Hum in new AB763 DR build Reverb circuit - increases as reverb pot is turned up

[Paul P]

I know you mentioned moving the tank had no effect, but did you move it far enough away, like at least 3 - 4 ft, and not under fluorescent lights or the like ?

My reverb had symptoms almost identical to yours (in post #1) and most if not all of the problem turned out to be the tank's position close to the amp and its orientation.

I've just flipped my tank upside down to get best performance, but I had to readjust the four little springs to keep the big springs centered.

[prongster]

Apologies if my reporting is confusing - I'm doing my best to report what I observe at the time I report it. Either something changed, or my reporting was in error. I have been poking around quite a bit, so there's the possibility that changed something.

Regardless, this is what I can confirm now:

-It hums with the PI in, does not really hum with the PI removed.

Here are AC voltage measurements at the speaker as I re-added the tubes:

V9, V8, V7 = 0.0 mVAC
+V6 = 11.7 mVAC (noticeable hum)
+V5 = 11.7 mVAC
+V4 = 13.5 mVAC + hiss becomes noticeable
+V3 = 13.6 mVAC
+V2 = 11.3 mVAC
+V1 = 11.8 mVAC

With all tubes in and the Reverb on 10, it reads 15.7mVAC and is very noticeable.

With the .001 Cap lifted and connected to ground it still hums.


And the hum is not so loud that the amp is unplayable - you certainly wouldn't hear it at band volume, but it is louder than any of my other tube amps, and I hope to use this amp for recording and would like for it to be as quiet as possible, especially with a lot of reverb applied.

[vintagekiki]

https://www.manualslib.com/products/Fender-65-Deluxe-Reverb-3425345.html

https://www.manualslib.com/manual/239144/Fender-65-Deluxe-Reverb.html

Fender 65 Deluxe Reverb for full drive develops 13 VAC measurements at speaker
13 VAC at 8 ohm = 21.125W
You measured AC (noise) voltage measurements at speaker
0.015 VAC at 8 ohm = 0.000028125 W

I accept measurement results with reserve, so I would recommend that you calculate S/N for you amp.
https://en.wikipedia.org/wiki/Signal-to-noise_ratio

If, despite thorough wiring search, you do not find hidden cause of buzz, it may be solution to heat tubes with DC instead of AC voltage.
1)


Question
When you record .m4a clips, at what distance from speaker is found microphone?

[prongster]

I had my phone pretty much on the speaker grill to record all those clips. But the hum is quite audible just being in the room with the amp. I can probably live with it as is, but you indicated earlier that the hum/buzz is not normal.

For a thorough wiring search, what am I looking for? Bad solder joints?

[prongster]

I know you mentioned moving the tank had no effect, but did you move it far enough away, like at least 3 - 4 ft, and not under fluorescent lights or the like ?

My reverb had symptoms almost identical to yours (in post #1) and most if not all of the problem turned out to be the tank's position close to the amp and its orientation.

I've just flipped my tank upside down to get best performance, but I had to readjust the four little springs to keep the big springs centered.

There's definitely a noticeable hum even with the reverb tank completely disconnected. If it's plugged in and the reverb is turned up, I can hear a change in the hum as I move the tank around, especially if it gets near the PT. I can find a less noisy orientation for it, but the baseline hum is there regardless.

[vintagekiki]

I had my phone pretty much on the speaker grill to record all those clips ... For a thorough wiring search, what am I looking for?

The way when¹⁾ something is measured or compared cannot be ad hoc, must be within some technical standards.
For acoustic measurements on speaker, measuring device should be away 1 meter from speaker.


You ask what you looking in wiring. If you carefully read comments these 120 posts, you will see that lot has been said in pictures and in words.
Again, copy/paste what has already said does not lead to anything, because what said is simply ignored, and some other story is persistently passed.
Maybe is best solution take away AB763 DR to qualified service somewhere in your immediate area.

According to your measurement results post #122 since AB763 DR is diy, buzz is within minimum standards (even for S/N ratio).
What else to say except bad luck. At least you learned something. Now you know, what don't know.
Don’t be disappointed in failure. Each new construction is based on the experience of previous construction.
We have all gone through same experience countless times.

[prongster]

I recorded the sound near the speaker, because I wanted it to be clear. There is a lot of ambient noise in my house, which I didn't think would be helpful to hear.

Sorry if I'm not following your instructions properly. Your choice of words is often confusing to me.

[vintagekiki]

I'm sorry also. I read somewhere.
Road to hell was paved with good intention.

[Greg_L]

I recorded the sound near the speaker, because I wanted it to be clear. There is a lot of ambient noise in my house, which I didn't think would be helpful to hear.

Sorry if I'm not following your instructions properly. Your choice of words is often confusing to me.

You might be getting the dreaded PT hum. If the cores of the PT and OT are not at 90 degrees to each other the PT can induce hum into other areas of the amp.

[vintagekiki]

If the cores of the PT and OT are not at 90 degrees ...
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[prongster]

You might be getting the dreaded PT hum. If the cores of the PT and OT are not at 90 degrees to each other the PT can induce hum into other areas of the amp.

It's a stock DR chassis from Mojotone, with Mercury transformers that are for the DR, and they aren't mounted weird or anything. Wouldn't that be ruled out since it doesn't hum w/o the power tubes?

[g1]

Sorry if I'm not following your instructions properly. Your choice of words is often confusing to me.

VK is not an english speaker and runs everything through a translate bot. This is often confusing and sometimes downright gibberish ("some solders are not very jubilee").
As he says, "Road to hell was paved with good intention".

We can accept that there are errors in his statements due to bad translations. What is absolutely unacceptable is when he berates others for misunderstanding what are translation problems.

[Greg_L]

It's a stock DR chassis from Mojotone, with Mercury transformers that are for the DR, and they aren't mounted weird or anything. Wouldn't that be ruled out since it doesn't hum w/o the power tubes?

I'm not sure if the power tubes pulled would rule out PT hum. I guess it could, but without them nothing can be amplified. So yes and no? Maybe? I'm not sure. I'm not a pro. I'm just throwing out any lame-brained ideas that come to me. Lol. I've been following along and I'd love to know what the solution finally is.

But I think you said that pulling the PI reduces the hum significantly? Check the fiberboard. Maybe you're getting weird cross talk into sensitive wires through the actual board itself. It's happened to me. Those paper Fender-style boards can be conductive....even new ones.

[Helmholtz]

I don't think your hum level is that bad (when you get a chance compare to an original Fender DR).

You might get some further improvement by:

- shielding the tank as explained earlier
- using tube shields
- covering the top of your cabinet with heavy aluminum foil that contacts the chassis
- using a humdinger instead of grounding the heater CT (highly recommended).
- using heater elevation with the humdinger
- employing DC heating.

BTW, direct crosstalk between PT and OT can be ruled out, because the hum stops with PI or power tubes pulled.

[prongster]

I don't think your hum level is that bad (when you get a chance compare to an original Fender DR).

You might get some further improvement by:

- shielding the tank as explained earlier
- using tube shields
- covering the top of your cabinet with heavy aluminum foil that contacts the chassis
- using a humdinger instead of grounding the heater CT (highly recommended).
- using heater elevation with the humdinger
- employing DC heating.

BTW, direct crosstalk between PT and OT can be ruled out, because the hum stops with PI or power tubes pulled.

OK, thanks guys. I'll see if I can get a friend that's familiar with the original Fenders to listen to it this week and see what he says about the hum.

In the meantime, I got a shorter cord for the reverb tank, and I'll try some of these additional shielding tips, and maybe give the humdinger a try.

I really appreciate your patience with me while I bumble around with this. I'm obviously an electronics neophyte - I'm just a musician that's taken an interest in how my amps work. I built a BF Princeton Reverb right before this DR that's much quieter, so maybe that skewed my expectations.

[vintagekiki]

This is often confusing and sometimes downright gibberish ("some solders are not very jubilee").
We can accept that there are errors in his statements due to bad translations. What is absolutely unacceptable is when he berates others for misunderstanding what are translation problems.

Greg, vk no accuses here nobody for not understanding translation, or for not elementary ignorance electronics.
I think this is technical not literary forum, so why is need to prove who knows literary language as much as possible. When I publish literary book, I will be free to call reviewer.
Anyone who says that is English speaker, by logic of things, must know simplified English. You raised that question few times, and at finally understood.
post #64 or
https://music-electronics-forum.com/forum/amplification/guitar-amps/vintage-amps/914562-big-vintage-celestion-q?p=915235
Simplified English Introduction

The phrase you call "some solders are not very jubilee" is balanced (human) variant for "you have cold solders in your soldering"
If vk disturb you so much (you keep follow and calling him) simply don’t follow him.
Ignore command is at your disposal. Please use it.