My 5F1 Champ is Sick - Low sound output and glowing 6v6 tube

[Wittgenstein]

Just the other day my Champ started giving me some troubles. I was on it for awhile when all of the sudden, it lost most of it's volume. When I turn the amp to max, the guitar to max, and strum loudly I can still hear the amp (as if the volume was on 4 when working) but it sounds broken up, distorted, and almost like it cuts in and out. The more I turn up the guitar's volume or the amp volume the more noticeable the blue glow from all sides of my 6V6 power tube is.

So far I have tried swapping in all new tubes (same results), testing all the tubes I was using in a different amp (tubes work fine), tested the speaker with a different head (speaker is fine), and tested the champ through a different cab (same problem). I recently moved and lost the sweet digital multimeter that I was using, but I did measure the voltages a few weeks ago when it started to give me trouble and from everything I could think to check, it looked good. I also did the old "pop trick test" while the amp was hooked up and running, but I could not tell much as it still makes sound, just not as much. I did not sound like it popped as loud as it should.

I plan on double checking for a bad solder joint, starting with the the input jacks > preamp tube socket> and back and will re-flow any solder joints that look even slightly questionable.

Any suggestions of what to try next?


Link to my previous thread about this amp build w/ pics.

[MWJB]

You say the voltages "looked good"...there isn't really a whole lot of things that could go wrong, and if something does go wrong it will often show up in the dc voltages...so record voltages at rectifier pin 8, power tube pins 3, 4 & 8, 12AX7 pins 1, 6, 3 & 8. I can't tell you how many amp problems have been diagnosed in around a minute using this technique & simple visual inspection.

[Wittgenstein]

Thanks.... I figured there was not much that I would be able to do until I get the Fluke meter back again. I will take a look and be sure to post the results here.

[MWJB]

A cheap meter from the hardware store will do for the dc voltages, but clip the black common wire securely to the chassis.

If you have spare 25uf electrolytic cap, just as a long shot, replace the 6V6 bypass cap, use a 50-100v rated cap (in fact, to eliminate it from your enquiries you might just remove the old one, gain will drop & the amp won't distort so easily, but it might tell us whether the bypass cap is an issue).

[loudthud]

In the other thread there was mention of problems with the 12AX7 socket. Did this ever get resolved? Carefully inspect the socket from the side where the tube plugs in. Clean the contacts if they look dirty. If any of the contacts look bent or out of alignment, try to bend them back with a sharp tool like an ice pick or metal scribe. Be sure the power supply caps are discharged before you do this! If you can find a solid wire that is the same diameter or slightly smaller that one of the 12AX7 pins, poke it in each socket hole to make sure there is good tention of the contacts.

[Wittgenstein]

In the other thread there was mention of problems with the 12AX7 socket. Did this ever get resolved? Carefully inspect the socket from the side where the tube plugs in. Clean the contacts if they look dirty. If any of the contacts look bent or out of alignment, try to bend them back with a sharp tool like an ice pick or metal scribe. Be sure the power supply caps are discharged before you do this! If you can find a solid wire that is the same diameter or slightly smaller that one of the 12AX7 pins, poke it in each socket hole to make sure there is good tention of the contacts.

I did fix my previous problems by changing out the 12AX7 (bad tube), but I was still suspect of that socket as well. I will make sure to give it a good once over. I do have a spare 25uf 50V I can try off the 6V6 but I'm not sure if I have any 50uf electrolytic caps. I will be picking up a multimeter on my way home tonight; I want my Champ back. Thanks for all the suggestions.

[JHow]

...the more noticeable the blue glow from all sides of my 6V6 power tube is.

Bad tubes can fluoresce and give off a purplish glow (plasma). If there is a light-show inside your tube, try swapping the 6V6?

[MWJB]

Bad tubes can fluoresce and give off a purplish glow (plasma). If there is a light-show inside your tube, try swapping the 6V6?

Good tubes do this too, it's not a sign of a bad tube per se, if the tube is glowing brilliant blue at idle this suggests some sort of failure (which we already know), look for signs of shorts. Power down & reinforce any grounded eyelets by bridging the grounded conection to the chassis, power up & note effects...power down & try the next ground point.

Got that meter yet?

[Wittgenstein]

Good tubes do this too, it's not a sign of a bad tube per se, if the tube is glowing brilliant blue at idle this suggests some sort of failure (which we already know), look for signs of shorts. Power down & reinforce any grounded eyelets by bridging the grounded connection to the chassis, power up & note effects...power down & try the next ground point.
Got that meter yet?

The power tube really only glows brilliant blue when the guitar and amp are turned way up, but it seems to glow more than I remember. I did pick up a cheap little digital multimeter on my way home last night, but I did not have time to take any measurements. My power was out for about 3 hours due to strong winds here in IL. I will have plenty of time this weekend to check it out. I am really missing that Fluke meter, as having to set the range for every measurement is getting very old. I also never had to worry about blowing the fuse in the Fluke. Something for the Christmas wishlist I guess.

[Wittgenstein]

Voltages

5Y3GT - Pin 8 -406VDC
6V6GT - Pin 8 -20.8VDC, Pin 4 -350VDC, Pin 3 -387VDC
12AX7 - Pin 8 -1.45VDC, Pin 6-197VDC, Pin 3-1.46VDC, Pin 1-200VDC

EDIT: Fixed
After seeing all the voltages check out, I figured it had to be a bad solder joint, most likely on the input jacks or the jack to the speaker. I re-flowed solder on all suspect connections, plugged it back in, fired it up, and it is loud again. Not sure which solder joint was bad, but I do not really care as long as it is playing. I am using a NOS 5y3 rectifer, any suggestion on how to further drop my B+ to be more in line with the 340VDC written on the Fender layout diagram?

[MWJB]

"I am using a NOS 5y3 rectifer, any suggestion on how to further drop my B+ to be more in line with the 340VDC written on the Fender layout diagram?"

2 suggestions...

1) Don't, if you want the amp to actually sound like a 5F1, you are closer as you are, your voltages are "Ball Park" for a genuine 5F1.

2) Add zener diodes in reverse polarity from the B+ centre tap to ground...but personally, in your case I wouldn't bother.

[Bruce / Mission Amps]

"I am using a NOS 5y3 rectifer, any suggestion on how to further drop my B+ to be more in line with the 340VDC written on the Fender layout diagram?"

2) Add zener diodes in reverse polarity from the B+ centre tap to ground...but personally, in your case I wouldn't bother.

Your 6V6 is idling well over 15 watts right now.. that is not the end of the world as MWJB is pointing out.... however, on this amp, you use a 2 watt metal oxide 510 0hm cathode biasing resistor for the 6V6 and to lower the B+ a bit more, you can lift the B+ wire from the rectifier tube socket and use a 5 Watt 12v-20v Zener diode right at the rectifier tube socket lug 8... just put it in place with the banded end facing the lug.

[Wittgenstein]

Pin Outs

5Y3GT
Pin 8 - 384VDC

6V6GT
Pin 8 - 20.4VDC
Pin 4 - 341VDC
Pin 3 - 380VDC

12AX7
Pin 8 - 1.5VDC
Pin 6 - 186VDC
Pin 5+4 - 44.7VDC
Pin 3 - 1.6VDC
Pin 1 - 185VDC

My champ is still giving issues with low output. When I have the amp cranked all the way up it sounds crunchy but like it is being attenuated. If I turn it below say 4 or 5 it is almost not audible. I have gone over every connection for continuity especially the wires that run underneath the board, checked all grounds, and the voltages check out. I tried playing a different head through my speaker and swapping all the tubes out for known working ones. An suggestion on where to go from here. Could it be a faulty electrolytic or something else that I am not able to check?

[MWJB]

44.7vdc on your 12AX7 heaters? Shouldn't be there? Have you dc referenced the heaters?

A 4vdc drop from B+ to 6V6 plate sounds wrong for a 5F1 unless you are using a very large, oversized OT? (I'd be expecting a 10-12vdc drop accross the OT primary in a stock 5F1). Can you check the turns ratio of your OT, should be about 40-50:1 for 4ohm output.

Pst some pics of the board & tube socket wiring.

[Wittgenstein]

44.7vdc on your 12AX7 heaters? Shouldn't be there? Have you dc referenced the heaters?
Pst some pics of the board & tube socket wiring.

Sorry about that, it was very late when I was posting last night. The 44 Volts on the heaters should have said AC not DC. Below are some photos of the board and tubes. This amp was playing fine and then one day it just sort of cut out and now has low output.