The Steel Guitar Forum

I have a 73 fender twin reverb that needs new tubes. The problem is that the tubes don't have the number on them just clean glass. Witch looks kinda cool if you take the time to take off the tube covers and look behinde your amp. This how ever dose nothing to help my perdicament(did I spell that right?) All the tubes are way past due for a changeing every thing is nice a fuzzy all the time. Can any one give me the numbers for tubes thanks!

Look at the tubes closely. Sometimes the markings will fade away but if you blow your breath on them it will give you enough to read what they are.

I thought there was a tube placement label on the side of the amp. Check to see if the tag is still there. It also says what chassis it is, e.g. AB768 or whatever.

From memory the first two are 12AX7's. And of course the power tubes are 6L6GC's.

As you look at the rear of the amp, from right (the side wall) to left (the center) the 6 preamp tubes are:


1)12AX7A/7025
2)12AX7A/7025
3)12AT7
4)12AX7(A)7025
5)12AX7
6)12AT7

The 4 power tubes are 6L6GC.

I'm unsure of the difference between 12AX7 and 12AX7A. And there are many variants of the 6L6's. If you talk with a good dealer or tech you will get his idea of what the best tube is. In the end you have to trust someone. My rule of thumb is that if he says 'such and such just plain sucks" he is probably not a useful source of practical advice. He just loves the sound of his opinions.






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Thank you all for your help. MY amp is a ltlle less mysterious but still cooler than heck.

The 12AX7A/7025 is a low-noise version of the 12AX7. I believe the difference is in the way the filament (heater) is constructed. I don't know if new production 12AX7A's have this characteristic, however.

When replacing the 6L6s, be sure to use the 6L6GC, as opposed to the 6L6GB, which doesn't have a sufficiently high voltage rating for the Twin. The Svetlana (sp?) 6L6s seem to be highly regarded these days. But another option is to get American-made NOS (new old stock) tubes, which are still available but can be expensive. Here's a web site with NOS tubes for sale, and some interesting articles. http://users.erols.com/bluestat/

If your amp is fuzzy it may have problem other than weak tubes. Might be worth having a tech check it out, especially for an amp that old. At the very least, he'll set the bias for your new power tubes, which is something that should be done.

hi larry. in addition to replacing your tubes, have a tech check your capacitors. most caps only have a recommended life span of 10 years. after that they could fail and harm other things in your amp. it is good preventative stuff for your vintage amp.
good luck!
brian

Larry. As a suggestion, if you're considering using Sovtek Tubes, you might want to consider their 12AX7WB for some of the preamp tubes, and the Electro Harmonix 6L6GC for your power tubes. You can order these in matched sets.

I bought a whole set of tubes for my 71 Fender Twin at www.tubesandmore.com and they have a lot of parts for Fender amps. I paid approx. $105.00 for the whole set of tubes.

I have accumulated these links over time. I have yet to do any business with any of them so I endorse none. For every positive review I read about a particular tube, I read a scathingly negative one somewhere else--either about performance or quality control or whatever. Some of these dealers claim to pre-screen tubes for microphonics etc.
I have had good communications with the Eurotubes dude and have read strongreviews of the JJ/Tesla tubes. I'm leaning that way myself for some preamp AX7s. Anyway, here goes--

http://www.eurotubes.com/
http://users.erols.com/bluestat/#index
http://www.newtube.com/content/
http://store.yahoo.com/triodeel/index.html
http://www.unclespot.com/tubeprices.html
http://store.yahoo.com/thetubestore/index.html
http://www.tubeworld.com/
http://www.vibroworld.com/