120Hz hum in a 50R

20 Studio, 50+, 50PA, 50R, L100, B100, L120, L120PA, L120R, 120 SLAVE, B120, B150, L150, L200, B200, Concord, and SMF

Re: 120Hz hum in a 50R

Postby tracynorton on Fri Mar 15, 2013 6:31 pm

Papa Dog wrote:Comparing that schematic to the 50+ and the reverb circuit on the SoundCitySite shows that there should be 2x 470k resistors between both preamp channels to the reverb circuit input. You schematic shows taps of 470k off the plates of the three EQ triodes. I think that someone has "modded" that amp to run the reverb post EQ instead of pre EQ as it was designed.
I still think that there is an issue with the bridge rectifier, but I could be worng.
Hope that helps some.

The reverb section is factory stock...untouched by a soldering iron....even the red checks marking on the aged solder joints are still there....original Piher resistors still in place. The ONLY mod this amp ever had was a recap.
tracynorton
Knight
 
Posts: 1356
Joined: Sat Nov 29, 2003 8:01 am
Location: Peenemunde CA

Re: 120Hz hum in a 50R

Postby Papa Dog on Fri Mar 15, 2013 6:41 pm

Tracy,

Up until today I have taking pot-shots at what you were desribing, based on what data was provided.
I think that most of what I have suggest COULD have caused the issue that you described, but obviously didn't.
Could be that the way that the 'verb tank is connected post EQ might have some effect on current draw, although I still do not understand why it is @120 hz and not 60. I will keep doing what I can from over here to try and figure out what might be causing this issue, but the best that I can do is suggest POSSIBLE issues.
The data which you have provided today will definitely give me something to think about during the odd idle moment, and if i can anything or think of anything else to try (short of buying and installing a new OT.
WOW! already thinking of some things, but I need to get out the schem which you sent and do a bit more comparison. I MIGHT actually have that figured out, but won't bother you with needless guesses unless and until I am confident of what I think
There Ain't No Such Thing As A Free Lunch.

"The time has come," the Walrus said,
"To talk of many things:
Of shoes--and ships--and sealing-wax--
Of cabbages--and kings--"
Papa Dog
Knight
 
Posts: 1337
Joined: Mon Mar 15, 2010 6:48 pm
Location: Narly Ampwerks

Re: 120Hz hum in a 50R

Postby tracynorton on Fri Mar 15, 2013 6:57 pm

Papa Dog wrote:Could be that the way that the 'verb tank is connected post EQ might have some effect on current draw

Reread my post...all the preamp power supply (incl reverb circuits) was disconnected...ripple still there
Papa Dog wrote:...although I still do not understand why it is @120 hz and not 60

because it is a full wave bridge rectifier
tracynorton
Knight
 
Posts: 1356
Joined: Sat Nov 29, 2003 8:01 am
Location: Peenemunde CA

Re: 120Hz hum in a 50R

Postby Papa Dog on Fri Mar 15, 2013 7:21 pm

tracynorton wrote:
Papa Dog wrote:Could be that the way that the 'verb tank is connected post EQ might have some effect on current draw

Reread my post...all the preamp power supply (incl reverb circuits) was disconnected...ripple still there
Papa Dog wrote:...although I still do not understand why it is @120 hz and not 60

because it is a full wave bridge rectifier


While I did know that it is a bridge rectifier, I was not aware that as such the CPS would be doubled. That is some good information.
And please do excuse my missing that you had dis-connected the pre-amp and reverb circuits from the amp, or rather that you had no re-connected them.
I just re-read you post, and am sorry that I assumed that you had re-connected when you founf that to not be the cause of the issue. Good additional information that is.

I also noticed that I had missed a response from you about the reverb tank and the manner in which it is joined to the amp. I believe that you are correct, if the resistors are original and the red die marks are still present, that it came from the factory that way. This is some valuable material for fure reference, and "corrects" so errors in other schematics. Thank you very much for documenting you work so carefully. Believe me, all the info that can be gathered now will surely save someone down the road a world of headaches.

You are a good man, Tracy Norton.
There Ain't No Such Thing As A Free Lunch.

"The time has come," the Walrus said,
"To talk of many things:
Of shoes--and ships--and sealing-wax--
Of cabbages--and kings--"
Papa Dog
Knight
 
Posts: 1337
Joined: Mon Mar 15, 2010 6:48 pm
Location: Narly Ampwerks

Re: 120Hz hum in a 50R

Postby Unit_1 on Fri Mar 15, 2013 8:12 pm

you know mercury magnetics offers a 100% money back no questions asked refund as long at the leads are not clipped

you could always pick one up, try it and if it still hums, return it.

you'd still be out the freight, but that's all...
Image
The ability to play/make music is a gift that not everyone gets. Those of us who have it should use it.

Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
Unit_1
Prince
 
Posts: 3713
Joined: Mon Oct 03, 2011 3:29 pm
Location: Kali4ñia (a small planet orbiting the west coast of the United States)

Re: 120Hz hum in a 50R

Postby Papa Dog on Sat Mar 16, 2013 1:07 am

Unit_1 wrote:you know mercury magnetics offers a 100% money back no questions asked refund as long at the leads are not clipped

you could always pick one up, try it and if it still hums, return it.

you'd still be out the freight, but that's all...


I am not and cannot speak for Mr Norton or anyone else, but that doesn't sit well with me. It just does not seem to be quite honest. But, I have different standards than most people, and I could not do what you are suggesting.
Aside from all that, the more I look at the schematics the more convinced I am that it cannot be the OT causing the problem. Thtat might be a deficiancy in my understanding of how tube amps work, but I am leaning more and more back to the bridge rectifier as the source of all evils. No matter how a diode tests, there can still be issues with them under load, and the output of a bridge should be very close to ripple free, even before all the filtering caps. I think that one of the diodes is installed backwards.
There Ain't No Such Thing As A Free Lunch.

"The time has come," the Walrus said,
"To talk of many things:
Of shoes--and ships--and sealing-wax--
Of cabbages--and kings--"
Papa Dog
Knight
 
Posts: 1337
Joined: Mon Mar 15, 2010 6:48 pm
Location: Narly Ampwerks

Re: 120Hz hum in a 50R

Postby tracynorton on Sat Mar 16, 2013 1:41 am

Papa Dog wrote:
Unit_1 wrote:you know mercury magnetics offers a 100% money back no questions asked refund as long at the leads are not clipped

you could always pick one up, try it and if it still hums, return it.

you'd still be out the freight, but that's all...


I am not and cannot speak for Mr Norton or anyone else, but that doesn't sit well with me. It just does not seem to be quite honest.

I'd do that but I have no respect for MM
Papa Dog wrote:I am leaning more and more back to the bridge rectifier as the source of all evils. No matter how a diode tests, there can still be issues with them under load, and the output of a bridge should be very close to ripple free, even before all the filtering caps. I think that one of the diodes is installed backwards.

brand new UF4007s...trust me, if one was backwards, there'd be more problems than just ripple
tracynorton
Knight
 
Posts: 1356
Joined: Sat Nov 29, 2003 8:01 am
Location: Peenemunde CA

Re: 120Hz hum in a 50R

Postby Unit_1 on Sat Mar 16, 2013 3:55 am

Papa Dog wrote:
Unit_1 wrote:you know mercury magnetics offers a 100% money back no questions asked refund as long at the leads are not clipped

you could always pick one up, try it and if it still hums, return it.

you'd still be out the freight, but that's all...


I am not and cannot speak for Mr Norton or anyone else, but that doesn't sit well with me. It just does not seem to be quite honest. But, I have different standards than most people, and I could not do what you are suggesting.


why? they're not loosing any money... they'll turn around and sell it to the next guy for list price...

and if it is the problem then they get the sale, that's the whole reason they *offer* this according to paul.

for what it's worth i've built 5 dr504's with mm iron and they all just blow your socks off!

the iron was copied from one of the first five dr504's ever built, and if i'm not mistaken it was rewound for victor owner of this site. i'm pretty sure paul from mm told me that.

of course i have very realistic dreams, so it could have been that too! :mrgreen:
Image
The ability to play/make music is a gift that not everyone gets. Those of us who have it should use it.

Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
Unit_1
Prince
 
Posts: 3713
Joined: Mon Oct 03, 2011 3:29 pm
Location: Kali4ñia (a small planet orbiting the west coast of the United States)

Re: 120Hz hum in a 50R

Postby tracynorton on Sat Mar 16, 2013 4:08 am

I built a SC 50W version of the L100 w/ Heyboer iron...it blew my socks off....
Anyway, If I can't determine anything by Mon, maybe Paul will loan me one if I promise to let him do the rewind (which is what the customer wants if that's the case)....
tracynorton
Knight
 
Posts: 1356
Joined: Sat Nov 29, 2003 8:01 am
Location: Peenemunde CA

Re: 120Hz hum in a 50R

Postby Papa Dog on Sat Mar 16, 2013 4:15 am

tracynorton wrote:
Papa Dog wrote:I am leaning more and more back to the bridge rectifier as the source of all evils. No matter how a diode tests, there can still be issues with them under load, and the output of a bridge should be very close to ripple free, even before all the filtering caps. I think that one of the diodes is installed backwards.

brand new UF4007s...trust me, if one was backwards, there'd be more problems than just ripple


Ok....so maybe not backwards. I like the 1n4007s myself. All I can say at this point is that if you can get the specs on that transformer, and if each side has the proper resistance you will know that it is not shorted internally. Otherwise I do not understand what could be wrong with an OT that would not manifest other, more serious problems. That only leaves on thing, which when put under load is giving you "ripple". and diodes are way cheaper than OTs, no matter who you buy them from. Really, how much trouble would it be to just re-do the bridge rectifier, make sure that all the connections are connecting and passing current, and see what happens? It can't hurt none, except for a bit of pride, and that is scarce reason to NOT do something.

OTOH, it is on your bench, so do what you think is best. Let us know how it is going and if there are any other things which I might help you mull over.
There Ain't No Such Thing As A Free Lunch.

"The time has come," the Walrus said,
"To talk of many things:
Of shoes--and ships--and sealing-wax--
Of cabbages--and kings--"
Papa Dog
Knight
 
Posts: 1337
Joined: Mon Mar 15, 2010 6:48 pm
Location: Narly Ampwerks

Re: 120Hz hum in a 50R

Postby Unit_1 on Sat Mar 16, 2013 4:20 am

tracynorton wrote:I built a SC 50W version of the L100 w/ Heyboer iron...it blew my socks off....
Anyway, If I can't determine anything by Mon, maybe Paul will loan me one if I promise to let him do the rewind (which is what the customer wants if that's the case)....


actually patrick now. paul is no longer with mm.... not sure if it was his idea or management and i haven't had the heart to ask him via linkedin....

if you send them the OT they can test it for you. but he'll probably tell you that anyway!
Image
The ability to play/make music is a gift that not everyone gets. Those of us who have it should use it.

Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
Unit_1
Prince
 
Posts: 3713
Joined: Mon Oct 03, 2011 3:29 pm
Location: Kali4ñia (a small planet orbiting the west coast of the United States)

Re: 120Hz hum in a 50R

Postby Unit_1 on Sat Mar 16, 2013 4:25 am

Papa Dog wrote:
tracynorton wrote:
Papa Dog wrote:I am leaning more and more back to the bridge rectifier as the source of all evils. No matter how a diode tests, there can still be issues with them under load, and the output of a bridge should be very close to ripple free, even before all the filtering caps. I think that one of the diodes is installed backwards.

brand new UF4007s...trust me, if one was backwards, there'd be more problems than just ripple


Ok....so maybe not backwards. I like the 1n4007s myself. All I can say at this point is that if you can get the specs on that transformer, and if each side has the proper resistance you will know that it is not shorted internally. Otherwise I do not understand what could be wrong with an OT that would not manifest other, more serious problems. That only leaves on thing, which when put under load is giving you "ripple". and diodes are way cheaper than OTs, no matter who you buy them from. Really, how much trouble would it be to just re-do the bridge rectifier, make sure that all the connections are connecting and passing current, and see what happens? It can't hurt none, except for a bit of pride, and that is scarce reason to NOT do something.

OTOH, it is on your bench, so do what you think is best. Let us know how it is going and if there are any other things which I might help you mull over.


or you could just pay a couple of bucks for a full wave rectifier, temporarily bypass that part of the circuit and see if that works. if not, then just de-bypass to keep as original as possible.
Image
The ability to play/make music is a gift that not everyone gets. Those of us who have it should use it.

Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
Unit_1
Prince
 
Posts: 3713
Joined: Mon Oct 03, 2011 3:29 pm
Location: Kali4ñia (a small planet orbiting the west coast of the United States)

Re: 120Hz hum in a 50R

Postby Papa Dog on Sat Mar 16, 2013 4:29 am

Unit_1 wrote:why? they're not loosing any money... they'll turn around and sell it to the next guy for list price...
and if it is the problem then they get the sale, that's the whole reason they *offer* this according to paul.
for what it's worth i've built 5 dr504's with mm iron and they all just blow your socks off!
the iron was copied from one of the first five dr504's ever built, and if i'm not mistaken it was rewound for victor owner of this site. i'm pretty sure paul from mm told me that.
of course i have very realistic dreams, so it could have been that too! :mrgreen:


I have had some interesting conversations with Paul. Seems like a nice enough guy, and it is Mercury who will be supplying the iron for a series of amps I shall be doing in the next couple years or so. Yes, they like to take burned out vintage iron and "reverse engineer" them, so that they are as close as possible to the originals. I might have dreamed it, but IIRC I was told that they are the only official builder of Partridge iron in the USofA now. They have the name and put the stickers on new product, so they must have the right to do it, or someone in England would be having a fit. They are not a FBN company doing counterfits.
Glad I am to know about this policy, though, as I shall be sure to specify that I do not want anything that has been shipped out "on approval" unless I can get it for a "used" price.
There Ain't No Such Thing As A Free Lunch.

"The time has come," the Walrus said,
"To talk of many things:
Of shoes--and ships--and sealing-wax--
Of cabbages--and kings--"
Papa Dog
Knight
 
Posts: 1337
Joined: Mon Mar 15, 2010 6:48 pm
Location: Narly Ampwerks

Re: 120Hz hum in a 50R

Postby Papa Dog on Sat Mar 16, 2013 4:41 am

Unit_1 wrote:or you could just pay a couple of bucks for a full wave rectifier, temporarily bypass that part of the circuit and see if that works. if not, then just de-bypass to keep as original as possible.


Except that it should be a bridge rectifier, not a full wave. There IS a difference in that "full wave" uses two diodes and a bridge uses 4. The idea of a bridge being that it should leave a barely noticeable ripple, whereas a full wave has to have good filtering to smooth out the bumps. One of the kewl things about the Sound City circuitry is that it uses the bridge rectifier and still lays on a lot of filtering, and in most cases a choke, so it SHOULD have one of the quietest power supplies on the planet. But we all know that some models are notorious for hum and hiss. Could be the cheap diodes they used, or that sometimes diodes will degrade over time and let things pass that should not. Or it could be the cheap wiring, or electrolytic caps that people sometimes miss. Interesting thing to me is that the design was ahead of its time, but the bean counters in the front office tried to save money and specified lowest cost parts for lots of things. Good thing that they used arguably the best iron available at the time, which makes a rebuild well worth the money. IMHO YMMV etc etc ad nauseum, et al
There Ain't No Such Thing As A Free Lunch.

"The time has come," the Walrus said,
"To talk of many things:
Of shoes--and ships--and sealing-wax--
Of cabbages--and kings--"
Papa Dog
Knight
 
Posts: 1337
Joined: Mon Mar 15, 2010 6:48 pm
Location: Narly Ampwerks

Re: 120Hz hum in a 50R

Postby Unit_1 on Sat Mar 16, 2013 4:42 pm

Papa Dog wrote:
I have had some interesting conversations with Paul. Seems like a nice enough guy, and it is Mercury who will be supplying the iron for a series of amps I shall be doing in the next couple years or so. Yes, they like to take burned out vintage iron and "reverse engineer" them, so that they are as close as possible to the originals. I might have dreamed it, but IIRC I was told that they are the only official builder of Partridge iron in the USofA now. They have the name and put the stickers on new product, so they must have the right to do it, or someone in England would be having a fit. They are not a FBN company doing counterfits.
Glad I am to know about this policy, though, as I shall be sure to specify that I do not want anything that has been shipped out "on approval" unless I can get it for a "used" price.


they didn't have these when i was building the dr504's. it would have been much preferable to have the partridge name, even if it was the same iron.... drats.... foiled again! :lol:
Image
The ability to play/make music is a gift that not everyone gets. Those of us who have it should use it.

Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
Unit_1
Prince
 
Posts: 3713
Joined: Mon Oct 03, 2011 3:29 pm
Location: Kali4ñia (a small planet orbiting the west coast of the United States)

PreviousNext

Return to Sound City

Who is online

Users browsing this forum: No registered users and 2 guests