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Best tubes for V-4B

big stubby

big stubby

Feb 1, 2007
198
129
#1
It's me again with more questions on my new v4b. The tubes in this thing have been in there since 1988. They are Mesa 6550-A's STR 418s. I don't think they even make these anymore. So I would imagine that they should be replaced after 22years. Any suggestions on what I should put in there? Iam going to take to a quality tech to get checked out, I just thought that replacing them myself might be cheaper. Thanks again
 
#2
I've got JJ's in mine and I love them. JJ's are a good bet for a quality tube for not a bad price. Can't go wrong.

On a side note...if you aren't having any problems and like the sound, then I suggest you leave your tubes alone. Tubes can last a super super long time (I have all original tubes in my 1966 Ampeg B-15N and they are still going strong). Just a thought.
 
#3
Leave em alone if you can.

When I buy a vintage tube amp I always take it to my tech for a once over. Have he/she test the tubes; they may not need to be replaced at all.

I had the original 7027As in my 70s V4b. They tested strong and the amp sounded great.
 
#4
If your amp is running 6550s it may have been converted in 80s when 7027s were out of production. I think your best bet is to have a tech check out the situation first. It's only a few simple mods to run 6550s, so it certainly wouldn't be much trouble, but if you put 7027s in there now the bias would likely be off and you won't be getting the best out of your tubes.

If you decide to stick with the 6550s, I'd recommend Winged C (SED) tubes (had those in mine, sounded great). If you go with 7027s, I'd say go with JJs.

Replacing the tubes yourself would probably be cheaper, however, as I said above given the tube swap it could need a little cleaning up in the circuit to run optimally. It may also be good to have a bias adjust installed if it hasn't been done already.
 
#5
Well from what I've read here, running 6550s is bad for the amp as they run hotter. I was thinking of swithching to 6L6 GC's or as I saw JohnK write, he uses NOS Philips 7581As. But I can't find those anywhere.
 
#7
I believe that EH makes some 7027A's, and JJ does definitely does (i prefer the JJ's). you'll have to have the bias circuit put back to stock if your amp was set up to run the 6550's that are in it now.

7581A's are definitely the best tubes for them (or NOS 7027A's) but will be very expensive if you can even find a matched quartet of them.
 
#11
the JJ 7027as are real junk. If you look at the internals of them, compared to the real deal nos...they dont even look close. Test em and the curves dont match either.

If you decide to stick with 6550s you may eventually have issues w/ the power transformer...maybe, maybe not.

Ideal is to track down a real set of 7027as and rebias for them.
 
#15
Here's a couple of links for info, on the 7027 tubes, first two, have plate dispersion graphs, the last link has a discussion of the development of the 7027 tube ... I believe Angela.com has a NOS JAN 7027 for 145.00 for a matched pair=$290 for a matched quad .... to expensive for my tastes ... the only current production 7027 tube that I know about is JJ's 7027 and Sovtek 7027 ... the JJ's sound somewhat better ... IMHO
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#17
big stubby said:
Corey, did you have the SED SV6550C's in yours? Also has anyone tried the 6550 winged "C" Svetlana MATDHED tubes that are at fliptops?
Click to expand...

SED is winged C (in North America at least). If you're getting a matched quad of winged C, go with Invalid Link Removed. They'll be a few bucks cheaper than fliptops every time, and they're great guys. I've never had an issue with anything I've order from them, parts, tubes, whatever.
 
#20
If the amp was converted for 6550s the screen resistors were also changed. 6550A's had a lower heater current draw, the newer 6550C's are killer tubes but do have a very high heater current draw (some V4-B's may even need a filiment trans installed). The differences in the 7027a and the 6L6(???) were slight and may be over shadowed by a KT66?
 

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