RCA 7025

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sixpakldp
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RCA 7025

Post by sixpakldp » Sat Nov 29, 2014 8:41 am

Swapped two RCA 7025's from my Twin and put them in V1 and V3 and they sound surprisingly good. Very smooth distortion characteristics if you ask me. Anyone else try these?

danman
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Re: RCA 7025

Post by danman » Sat Nov 29, 2014 12:00 pm

I run an RCA in my 1986 clone from time to time also. Very smooth tube like you say!

sixpakldp
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Re: RCA 7025

Post by sixpakldp » Sun Jan 11, 2015 10:20 pm

Had to update this thread . . . Just bought a i61 mullard 12ax7 off of a friend. A while back I swapped his into my amp and fell in love with it. He was nice enough to grab one for me and give it to me as a gift since I liked his so much. I had been running RCA 7025 v1, sylvania jan 12ax7wa in v2 and RCA 7025 in v3. I popped the mullard in v1 and played a whole practice with it. To my surprise the RCA had much more gain and was just right. Not sure if the mullard tube is just a lower gain tube or if the 7025's are hot. I switched back to what i previously had in there. In any case this particular combo of tubes is like magic in my amp. Sustain forever and doesn't get too muddy on the neck while having a really smooth distortion. For some reason the sylvania pairs really nice with these two. Has a little bit of edge to it and seems to really impart the perfect amount of attitude in the amp when paired with the others. I highly recommend checking this combo out. The other thing that was intriguing was that the construction of the 7025 and mullard seemed almost identical, only exception being the plates were rotated about 90 degrees comparing one to the other.

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Carbia
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Re: RCA 7025

Post by Carbia » Mon Jan 12, 2015 3:49 pm

RCA and Sylvania tubes use to be very hot, at least most of mines are.

I usually get readings around 2000 mohms of transconductance (or more) out of them, while is difficult to find a european tube over 1600.

danman
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Re: RCA 7025

Post by danman » Mon Jan 12, 2015 5:02 pm

Like Carbia mentioned, some brands just seem to test higher for transconductance more consistently than others. I also find that most Sylvania's seem to test at the higher end of the scale if you get a fresh one. Other brands may test lower but still be well within the manufacturers specs for a new tube. It could be that the Mullard that you tried just happened to be at the lower end of the scale while the RCA could have been in the higher range. The main thing is how they sound in your amp and that you have found a combination that you are happy with!

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Carbia
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Re: RCA 7025

Post by Carbia » Mon Jan 12, 2015 7:21 pm

I've tested many Mullards and the best I've tried scored 1600/1700 in each triode in my tester (where the minimum acceptable is 800, so, very strong tube) but most of them tested around 1200-1300 sounding great, while all tubes that I measured around 900-1000 sounds weak, so I trust my tester. New production tubes, brand new, use to be around 1200, which isn't very nice.

But I get a lot of Sylvanias 12ax7 (12 tubes), supposedly NOS, and all of them scored over 1700, and maybe half beyond 2000.

So, I've assumed that Sylvania made very strong tubes in terms of transcontuctance, while europeans, sounding gainer and great, doesn't reach that transconductance levels.

sixpakldp
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Re: RCA 7025

Post by sixpakldp » Tue Jan 13, 2015 8:43 pm

Good info! Thanks guys.

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