new power supply caps, now motorboats

[jstich]

Hello, I just replaced 4 of the electrlytic caps in the power supply. Now on some bassy notes I get a buzz motorboat sound similar to touching the plug that goes in the guitar. When it comes, I can sometimes turn the vol. pot up or down to get rid of it. It has a tube rectifier and a 6eu7 pre, and two el 84's I thought I replaced all the electrolytics, but could that be the prob?Also, it isn't as loud as it seems it should be. Would old power amp tubes cause the buzzing? Thanks for any help!

[52 Bill]

First question, did it make this noise before you changed the filters? If not then first double check your work for bad solder joints, loose wires etc. Sometimes moving something around can cause other things to come loose.

Second question, How loud should it be? The volume of any amp can be different based on the design of the circuit, etc. What kind of amp is it?

[jstich]

thanks.

Thanks for the help! It just sounded weak with no bass. It's an old record player amp by Magnavox with rca inputs. And now that I think of it , maybe that's why it sounds so good. Maybe the circuit isn't designed to be too loud. Thanks again.

[52 Bill]

Loss of bass response sound more like bad coupling caps. Leaky coupling caps can also cause any number of distortions and hums. I'd check them if I were you.

A lot of phono amps were designed to operate with a ceramic phono cartridge. These things used to put out a few volts of output. When used with guitar pickups or magnetic phono cartridges as well, they can be really weak sounding, as the magnetic pickups have far less output available to drive the input of the amp. You may need to add a pre-amp stage to get full output from the power amp.

Also check to see if the amp has a built in RIAA tone compensation circuit, as this will effect the tone when used as a guitar amp.

[jstich]

sorry

Sorry, I should have pointed out that I always use a Zoom, etc. processor to feed into the input, so I think I'm providing enough signal. (?) Also, it seems like I need to replace the coupling caps. Any clues about them? Are they disk caps, electrolytics?

[52 Bill]

Coupling caps can be discs or tubulars but rarely electrolytics in a tube amp. That is more common in solid state amps. They are found in the signal path at either the input grid circuit or in the plate to grid circuit.

Do you have the schematic for this amp?

[jstich]

no schematic, but.......

Hello again. I don't have the schematic, but I noticed only one of the el 84's has a tiny orange light coming through the middlle of the sockets when viewing from the bottom of the sockets.That means I have a bad power amp tube, right? Thank you.....

[Enzo]

I believe you are looking up the hole in the socket and seeing the bottom end of the heater in the tube. No I don't think it is bad for that reason. It might be bad, but that is not why.

Take a screwdriver, and hold the blade, now with the amp running, whack the end of the chassis of this little thing with the screwdriver handle. If you have a small rubber mallet, use that. Does the amp make any noise when you hit it? If so, it means a loose connection.

perhaps you might inspect the solder you did on all these caps. Make sure it is well done and also that ther are not solder bridges where they do not belong.

Does your zoom put out line level signal or was it meant to plug into the front of a guitar amp? The voltage from a ceramic cartridge is a WHOLE lot larger than from a guitar.

[jstich]

tapped chassis...

Hi ,I tapped the chassis with a screwdriver and got a buzz/pop similar to a microphonic tube.The volume of the noise /buzz is the same regardless of the amp vol knob setting. Thanks......