/pull amplifiers that require matched tubes), to even possibly a leaky(ie: bad) Audio Output Transformer among many other possibilities.

mike tn[]

[seti]

The suggestion to just hook the amp up and proceed from there is the best advice to start trouble shooting your hum problem.

Hey seti

Just to be clear when I made the above suggetstion I was meaning that it is best to start very simple and make sure that the Hum is due to internal problems and not from ground loop problems from system issues.

The best way to do that is to short the input(so that no signal is seen by the input circuit and by doing this the Amp should exhibit only noise created by the amplifier) with some RCA Plugs made up to do that.

Hum problems due to actual amplifier problems are often due to bad filters in the power supply but can be caused from bad internal ground connections, badly matched output tubes(in push/pull amplifiers that require matched tubes), to even possibly a leaky(ie: bad) Audio Output Transformer among many other possibilities. 

mike tn[]

I took it that way. 

The only option here that would make me grumpy would be the bad transformer everything else can be dealt with easily. When it was damaged in shipping the fuse plug was completely broken off and had to have another installed. I am going to ship the amplifier to the tech I found and see if they can find the problem as well as making a couple changes for me. If they get that one working I'll send the other monoblock to be rebuilt as well. I have been very anxious to hear these as they are just monsterous.

thanks

[Erik Mandaville]

As Mike said, lots of possibilities. There's a difference between 60 Hz and rectified hum, and you're sure this is 60 cycles you're hearing? I've located the speaker out jacks in you pictures, but can't seem to see the input (RCA) jack. Where was that installed, and are there any AC carrying components or leads in close proximity? If the jack is within a few inches of the house suppy input or power transformer, particularly given the high input impedance of this amp (which makes it more prone to noise pick up, there is a chance it could be part of the cause of this -- meaning it's not necessarily a ground loop.

Erik

[Erik Mandaville]

Okay, it's got 6.3 volts AC on filaments, with a grounded center tap. Wish I could look inside this thing, pictures are hard to use for diagnostics.

[seti]

Okay, it's got 6.3 volts AC on filaments, with a grounded center tap. Wish I could look inside this thing, pictures are hard to use for diagnostics.

I imagine it is very difficult to do with pics! I did the best I could without a great macro.

[seti]

As Mike said, lots of possibilities. There's a difference between 60 Hz and rectified hum, and you're sure this is 60 cycles you're hearing? I've located the speaker out jacks in you pictures, but can't seem to see the input (RCA) jack. Where was that installed, and are there any AC carrying components or leads in close proximity? If the jack is within a few inches of the house suppy input or power transformer, particularly given the high input impedance of this amp (which makes it more prone to noise pick up, there is a chance it could be part of the cause of this -- meaning it's not necessarily a ground loop.

Erik

The input is in the lower left hand corner of this pic.

Upper right in this one but this photo is before the rebuild however this section looks the same just an rca jack was added.

here is a close up but it is behind the round thingy.

What a mess I don't see how you guys do this kind of work.

THANKS FOR LOOKING

[Erik Mandaville]

Okay, those help, and good job on the pictures, btw. I have to say that one dense little area is questionable-looking (to me) because of how the leads and resistors are, well, installed. Do you see the bare piece of wire in common with the two potentiometers? That is most likely a common/shared ground connection. I want you to check something for me if you can: Do you see the potentiometer on the right hand side in the very close up picture? Now look due North (straight upward) to about 1 inch away from the body of the pot. I see what appears to be a black lead that isn't connected to anything. The end of the lead is pointing roughly to the right. Do you see that? If you can, please try to find where the other end of that wire goes -- and in particular if, just by chance, it's connected to the same connection point that the shared bare wire is connected (the furthest solder lug to the right on the potentiometers).

Erik

You also have an AC filament twisted wire pair exactly in that area, which just possibly could be part of the problem.

[Erik Mandaville]

Well, I think I have to correct myself. That wire I thought wasn't connected to anything may just be how the lead is curving around, and I'm perceiving the curved section as an unconnected wire. There is a common ground connection point, which is the center lug on the solder terminal strip, and I was wondering if the ground lead that goes to that was somehow left unconnected when it was worked on. The new filter cap above feeds that same stage of the amp, and you can see its ground lead going to that common chassis ground node.

Erik