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I installed a 10-turn Hum-pot on each pair of 26's on my 26-26 DC45 amp....
the results were very good, the hum level on my Ver.#2 amp dropped to almost nothing ... Thanks Vinnie!
Willie
Follow Ups:
My pleasure Willie, and thank you for sharing the great designs you did on the 26 pre and the deuce26/45 amp!
Now, if you really want to bring it home, you need to put a separate filament transformer and 10 turn hum pot on each tube, including the 45's.
I know, I know, it's a lot of iron, but Tre' pointed out a while back that if you don't have a separate transformer and hum pot on each tube they will interact and you won't get a true cancelation of the hum. Hammond has nice little 2.5 volt filament transformers for about $18 each that work very nicely. What you can do is use a smaller rheostat (I used 25w/2500 ohm) in front of each pair of transformers and adjust those to get 1.5vac with the tube filaments lit. There is a guy selling the rheostats on ebay for not too much money. Makes it easier to get everything just right.
I have chaged my mind about the chinese 10 turn pots though, they don't seem to be very consistent. I am going to start looking for good quality used ones at hamfests as the new ones can be expensive. If all else fails though, Mouser has some that look pretty good in the $15-20 range.
Anyway, if you do all that you will be able to get the hum so low with AC filaments you will have to have your ear against the speaker to hear it.
What you working on now Willie?
Bourns wirewound precision pots, three or ten turn.Jeff
Edits: 01/25/16
That's interesting.... the pots I got from China are an exact copy of the bourns 3590 series of 10 turn pots; at least on the outside. Any idea of the country of origin? I will have to do a serach I guess. Mouser sells the bourns for $13, the Chinese ones are $6. I did have one of the chinese ones be scratchy and noisey right out of the box though.
Edits: 01/26/16
I have the bill of materials of the Bourns, and its fabulously made Vinnie. Will be happy to send it to you privately, or, ASK the company and they will send it to you.I really like the three turn precision pot, handling wise !! Here is my " quickie" one I use now in setting-up my Altec VOTT A7-800 system, an on-going work in progress.
http://www.audioasylum.com/forums/set/messages/8/80842.html
Jeff Medwin
Edits: 01/26/16 01/26/16
.. DC filaments on both pairs of 26's. I was getting a weird Hum ,depending on which pair of 26's I used...... The humpot seems to help correct that condition.
I originally bought the Hum-pots and couple of Hammond 166Q2 filament trannies, with intentions of building a 1.5VAC supply for the 26's. ...
So I decided to go ahead and install the Hum-pots before I build the AC supply...... and they did some magic.
Now I can take my time and build a decent 1.50VAC supply, and give that a listen !!
Willie
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