Newbie with 5F1 problems...

[mnexsen]

Hi all. First, wow what a resource to find this site! I'm a newbie with limited electronics experience--I've used a bunch of different stuff from broadcast radio to PA and tube amps and dabbled in "simple" repairs.

Some years ago my son expressed an interest in tube amp electronics and I gave him a 5F1 Champ kit from STF. The kit was not adequately documented for a beginner with only a schematic and poorly legible layout and some of the components didn't match the schematic values but he made a pretty good start on putting it all together. He's overseas in the military now and hopefully will be back in the states soon and I'd like to have this finished for him when he gets home.

Initial questions:
1. I'm not clear about the AC wiring to the back of the switch--does it matter which terminal gets the black wire?
2. I can't figure how to wire up the input jacks: I assume ring and shield are tied; but I'm unclear about where the 1 meg resistor goes.

Measurements:
At each of the first 3 filter caps I'm seeing 492 vdc to ground.
At the 6v6 cathode to the 470 ohm/25ufd cp I'm getting 0 vdc.
On the 0.2 ufd/600v cap closest to the filter caps feeding pin 1 of the 12ax7 I'm getting 489 vdc.
On the second 0.2 ufd/600v cap feeding pin 6 of the 12ax7 I 'm getting 0vdc.

All thoughts appreciated...

[mnexsen]

More info...

It seems therer's nothing getting to the 6v6 or the 12ax7. Neither tube seems to warm up and there's no glow. Maybe that accounts for the measured voltages being too high. So, tracing the wiring for the 6v6,it looks like the connection from pin 7 of the 6v6 to the pilot light switch and to the 12ax7 filament heater (?) might be questionable. Cananyonepoint me in the right direction here?

[RWood]

It sounds like your filament wiring needs to be gone over and sorted out. Remove the tubes until you get 6-7 VAC between pins 2 & 7 on the 6V6 socket and between pins 4-5 & 9 on the 12AX7. You should also get the same reading on the two lamp terminals. You mention "lamp switch" but your power switch should not have anything to do with a 6.3V lamp or the filament wiring.

So follow what should be two green leads out of the power transformer and make sure you have good connections to three areas mentioned above. While you're at it, make sure your other filament leads, probably yellow, that go to the 5Y3 rectifier are well soldered.

When you are confident that you have the filaments wired up correctly, turn it on without tubes and measure your AC voltages. It'll read a little high with no tubes installed but should be around 7VAC for the power and preamp tubes and 6V for the rectifier.

If you have any doubts, post some pictures here of your chassis wiring - there are some sharp eyes here that will spot any potential problems. We'll help you get that amp crankin' before your son gets home!

RWood

[RWood]

Initial questions:
1. I'm not clear about the AC wiring to the back of the switch--does it matter which terminal gets the black wire?
2. I can't figure how to wire up the input jacks: I assume ring and shield are tied; but I'm unclear about where the 1 meg resistor goes.

1. The black wire from your power cord makes a series connection to either one of the black PT primary wires, first through the fuse and then through the power switch.
The white wire from the power cord connects to the other PT primary lead.

2. Take a look at this picture. The 1M connects from the hot lead to ground, and when the jack is unused the hot lead goes directly to ground:

[mnexsen]

Getting close...

OK, so I figured out I wasn't powering the filament heaters. Rewired that and fixed the input jack wiring (thanks RWood) and IT WORKS!! I can't push it now because I only have an 8 ohm speaker and the OT is a 4 ohm but it's quiet and works well.
I do still have some questions:
1. Is it OK for the AC and DC to share a common ground?
2. I don't have the pilot wired correctly--the green transformer lead goes to one terminal; what goes to the other?
Thanks again for everyone's help...

[RWood]

it's quiet and works well.

Do you mean that it's quiet at full volume or you just haven't cranked it yet? If you haven't, turn it up!

1. Is it OK for the AC and DC to share a common ground?

Your AC power cord should have its own dedicated ground, a crimped-then-soldered ring terminal that is bolted to the chassis with nothing else. That green ground wire should also be longer than the black or white, so that in case the cord is yanked out of the amp your ground is that last to remain connected.

DC grounds......that is a huge topic with lots of opinions. Do a search and go with some of the experts such as Randall Aiken and R.G. Keen

2. I don't have the pilot wired correctly--the green transformer lead goes to one terminal; what goes to the other?

The other green transformer lead. It has a filament inside a vacuum, too, just like those firebottles.