Low hum in a tube echoplex EP2, please help

[Revbrodiddley]

Hi everyone.
I have an EP2 that sounds amazing. I actually have two EP2's and one EP3 and this one is by far the best sounding of the three. However, there is a low hum that increases when the volume of the echo is increased that makes the echo pretty much unusable for recording purposes and almost unusable for live use. Are there any things I can do to track the problem down and fix it? All the echoplex repair guys I know of cost a freaking fortune. I am a very novice tech sort of person but am very willing to be patient and learn how to fix this!

the unit currently has the original two prong plug. I was thinking about putting in a 3 prong as it could just be a grounding issue? I can post videos on youtube if that'll help anyone diagnose. Thanks in advance for any help!!

-Bro

[52 Bill]

Welcome to the place. Which model EP-2, with or without SOS?

Adding a three wire ac cord will not hurt anything, but I doubt that it will cure your problem. In fact I would suggest not changing it until you have the hum sorted out.

If the hum only happens when you turn up the echo volume, then the problem lies in the playback circuitry. It could be a bad tube, a bad head, a bad ground connection or any number of simple components.

Have you tried testing or replacing the tubes? The specific tube that you need to check is V1, a 6EU7 twin triode. If you don't have a new tube, you could just swap the 2 6EU7s and see if the problem changes.

Do you have a multimeter? Do you understand that there are voltages inside this unit that can do you physical harm?

[soundguruman]

Generally, it's not a 3 prong plug that will cure it.
Changing the power supply capacitors and or making the preamp filaments DC, is usually enough.
But you could just have a bad tube too.
But old equipment had a lower standard for noise. Hum was considered acceptable, back then.

[Revbrodiddley]

ep2 echoplex

I do indeed understand the danger of the charged caps. I've worked on amps with varying success in the past. Never been shocked, always touched a rubber handled screwdriver to the end of a cap and then brought the remaining metal part of the screw driver down to ground to 'unload' the charge. i imagine the same principle works here?
My buddy who worked on it a month ago (also not an expert but knows more than I) said he compared the guts of mine to a picture of someone elses and said it looked like mine had several extra capacitors, so his best guess is that.

I'm about to post some pics I just took. Yes, its an SOS version.

thanks for getting back so quickly!

Welcome to the place. Which model EP-2, with or without SOS?

Adding a three wire ac cord will not hurt anything, but I doubt that it will cure your problem. In fact I would suggest not changing it until you have the hum sorted out.

If the hum only happens when you turn up the echo volume, then the problem lies in the playback circuitry. It could be a bad tube, a bad head, a bad ground connection or any number of simple components.

Have you tried testing or replacing the tubes? The specific tube that you need to check is V1, a 6EU7 twin triode. If you don't have a new tube, you could just swap the 2 6EU7s and see if the problem changes.

Do you have a multimeter? Do you understand that there are voltages inside this unit that can do you physical harm?

[Revbrodiddley]

[Revbrodiddley]

[Revbrodiddley]

[Revbrodiddley]

I guess I'm going to order some tubes for it. They're all sylvania. Are there 'better' tubes for an ep2 while I'm at it?

[Revbrodiddley]

Yeah, if it were a little hum, thats no big deal. But this is like maybe between 5 and 7 db quieter than any INTENTIONAL sound coming through it. Its cool you're going for a VERY noisy '40s or '50s kinda recording but man I just know it could be so much better. My other ep2 is noisy, but not nearly THIS noisy. Thank you for your suggestions, I will stock up on caps also.

Generally, it's not a 3 prong plug that will cure it.
Changing the power supply capacitors and or making the preamp filaments DC, is usually enough.
But you could just have a bad tube too.
But old equipment had a lower standard for noise. Hum was considered acceptable, back then.

[52 Bill]

Yeah, if it were a little hum, thats no big deal. But this is like maybe between 5 and 7 db quieter than any INTENTIONAL sound coming through it. Its cool you're going for a VERY noisy '40s or '50s kinda recording but man I just know it could be so much better. My other ep2 is noisy, but not nearly THIS noisy. Thank you for your suggestions, I will stock up on caps also.

From the photos I can't quite tell everything that has been replaced, but there has been a lot work done on this unit. I would assume that the added filter caps are there to replace the existing multicap can. In doing this the last person to work on this may have caused the hum problem by creating a ground loop.

Please, whatever you do, don't just start throwing parts at this, it's a waste of time and money.

[Revbrodiddley]

ok. thank you for the warning! how should I proceed? I can put more detailed pics up?

[52 Bill]

Start by getting a copy of the schematic for your unit and then try and figure out what has been done to it.

If the old can cap has been replaced it should have been unhooked from the circuit. Do the new grey caps connect to the same places as the original can cap did? If they do, then the fact that they have each been grounded at different spots could be the cause of your hum.

If you have a second EP-2, how do the two chassis' compare to one another?

[Revbrodiddley]

yeah, as you figured...its obvious the one i'm having problems with has been modified...looks like a LOT! Here's the other one that was refurbed by the guy at Orbit electronics: ,

[Revbrodiddley]

[Revbrodiddley]

and here's the one I'm wanting to figure out.