OT: Champ 5F1 clone bad distortion...

[puretube]

(just looked up "pummeled" in the dic: just what I had expected...)
so, Paul, we`re thinking the same: there might even be an
arcing-over to be seen inside the 6V6 in the dark?
My (old) databook says: Ua-max: 315V; Ug2-max: 285V;
Qa-max: 12W; Qg2-max: 2W;

Uk=23V div. by Rk=470ohms equals: Ik= 49mA thru the tube;
now if we took only the measured 366V at the screen-grid
multiplied with Ik= 49mA (which is Ia+Ig2) we get 18Watts;
if we calculate more realistic Ig2=6mA@366V equals 2.2W,
plus Ia=43ma@426V equals 18.3W, sum= 20.5W.
That`s 46 % overload for a "good old 6V6".

am I overlooking something?

[marrstians]

my output tranny is from hoffman amps... it says it's a champ eq....  the only thing with the power is that i tried changing the first 10k resistor to a higher value which significantly dropped my voltages but it still made the same sound... unless when i droped the voltages the bias was still off because i didn't change any of the bias resistors?>?

[puretube]

I`d like to see the first HV (B+) at the plate lower - the others will follow down - I`d try a 1k or 1.2k resistor (5W) between rectifier output and first el.-cap - this would lower the B+ by roughly 50V.

this is not a recommendation, but what i would do, if it were my amp...

[Paul Marossy]

Yep, that's what I was getting at puretube.
I also was thinking B+ was a little too high, as I mentioned earlier.
My bet is on the power tube is overloaded.  

[Dave Z]

There is a lot of talk about how to drop voltage after the rectifier on this site:

http://www.firebottle.com/fireforum/fireBB.cgi?cfg=dlx&enter=go

search on "zener diode" or "dropping voltage"

You don't want to use a resistor as its behavior is voltage dependent - you'll get LOADS of sag with a resistor. Zener diodes have a flatter behavior and are preferred in this case. They DO get hot, be warned....

[puretube]

sag is no big problem here:
a.) R is before 1st reservoir cap;
b.) class A PA: quite "constant" current flow;

[marrstians]

hey... tried the screengrid resistor... i think i did it right... i just put a 470 ohm resistor in series with pin 4 of my 6v6 right? that didn't help at all if that's what i'm supose to do.... i'll have to try and find a 1k 5watt resistor somewhere... the local store only had 1 watt, i don't think that would be safe... so i might have to wait a couple of days.. this problem really sucks but i've learned more about amps and the terms used with them in the last week than i ever did reading crappy books... thanks to everyone that's trying to help....

[puretube]

five  4.7k/1W in parallell...

[aron]

What about pictures of the inside? Maybe that would tell us something?

[Dave Z]

yup, puretube, good point on the class 'A' bit, a resistor would work. Either way, this thing will make a great room heater....

[marrstians]

alright... i finally got that 1k5w resistor and put it in series with b+... it dropped my voltages down alot, my b+ is almost right at the 360v that it's supose to have... it helped a little bit but it's still doing the same mis-biased sounds... i'll try and take some pics this week but i'm running on fumes with ideas now... i'm about to send it to someone else to try and figure it out...  :cry:

[marrstians]

well... i think i may have got it.......... i started the whole process over with the new lower voltages... after i got a 22k resistor on gird 2(pin 7) of my preamp tube it seemed to go away... my question is why did this seem to work and why wouldn't it work with the old b+? thanks to all who helped out with this thread...  

[marrstians]

well... i think i may have got it.......... i started the whole process over with the new lower voltages... after i got a 22k resistor on gird 2(pin 7) of my preamp tube it seemed to go away... my question is why did this seem to work and why wouldn't it work with the old b+? thanks to all who helped out with this thread...