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Loud 60 cycle Hum from tube amp.
Loud 60 cycle Hum from tube amp.
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Old 14th June 2008, 09:14 PM   #1
Brenden is offline Brenden  United States
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Default Loud 60 cycle Hum from tube amp.

My first post here, a lot of the threads here go right over my head, but I enjoy reading them anyways .

So anyways, I've recently gotten a whole bunch of old electronic... junk. But hidden away in this junk was a really neat old "RCA Victor" record player. After some fiddling I got it to start turning and make some noise. The problem is that it's a very loud 60 cycle hum coming out of the speaker. The speaker is directly hooked up to an old tube amp that has one 35W4 tube and a 50L6GT (both RCA). I'm fairly certain the problem isn't coming from them, as I only see the heater heating up and not the plates. This is making me think it's a capacitor, because dead capacitors are a sure sign of a hum like that, right? The three capacitors are labeled as such:

1) RED 80 MFD 150WV, GREEN 20 MFD 150WV, Black Common

2).082 MFD 600VDC "Outside Foil"

3).047 MFD 600WVDC "Oil Capacitor"

The first one is to me the likely culprit as it is the largest, made out of paper and feels like it is slightly bulging at the top. But the first also confuses me the most as I haven't seen a capacitor that's rated at two different values and has three leads. The other two just generally confuse me, as they are coated/encased in some kind of waxy/sticky material.

So my questions are:
Do I need to find exact replicas of these capacitors or could I replace them with electrolytics or something else? And if so, what would you recommend?
The labeling of these capacitors is all over the place, I get that VDC is a DC cap, but what's the difference between that and WVDC or WV?

Pretty sure I need to replace a potentiometer also, but I've got tons of those...
Thanks for the help, let me know if I can clarify anything else, I could even take pictures if needed.
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Old 14th June 2008, 09:37 PM   #2
DigitalJunkie is offline DigitalJunkie  United States
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The first big capacitor,is actually 2 caps in the same case,with the negative/'common' terminal tied to the negative side of each cap (it's shared) The other two terminals are the (+) of each cap. Red=80uf + and Green =20uf +

80uf and 20uf.. 100uf and 22uf are probably the closest values you'll find easily,and shouldn't cause any problems. Also,probably easier to find in values of 200V or 250V.

The other two caps are probably coupling caps,or some sort of bypass/tone control setup.
Some plain old Sprague "Orange Drops" should work nicely,and only cost a couple dollars. (or any other similar 630V rated caps.No need to get all $Fancy$!)


Edit:

WVDC = Working Volts,Direct Current
VDC= Volts,Direct Current

They're basically the same thing. Just the caps's voltage rating.
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Old 14th June 2008, 09:37 PM   #3
Miles Prower is offline Miles Prower  United States
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Default Re: Loud 60 cycle Hum from tube amp.

Quote:
Originally posted by Brenden
So anyways, I've recently gotten a whole bunch of old electronic... junk. But hidden away in this junk was a really neat old "RCA Victor" record player. After some fiddling I got it to start turning and make some noise. The problem is that it's a very loud 60 cycle hum coming out of the speaker. The speaker is directly hooked up to an old tube amp that has one 35W4 tube and a 50L6GT (both RCA). I'm fairly certain the problem isn't coming from them, as I only see the heater heating up and not the plates.
In the first place, I'd be real careful with that. In those days, these cheap record players used power supplies connected directly to the AC mains. That is extremely dangerous, and could easily lead to: That goes in spades since you've already said you aren't real familiar with hollow state. They weren't kidding when they called those things "suicide boxes". It is questionable whether that sucker is salvageable. According to the spec sheet for the 50L6, the THD= 10%. That's running pure, single-ended pentode mode which means lots of pentode nastiness. Neither did they include the necesary RIAA equalization, or any sort of NFB. That will sound like:
An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.


Quote:
1) RED 80 MFD 150WV, GREEN 20 MFD 150WV, Black Common

2).082 MFD 600VDC "Outside Foil"

3).047 MFD 600WVDC "Oil Capacitor"

The first one is to me the likely culprit as it is the largest, made out of paper and feels like it is slightly bulging at the top. But the first also confuses me the most as I haven't seen a capacitor that's rated at two different values and has three leads. The other two just generally confuse me, as they are coated/encased in some kind of waxy/sticky material.
Back in those days, it was common to bundle several electrolytic capacitors of differennt ratings/voltages in one can. What you have there is an electrolytic that's on its way out since it's bulging. It could poof at any time, and you're lucky it didn't when you powered that puppy up. The others are typical foil-and-waxpaper capacitors. They don't last forever either.

Quote:
So my questions are:
Do I need to find exact replicas of these capacitors or could I replace them with electrolytics or something else? And if so, what would you recommend?
The labeling of these capacitors is all over the place, I get that VDC is a DC cap, but what's the difference between that and WVDC or WV?

Pretty sure I need to replace a potentiometer also, but I've got tons of those...
Thanks for the help, let me know if I can clarify anything else, I could even take pictures if needed.
I really wouldn't bother. You can add new components, and an isolation xfmr would be priority number one. By the time you go to all that expense and bother, you still won't have anything you'd like to listen to. These cheap record players are what Mom and Dad bought Junior so's he'd keep his paws off the good stereo. They also had the reputation for quickly ruining vinyl.
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Old 14th June 2008, 10:24 PM   #4
nigelwright7557 is offline nigelwright7557  United Kingdom
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Default Re: Loud 60 cycle Hum from tube amp.

Quote:
Originally posted by Brenden
My first post here, a lot of the threads here go right over my head, but I enjoy reading them anyways .

So anyways, I've recently gotten a whole bunch of old electronic... junk. But hidden away in this junk was a really neat old "RCA Victor" record player. After some fiddling I got it to start turning and make some noise. The problem is that it's a very loud 60 cycle hum coming out of the speaker. The speaker is directly hooked up to an old tube amp that has one 35W4 tube and a 50L6GT (both RCA). I'm fairly certain the problem isn't coming from them, as I only see the heater heating up and not the plates. This is making me think it's a capacitor, because dead capacitors are a sure sign of a hum like that, right? The three capacitors are labeled as such:

1) RED 80 MFD 150WV, GREEN 20 MFD 150WV, Black Common

2).082 MFD 600VDC "Outside Foil"

3).047 MFD 600WVDC "Oil Capacitor"

The first one is to me the likely culprit as it is the largest, made out of paper and feels like it is slightly bulging at the top. But the first also confuses me the most as I haven't seen a capacitor that's rated at two different values and has three leads. The other two just generally confuse me, as they are coated/encased in some kind of waxy/sticky material.

So my questions are:
Do I need to find exact replicas of these capacitors or could I replace them with electrolytics or something else? And if so, what would you recommend?
The labeling of these capacitors is all over the place, I get that VDC is a DC cap, but what's the difference between that and WVDC or WV?

Pretty sure I need to replace a potentiometer also, but I've got tons of those...
Thanks for the help, let me know if I can clarify anything else, I could even take pictures if needed.

If its worth fixing I would replace all the caps with modern equivalents. The dual caps might be a problem if space is at a premium.

As others have said be very careful as voltages on these valve amps can kill even after they are switched off !!!!!!

I always discharge the caps with an INSULATED crocodile lead and a low value resistor just to be sure.

If in doubt get an expert to fix it......
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Old 15th June 2008, 01:52 AM   #5
Brenden is offline Brenden  United States
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Join Date: Jun 2008
Default Re: Re: Loud 60 cycle Hum from tube amp.

Quote:
Originally posted by Miles Prower


In the first place, I'd be real careful with that. In those days, these cheap record players used power supplies connected directly to the AC mains. That is extremely dangerous, and could easily lead to: That goes in spades since you've already said you aren't real familiar with hollow state. They weren't kidding when they called those things "suicide boxes". It is questionable whether that sucker is salvageable. According to the spec sheet for the 50L6, the THD= 10%. That's running pure, single-ended pentode mode which means lots of pentode nastiness. Neither did they include the necesary RIAA equalization, or any sort of NFB. That will sound like:
An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.




Back in those days, it was common to bundle several electrolytic capacitors of differennt ratings/voltages in one can. What you have there is an electrolytic that's on its way out since it's bulging. It could poof at any time, and you're lucky it didn't when you powered that puppy up. The others are typical foil-and-waxpaper capacitors. They don't last forever either.



I really wouldn't bother. You can add new components, and an isolation xfmr would be priority number one. By the time you go to all that expense and bother, you still won't have anything you'd like to listen to. These cheap record players are what Mom and Dad bought Junior so's he'd keep his paws off the good stereo. They also had the reputation for quickly ruining vinyl.
Alright then...
Good thing I asked first
Sounds like that's the plan then, dump it and get on with other stuff.
Thank you kindly gentlemen.
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Old 15th June 2008, 04:17 PM   #6
mashaffer is offline mashaffer  United States
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Join Date: Jun 2004
Location: Indiana
I hope you don't mean literally dump it. For completeness I would check the model number and make sure it is not a collectable (probably not but check). Also if it plays 78s it might not be totally worthless. If nothing else part it out before (as out British friends say) binning it.

Even if you are not into tubes yourself you may be able to trade some parts like the output transformer for things you do need. Waste not want not as they say.

What else did you get in your "junk" pile? You never know what treasures might lurk in a pile of junk.

mike
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Old 15th June 2008, 08:23 PM   #7
Brenden is offline Brenden  United States
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Join Date: Jun 2008
It wasn't all junk, I finally got my hands on a signal generator (an old RCA WA-44C) that works, a dictaphone time-master of all things, more transformers than I can shake a stick at (including two old 15kv neon sign ones that I really have no plans to use), quite a few big silvery capacitors that I have yet to sort through and another record player that's missing it's box but has 4 speed settings (78, 43, 33, 16) and a lot of tubes, some of which I think are pretty fried.
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Old 15th June 2008, 09:52 PM   #8
mashaffer is offline mashaffer  United States
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Location: Indiana
Well if you ever find a use for those 15kV trannies I have a couple of 6BK4 high voltage shunt regulators (good for about 25kV regulated supply ) that I could trade for some nice iron or horizontal sweep tubes or the like.

Sounds like you have fodder for a few fun evenings of discovery. Best wishes.

mike
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Old 15th June 2008, 11:04 PM   #9
Brenden is offline Brenden  United States
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Alright, I figure since my first question is answered I should be able to hijack my own thread, right?

So I sorted through the tubes and picked out the icky looking ones and here's what I have left:

RCA 5651A:1
National 6AU6A:1
GE 12B4A:2
RCA 12AU7A/ECC82: 1 National:2
Amperex ECC88:1
RCA 6U8A/6KD8: 3
GE 6C4:1
RCA 6AQ5A:1
RCA 35W4:1
RCA 6AkS:1
National Union 55L6GT/C:1
6AL5:1
Westinghouse 6CB6:2
GE 6AU6:1 Motorola:3
GE 6DJ8:1
6BC5:1
Motorola 544GB:1
RCA 6X5GT:1
12SN7GTA:2
12SN7GT:1
Raytheon 6SL7GT:1
RCA 6186:1
GE 6J6:2
Westinghouse 6AV6:1
Raytheon 6AH6-V:1
RCA 12AU7A:2
Westinghouse 12AX7:1

Are any of these sellable? Any of them usefull?
And after googling around for a while I've had trouble finding info about these transformers on the internet other than "model #XXXXXXX transformer" in some nook in the interwebs. Are there any websites that I could find usefull for identifying them? And what could you possibly need a 2100V .74uf Cap for?
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Old 16th June 2008, 04:10 AM   #10
Richard Ellis is offline Richard Ellis  Argentina
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Default Hum..

Try dropping one of these in place of your single multisection cap....less then $15....see what you get...not dead on spec but will probably get it working.
Those old caps dry out rather consistantly.
_________________________________________Rick..... .
50uF + 50 uF @ 500VDC
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