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Ampeg PF-50T Humbuster

#402
Martin Beer said:
Yep, that's me in the thread linked. My Pf-50t is one of the last of the LOUD units, which there are some nice clearance deals on. The mod appears the same as Bertr's method on this thread, except the additional resistor is positioned differently (they lifted r128 instead of the diode leg), and the added capacitor goes to a different ground trace. But electronically, it's the same.

View attachment 3166997
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Question, was this mod done by Ampeg or by a dealer? Wondering why they're now shipped without the mod.
 
#403
RandomKaren said:
Question, was this mod done by Ampeg or by a dealer? Wondering why they're now shipped without the mod.
Click to expand...

Hard to know for sure at what point in the supply chain mine was modded, but it may have been at the UK distributor at the time, Polar. If that's the case it might not be indicative of whether they come with the mod elsewhere in the world, or now that the distributor has changed.
 
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#404
Martin Beer said:
Hard to know for sure at what point in the supply chain mine was modded, but it may have been at the UK distributor at the time, Polar. If that's the case it might not be indicative of whether they come with the mod elsewhere in the world, or now that the distributor has changed.
Click to expand...
UK mods were definitely done by Polar when they were the distributor, I drove down with my head to check to see if the mod was done and the guy I was chatting to was the guy at polar that did the mods.

As far as I'm aware Ampeg have never rectified this issue in production. Which is just dumb!
 
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#405
Bringing this thread back to the forefront: If you were on the fence about bothering with this mod (as I was), GET OFF THE FENCE! ;)

I got my 50T early on in its release as a B-Stock from Sweetwater. Perfect condition, I'm assuming it was a return... Mine definitely exhibited the humming, that was easy to hear up close, but after using it in a few live contexts I found it negligible.

Fast forward a few years and the 50T is my primary studio amp in my home studio. Sometimes I use the 15" Portaflex cabinet that the head lives in, sometimes an Aguilar SL112 - both sound great. I heard the hum on the various tracks have been doing for clients but I don't mind some noise in a mix and it was easy to duck any silent passages in a track during editing. I just had a producer client comment on it, however, and I'm sure they just used the raw DI track I always send instead. I decided it looked easy, so what's the harm?

Dead. Silent. This mod is so worth the hour it takes and pennies in parts! I copied the methodology outlined in post #39 of this thread (page 2, "Garybass") which is a variation on the Bertr mod. Just added the 2 components and an adjustment using the stock bias pot & bingo! Zero noise. I didn't know what I was missing (or not missing?) as I'm so used to guitar amps and high power bass amps having some kind of noise floor.

If you know how to safely work on your amp it's so easy. I cant imagine it taking a qualified repair person more than an hour to complete either! Most of the time is spent unscrewing the chassis and mounting.

Love this amp even more now.
 
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#406
Has the issue been resolved in new units? The mod is trivial and I can do it myself but I've never worked on an amp, only pedals.

I don't know how to discharge the filter caps and check that it's safe to work in there other than having watched how to videos. Otoh it's a good chance to learn this stuff.
 
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#411
I swapped out my original radial cap for an axial, a much neater solution. Easily clears other components.

IMG_4491.jpeg
 
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#413
jnewmark said:
Let me ask a stupid question: Why aren't they doing it at the factory for all new heads ?
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Have you ever worked in a megacorporation before? Lol.

That being said, if I bought a new one from a major vendor in Fort Wayne, IN, would they perform the mod if there was indeed hum? Not sure if I want to just get a used one and have a local tech work on it or shell out extra money to get a new one and have the vendor take care of the mod.
 
#414
I e-mailed Ampeg support just the other day about this, I got this as a response,not sure they will fix before you buy but they say its a warrenty repair.Which is kind of goofy,but i guess its the way it goes.
 

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#415
yonkrz said:
I e-mailed Ampeg support just the other day about this, I got this as a response,not sure they will fix before you buy but they say its a warrenty repair.Which is kind of goofy,but i guess its they way it goes.
Click to expand...

I'm guessing that's only a US thing, not sure it's being offered here (UK). Mine has no warranty now with me having done it myself :(
 
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#417
Pretty sure I would get no support whatsoever from anyone here in Poland. Might as well fire up my soldering iron since I don't think any amp experts live in my area. Guitar stores don't even have single guitar strings here lol

The question is, is it worth it to buy this amp for live gigs in small bars? I play a Rumble 100 with 2 guitarists and a loud drummer (aka a drummer) and it struggles. I keep reading conflicting info, like 50W tube into a 1x15 would be plenty or "no way, you need at least 300w into an 8x10!"
maybe I'm better off with a class D head and a tube preamp?
 
#418
andare said:
Pretty sure I would get no support whatsoever from anyone here in Poland. Might as well fire up my soldering iron since I don't think any amp experts live in my area. Guitar stores don't even have single guitar strings here lol

The question is, is it worth it to buy this amp for live gigs in small bars? I play a Rumble 100 with 2 guitarists and a loud drummer (aka a drummer) and it struggles. I keep reading conflicting info, like 50W tube into a 1x15 would be plenty or "no way, you need at least 300w into an 8x10!"
maybe I'm better off with a class D head and a tube preamp?
Click to expand...


I have only played my PF50T, which I bought previously loved. I don't feel it is particularly powerful for a 50W amp. In fact, I also own an Ashdown LB30 Mk1, LB30 Mk2, and CTM 30 Little Stubby. My impression is the LB30s have slightly more clean headroom and the Little Stubby is about the same. They might work okay for a background music gig, but I certainly would not want to depend on one of them to hear in a cover band. I have gigged an 85W tube amp in a cover band, so it can be done. Given the choice, I would prefer 150W or more, and an efficient cab.

However, it's entirely possible you would find the PF50T perfectly sufficient (YMMV)....the sensitivity rating of your cab will be a huge factor. Double the power results in +3dB.

Example:
50W to a cab rated 103dB 1W/1m = ~120dB.

If your cab's sensitivity is only 97dB 1W/1m, you require 4x the power (200W) to achieve the same SPL. I.E. 50W to this cab would produce only ~114dB.


I did the mod myself. The mod requires minimal parts and is easy for someone with basic electronics know how.
 
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#419
andare said:
Pretty sure I would get no support whatsoever from anyone here in Poland. Might as well fire up my soldering iron since I don't think any amp experts live in my area. Guitar stores don't even have single guitar strings here lol

The question is, is it worth it to buy this amp for live gigs in small bars? I play a Rumble 100 with 2 guitarists and a loud drummer (aka a drummer) and it struggles. I keep reading conflicting info, like 50W tube into a 1x15 would be plenty or "no way, you need at least 300w into an 8x10!"
maybe I'm better off with a class D head and a tube preamp?
Click to expand...

I've gigged with a PF-50t, fine for small bars but the more speakers the better. I'm currently using two 112 cabs. But if clean headroom is what you want a small tube amp is probably not the way to go.
 
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#420
Wasnex said:
I have only played my PF50T, which I bought previously loved. I don't feel it is particularly powerful for a 50W amp. In fact, I also own an Ashdown LB30 Mk1, LB30 Mk2, and CTM 30 Little Stubby. My impression is the LB30s have slightly more clean headroom and the Little Stubby is about the same. They might work okay for a background music gig, but I certainly would not want to depend on one of them to hear in a cover band. I have gigged an 85W tube amp in a cover band, so it can be done. Given the choice, I would prefer 150W or more, and an efficient cab.

However, it's entirely possible you would find the PF50T perfectly sufficient (YMMV)....the sensitivity rating of your cab will be a huge factor. Double the power results in +3dB.

Example:
50W to a cab rated 103dB 1W/1m = ~120dB.

If your cab's sensitivity is only 97dB 1W/1m, you require 4x the power (200W) to achieve the same SPL. I.E. 50W to this cab would produce only ~114dB.


I did the mod myself. The mod requires minimal parts and is easy for someone with basic electronics know how.
Click to expand...
The only cab I can afford is the Rumble 115. Can't find the sensitivity right now but anyway it looks like the PF50T is not a sensible purchase for me. With the Rumble 100 into the PA, the audience hears me well and I hear myself on stage so if I have to buy another amp, it better deliver way more headroom. Maybe the Venture V7.
 
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