I have a Magnavox Berkeley 134 and bought two JJ Tesla 6L6 when these were less $$. The original Ken Rad 6L6G seem to be OK, so the JJ's made little difference.
Matching tubes is necessary if closer to design limits, but Magnavox is usually tame enough on two good tubes, so this is a non-issue.
This amp is rated for 20 watts in Magnavox CR198 here
http://www.nostalgiaair.org/PagesByM...5/M0010335.pdf
But 1947 sales literature I for the Berkeley stated 15 watts from the two speakers. Looking at Antique Electronic Supply website, a 5881 will work, listed for $26.
RCA or Ken Rad (GE) metal versions of 6L6, of which my 1948 Windsor has four, is rated 45 watts. These are more reasonably priced.
https://www.ebay.com/itm/35423726914...Bk9SR-DLz7fbYA