trying to chase and kill hum in tube echo and reverb

[imo]

I have both a standalone tube echoplex and a brown tolex fender reverb that i am trying to fully resurrect. I have replaced the power supply caps in the echoplex and in the reverb. I have tried different tubes in both as well.
They both are too buzzy to use.
-I am wondering if anybody has any tips on how to troubleshoot and localize buzz(60 cycle hum). I have a sig generator and a scope, and have done some poking around, but don't honestly know where to start and a logical procedure for getting everything as clean as it can be
Thanks
Ian

[Tom Phillips]

Ian
First off you say "...buzz(60 cycle hum)" buzz and hum are two different things. 60 cycle hum is a low frequency clean type of sound. To me "buzz" is like the sound you get when you touch the open end of a guitar cord with the other end plugged into the amp.

Let's stat by localizing the source of the problem.
1) Does it do it with just the amp turned on with nothing plugged into it?
2) Does the buzz start only when the guitar plugged into the amp? (Echoplex not hooked up)
3) Does the buzz / hum (which is it) only show up when the Echoplex is connected to the amp.

There is more to try but these are the first steps.

Regards,
Tom

[imo]

Tom,
Thanks for the quick response. The amp is reasonably quiet by itself. It is as well reasonably quiet with a guitar plugged in. there is a marked increase in 60 cycle hum with the echoplex plugged into the amp input, whether the guitar is plugged in or not.
I have completely rebuilt the echoplex in terms of electrolytic caps. It was really buzzy and i was hoping to sove the problem by doing this. There was a slight improvement but it is still pretty unusable currently
Ian

[Tom Phillips]

It's possible that you have a ground loop issue. Especially if the equipemnt has been upgraded to grounded (three wire) power cords. Is that the case?
Tom

PS: I'm just on my way out so will be unavailable for a while.

[imo]

Tom,
I did upgrade to a 3 prong cord. I am thinking it is some type of ground loop.
I am hoping to solve to problem, but also in doing this understand a bit more about locating ground buzz methodically. I have a number of old amps and i have been really trying to understand this part of servicing. I am getting pretty familiar with the general structures of most fender/marshall/vox amps, but when it comes to ground noises it seems like i'm completely in the dark
Ian

[Tom Phillips]

If you have grounded power cords on both the Echoplex and the amp then you can break the ground loop in several ways.
For a quick test to verify the problem is caused by a ground loop use a three prong to 2 prong adapter (cheater plug) on the amp or the Echoplex and see if the hum is reduced or eliminated. Then we can work on a permanent solution.

Disclaimer: This is just my idea presented for entertainment purposes only. You are responsible for your own safety and you should not proceed if you do not feel that you can do this without causing harm to yourself or others.

Practical comment: My generation grew up using ungrounded equipment. I didn't get electrocuted. None of my friends got electrocuted.

[imo]

i have actually tried the groudlift for that reason, and the change is negligable unfortunately.
What about some type of star ground system? I was wanting to keep things as original as possible, but of course am willing to change things to make them work better
Ian

[Tom Phillips]

i have actually tried the groudlift for that reason, and the change is negligable unfortunately.
What about some type of star ground system? I was wanting to keep things as original as possible, but of course am willing to change things to make them work better
Ian

It shouldn't be necessary to re-wire the Echoplex.

One thought. Did you try reversing the Echoplex power plug when the ground was lifted. Any improvement?

If the ground look is not causing the problem then you need to consider that there is a problem in the Echoplex that is causing the excess hum. Bad or misplaced ground etc. It's troubleshooting time.
Does the Echoplex hum just as bad when plugged into another amp?
What test equipment do you have? I'd be measuring the ripple on the power supply lines, pulling one tube at a time to see when the hum stops, scoping the output to see the hum etc. And obvious stuff like verifying a known good signal cord being used between the Echoplex and the amp.

Note: The ground loop hum is annoying but usually not real loud.

[imo]

Tom,
I don't have any groundlifts that have reversible plugs, so i'm not able to switch there.
I have a scope and a sig generator.
What is the best way to scope for ripple? could i use an AC meter or would i be better off with the scope?
I don't know how to post a schematic, but it is the EP2 tube echoplex schematic. I could email it if that worked
Thanks for the help
Ian

[Tom Phillips]

Tom,
I don't have any groundlifts that have reversible plugs, so i'm not able to switch there.
I have a scope and a sig generator.
What is the best way to scope for ripple? could i use an AC meter or would i be better off with the scope?
I don't know how to post a schematic, but it is the EP2 tube echoplex schematic. I could email it if that worked
Thanks for the help
Ian

Ian,
I have the schematic.
The easiest first thing to to is to measure the ripple on your B+ supply line.
Just use your multimeter. Measure the AC voltage and the DC voltage at each of the 4 power supply notes at the can cap. % ripple is AC volts divided by the DC reading X100 to convert to %. I think it should be fairly low (Less than 1%)at C18A and quickly fall to a small fraction of a% as you progress to C18B, C & D.

Another question: What's the history of the EP-2? Has it always hummed since you have owned it?

Tom

[imo]

I will try to get into it tonight. I have a recording session currently.
Yup, the plex has always hummed. I got it really cheap and figured i would refurbish it as i got time/money.
They sound so great, even as a recording send, so i am trying to get it to a more usable space

[Tom Phillips]

Also check the routing of the AC line input inside the chassis.
It should go "up and around" the chassis then down to the PT. If it gois routed down near the 6EU7 tubes they will pick up radiated 60 cycle hum.
Tom

[Enzo]

Do ANY of the controls on the Echoplex have ANY effect on this hum?

[imo]

I measured voltages: 308dc, 197dc, 169, 140
% ripple was .35%, .009%, and .00001 and on.

The powersupply does come in close to the actual tube, but its on the other side of the chassis. I could reroute it to the other side, though it is built coming in there.

Enzo, there is additional noise as i turn up the echo level. I would like to attack that as well, but i am trying to rid the unit of any groundbuzz first. That buzz is there plugged into any amp without anything going into the echoplex and with the echovolume all the way down

[Tom Phillips]

Ian,
From your measurements it seems that the power supply line is OK. Since there is no position of the controls that eliminates the hum I would think that it is not originating in the playback circuit.

I suggest that you verify that the heater circuit ground reference is correct. Measure each side of the heater voltage with respect to chassis ground. you should read equal voltage on each side of approximately 3.15V AC.

Because the unit has always had this problem since you have owned it the cause could be just about anything such as a wiring mistake, bad ground connections etc.

Tom