AC30 tube swap.

[GrooVey]

Back at the AC30CH. Found a toasted power tube about two weeks back. After learning more about the AC30 (they run hot, they eat tubes) I went with what is advetised as 'sturdy.' There were a few choices but I went with the SovTek EL84M. It's supposed to be 'military specs.' Hopefully they take the heat and vibrations.

Of course everything sounds great at first. After an hour or so they still sound good. I'll be playing them all day to give them a solid testing.

Will report back.

 

[Thatbastarddon]

Sounds like a plan.
There was no sign of carbon deposits anywhere?

 

[GrooVey]

Sounds like a plan.
There was no sign of carbon deposits anywhere?

Nope.

Let me qualify. No I didn't see any.
And I focused on the base of the tubes and the tube sockets. Clean as whistle.

Are there other locations I could check?

 

[Thatbastarddon]

Are there other locations I could check?

Not without pulling the chassis.

 

[GrooVey]

Not without pulling the chassis.

Maybe tomorrow. While I'm working on it. I'd rather do it now when I'm in fix it mode.

After approximately 5 hrs, there is a slight bit of crackling. As if the cord is bad. Ordinarily it wouldn't bother me. But this crackling preceded the last toasted tube.

 

[GrooVey]

Sure does sound sweet now. Especially with the Semi Hollow.

I've read so much lately. Perhaps this is the 'magic' described when the tubes are hot? If such hot tube magic exists.

 

[Thatbastarddon]

Sure does sound sweet now. Especially with the Semi Hollow.

I've read so much lately. Perhaps this is the 'magic' described when the tubes are hot? If such hot tube magic exists.

Just avoid the “magic smoke”.

 

[GrooVey]

Lol, For sure @Thatbastarddon
Had the amp on from about 11 am to 6:15pm Eastern. Had everything mostly on 11. Backed off the top boast treble slightly. I did take breaks throughout the afternoon. Amp was on standby for the resting periods.

No smoke, nor excessive heat. Heat from the tubes just felt 'normal.'

Fingers crossed. Back at it tomorrow. I'll run the normal channel.

 

[Robb]

Lol, For sure @Thatbastarddon
Had the amp on from about 11 am to 6:15pm Eastern. Had everything mostly on 11. Backed off the top boast treble slightly. I did take breaks throughout the afternoon. Amp was on standby for the resting periods.

No smoke, nor excessive heat. Heat from the tubes just felt 'normal.'

Fingers crossed. Back at it tomorrow. I'll run the normal channel.

Should be stable after that test.

 

[syscokid]

And I focused on the base of the tubes and the tube sockets.

And the power tube’s screen resistors too?

 

[GrooVey]

And the power tube’s screen resistors too?

Nope.

Are they located directly under the tube socket?

 

[syscokid]

Are they located directly under the tube socket?

At least somewhere close by. Do you have any pics of the power tube sockets on the component side of the circuit board?

 

[syscokid]

Does your Vox look like this? The screen resistors are probably the ones encircled in yellow. Look for signs of heat damage, and measure their resistance values. The smaller resistors to right of the screen resistors should be the grid resistors for the power tubes.

 

[67plexi]

all resistors are under the tube socket PCB the hand wired version you can switch between 50 ohm 10 watt and 80 ohm 10 watt
the ones I have serviced I used a 100 ohm 10 watt have fun you have to remove the tube socket PCB

 

[GrooVey]

any pics of the power tube sockets on the component side of the circuit board

No pics. I've not been too far inside.
I can peak around tomorrow. For sure. I'd like to know as much as practical about these things.

Does your Vox look like this?

Close. The tube arrangement is the same. But my tubes are acessed from the bottom. They are in an isolated compartment. I'll pull the back off and the chassis if necessary. Tomorrow.

 

[GrooVey]

all resistors are under the tube socket PCB the hand wired version you can switch between 50 ohm 10 watt and 80 ohm 10 watt
the ones I have serviced I used a 100 ohm 10 watt have fun you have to remove the tube socket PCB

Hi 67...

I've been reading... Is this the mod to affect the bias? Makes it a bit cooler?

The last few wiring harnesses I've made came out great. Then I saw the burn marks on the computer screen. I'm pretty good with the soldering iron, but I'll not be taking an iron near all that. Bit I know a guy if necessary.

 

[GrooVey]

Thank you @syscokid !

That was painless. All I had to do was pull the back panel. (There is a bottom panel for pulling the tubes.)

Yes. Mine does look the pic.


And here is a close up of the resistors. V4 and V5


And V5, V6, V7


Resistors look clean and healthy to my eye. What do you think?