Tube rolling Issue

[prs999999]

Hi,

Last night I tried rolling my 12au7 tube and now my amp is really quiet, if I turn the volume up to the maximum I can just about hear the sound.
I am using HD650 headphones which I have checked and are ok, it is a standard crack with the speedball upgrade fitted, other than that it is as factory shipped

I have previously rolled my power tube a good while ago from the original one to a Thomson 6080 FSE- 8408 FF and have listened to it in this configuration for months.
Last night I tried rolling the supplied tube 12au7a (my first roll of this tube) for a Mullard 12au7 CV4003 ECC82 I bought off of Ebay, it was sold as a used tube but with photos of the tube in a tester showing it as good.

When I listened to the tube it was quiet as described above. I have since put the original tube back in and the sound is still quiet.

Does anyone have any idea what might have caused this?
Could it have been a dodgy tube that has blown something else? (a quick look under the hood shows nothing obviously blown and the heaters on the power tube appear to be on)

Any ideas on where to start would be greatly appreciated

Thanks

[Tom-s]

By placing the tube in and out you've probably exposed a weak solder joint on the tube socket.
Flip the amp over, look and feel for problematic connections. Or just resolder all 9 connections on the small socket (what i'd do). Take an extra look at the complete ground path of the amp. The black wires. Espescially near the front tube socket and the headphone connection. Then do a resistance test (follow manual), if all ok, do a voltage test with the original tube.
If all ok, plug in new tube and test voltages again, post here.

[Paul Birkeland]

Measure the voltages.

[prs999999]

Thanks for the info, I will stick it on the workbench tomorrow, take a look and post back

[prs999999]

Hi,

I have had the meter on it and I have found the following, also I am in the UK so this is the 240v version of the transformer

Voltages, all are within the tolerances other than the ones below which are different

pins 2, 4, 13, B2, B5 should all be at 170 and are at 220 or there abouts
pins 7, 9 B3, B6 should all be at 100 and are at 140
pin 15 should be at 185 and is at 220
pin 21 should be at 206 and is at 223
pin A1, A6, B4 should be at 90 and are at 80

Resistance readings wise both pins 7 and 9 are open circuit which i'm guessing definitely needs resolving first up. is this anything to do with the transistors on the speedball upgrade?

Thanks

[Paul Birkeland]

pins 7, 9 B3, B6 should all be at 100 and are at 140
pin 15 should be at 185 and is at 220
pin 21 should be at 206 and is at 223

Since you have a bunch of tubes, I would try a different 6080.

pin A1, A6, B4 should be at 90 and are at 80

The range is 75-90, 80 is perfectly OK here.

Resistance readings wise both pins 7 and 9 are open circuit which i'm guessing definitely needs resolving first up. is this anything to do with the transistors on the speedball upgrade?

The resistance readings on 7 and 9 won't be 3K unless you take the Speedball out and put the resistors back in. 

[prs999999]

Great, thanks

The resistance readings on 7 and 9 won't be 3K unless you take the Speedball out and put the resistors back in. 

would you expect these 2 pins to be open circuit

Thanks

[Paul Birkeland]

Yes.  OL is fine.  Zero is not fine.

[prs999999]

Hi,

so a quick update, I have tried the amp again and it appears to be even worse now I have re-soldered the small tube holder, its now quiet and crackerly, the next port of call i think is to dig out the existing resistors and remove the speedball upgrade and try again. Does this sound like a good idea?

Thanks

[Paul Birkeland]

That is certainly an option.  Can you try a 12AU7 in the amp?  Don't worry about switching the R1 resistors just to do a simple and short evaluation.

[prs999999]

I have tried the amp with both the original tubes that came with the amp and I sadly still get the same result

Thanks