Ampeg PF-50T Humbuster

[JimmyM]

This is my first all tube amp, I will look for the mod inside as posted in pics here- if you say you can hear it, then I may be out of the loop on what to expect here. Just plugged in my Tonehammer 500- it has a hiss that is a bit quieter than the PF50 hum.

Well it's possible it's pre-mod. Don't know what the noise floor is in the Aggie but the mod does drop the noise floor noticeably and it should at least be in the ballpark with the Aggie, maybe a tad louder, if that. See if you can get your Sweetwater rep to find out. Can't say what they'll do but they're aware of the mod and did fix another guy's amp.

 

[Garret Graves]

Well it's possible it's pre-mod. Don't know what the noise floor is in the Aggie but the mod does drop the noise floor noticeably and it should at least be in the ballpark with the Aggie, maybe a tad louder, if that. See if you can get your Sweetwater rep to find out. Can't say what they'll do but they're aware of the mod and did fix another guy's amp.

Thanks- will do- I’ll chime back in when I find out

 

[AboutSweetSue]

I bought the PF-50t back in late August. It is very silent.

One thing that is odd is the ringing. Any time I play a D it sounds like springs are rattling against metal. This is my second one, the first did it too so I sent it back. The second one is now doing it.

 

[beans-on-toast]

I bought the PF-50t back in late August. It is very silent.

One thing that is odd is the ringing. Any time I play a D it sounds like springs are rattling against metal. This is my second one, the first did it too so I sent it back. The second one is now doing it.

If it’s coming out the speaker, it could be a tube. Try it with the amp on a bed, isolated from the cabinet.

If it’s inside the chassis, something could need tightening to prevent vibration. Try removing the tube cage for a start.

 

[AboutSweetSue]

If it’s coming out the speaker, it could be a tube. Try it with the amp on a bed, isolated from the cabinet.

If it’s inside the chassis, something could need tightening to prevent vibration. Try removing the tube cage for a start.

I’ve isolated it to the cage. My guess is that because it’s only ringing on the D (for some reason the D is prone to rattling everything, including instruments on my wall) that it may be something getting loose. I’ve got it firmly screwed to the flip top, so I suppose it’s possible due to the immense bass this thing puts out.

I also listened for any humming, none. There is some light operational noise, but it’s near impossible for me to hear unless I really pay attention. I’m guessing I either got lucky or it’s a modded unit.

 

[beans-on-toast]

I’ve isolated it to the cage. My guess is that because it’s only ringing on the D (for some reason the D is prone to rattling everything, including instruments on my wall) that it may be something getting loose. I’ve got it firmly screwed to the flip top, so I suppose it’s possible due to the immense bass this thing puts out.

I also listened for any humming, none. There is some light operational noise, but it’s near impossible for me to hear unless I really pay attention. I’m guessing I either got lucky or it’s a modded unit.

Rattle from the tube cage can sometimes be fixed with a better rubber gasket under the cage.

 

[AboutSweetSue]

Rattle from the tube cage can sometimes be fixed with a better rubber gasket under the cage.

As soon as I get around to it I’ll start with the cage, take it off, see if it’s fixed, move on from there.

I’ve isolated it to the cage as in it might be the cage or within the cage. My hope is that it is just the cage itself.

 

[beans-on-toast]

As soon as I get around to it I’ll start with the cage, take it off, see if it’s fixed, move on from there.

I’ve isolated it to the cage as in it might be the cage or within the cage. My hope is that it is just the cage itself.

You’re well on your way to figuring it out.

 

[Garret Graves]

So it would appear the PF50t I just received from Sweetwater is not the revised version? I believe the resistor they add on the mod is at what is labeled d29. Damn- thought for sure I’d get an updated version, maybe they don’t rotate stock they way they should. Can someone verify for me that I’m right?
Thanks
In the lid it does say REV A
@martinbeer

 

[JimmyM]

View attachment 3256652
So it would appear the PF50t I just received from Sweetwater is not the revised version? I believe the resistor they add on the mod is at what is labeled d29. Damn- thought for sure I’d get an updated version, maybe they don’t rotate stock they way they should. Can someone verify for me that I’m right?
Thanks
In the lid it does say REV A
@martinbeer

It was, but don't panic yet. Bertr suggested Ampeg do it this way:

"For Yamaha people interested in modding the PF50T at low cost:
- Do not change the board (yeah!! Money saved!)
- Change R128 in the manufacturing process with a 3.9k resistor instead of 680R (see tracing of MNATS page 1 of the current thread)
- When mounting the board in the chassis, have the person doing the assembly solder a 100uF 100V from back of the diode to ground.
Done."

So it's possible they did it at R128, which I couldn't find in your pic, but I could have just missed it. Great pic, though...lots of detail. Makes it a little easier for my wack eyes.

 

[Garret Graves]

Comparing two photos at approximately same zoomed in spot- first is Martin Beer photo with the capacitor laying down. Then second is my photo- which doesn’t include the capacitor to be seen.

 

[JimmyM]

View attachment 3256758 View attachment 3256756 Comparing two photos at approximately same zoomed in spot- first is Martin Beer photo with the resistor laying down. Then second is my photo- which doesn’t include the resistor to be seen.

Well honestly, it's out of my league so I'll let one of the experts say. Might want to post up a shot of the area around R128, too. Did you check with Sweetwater?

 

[Garret Graves]

Well honestly, it's out of my league so I'll let one of the experts say. Might want to post up a shot of the area around R128, too. Did you check with Sweetwater?

I shot an email to them- hopefully hear back Monday or by Wednesday, day after Xmas. EDIT: I can see R128 in Beer photo is baby blue, in mine R128 is brown. In Root Cellars post, he did self mod- R128 is also brown with same striping. This is further confirmation to me- no new capacitor, and same unrevised resistor means no mod most likely Thanks for your help!

 

[beans-on-toast]

Unless the additional capacitor is mounted on the bottom of the PCB, it doesn't appear that the mod has been performed.

 

[Garret Graves]

Unless the additional capacitor is mounted on the bottom of the PCB, it doesn't appear that the mod has been performed.

How would one check that? I’ve closed it back up, but we’re i to open it, is it held in by screws?
Also, the R128 brown resistor is probably a clue they didn’t make the change- why would they put another resistor on the back of the board, instead of changing the value of the resistor at R128? Also, there is plenty of room for mod on top.

 

[beans-on-toast]

How would one check that? I’ve closed it back up, but we’re i to open it, is it held in by screws?
Also, the R128 brown resistor is probably a clue they didn’t make the change- why would they put another resistor on the back of the board, instead of changing the value at R128?

I wouldn't do that with an amp that you may be returning. At best, you could inspect the other side with a dental mirror and flashlight.

Unfortunately, it happened over Christmas. If the mod hasn't been done, shame on Yamaha.

 

[Garret Graves]

I wouldn't do that with an amp that you may be returning. At best, you could inspect the other side with a dental mirror and flashlight.

Unfortunately, it happened over Christmas. If the mod hasn't been done, shame on Yamaha.

True. Still on a LOUD circuit board.Not sure, but my best bet is there was a failure to rotate stock at Sweetwater, the stock person most likely put new PF-50’s in front of old, then, as stock cleared the shelf, the older non mod PF-50s were on deck for shipping, and here I am at hum-town, next stop Buzzville- ALL ABOARD! Singing the 60 hz blues. Beautiful sounding amp though- I love it, but for the hum.

 

[beans-on-toast]

When Loud bought SLM, they used the SLM marked boards for years in some amps.

 

[Engle]

You’re well on your way to figuring it out.

On mine, the right transformer has started to vibrate audibly -sometimes. If I grab it I can usually get it to stop.
It has the 60hz hum, but I’m thinking I should hold off on the mod because I’ll need to bring it in under warranty.
This is actually a warranty replacement...The first one had a high pitched whine.

 

[El Snooperino]

I’ve isolated it to the cage. My guess is that because it’s only ringing on the D (for some reason the D is prone to rattling everything, including instruments on my wall) that it may be something getting loose. I’ve got it firmly screwed to the flip top, so I suppose it’s possible due to the immense bass this thing puts out.

I also listened for any humming, none. There is some light operational noise, but it’s near impossible for me to hear unless I really pay attention. I’m guessing I either got lucky or it’s a modded unit.

Hi AboutSweetSue,

a certain note rattling instruments on the wall to me indicates room resonances. In my case the main culprit is the E at 82Hz.
By "D" do you mean the note at 73Hz? You can check out your room here: Invalid Link Removed
Just type in the measurements of your room and if you get a red or purple bar at or close to 73Hz (or wherever your D is) you have your answer.
In that case no amount of screw-tightening/gluing/fiddling will help. Only a notch filter, generally cutting bass (on the amp or with an HPF) or turning (way) down. Or moving to a bigger room. Physics is a harsh and cruel mistress I'm afraid.

Edited to include: you could also make/buy bass traps tuned to the problematic frequency, but that can get expensive and impact the looks and usability of your room quite a bit...

Have a nice day,
Walter