5f1 DIY...No Guitar Sounds....

[bradberry00]

Hey all,

I just got done throwing together a 5f1 Champ circuit. However, Im not getting any guitar signal through it. When I power up the amp i get the faint hum/hiss of a working amp though the speakers, but no sound when I play my guitar through it. I thought it was just as simple as wiring the input jacks wrong, but I cant see any errors in my wiring there.

The only thing i did that is not stock is replace the 10k resistor on the filter caps with a choke and with it I, added a screen resistor on the power tube (the resistor goes across pin 1 and 4 of the power tube socket)

Can anyone think of some easy things to look for....it could be an accidental grounding or something, but I really can't see any errors there either.

I can get pictures tomorrow if they would help. I can also get some voltage measurements if they are needed.

Thanks in advance!

-david

[MWJB]

OK, probe the plates of the 6V6 (pin 4) for dc voltage, note what you get but also listen for a pop/tssk sound, whilst you are there record dc voltages at pins 4 & 8. Then probe pins 6 & 1 of the 12AX7...where does the popping noise stop? Be aware that as you get nearer the input the pops will get much louder, so set your volume accordingly and don't panic, probe at the jnction of the 100K resistors & 0.02 coupling caps rather than at the tube pin on the 12AX7.

[bradberry00]

cool it is a start, i hope to take these measurements tomorrow when I have some free time!

Thanks, I will report back

-david

[loudthud]

This thread has a resistance check for the input jacks. It was done on a 5E3 so all the checks don't apply to the 5F1 but you should get the general idea.

http://music-electronics-forum.com/t12667/

[bradberry00]

Ok i checked the voltages on pins 4 & 8 of the 6v6 and 1 & 6 of the 12ax7....i didnt hear any popping/hssing.

6V6
pin 4 ---- 380v <---seems high maybe not??
pin 8 ---- 21v

12ax7
pin 1 ---- 213v
pin 6 ---- 208v

[bradberry00]

Loudthud...everything checked out exactly as your specs on my input jacks.

[MWJB]

If you didn't hear any popping output, triple check your output transformer & speaker/speaker wiring.

I seem to have given you the wrong pin no. for the plate so check pin 3 (pin 4 is the screen) as well.

[bradberry00]

on pin 3 i did have popping, but that is the only location where there was popping/hissing. I dont remember the voltage i will remeasure.

[MWJB]

Good, that suggests that you are at least getting signal from the 6V6 to the OT & speaker. Your break, or inadvertant ground in the circuit that is killing the signal, must be between 12AX7 pin 6/7/8. Wire from coupling cap at 12AX7 pin 6 should run to 6V6 pin 5, check continuity from top of said cap to 6V6 pin 5, also check resistance to ground. Check voltage at pin 8 of the 12AX7.

[bradberry00]

Thank You MWJB and Loudthud! With your help I got this project up and running. It was indeed an accidental grounding as I originally suspected (somehow the wire from the .022 coupling cap to pin 5 of the 6V6 got pinched between the turret board and one of the output transformer nuts). MWJB with your help I was able to isolate the problem to a single wire. Not only did you two help me get my amp working, but also taught me some excellent tips for troubleshooting future builds! Thanks again, and I hope you guys are around when I inevitably need help again!

-david