I made a few changes to my AA764 champ but

[catnine]

At first I had a f&t 47 uf for the first filter cap and everything sounded fine . It did have some over bearing highs so I took out the ruby 12ax7 and used a JJ ECC83 which really helped cut the highs .

Then I got all caught up in the 5Y3 GT being stressed by a 47uf reservoir so I changed it to a 30 UF and lost some bottom end and got icepick highs .

So I changed the old RCA 6V6GT to a JJ 6V6S and then I got some pick sensitivity I did not have before yet the loss of bottom bugged me So I took some advice and put back another F&T 47 uf cap , don't have a way to read a cap because I don't have a meter for this . The advice was to place a 47 ohm resister between the 5Y3 pin 8 and the reservoir cap and I did this and now it seems like I lost the sensitivity I gained by using a new JJ 6V6S .

It may be me having a bad day so I have to wait until monday to crank this thing up again because the last time I did play it I had the amp at lower vol setting which will affect things.

Is there any reason a 47 ohm resister between the reservoir cap and the pin 8 of the 5Y3 would affect the amps sound?

I still have the 30 uf cap and can put it back in although it is quite a task with so little room . Trying to get all the solder out even with a good solder sucker is not easy , if I remove this cap again I will need to lift the eyelet board because I see some solder hanging below the eyelet but clear of the chassis .

It's really difficult to tell if it's my ears or the amp changes and I don;t know what the orig 47uf cap cap really measured or what the new 47 uf cap measures because as I said I don't have a meter that reads caps.

The amp sounds good over all and did get back the bottom end I lost and the icepick highs are gone . With the 30 uf cap and the JJ it did seem to break up sooner more in a raspy way , that I did not like .

It seems you can't have everything out of a simple build as a AA764 champ . All the 47ohm resistor did was drop 2 VDC off the B+. Perhaps it's just the stiffness of the 47uf reservoir cap over the 30uf . Maybe I need a differnt 12ax7 of the RCA 6V6GTA back in there.

It just gets frustrating because one change seems to make a difference and I am not tech savy enough to know why . Sometimes I do think it's me and not the amp at all .

[scole]

hey cat
i went through the same thing with my bf champ build. i did a bunch of mods trying to get the plate voltage down, the bottom end up, etc. it was driving me crazy, so i went back to the stock layout except i used a jj 40,20,20,20 cap can with the 40 at the first node. i put in an rca 5y3, an nos phillips 12ax7, and a sylvania 6v6 and its perfect. bright and jangly with godd break up. also im using a new jensn ceramic c10r. this champ build turned out to be more challanging and educational than i thought. it was supposed to be a quick easy fun build.

[catnine]

hey cat
i went through the same thing with my bf champ build. i did a bunch of mods trying to get the plate voltage down, the bottom end up, etc. it was driving me crazy, so i went back to the stock layout except i used a jj 40,20,20,20 cap can with the 40 at the first node. i put in an rca 5y3, an nos phillips 12ax7, and a sylvania 6v6 and its perfect. bright and jangly with godd break up. also im using a new jensn ceramic c10r. this champ build turned out to be more challanging and educational than i thought. it was supposed to be a quick easy fun build.

Scole:

Mine is pretty much stock all the was through . I didn't have voltage issues .

It's trying to get the bottom end as best as can be and I used a weber ceramic sig10S which is a lot like the C10R jensen , I have one of those too.

But to get the balance right between the highs and lows is most of the issue I have . If not for the JJ 6V6S I would not have heard the nice pick sensitivity that tube added, you could hear the fingers slide down the strings.

Somehow that changed ar at least seemed to when I put the 47uf cap back in place of the 30uf . I really need to crank it up before I decide because there are only certain times and days in the week I can crank it up to 6 , so last time I played after the cap change I had it at 3 and that makes a difference.

The JJ 6V6 sounded great but it did add a brittle edge to the breakup .

This tweed chassis is small and filled so just to replace the reservoir cap is a battle so if I can avoid doing that again I certainly will .

I loaded the board before I installed it and that is easy when it's out and just componants and wire leads , now to lift it out will be a job .

When I built it I built it to stay done because I used the fender wiring diagram and all the componant values that my 73 SF champ had and that had a 40/20/20 UF cap can stock , this eyelet board is narrow so F&T caps fit well so the closest was 47/22/22 uf caps , no place for a cap can so I did it the old way on the board .

I did not know about 5Y3s and so called spec size reservoir caps and I knew because I ran across this a few times on forums , that was the mistake , if the 5y3 blew then I would go oh gee's and get another one . It lived and was in there a year of more and still it lives .

It's difficult to remember how the amps sounds before and after a change , recording it does not quite work to tell me anything . Then I end up focusing rather than just playing yet I hear differences . Here is a photo of the chassis.

http://i286.photobucket.com/albums/l...sischamp-1.jpg

[catnine]

My AA764 champ build again, Sigh.

I have a 1k 1st dropping resistor when the line is 119.5 VAC as it was today across this resistor I have B+ of 376 VDC across the 1k it's 373 VDC which is my screen even with a 470 ohm screen resistor. The 2nd node is 10k ohm and I have 351 VDC across that . My plate is 362 VDC so my screen is 13 VDC higher than the plate and the resistors are on spec and 3 watt .

I may have asked this before ,couldn't find it , the amp sounds fine , seems like the JJ 6V6S raises my screen about 7 VDC above the old RCA 6V6 GTA . this should not be an issue is that right ?

Now I checked again: Even with a 470 ohm screen resistor there is no voltage drop across it. At times I see 1 VDC drop . This was all at idle vol at 0 nothing plugged in the amp. This time I had 117.9 VAC line , it is up and down so often in thhis old building that it's difficult to get proper readings . It can go from 117.2 VAC to 119.9 VAC so I keep the 680 ohm cathode in there just in case then it's close to 13.0 IPD.

With the JJ 6V6

B+=372 VDC
plate = 358 VDC
screen= 368 VDC

cathode across 680 ohm = 25.0

Node 1= 368 across 1k ohm
node 2 = 346 across 10k ohm

IPD = 12.24

RCA 6V6 GTA

B+= 372VDC
Plate = 360 VDC
screen = 367 VDC

cathode across 680 ohm + 23.8 VDC
nod 1 = 367vdc across ik ohm

node 2 = 346 VDC across 10k ohm

11.76 IPD

here is the latest photo of this amps chassis

http://i286.photobucket.com/albums/l...6-1658_IMG.jpg