OT: Champ 5F1 clone bad distortion...

[marrstians]

ok.... no dc on the pot... the grids on the preamp tube is fine... the power tube i get 0v when the volume is turned down, if i turn the vol all the way up i get a +.089 .... i don't know if that would do anything... i haven't tried the grid stopper thing, i'll have to do that when i get some more time... disconnected the 22k feedback resistor and it didn't really help at all... if there is a dc leak what would be the culprit, bad parts or bad builder...? :wink:

[Paul Marossy]

What about lead dress? Have you tried seeing if any the wiring could be causing the problem? It could be a problem with oscillation. Maybe pushing some wires around could make the problem disappear. I use wood chopsticks, as they are non-conductive.

[puretube]

bad parts...

(assumed the values of the parts are correct,
and wired according to the schematic)

[puretube]

got it: (or not...)

the schem doesn`t show a connection from heater supply
to the general ground.

If you followed the original layout, it should be somewhere.

Is one of the heater-windings connected to circuit ground,
or are they both "floating"? *

If floating, hook one of the 2 filament wires to ground;
check if any hum should occur, if grounding the other
wire sounds better;
if hum is too loud, connect 2 100 Ohm/0.5W resistors in series,
and hang them between the 2 filament wires, and hook
the middle of the 2 res. to ground...

*: this concerns only the 6V3 audio-tube filaments (green wires)
of the 12AX7 & 6V6,
NOT the rectifier filaments (yellow)!!!

[puretube]

read edit on bottom of last post!

[marrstians]

ok... tried the grid stoppers, no help there... the only thing i didn't do is insert a 470 ohm 1W res. (short-cut lead) directly at the screengrid lug on the 6V6 socket.  i'm not exactly sure what's the screengrid lug?.?...  also just for fun i re-routed the heater wires to see if that was messing anything up, no help either... i've moved wires around, cut some leads shorter... we're running out of options here...

[puretube]

the screen-grid is the grid close to the plate,
which goes to the node of 10k & 8µ/450V & 22k
on the hi-volt side.

did you ground one side of the filaments yet?

like mentioned: it is not shown in the schematic,
but very usual practice...

[marrstians]

yeah... i grounded one of the green wires... i'll try the 470ohm next and see if that helps...

[puretube]

oops, re-read the old posts, and seemed to have missed the HV details:

420V is very high for 6V6...
320V is more of what they like.
(Fender seems to love taking it to the limits... :roll: )

Is the cathode resistor (470ohm) of the 6V6 a hi-watt type (>1W)?

Tell us more on the voltages (with no input signal):
1st, 2nd, & 3rd hivolt electrolytic;
plate & cathode 6V6;
plate & cathode 1st & 2nd triode;

[Johan]

(b) blatty distortion comes from two sources, bias problems and oscillation.

I have to go with R.G. on this one..probably oscillation. especialy since it happens halfway on the volumepot, where the impedance to ground or signalsource is largest. try to re-rout the cable going from the centretap of the pot to the tubegrid. it is not unlikely that it is picking up the signal in phace from one of the other stages...

Johan

[Paul Marossy]

Oscillation could be happening here. Although, I still think the power tube might be getting pummeled from the higher voltage being supplied to it compared to what is specified on the schematic. I think doing something to lower the B+ voltage a little bit might help (bigger series resistor), and checking the power tube bias again to make sure it is right with the lowered B+ voltage.

[puretube]

(b) blatty distortion comes from two sources, bias problems and oscillation.

I have to go with R.G. on this one..probably oscillation. especialy since it happens halfway on the volumepot, where the impedance to ground or signalsource is largest. try to re-rout the cable going from the centretap of the pot to the tubegrid. it is not unlikely that it is picking up the signal in phace from one of the other stages...

Johan

this kind of oscill. wouldn`t be the one we tried to remove with gridstoppers, but have tried to exclude under "proper wiring/chopstick"...
but worth checking once more...

BTW: are the wires running to the filaments twisted tightly (mostly for hum-reduction, though...)

Next thing from my side would be wanting to hear a soundclip/seeing some pics of the layout/scopetrace of output... :lol:

[marrstians]

ok... here's my voltages...

from tranny: red 376v yellow 426v

1st hivolt elec 426v(16uf-10k)
2nd hivolt elec 375v(8uf-pin 4 of 6v6)
3rd hivolt elec 250v (i upped the 22k resistor to 68k to get the voltages down on my preamp tubes but i still had the problem before i changed that resistor...  
from the 470ohm-25uf-pin 8 6v6 is 23v...
6v6 pin 4 366v, pin 3 418v
12ax7 both at 153 volts...

i don't have a scope so i can't do any of that stuff.... i tried poking and moving stuff for about 15 mins last night but not a lick of difference there...

[marrstians]

ok... more notes... i rerouted the pot to see if that would help... it didn't... i lowered the voltages by changeing the 10k resistor just to see if that could make a difference, it didn't...  i've tried the chopstick thing with no avail... i tried a 6l6 in the circuit also to see if the voltages or anything was the problem but it still does it... i've also noticed that it still makes the sound with the volume all the way up but it's not as noticable as when it's at 5-6, maybe the natural distortion was fooling my ears for a minute... what should i check next?

[marrstians]

i've read a few things about old fenders and it seems that quite a few were at the voltages that my trannys putting out... so i don't think the voltage is the problem... is there other stuff that i could definetly rule out as the problem... could it be the output tranny? my caps? ect...   i know it's not the tubes, i've changed them a few times to check... i don't believe it's the pt from what i've tried and read about old fenders...  i've rechecked my resistors with my voltmeter to see if they were the right values instead of just a visual check and they all read right... the heater lines usually only cause grounding problems as well as the way you ground the actual circuit, correct? it sounds almost identical to a misbiased tranny in a pedal but coming from my amp... do you think it could be a bias problem with the tubes?

[Lonestarjohnny]

With out scopin the thing guessing is not a good choice, but you for sure got a DC voltage messin around with your AC signal, you look close at your bypass cap's to make certian that they are + side to the Tube ?,You might try another .02 coupling cap that feeds your tone pot, could be leaking, also tug on those bypass resister's to ground and make sure non are loose or cold soldered, if it was a voltage problem disconnecting the 22 K neg. feedback resistor would change it in someway, you did use Axial cap's for the bypass cap , you can use radial's but they look funny stickin up on the board. maybe if you post some voltages that you can read on the pre amp and phase inverter someone here will figure it out, 2 head's are better than 1, Sometime's :lol:
Johnny

[Lonestarjohnny]

after reading all your test's you've run i only see 1 thing that catche's my eye, on most Fenders i've worked on pin's 3 and 4 will have close to the same voltage reading, your pin 4 look's a tad low for some reason and also, fender ran most of there 6V6 amps over 400, some around 390 on the B+, that's what makes the B/F Delux very costly to buy, it do sing on 425v's
Johnny

[puretube]

this version got the screen grid to B2, which is lower.
other versions got it right to the OT, where it`s closer to plate voltage.

It appears to me, that the screen grid voltage has 2 values:
366V @ pin4;
375V @ 2nd el. cap;
in the schem, it`s a direct connection...
oscillation here? (screengridstopper, 470 Ohm/1W at socket).

BTW: is the OT a single-ended suitable type? (air-gap?).

[puretube]

ok... here's my voltages...
1st hivolt elec 426v(16uf-10k)
2nd hivolt elec 375v(8uf-pin 4 of 6v6)
3rd hivolt elec 250v (i upped the 22k resistor to 68k to get the voltages down on my preamp tubes but i still had the problem before i changed that resistor...  
from the 470ohm-25uf-pin 8 6v6 is 23v...
6v6 pin 4 366v, pin 3 418v
12ax7 both at 153 volts...

ok, here`s Aspen Pittman`s Tube Amp Book (4th ed.) corresponding 5F1 voltages:
1st cap (B+) 340V;
2nd cap (B2 = screengrid) 295V;
3rd cap (B3) 250V;
Uk[6V6] 18V;
Ua[12AX7 a/b] 150V;
Uk[12AX7 a/b] 1.5V;

though it says all voltages +/- 20%, your readings look close to/over
the edge of SOAR from my databook.

Someone else here will guide you to re-bias things into the green zone, if that is the problem (and if nothing else, or the combination of some, helps).
:oops:

[Paul Marossy]

I still think the power tube is getting pummeled. One thing that you have to remember when looking at these data sheets on the 'net is that they are 30-40 years old and created around the time when tube manufacturing technology was at its peak. I am not so sure that new manufacture tubes live up to the old standards. This situation could be a case where this is true. And the bias current is probably messed up, adding to the nasty distortion sound.