Wards Airline GVC-9056A cuts out on one channel

[Resonator Guy]

My current problem involves a Wards Airline PA head that I play guitar through.
I recently put in new electrolytics and a 3 prong cord. The tubes are good.

Channel 2, the single input one, seems to work fine. I haven't played it for hours on end, but it has never given me a problem.

Channel 1, the three input one, will, at irregular intervals, cut out. The sound will weaken while going fuzzy or fizzy. At times it will snap back to normal on its own without disappearing completely before I can move. Other times it will weaken the same way then cut right out. A poke of the reset switch or a quick flip to standby and back will bring it right back.

The head sounds real good and looks incredibly cool, like an old Buick dashboard. It even has a little neon power monitor that flashes along with the music.

I don't play it very loud. Two 6L6s are way too much for my music room.

Can anyone point me where to start or suggest some specific areas to check? I don't want to lift and check every cap and resistor on the first two terminal strips but I will if I have to.

Any assistance would be greatly appreciated.

(Sorry for the fuzzy schem. Schematic Heaven is not accessible this afternoon.)

[Jazz P Bass]

A good place to start is swapping the input tubes around.
If that is not any help it's time to open her up.
The good thing is you have a working channel.
Check the dc voltages on the preamp tube plates (pin 1 & pin 6) & cathodes (pin 3 & pin 8).
Compare them to the print & to the other channel.
We need a clue as to what is at fault.

[Chuck H]

+1
It could also be dirty or loose pin connections. If cleaning and re tentioning the sockets doesn't fix it get a known good 12ax7 and swap it for each one in the amp one at a time and see if the problem stops when one is substituted.

[Resonator Guy]

Thanks Jazz and Chuck. I have tried known good tubes in V1 with no change. Some did sound better than others though. I will do some cleaning and retensioning today, as well as check those voltages. One odd thing, I had the chassis out of the cab and set it up on end so I could see both the guts and the preamp tubes for any possible flashing or stuff . I played for about half an hour and no problems. Maybe I just need to set it up that way.

[Chuck H]

Hmmm... Could be that turned upright there is a cold connection that is less intermittant. Poke around inside with a chop stick. Poke everything and to see if it make a noise.

[Resonator Guy]

Chuck, I have done A lot of chop stick poking and couldn't make any noise. However, I have just now cleaned and retensioned the first two 12AX7s. I could only play a short time after (my wife is tired of hearing Fortune Teller blasting up from my workshop) but no cutting out. It usually happens fairly quickly. I will test play more tomorrow if I can.

I took voltage readings as Jazz suggested.

V1 Pin 1 164V V2 Pin 1 169V schem says 200V
Pin 6 260V Pin 6 268V schem says 280V
Pin 3 2V Pin 3 1.86V schem says 2V
Pin 8 2.8V Pin 8 2.85V schem says 2.8V

I don't know how great my multimeter is but they all look pretty good except for both Pin 1.

[Resonator Guy]

Well I played it for about an hour and a half yesterday without a problem so I think that cleaning and retensioning the sockets may have done the trick. Thanks for that suggestion.
Do you think the lower than specified voltages on pin 1 of both preamp tubes might cause some other problem or is that within tolerances?
I want to get this one ready to sell so I can add another old Gibson amp to my collection.

[Resonator Guy]

Its back to the bench with this one.
I am going to have to open this up and check all the resistors and caps. It is indeed still cutting out but now it does it cleanly, no fizz or fuzz just out and then back on in a moment. Very frustrating.