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In Reply to: Re: Can anyone help me understand "hum" posted by djn on December 30, 2006 at 07:48:57:
It's there all the time unless you can adj (null) it out. I would like to see schematic. The 26 is a DHT as well and they should each have their own hum pots. (if they have AC filaments)
Follow Ups:
This is another of the famous amps designed and built by John Hogan who recently passed away. There is no schematic available yet, but you may try contacting "njjohn" on the TubeDIY forum to see if he has been able to obtain one yet.
I know that preamp is a srpp 6sn7 design. The 300b circuit is probably a typical one and the 26 is probably also a standard. He fooled around with the 26 circuit for the 45 amp but I don't think he did for the 300b.That amp was built after the beginning stages. In the beginning he built about 10 or so various 6sn7/300b's, some of which were pairs of monos. He use to do alot of esoteric reading on the internet, I don't know where, and he came up with wanting to use the 26 tube. He built the 26/300b which in itself has quite a captivating sound but not enough gain. So he built the seperate 6sn7 pre. At some point he had switched from a fi primer 6sn7 to a srpp 6sn7, the latter being more high end sounding. Later, I got him to revert to the fi primer but for seperate chassis he could not use it saying it had potentially dangerous voltage by itself so he used a vtv circuit.
I felt that the 6sn7/26/300b was really quite an advance over the 6sn7/300b but I also really appreciate the 6sn7/300b.
The 26 tube is a major hummer and he said that is why most people don't use it or if they do, they use dc on the filament.
I know the hum that you are talking about though, and it gets pretty negated through the hum pots. If you get a hum that is not affected by the hum pots, I think it is generally traced to a tube. In fact, John use to switch the two 26 tubes just to show how hum is decreased or increased by this.
I know it is the opts that make John's amps special. In fact, he gave a pair to Ray who posted above who built an p-p amp with them. Although I think that there was an issue with the amp and Ray was not fully satisfied with it when I heard it at a bottlehead show, I still heard the special qualities of the opts even in the p-p amp.
Hi John, good to hear from you. I hope all is well. When I hook up less efficient speakers the hum is not an issue but with my Edgarhorns, it is fairly promenent and goes away when the music is playing. I think it is like having a hairline crack in a car rim. It does not hurt anything but knowing it is there drives you crazy. On another note. I know you like the WE300B and wondered if you have heard the new version. I want to upgrade the EH 300B I got from you and am going back and forth between the new WE and the TJ.....any thoughts? The EH 300B is smoky or cloudy if you will...or maybe not as open as I'd like. Cheers.
Hi Dennis,The EH's are not bad for an inexpensive tube but the TJ's are a big upgrade. Since I prefer more openness and what the TJ's offer, I prefer them over the WE's. I guess you can say that I prefer the TJ's for John's amps.
The WE's have great tone but are not as good for SET openness. I just don't recommend them for the open and dimensional sound experience.
If the hum is fairly prominent, I believe it might be a tube or something that can be corrected, although a low level hum might be there with fairly high effeciency speakers.
I'm sure some hum has saved me some on my electric bill because if I go into an otherwise totally quiet room, I know if I left the amp on or not. lol
If you get tired of it, I'll swap you for a perhaps little more quiet 6sn7/300b or I'll swap you one for something good in speakers. :)
Hi John, I love that amp tooo much to even think about a swap ;> ) I guess I will just bite the bullet and order the TJs. Is there a good place to order from? or are all the retailers the same? When I hook that amp up to my Omega 3s, there is no noticeable hum but on the Edgars, I can hear it well...but.....when the music begins, it is wonderful. Cheers.
i guess all the retailers/distributors of the TJ's are good. I just happen to deal with Sophia Electric.I really do like the 26 tube, I really like it with the 300b as well as the VT-52, the 50 tube, and the 45. There are not too many amps around with a 26 middriver especially with ac and I would hold onto that amp. It is special.
Hi Tre, I don't have the schematic for the amp. I am not sure of its configuration but will try to find out. There is a hum pot for each channel. I can get the hum down low but not eliminated. Cheers.
Take them out of the stand, get a little more seperation, see if that helps, although they do appear to be far enough apart.I had some amps I thought had a problem, but when I seperated them more the hum went away.
Last but not least - changing out the pots to a different pot may in fact reduce the hum further - I saw a post thanking the original poster for his input with the past ten to 14 days, either in this forum or DIY.
IIRC, the poster thanked Allen Wright for his suggestion to a different brand of pot that solved his problem.
Before I made the stand, I ran the amp and pre amp about two feet apart, out of nessessity, and the hum was the same. Cheers.
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