Deluxe Reverb Idle Noise

[TurboGuitarMelton]

Hi,


My deluxe reverb build seems to have a good bit of 60hz hum at idle but other than that works and sounds great! The B+ is higher than normal due to the power transformer. Im getting 354V going to pins 4 and 6 on the rectifier. With a 5u4gb im getting 450v B+ and when the amp is on standby it goes up to 495! Is that normal? Concerns me because my filter caps are rated for 475v.


If I were to buy a new power transformer with 325v im pretty sure that would get my B+ where I want it. Could the higher voltages in the amp cause the amp to be noisier at idle? Or is that unrelated? Ive swapped preamp tubes and the idle noise doesnt change. Maybe some bad power tubes?


More info:


Hum also doesnt change with volume knobs. And is happening with both channels.


I modded the tone stack on channel 1


Both channels have reverb and tremolo (used robrobinette 220k mixing resistor method)


Also: poking around with a probe and my multimeter I noticed that all of the 100k plate resistors are sensitive. When i get the probe near this part of the circuit on any tube, the hum gets louder.

[tubenit]

When you say it gets noisier when the probe is near the 100k resistors …………….    Does that mean not touching the 100k plate resistors but simply near them?   

IF so, it may be worth considering to switch those out for metal film resistors which are quieter?

Are you using a pair of 100ohm resistors to ground as an artificial CT for the heater wiring?  OR is there a wire for the CT for the heater wiring?

Is this with a guitar plugged in the amp?   Is the bridge of the guitar grounded?  Is the guitar with single coils?  Is cavity of guitar shielded?

Is the chassis in a head or combo cab where there is shielding on the top underside of the cab?  Is the amp in a room with a ceiling fan and a rheostat?

IF you don't have a good solder joint, that can definitely contribute to noise.

How do your preamp and LTPI  12A_7 voltages compare to the Deluxe Reverb layout?   

https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_reverb_ab763_layout.pdf

Have you tried different preamp tubes or simply swapped positions of the same tubes?    Have you tried a 5Y3GT rectifier to see if the lower voltages lower the hum? 

If you pull V1, does it still have noise?   If you pull just V2 does it still have noise?  etc...……   Can you determine an area that is problematic or OK?

IF the voltages on the preamp tubes are high & that "seems" to be contributing to the noise (based on trying a 5Y3GT and lower noise with lower voltage),  then you might consider increasing the resistor between node B and node C on the B+ rail to lower preamp voltages?   I would be very surprised if switching out the PT will be your answer?

JJ 6V6 tubes are pretty rugged and they can handle some pretty high voltages.  I had a pair in an amp with 476 volts on the plates and they lasted for years. 

Your build quality certainly looks great!  I think you will eventually get this figured out and make it quieter.

With respect, Tubenit

[TurboGuitarMelton]

Thanks Tubenit!


With the probe near the 100k resistors NOT touching the noise gets louder. Maybe I have a baf connection in that area or possibly one of the resistors is bad. Ill check the resistances and the solder joints.


My transformer has a center tap for the heater wires.


Noise is present with or without a guitar plugged in


Its a standard Deluxe reverb combo setup and yes there is a sheet of aluminium foil on the top of the cavity.


I dont know why but I didnt check the PI voltages. Ill check those. However, because of the PT the entire amp is running about 20-30v over the standard fender voltages preamp and all. Had 190v on V1 if I remeber correctly.


I have tried multiple tubes and swapped them around. I didnt get much time to do that though. But it didnt seem to fix it.


Ill try pulling V1 and V2 also!  Dont know why i didnt think of that!


Tried a 5y3 this morning and there wasnt a change in the noise... If anything it got noiser!


Yes, Ive heard of the wonders of the JJ 6v6! Lol I have groove tubes 6v6S's in there which are just rebranded jj's.


Here is a primitive soundclip of the noise. If you listen with headphones you can hear the low pitched hum that accompanies the hiss. This is with all controls at 0 and at one point I turn up the volume to 10.


https://soundcloud.com/user-204022586/deluxe-reverb-noise

[tubenit]

OK,  you've done a lot of trouble shooting already which tells me you're thinking thru this well & should increase confidence that you WILL get this issue resolved.

Disconnect negative feedback.  Sometimes if the OT wires are "backwards" the amp will squeal and howl horribly.  Sometimes, it's just makes a humming noise which I have had happen.

Looking at the layout, from right to left ……….    V1 being the "normal channel" …………….. pull V2 (stages 1 & 2 of the vibrato channel), V3 (12AT7 reverb send), V4  (reverb return and 3rd gain stage of the vibrato channel), & V5 (vibrato tube).

https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_reverb_ab763.pdf

Now you have the normal channel going into the LTPI.  Does it hum with or without guitar plugged in?  IF you are not getting any sound then replace the V5 vibrato tube.  Now is there hum?   What you are trying to do is locate/isolate the area that is problematic.

The other thing would be to bypass sections of the signal chain to see if bypassing one significantly reduces the noise.  You  would do this carefully, safely with insulated alligator clipped wires.

Did you try the amp without the Rob Robinette mods?  IF so, did it hum?   If not, then I'd rewire the amp to stock Fender and see what happens?

Occasionally, there can be a leaky cap allowing voltages going on to a pot making that pot noisy?  You can do a search on how to test for that.

IF there is a bad solder joint on the B+ rail around a dropping resistor or such, that can definitely cause hum.

I do think you will get this resolved and have a quiet amp.

Did you use Doug's grounding scheme?    https://el34world.com/charts/grounds.htm

Any chance that if you used shielded wiring that you grounded it on both ends instead of one?

I once had a small cap like 500p or less be bad where I was using it as a bright cap and that induced a considerable amount of noise.  I think Platefire once had a cathode cap that proved to be adding noise & when he changed that out, the noise was resolved.  You'd de-solder on side of the cap to see if that stopped the noise.

With respect, Tubenit

[TurboGuitarMelton]

Alright, I got some time to do lots of troubleshooting yesterday.

Tubenit, disconnected NFB with no change. Changing OT wires made it squeal so that wasnt it. Im using dougs ground scheme. No sheided cables, all cloth pushback wire.


Ive narrowed down the hum to V6 the LTPI. It only goes away when i remove that tube. When i pull V4 I get no output, but the hum is still there also makes no change when i remove v5. If I touch the pin7 wire on V4 the hum goes away mostly. Ive resoldered this wire but it made no change. Also tried moving it around to no avail. Moving V6 wires also makes no change and there arent any sensitive wires like pin 7 on V4.... Could it be a bad reverb driver putting noise into the power supply? Ive changed all the transformers except that one. And as i recall the amp was equally noisy before I rewired it.


I checked all resistors and caps to V4 and V6 but nothing is bad. Could it be the wires coming from the filter cap board? I have the wires twisted together.


Tried new power tubes too. No change.

[sluckey]

Look at the layout that tubenit posted. Locate V6. Follow the wire from pin 2 back to the board. It connects to a .001µF cap. put a ground jumper on the other side of that .001 cap. Does that kill the noise?

[TurboGuitarMelton]

Sluckey,


Grounded input of PI inverter cap and the "hiss" goes away. Reverb return gainstage is generating the hiss but i can deal with that considering i used carbon comp resistors and the tubes are older.


The low pitched hum is not going away when i ground the PI input...  Im guessing this means that the issue is in the PI/output section of the amp. I get no hum when i remove V6. Ive also tried a few different 12at7s in V6 but it seems to make no difference.

I do have a negative feeback switch that adds 1.5k resistance so i can get stock 820ohm or 2.3k feedback options. When i have more NFB (820) the sound gets quieter. With the 2.3k resistance it gets a bit louder. This is to be expected right? Less negative feebdack more noise.

I also want to add that the hum is a 60hz low pitched mellow toned hum. I tried other power tubes too to see if it was those tubes but the hum returned.

The high voltage wires that come from filter cap board are also laid out different than Ive seen on fender layouts. I have them going over the top of the board (yellow wire) you can see them above the LTPI and above the trem circuit. On fender schematics I notice that these wires come from a second hole near the reverb driver and third hole near v6. Should i have those wires coming from those locations? Is the high voltage creating a hum going over the board?

Ive attached close up pics of this area of the amp.

[tubenit]

Is the high voltage creating a hum going over the board?

I think that could be a possibility?   I use turret boards the majority of the time and I typically run the B+ wiring underneath the turret board next to the chassis and then have it come up to the (B+) turret as close as I can. 

I honestly don't know if it will resolve your hum, but IF it were mine ………. I might try drilling a small hole  next to the eyelet you want the B+ at and then running a wire thru the hole under the eyelet board (if there's room and that's possible) back to the filter cap/s.  That may or may not be useful?  Then you would insert the B+ wire from the top into the eyelet in the same way that you are now.

IF that idea doesn't work, then I might run the B+ wire (laying on the chassis) at the edge of the eyelet board on the tube socket side and then back up on to the board as needed.

With respect, Tubenit

[sluckey]

Grounded input of PI inverter cap and the "hiss" goes away.

That indicates the "hiss" is coming from the preamps.

The low pitched hum is not going away when i ground the PI input...  Im guessing this means that the issue is in the PI/output section of the amp.

I agree. Looks like you have two issues.