#133387  by boater1941
 Mon Oct 21, 2013 9:51 am
My final test was to use my two NOS RCA 7025's in both V1 n V2. I know you guys have said the 7025 are just a heavy duty version of the 12ax7's but the tonal response and string sensitivity are through the roof. This SMSJG is so potent I don't even bother with the rocktron300 any more. I mounted the budman in the bottom of my rack with Brad's padding knob fully open at the back. I send this out to my two E's wired for 4 ohms in parallel.
Once again I can't turn my 2300's volume up even close to what I was playing with in a garage (front door) open. There has to be a better explanation then just heavy duty. We need some SMS creator's opinions on this if he's available. If he could explain the sms signal path in comparision to the twin's ab763 path might enlighten us on the subject.
From what I gather both channel and vibrato inputs each hit a separate 7025 first. Then I get lost There's a 12at7 next which doesn't go to any tone stack knobs. Then we have a 12ax7 possibly reverb send followed by most likely is reverb return 12at7.
I can't see these happening in the sms because the reverb is digital not a spring tank send and recovery. Hope Brad can elaborate for us here and a sweet Jerry tube combo incase we went the NOS route like I've been playin with.
Thanks guys.
 #133391  by Smolder
 Mon Oct 21, 2013 10:50 am
All 12AX7's and 7025's are listed with a (theoretical) gain value of 100. Many test lower... and as they age (wear out) this can go even lower. Most new production tubes will not test at or near 100. If you have an old tube not only can the gain produced be lower but the fidelity can drop and the tone get dull. Add to that, they didn't exactly have six sigma manufacturing tolerances in the 40's and fifties... these were largely hand made and some variance is expected. Also... you'll find grey plates and black plates from RCA, not to mention short vs long and several different types of getters... they can all sound different. Lot's of variables in preamp tubes... that's why we roll ; )
 #133396  by boater1941
 Mon Oct 21, 2013 1:18 pm
Thanks for the reply smolder. Seems like no one has got any input on tubes especially original sms owners or guys cleaning up a 64-67 board. All I can say is unbelievable difference and unreal sensitivity. Back to back 7025's is just too much for the sms. The worst 7025 readings I was getting approx. 75% on my B&K tester. The other's average close to 85% factory specs.
My conclusion is to leave the best read 7025 in V1 and Brad's 12ax7 in V2 to smooth things out.
Never thought I'd have a problem with to much clean headroom and volume. With the back to back 7025's I had the pad on the back dialed to about 25% and the front about 10 oclock. Even on 3-4 my E's hooked to my 2300 could fill a theatre. Nailing finger rolls like crazy.
I just don't have a building to play with that power, So for you guys who have gigs and don't want to have to crank your equipment buy some 7025 with good readings from GE,RCA or JE. Most guys selling them post the readings in their ad.
I don't know what it is?????You guys just say it's just a heavy duty 12ax7 but playing them especially back to back the way I did there's more to it than that. Gonna put Brad's 12ax7vka or something like that in V2 to tame this beauty.
 #137392  by tatittle
 Sun Mar 09, 2014 1:02 am
I read somewhere recently that GE had plans to start producing tubes in the USA again sometime. Not sure if that mssg. was distorted through the grapevine and they will be rebranded 2nd/3rd world.

Historically I believe the Fender 763's came with grey plate 7025's in the 1st spots and RCA 12ax7(a)/12at7 down most of the time. The white lettered blackplate RCA's are from the 50's mostly and came in Tweed amps---though I forget the exact year they switched. I have seen a few blackplates with red lettering. You could find other high quality brands in a stock Fender from those era's for sure though. The RCA's are widely regarded as the best match for the original circuit ime. In the 70's it became more common to see GE's and eventually Sylvanias especially power tubes.

As Smolder said, 7025's are low noise rugged 12ax7a's best of the best. Sometimes they have contruction differences to help this. The only difference with 12ax7's from the a's is they cannot be used in a series circuit (or is it parallel ?) which is not applicable to Fender guitar amps. There are significant variations between tubes even of the same manufacturer and type brand new though. Sounds like you got some primo 7025's, nice. Were you comparing them with modern 12ax7'a?

woops...just noticed the date lol. :idea: