I bought my PF50-T a few weeks ago and was totally unaware of the hum-problem when I ordered it. So needless to say, my disappointment was really huge when I hooked it up to the speaker and it felt like the whole room was vibrating at 50HZ. At first I thought it had to be a tube that had bad connection, but not so. After a couple of days with the irritating noise I was ready to return the amplifier. Luckily I decided to make som searches on the Internet and found this page. Since I have some experience fixing my own gear I ordered the parts needed for the mod and it worked 100%. The amplifier is now as quite as a quality amp should be. So I would like to express a big thank you to those who posted the easy solution to the problem. It is a true shame that Ampeg are still selling these the same way as they did in 2017 well knowing about the flaw.
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Ampeg PF-50T Humbuster
- Thread starter mnats
- Start date
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- Tags
- ampeg ampeg pf-50t pf-50t
So I’m trying to send this info to the Ampeg tech in my area and the Humbuster page links take me to Flannagans Pub. Are the links broken for anyone else or Is it just me? Have I slipped into an alternate reality where the fix is a pint of Guinness? Does anyone have the info archived that I could send to the tech? He’d never heard of the issue when I talked to him on the phone.
I also saw that. I'm sure your amp tech will appreciate the recommendation to go have a beer, but it's a shame the website is gone.
You shouldn't need the whole page. I have some of the images saved and edited
Original Bertr Mod added components RT 3.3k resistor and C1 220uf/100V electrolytic.
Top image stock circuit. Bottom image Bertr mod with C1 and RT added/labeled.
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A revised (IMHO improved) version is to replace R128 with 3.9k instead of adding RT.
Ref: https://www.talkbass.com/threads/ampeg-pf-50t-humbuster.1306043/page-5#post-21338053
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I'm not an electronics expert but i think there's no difference between the two if the total resistance is the same, and because of parts tolerance you're going to be in the ballpark either way. It comes down to which is simpler and cleaner to do, replacing a resistor or adding one to the board.
Just chiming in to add I had the same problem (I think) as @Wasnex posted a few years ago.
Upon starting up, there was a fuzzy cracking sound that would last 30-60 seconds. I had purchased a spare pair of Ruby 6L6s when I got the amp, so I swapped those in and the noise is gone.
I guess I should buy another backup set of power tubes
Upon starting up, there was a fuzzy cracking sound that would last 30-60 seconds. I had purchased a spare pair of Ruby 6L6s when I got the amp, so I swapped those in and the noise is gone.
I guess I should buy another backup set of power tubes
