Audio Research REF 3

Hi Reference 3 Owners,
I replaced the tubes from my reference 3 with Sovtek 6H30 (matched tubes) and 6L6GC from SED.
The overall performance improved, but i was not fully satisfied, then i re checked my full system in term of cabling and speaker connection, then i discovered that my pair of JBL 2405 tweeters were not connected properly (they were not on phase : the + plug was on - cable and the - plug on + cable). I guess i did some tests in the past when my LS25MKII get sold and i think i tried several things to improve the performance of my spare preamp an Audia flight Pre to improve it at LS25MKII level without success !!!, it was just a bad thing !
So now the image is much much better, i'm satisfied with the overall result and i found the Reference 3 totally different in term of 3D image than the LS25MKII. The LS25MKII is providing a flat image in comparison with the Reference 3 with really gives a 3D image with a lot of space all around the instruments and voice. In comparison with LS25MKII the voices seem a little bit behind, so i need to be familiar with that new sound image. It maybe required more time on the tubes to get the voice as they were with the LS25MKII.
I checked inside my Reference 3 and the bypass capacitor are in place if i well understood where they are located (just behind the 4 golden capacitors), so i don't need to get some from Audio Research.
For the 6550 tube in place of 6L6GC can i just remove the 6L6GC and put a 6550 tube on the power supply stage ?
If yes, i will do the try with a new Sveltana 6550c i have in spare, and i will order a Tung-Sol 6550 Black plate as suggested by Elberoth2
So if you can confirm me for the 6550 tube it will be nice
Laurent

While I am looking for a new pre amp...and have considered the ARC Ref 3...I have heard that there have been a number of revisions to the unit...changes...given ARC's history that should be expected...has anyone document any changes.??? if they actually exist

J

As I understand there are at least 2 iterations of the original REF 3.If you are considering purchasing used that would be a fair question to ask.

According to ARCDB.WS, only 1 revision was ever made to Ref 3, and this was about 6 months after release. . . the 6G6 in the power supply was replaced by the SED 6550C, and 4 bypass caps were added. . . the bypass caps were apparently planned since day 1, but were not available from the supplier at first customer ship date. See:
http://www.arcdb.ws/REF3/REF3.html

Hi,
Could someone please confirm that the 6L6GC can be changed by a 6550c with no risk. I guess i should the 4 by pass capacitor on directly on the back of the board where the 4 golden caps are located (0.024 µF cap i guess)
Thanks in advance
PS : i'm starting to be extremely happy since news tubes are into my Ref3 !