2204 clone build no current to heaters

[Hspencer]

Hey,

Been following the forum for a while now but never posted. Building my first tube amp, a 2204 clone from mojotone. On first power up, no tubes, I get 120vac coming in as expected but no current on the heaters. Can anyone direct me where to start looking to troubleshoot?

[martin manning]

Could be a transformer problem. Measure AC voltage across the heater pins and also from each side of the string (pin 2 and pin 7) to ground. Do you get anything?

[Dr Tony Balls]

With no tubes inserted there shouldnt be anything pulling current on the heaters. I agree with Martin, check your voltages on the heater pins.

[bmx]

Anyone else object to the -Vbias being post Standby switch?

My advice to new builders or new repair guys is to power the amp up in standby and measure -Vbias at the power tubes. If it's there, a lot less to worry about. Great first step.

Let's say the builder of one of these puts the -Vbias rectifier backwards. How long does it take to get the meter and connect it to the power tube grids, AFTER taking the amp off standby? Longer than it takes to smoke the power tubes and or the output and power transformer.

It's just one more turret and one more wire! Otherwise its a totally great kit.

[pdf64]

Anyone else object to the -Vbias being post Standby switch? ...
It's just one more turret and one more wire! Otherwise its a totally great kit.

It's rather depressing, how such an unbelievably stupid design has become so ubiquitous.

[Stevem]

So neither the on off main switch or the standby switch does not light up?

Do you have a fuse in the fuse holder that’s on the primary side of the power transformer

Also it’s real hard to tell from your photo, but I don’t think I see the needed jumper wire from one side of your ac on / off switch to the other side.

[Hspencer]

My initial voltage readings on the heaters were off due to a fault MM. New MM up and running and the heater voltages are the following.
With no tubes in v1 thru v5 all measure at 6.5 VAC
With the tubes in v3 thru V5 all measure 6.8 VAC
V1 and V2 heater pins are only reading 3.2 VAC.

Shouldn't these all measure out the same?

[Hspencer]

So neither the on off main switch or the standby switch does not light up?

Do you have a fuse in the fuse holder that’s on the primary side of the power transformer

Also it’s real hard to tell from your photo, but I don’t think I see the needed jumper wire from one side of your ac on / off switch to the other side.

The power switch and the standby switch both work fine.

[Stevem]

You still have a measuring problem if with 5 tubes in your ac reading is higher then with 5 tube out like you posted up.

Please post up some good photos of the preamp tube sockets and there wiring .

Do you still get that low heater voltage reading with no tubes in those sockets ?

[sluckey]

Measure your filament voltage across the filament pins, not from one pin to chassis. For the little tubes, one probe is connected to pin 4/5 and the other probe is connected to pin 9. For the big tubes, one probe is connected to pin 2 and the other probe is connected to pin 7. Tubes should be plugged in. Switch set to standby to remove B+ from the sockets.

[Hspencer]

I've got the heater voltage issue worked out. Replaced the wire running from v3 to v2 and I'm getting consistent 6.4 volts. I am also getting signal through the amp now and controls are working as expected.

Issue I have now is that the V4 el34 appears to be overheating. Any thoughts on the issue?

[Hspencer]

Here is a picture of V4

[martin manning]

That photo of V4 red plating is with the amp just idling, no signal? I would guess that tube has an oscillation going on, most likely cause is lead dress issue.

[Hspencer]

That was with a signal. That tube, swapped into the V5 location, still red plated. I'm thinking bad tube.

How do I check the lead dress?

[martin manning]

If the red plating follows the tube then you are right to suspect the tube. Lead dress can be tricky, often just pushing leads around with a chopstick can reveal the source of unwanted feedback. An oscilloscope is the best tool to confirm or deny the presence of an oscillation. I would replace the tube or better yet the pair with a matched set.