Can you take a look at my clone?

[C Moore]

I bought all the parts and chassis from Ceriatone. I used most of their parts including the power and out trannies. The only real changes I made were:
1. Allesandro volume pot.
2. Changed the resistor on V1 pin7 from 15K to 68K.
3. Changed the cap on the presence pot from 0.10 to 0.68.
4. Change the NFB resistor from 100K to 150K.
5. Changed the resistors on pin 5 (control grid?) of the power tubes from 1.5K to 4.7K 2 watt.
6. The tubes are:
V1. NOS 5751
V2. TungSol ri 12AX7
V3. JJ12AT7
Power tubes are =C= EL34. I am at about 407V on the plate and 37MA plate current.
There is no squealing or oscillation, the hiss is at "normal" levels for this type of amp I think. My only real complaint is the feed back. It starts to get pretty bad with the volume at 11:00, T M B all at noon, and the presence at 11:00.
Sorry for the huge post, but I wanted to be as honest as possible. Do you guys have any suggestions as to how I might be able to discipline the feed back?
My pictures are not the best. I will try to take some better close ups.
Thank You
OK, not sure if these are any better; but it is the best I can do.
Thanks Again

http://i111.photobucket.com/albums/n143 ... ck2001.jpg
http://i111.photobucket.com/albums/n143 ... ck2002.jpg
http://i111.photobucket.com/albums/n143 ... ck2003.jpg
http://i111.photobucket.com/albums/n143 ... ck2004.jpg
http://i111.photobucket.com/albums/n143 ... ck2005.jpg
http://i111.photobucket.com/albums/n143 ... ck2007.jpg
http://i111.photobucket.com/albums/n143 ... ck2011.jpg
http://i111.photobucket.com/albums/n143 ... ck2013.jpg
http://i111.photobucket.com/albums/n143 ... ck2014.jpg
http://i111.photobucket.com/albums/n143 ... ck2015.jpg
http://i111.photobucket.com/albums/n143 ... ck2016.jpg
http://i111.photobucket.com/albums/n143 ... ck2017.jpg
http://i111.photobucket.com/albums/n143 ... ck2018.jpg
http://i111.photobucket.com/albums/n143 ... ck2019.jpg
http://i111.photobucket.com/albums/n143 ... ck2020.jpg
http://i111.photobucket.com/albums/n143 ... ck2021.jpg

[M Fowler]

It has taken me many months poking around my express by ceriatone to get it under control.

I changed the NFB to 68k or so depending on what you have, I think 150k is too high but others can jump in here anytime. Did you make your shielded wire from input to 15k on pin 7 V1 or did it come made up in your kit. Also I didn't notice any difference using that 15k resistor. Nik only recently added that to his schematic. I told NIK about their shielded wire being bad so he was going to check on that. I made my own and that helped my amp 100 percent. There will always be the high gain hiss. Also I have been using 12ax7 V1, 5751 in V2, and 12ax7 V3. For lower gain you can use what you have.

Mark

[C Moore]

It has taken me many months poking around my express by ceriatone to get it under control.
Mark

Are you saying that you lowered the value of the NFB resistor to 68K? As I said earlier, I raised the NFB from 100K to 150K and it did help. I used the shielded wire that came from Ceriatone. Our amp is probably a year old or more, so I will try substituting some of the shielded stuff that I have. Thanks for the tip, never would have thought of that. Was there some type of trouble with the shielding?
Thanks

[billyz]

A Lower value resistor in the NFB loop from the OT will definitely help the feedback issue. I don't use any shielded wire in my builds with zero issues. Also the presence cap value could be the culprit as well. It will change the frequencies that are accentuated. try using stock values. Chopstick your wires to see if any are microphonic. Actually chopstick all the components, I have found microphonic caps too.

[Allynmey]

I would change all the values back to the proper ones first. I'm not sure what Nik uses these days but, get rid of the grid resistor on V1, change the presence cap back to .1, change the NFB back to 100K and make sure the signal comes off of the 8 ohm tap. Get the thing working as designed then do one tweak at a time.

[rooster]

.........Wait a sec. Are you saying that your gtr starts to howl? Or are you saying that the feedback circuit is howling?