• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Vintage Tube Amp Hissing and Popping

Hello. This is my first post to this forum.

I have a little vintage tube amp that I run with an iPod into the RCA ports, and a pair of The Smaller Advents speakers.

I listen mostly to old jazz vocals or chillhop.

Recently my system has started hissing, popping and changing volume.

The amp has been gone over in the past by an instrument tube amp repair guy. I think some parts have been replaced by him. The tubes are some kind of new old stock I believe.

I am comfortable with wiring and soldering from my automotive pursuits. But I don’t know much about analog electronics. I would be willing to try to replace a cap or resistor, but not sure which one. Or I could reflow all the joints if that is a possible cause.

The large aluminum “can” on the upper side of the amp I understand to be a multistage capacitor for the power stage. I’ve seen where people replace that. Not sure if mine is original but it looks to be.

There is another smaller aluminum can on the underside of the amp (upper right hand corner in the picture) which does not look like something made recently.

I lightly tapped all the components up top with a pencil while powered up but did not detect any unusual sounds. I've poked around on the backside while powered off to see if there were any obvious loose connections and did not find any.

I could use some guidance if anyone has any. I really love this little amp. If I cannot figure something out on my own I will send it to a repair person.

Thank you.

amp%201-L.jpg


amp%202-X2.jpg
 

pcan

Member
Paid Member
2015-12-31 4:57 pm
Put the contact cleaner also on the potentiometer marked with the red arrow, and check the solder joint marked with the green arrow. Be aware that the connections from the power cord to the power transformer primary are not compliant with current electrical safety regulations.
 

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Thank you PRR, Eli and pcan. I did spray some DeoxIT into the tube sockets from above. I did not clean the pins on the tubes, so I will try that. And I did not retension the tube sockets. The very large tube which I believe is part of the power supply? is a bit wobbly. It takes pressure to insert it into the sockets, but then it wobbles around a bit.
I'll put some DeoxIT on the balance control pot also.
Btw, this amp has no bottom cover, it never did. So I run it with the bottom open, sitting on a nightstand. Never seemed to be a problem but I have always wondered about it.
Thank you all again.
 
It appears to be an amplifier from an old Zenith console stereo.
Likely around 1959-1962 age.
By now, they all need proper restoring - resistors go out of tolerance, capacitors get leaky, etc.
Do yourself a favor, and have a qualified tech do the job, and allow you to have peace of mind.
Also have a safety fuse installed, some fresh wiring, to bring it up to current electrical code.
And have a metal bottom cover made - because that is another "no no" in electrical terms - it's a dangerous shock hazard as is.


People don't realize that if a fire in the house should happen, and stuff like this is found, it causes issues with homeowners insurance claims.



I've worked on many of those old amps, I should know.
 
The large, Octal base, tube is the rectifier. It's likely a 5Y3.

Somebody has already installed an "inline" holder for an AGC/3AG type fuse.

The power cable seems to be a replacement. Notice the white stripe, which indicates the presence of a polarized plug. That's better than nothing, but upgrading to a 3 wire, safety grounded, power cable should be done.

The large aluminum can mounted near the rectifier is an electrolytic capacitor. Those things literally dry out over time. Replacement is overdue. Another cap. issue is the orange disk. I can't tell from the photo if that part is the notorious "death cap." or "merely" wired across the AC power mains. In any event, that part needs going over by a capable technician. "Death caps." get removed and parts placed across the AC mains get replaced by specially rated items.
 
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pcan

Member
Paid Member
2015-12-31 4:57 pm
This amp seems to have been serviced previously by a guitar amp service technician. Minimal component changes, new guitar-amp friendly NOS output tubes, and no preventive capacitor or resistor replacement unless the client ask for it, because "the amp may lose the mojo". Due to components decayed and out of tolerance, I guess that this amplifier does now have a pretty unique sound signature; it may change slightly after a complete servicing to original specifications. The fault has probably a quick fix. I suspect a bad solder joint on the power supply circuit (see the green arrow on my previous post), it may also be some tube socket oxidation. But it would be useful to give consideration to the wiseoldtech suggestion. There is a fire and shock hazard. If you rather want to just fix the issue and pospone the restoration, I suggest to put the amplifier inside a sheet metal junction Box, with the box opening facing upward and no top cover, to ensure ventilation. This will at least contain fire and avoid accidental contact to 250V DC.
 
The large, Octal base, tube is the rectifier. It's likely a 5Y3.

Somebody has already installed an "inline" holder for an AGC/3AG type fuse.

The power cable seems to be a replacement. Notice the white stripe, which indicates the presence of a polarized plug. That's better than nothing, but upgrading to a 3 wire, safety grounded, power cable should be done.

The large aluminum can mounted near the rectifier is an electrolytic capacitor. Those things literally dry out over time. Replacement is overdue. Another cap. issue is the orange disk. I can't tell from the photo if that part is the notorious "death cap." or "merely" wired across the AC power mains. In any event, that part needs going over by a capable technician. "Death caps." get removed and parts placed across the AC mains get replaced by specially rated items.


That fuseholder is a CAR audio inline fuseholder, NOT rated for 120v line operated AC use - a sloppy way, and not to electrical code standards.
Additionally, the polarized cord is wired backwards - white stripe is Ground, yet it's wired on the hot side of the switch/fuse.
Whoever did that isn't educated in PROPER wiring, and so this amp is a disaster waiting to happen.
Also, some of those parts are soldered in a "flying support" arangement, and not stabilized properly on tag strips.

It's a mess.

Get it serviced by a REPUTABLE tech.
 
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OK then. Thanks to all for your replies.

I have no problem sending my little amp out for service. I have limited time to try to sort this out on my own as we are about to start building a house.

Perhaps this is a good place to ask:

Can anyone recommend a good tech who would be willing to take a look at my amp? I've tried searching online and almost all of what I find is guitar amp techs.
Wiseoldtech, despite your handle, I don't want to just 'assume' you are in the business of restoring amps for folks.

Any suggestions appreciated.
 
I took a few more pics just for fun.

To wiseoldtech and Eli, yes there is an inline fuse added by the last tech. And yes, it is an automotive type fuse holder. And for pcan, yes, he was a guitar tech :)

For Eli here is a pic of the suspected "death cap":

death%20cap-L.jpg


And here is the octal base rectifier (?)

rectifier-L.jpg


For pcan here is the solder joint you pointed out with your green arrow. It's not loose per se, but looks less than ideal:

power%20lead%20solder%20joint-XL.jpg


Here is a pic of what I now know to be an electrolytic cap (just from a little reading this morning). I assume it's old and therefore suspect:

electrolytic-L.jpg


Thanks again all...
 

pcan

Member
Paid Member
2015-12-31 4:57 pm
I've already seen more than once the misuse of a car inline fuseholder inside a tube amplifier. Due to the unfortunate recent widespread use, a self-taught service technician that does not have the required technical background and knowledge may not even recognize the danger. I attach a picture of what I've found inside a popular tube amplifier that is sold online in Europer by a well known German brand name. The CE mark is stamped on the bottom plate of the product, the instruction manual and the box, but there is no CE declaration of conformity inside the product manual. The black inline fuse holders are on the connection between the printed circuit board and the output transformer primary center taps (400V). The fuseholder (a safety component) does not bear any mark, not even the manufacturer name. This exact shape and material is commonly used on car fuseholders, rated 50V DC by the manufacturer. It does seems to be yet another case of component substitution due to a cheap manufacturing process and insufficient quality control, and one of the motivations why some reputable technicians are reluctanto to service to this kind of products and people are forced to bring them to less reputable service shops.
 

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The inline fuse holder currently installed is unsafe, but an inline fuse holder can be satisfactory. Look here.

The 5U4GB rectifier can provide up to 250 mA. of B+. That's more than the signal tubes present require. Assuming that's the correct tube, the chassis was also powering something like a tuner.

A "death cap." is connected to the chassis. Please look closely.
 
The 5U4GB rectifier can provide up to 250 mA. of B+. That's more than the signal tubes present require. Assuming that's the correct tube, the chassis was also powering something like a tuner.
Since this amp presumably came from a console, that would seem plausible.

A "death cap." is connected to the chassis. Please look closely.
It seems to be straddling the hot and neutral leads on the incoming power lead.
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
Eli Duttman said:
parts placed across the AC mains get replaced by specially rated items
It seems to be straddling the hot and neutral leads on the incoming power lead.
These are designed to behave in a specific and predictable way when they fail. They should also be placed correctly with respect to the position of the fuse.
 
OK then. Thanks to all for your replies.

I have no problem sending my little amp out for service. I have limited time to try to sort this out on my own as we are about to start building a house.

Perhaps this is a good place to ask:

Can anyone recommend a good tech who would be willing to take a look at my amp? I've tried searching online and almost all of what I find is guitar amp techs.
Wiseoldtech, despite your handle, I don't want to just 'assume' you are in the business of restoring amps for folks.

Any suggestions appreciated.


I've been in the service business for over 45 years now.
Ran several repair shops, along with doing consumer audio/video sales.... AND from 1977-1983 did side work as a "disco DJ" until my mom died in 1984, when I was 31.


I'm currently semi-retired now, and had more than my share of fixing people's broken stuff, including restoration of vintage consumer audio and doing custom work.

I know guys like me are few and far between, and even fewer can do the work properly.