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Ampeg PF-50T Humbuster

#321
MarcVador said:
Je suis tellement content de cet ampli ! Je l'ai utilisé pour un concert de rock dans un grand bar avec deux 12" DIY... quel son !! Et j'avais encore pas mal de place...
Vraiment un grand merci à ceux qui ont pris le temps de créer ce changement !
Click to expand...

Je te comprends seulment imparfaitement, mais je suis content que tu es content! ;)

Traduction anglais (attempted):
I am so happy with this amp! I used it for a rock concert in a big bar with two 12" DIY [cabs]... what a sound!! [<<Et j'avais encore pas mal de place>> <--- Je ne comprends pas. "And I had still...?"]

Truly, a big thanks to those who took the time to make this change!

​
[Editor's note: I know you all (those who need to) can paste this into the web translator of your choice, but thanks for humoring my self-indulgent attempt to keep my linguistic brain at least slightly limber!]

EDIT: ...and I had still...not... badness of place? :bag:
...
...
...
Interwebs translator says, "I still had a lot of room," which I take to mean "headroom/room to turn up."
 
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#322
Alper Yilmaz said:
I just took care of the mod on the my PF-20T after exchanging messages with Mako (mnats) and Bertrand (Bertr). Actually, Bertrand got out of his way by sending a detailed explanation of each step in a Word document. I would like to take this opportunity to thank both of them one more time here!

In my initial attempt, I totally forgot about the directionality of the cap--the idiot me--and soldered the (-)ve end to the ground. I turned the amp on, and of course the bias pot did not work. The light in front of the amp started blinking between red and violet, and after a minute or so, there was some smoke coming out of the amp.

I turned it off immediately and waited for half an hour to make sure all the caps were discharged; and when I looked at the burnt cap, I realized my mistake. As I had already voided the warranty, I simply said "what the hell," and without much hope, I just wanted to give another try. I am glad I had ordered two of the same caps, so when I soldered the other one with the correct directions, the amp started fine and it sounds like charm now!

By the way, it is with the 10k resistor (9.72, more precisely in my case) after Johan's mod and a 220 uF 100V cap.

Cheers,

Alper

AlperView attachment 4595025
Click to expand...
Glad it came out well in the end! Now that the warranty is voided, you can live a free man. ;)
 
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#324
B3DkNExl.jpg


New acquisition. I'm happy to report very little hum through the Mesa SW115 cab.
 
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#335
Hi!
I’m a little confused about the hum, hum buster, no hum version, etc. of that amp.

Just to know… is there different versions of that amp? I’ve heard about a factory fix they’ve made at a certain point, can I tell if it’s that version by checking the serial number? Any other way than my ears to know if the amp will hum while looking at used ones?
 
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#336
Inconnu said:
Hi!
I’m a little confused about the hum, hum buster, no hum version, etc. of that amp.

Just to know… is there different versions of that amp? I’ve heard about a factory fix they’ve made at a certain point, can I tell if it’s that version by checking the serial number? Any other way than my ears to know if the amp will hum while looking at used ones?
Click to expand...


My understanding is the unmodified amps actually meet spec. The Signal to Noise ratio is 60dB, which is fairly low. Meaning you can easily hear the hum.

I don't know what serial number the factory mod starts at.

I believe this is what the factory update looks like.
upload_2022-12-20_21-12-58-png.4909205


AFAIK boards with the factory mod are labled Rev B (rather than revision A).

upload_2023-1-2_14-50-15.png
 
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#337
Did a version of the Bertr humbuster mod on my PF50T. Rather than adding a resistor, I replaced R128 with a 3.9K 1/2W metal film. I was surprised by how small the resistor is.

I removed and replaced the anode connection of D29. This was so I could connect the negative lead of the 220uF 100V capacitor to the same junction.

The capacitor I bought has super short leads, so I had to solder wire leads to it.

I connected the positive lead of the capacitor to JMP14.

I also made the mistake of connecting the capacitor backwards :banghead:. I noticed the transformer humming and turned the amp off before any magic smoke came out. Reversed the capacitor connections and hopefully the capacitor was not degraded too significantly.

After confirming proper operation, I used some MG Chemicals RTV silicone to mount the capacitor in the same location Ampeg uses for the Rev B.

There is still a slightly perceivable hum, but it's way better than before.

:thumbsup::thumbsup::thumbsup: :drool:
 
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#338
Wasnex said:
Did a version of the Bertr humbuster mod on my PF50T. Rather than adding a resistor, I replaced R128 with a 3.9K 1/2W metal film. I was surprised by how small the resistor is.

I removed and replaced the anode connection of D29. This was so I could connect the negative lead of the 220uF 100V capacitor to the same junction.

The capacitor I bought has super short leads, so I had to solder wire leads to it.

I connected the positive lead of the capacitor to JMP14.

I also made the mistake of connecting the capacitor backwards :banghead:. I noticed the transformer humming and turned the amp off before any magic smoke came out. Reversed the capacitor connections and hopefully the capacitor was not degraded too significantly.

After confirming proper operation, I used some MG Chemicals RTV silicone to mount the capacitor in the same location Ampeg uses for the Rev B.

There is still a slightly perceivable hum, but it's way better than before.

:thumbsup::thumbsup::thumbsup: :drool:
Click to expand...
Replace the cap, it’s almost certainly damaged by the mistake. It may fail unexpectedly and cause additional damage to the amp.
 
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#339
Wasnex said:
My understanding is the unmodified amps actually meet spec. The Signal to Noise ratio is 60dB, which is fairly low. Meaning you can easily hear the hum.

I don't know what serial number the factory mod starts at.

I believe this is what the factory update looks like.
upload_2022-12-20_21-12-58-png.4909205


AFAIK boards with the factory mod are labled Rev B (rather than revision A).

View attachment 4921976
Click to expand...

When this started, people with 50Hz line power found the hum to be more evident. The change to a Pi-filter with the extra filtering stage resolved it. That may have not been necessary if the capacitor was selected to deal with the 50Hz discharge time. The designer worked at 60Hz and clearly didn’t encounter the issue. A lesson for designers is to test at both line frequencies.
 
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#340
beans-on-toast said:
When this started, people with 50Hz line power found the hum to be more evident. The change to a Pi-filter with the extra filtering stage resolved it. That may have not been necessary if the capacitor was selected to deal with the 50Hz discharge time. The designer worked at 60Hz and clearly didn’t encounter the issue. A lesson for designers is to test at both line frequencies.
Click to expand...

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.
 
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