Ampeg PF-50T Humbuster

[beans-on-toast]

My amp is running at 60hz. I suspect the degree of hum is somewhat dependent on how well matched the output tubes are. Perhaps the tubes are a bit too far out of balance. The hum is barely noticeable now.

Unbalanced power tubes can produce hum. It also will produce more THD. The balance on the vintage and SVT-VR is adjusted with test equipment to minimize THD. Failing that, on some amps it’s adjusted by ear for minimal hum. Same procedure as the heater pot adjustment.

The hum-buster fix was proposed to reduce hum related to the bias circuit design.

 

[_Obra_]

Just got my new T50 today. It has pretty loud hum, but as I read in this thread it can be fixed.

Next to the hum, it arrived with all three screws broken from one side, probably from a long transport.

Can someone tell me what is the screw size so I can try to found the same one, or shall I just return the amp to the other part of Europe?

 

[Wasnex]

Just got my new T50 today. It has pretty loud hum, but as I read in this thread it can be fixed.

Next to the hum, it arrived with all three screws broken from one side, probably from a long transport.

Can someone tell me what is the screw size so I can try to found the same one, or shall I just return the amp to the other part of Europe?

View attachment 5026475 View attachment 5026476

I would find it important to inspect the inside of the amp. Often sheered off connectors are evidence of a hard shock. IMHO, make sure there is no internal damage.

I have no idea what the size or thread of the screws are. Here in the US, most hardware stores sell common screws in both metric and SAE thread patterns. If you have a similar resource in your area, back out a good screw on the other size of the chassis, and go find some suitable substitutes.

The screws appear to be flat-head, Philips with a black oxidized finish.

It may be difficult to find black oxidized screws locally. If you can figure out the size and thread pattern, you may have to special order unless you are okay with regular machine screws.

 

[OldogNewTrick]

Finding UNC screws in Europe is a bit of a challange...
If I do need them I order them here Invalid Link Removed Zollshop

Since the amp is made in China, there is a good chance the bolt is metric.

 

[GR7G5TER]

Just got my new T50 today. It has pretty loud hum, but as I read in this thread it can be fixed.

Next to the hum, it arrived with all three screws broken from one side, probably from a long transport.

Can someone tell me what is the screw size so I can try to found the same one, or shall I just return the amp to the other part of Europe?

View attachment 5026475 View attachment 5026476

If it's a new amp and it's arrived like that, I'd send it back. Takes a fairly hefty impact to shear the screws like that and you don't know what else is damaged or waiting to break.

 

[J-Bass RMR]

Just got my new T50 today. It has pretty loud hum

Is it "new to you" or brand new?

Just curious; I skimmed back a few pages and couldn't find it, but thought I'd read once that the new production units had the "mod".
Especially interested, as I've had a PF 50T on order since January...

 

[_Obra_]

Is it "new to you" or brand new?

Just curious; I skimmed back a few pages and couldn't find it, but thought I'd read once that the new production units had the "mod".
Especially interested, as I've had a PF 50T on order since January...

It's brand new.
After reading all of the 18 pages, I decide to go for Humbuster mode. At the same time, I will also change the screws that broke during transport.

That's not how I imagined buying a new expensive amplifier, especially from such a famous brand, but my other option is to send it back and wait for more than 2 mounts for sure, just for three new screws (the question is whether they would do something about the hum).

 

[GR7G5TER]

but thought I'd read once that the new production units had the "mod".

I'm pretty sure that is the case, I got my 50 back in Feb 2019 and Polar (the then distributor were performing the mod on all units that came in and i'm pretty sure this was resolved at the factory at some point after.

It's brand new........................
just for three new screws (the question is whether they would do something about the hum).

Before you go do anything to your amp, speak to Ampeg, there is better than fair chance that your unit is damaged and what you are hearing is a result of the damage and may not be resolved with the humbuster mod.

 

[_Obra_]

I'm pretty sure that is the case, I got my 50 back in Feb 2019 and Polar (the then distributor were performing the mod on all units that came in and i'm pretty sure this was resolved at the factory at some point after.



Before you go do anything to your amp, speak to Ampeg, there is better than fair chance that your unit is damaged and what you are hearing is a result of the damage and may not be resolved with the humbuster mod.

Yes, I'll do that for sure. I have already contacted the dealer from Denmark that sold it to me and waiting for his answer tomorrow.

 

[marchone]

@JimmyM What and where is Birddog?

Has anyone here found a shop in NYC that can do the mod?

 

[Wasnex]

It's brand new.
After reading all of the 18 pages, I decide to go for Humbuster mode. At the same time, I will also change the screws that broke during transport.

That's not how I imagined buying a new expensive amplifier, especially from such a famous brand, but my other option is to send it back and wait for more than 2 mounts for sure, just for three new screws (the question is whether they would do something about the hum).

If it's new I would contact the vendor. They should work out a repair or replacement.

AFAIK, recently made PF50Ts will have a factory installed humbuster. I believe an authorized Ampeg repair facility may do the mod free of charge if you go through proper channels. It's possible the amp is new old stock.

The amp may have the mod and the hum is evidence of damage that occurred in shipping.

I realize waiting is a hassle, but a damaged amp may have chronic problems.

 

[Wasnex]

@_Obra_ This page claims to show the Ampeg version of the mod:
Ampeg PF-50T Humbuster

 

[JimmyM]

@JimmyM What and where is Birddog?

Has anyone here found a shop in NYC that can do the mod?

Chuluota FL, a little boonies town just outside of Orlando.

 

[marchone]

Thanks.

 

[Engle]

It's brand new.
After reading all of the 18 pages, I decide to go for Humbuster mode. At the same time, I will also change the screws that broke during transport.

That's not how I imagined buying a new expensive amplifier, especially from such a famous brand, but my other option is to send it back and wait for more than 2 mounts for sure, just for three new screws (the question is whether they would do something about the hum).

Unfortunately that amp must have been subjected to a substantial impact. I would be concerned about other damage that you can't see.

 

[_Obra_]

Unfortunately that amp must have been subjected to a substantial impact. I would be concerned about other damage that you can't see.

I was concerned, and I tried it today with some different cabs. It works just fine except the hum (that is not so bad when You play it loud).
Anyway, I'm waiting for seller to let me know what to do after he speaks to the main dealer. Will not touch anything because of the warranty unless told otherwise.

 

[_Obra_]

One more happy user of humbuster mode . No more hum.

Regarding the sound, it's the same. I recorded 4 different bass guitars on even more settings on the amp before humbuster mode, and check it out again after, and the sound is exactly the same, so no worry about that.

 

[dmk]

I received a new PF50-T today. After reading through all of the threads, I was pretty confident that the hum problems would have been sorted out by now. Unfortunately, the hum is still present on the new models, and in addition, on my new amp there is a loud pop that occurs every 8-10 seconds.

The serial number indicates it was made in 2023, but there doesn’t appear to be any resistor or capacitor modifications that I can see.

Needless to say, I’m a bit disappointed and will be sending it back.

 

[tchristian]

It's a shame - they sound so good when they're healthy. I too would send it back.

 

[_Obra_]

Just wanted to share today's experience from the studio with my Ampeg PF-T50.

I recorded a song playing Fender precision CS with my Ampeg PF-T50 head using a Transformer balanced line out.
After some time, the producer told me that there are certain bass frequencies that sound quite bad and bother him a lot in the mix (especially when I play an F note). Also, each C note is significantly quieter than the others.

After that, we did a test, where I played all the tones on all the strings at the same volume. It turns out that it is exactly as I wrote earlier, each F hums and sounds 9 dB louder than the others, and the volume decreases going towards the tone C (where each C is much quieter).

Then we recorded everything through the preamp out, and all the tones were at the same volume and without any interference.

I wonder if it might have something to do with the "humbuster" mode that I applied to the amplifier because of the very loud noise it produced when the speaker was turned on?