Need Help with PreAmp Tubes

[mcdmgb]

I am not particularly knowledgeable on the intricacies of tube equipment. I have a Scott 222C which was restored a number of years ago. Lately It's starting to hiss and become microphonic when using the phono. I am guessing that its the preamp tubes. The installed set is a mixed-bag of 7025s of unknown age and usage. I installed a new set of SED 12AX7-WCs which I had on hand. After installation, there was no sound in phono and a very weak signal from a CD.

Are the 12AX7s the wrong tube for this application? If they should work, what else should I be looking at?

Thanks

 

[Catmanboo]

What's it say on the chassis? Use that. 7025 is the "ruggedized"12ax7, if I recall.

 

[Dswankey]

I have a Scott 222C which was restored a number of years ago.

Are the 12AX7s the wrong tube for this application? If they should work, what else should I be looking at?

Thanks

No

Your problem sounds like it might be something other then the tubes, when you say weak signal from the CD I'm assuming you have the CD player connected to the AUX port?

They're considered a very nice amp, here's hoping it just needs a little TLC.

 

[jkaley]

Power off. Pull all the tubes in and out a few times and then make sure they're firmly seated and power on.

 

[mcdmgb]

After my initial posting, I put the 7025s back in, in no particular order. So far no problem. Possibly the problem is one tube and it wasn't put back in one of the positions for the phono?

 

[trainbuftony]

An open filament in any of the 12ax7s will shut power off to the whole string. Its Its highly likely that your old tubes just needed to be reseated in their sockets. Enjoy, you have a nice piece of stereo gear which will never be obsolete.

 

[mcdmgb]

An open filament in any of the 12ax7s will shut power off to the whole string. Its Its highly likely that your old tubes just needed to be reseated in their sockets. Enjoy, you have a nice piece of stereo gear which will never be obsolete.

The 12ax7s were a bit loose in the sockets, so that may contributed to the problem. Since I don't seem to be having a problem after putting the 7025s back in, I don't think that I will worry about it.

You're right about the 222C I also have a 299 that gets used in my office. Both were restored by Craig at NOS Valves. Every time that I listen to them, I am amazed that 50+ years old stereo equipment can sound that good.

 

[mnmmt]

My guess is the pins on the old 7025s are fatter than the ones on the 12ax7. To use the 12ax7s in it, you'd want to tighten up the tube sockets--make sure the caps are discharged, otherwise you could get shocked.