Ampeg V-2

soundmasterg · Post by **soundmasterg** » Tue Aug 10, 2004 9:29 am

There is a lot of speculation (and rightly so) that the 7027 always was a 6L6GC with slightly different basing. If you take an RCA 6L6GC and an RCA 7027 and dissect them, you'll see what I mean. The only thing that may have been different besides the basing is that the 7027 may have had a harder vacuum, but no one nowadays really knows for sure. The tubes nowadays aren't as well made as the older stuff on the whole, but some SED 6L6GC's would work fine. Or you can get some 7027's from JJ or EI, and perhaps EH also.

Transistor amps usually do not have an output transformer, and the power transformer in them is much smaller than a tube amp, so those two things account for most of the weight. The output transformer in my Sunn 2000S is as big as a baby's head, and the power transformer isn't that much smaller either. That amp weighs a ton! The cool thing about tube amps is that they are made to last as compared to the throwaway transistor amps nowadays....

jps · Post by **jps** » Tue Aug 10, 2004 1:04 pm

Some amps require filament transformers because of the current drain of the filaments from the output tubes, primarily those amps with 6550s.

rictified · Post by **rictified** » Sat Aug 14, 2004 4:41 am

I had a Sunn 2000S head years ago, also had two 2000S cabs with JBL D140's in them years ago. (had them at different times) I used a Marshall Major with the Sunn Cabs and a flat wound P bass, moved a lot of air, one place used to call us the big wind, haha!

rictified · Post by **rictified** » Sat Aug 14, 2004 4:50 am

Greg what do you mean by basing? The pins are different, or biasing? I also have heard that the 7027A's were a strong 6L6. But I would still throw 7027A's back in. Different tubes seem to change the sound, when I got the SVT with the 6L6's in it, it sounded like a big Fender, seriously. Actually sounded kind of nice.

soundmasterg · Post by **soundmasterg** » Mon Aug 16, 2004 11:03 am

Bob, if you look in a tube manual like the RCA one, they refer to the different pinouts as different basings. There are different number codes for each basing style, and the 7027 has a different one than a 6L6 or 6550, etc. It means teh same as saying the pins are different, but it doesn't really matter. Basing, pinout, pins....all the same.
If you had an RCA 7027A and an RCA 6L6GC, they would sound VERY close to each other, and would even look VERY similar on a scope I would guess. With modern tubes, say a JJ 7027 or a JJ 6L6GC, hard to say, but I would guess they are the same with a different pinout. It makes sense for companies to do that as they save money for tooling costs, and make teh consumer think it is a different product...kind of like GM with Pontiac and Chevy and Buick and minor changes between the two.

I'm going to get a 2000S cabinet made up so I can get the "Sunn" sound again. I've got some JBL D140's...just need the cabinets now. That doesn't mean my SVT is going away...not a chance there!

rictified · Post by **rictified** » Mon Aug 16, 2004 6:17 pm

I used to fit two Sunn 2000S cabs in the back seat of a 4 door 64 Chevy, haha! they don't make em like that anymore.
I thought that was what you meant, I've never heard that term before, I've heard pinout, but it makes sense.
BTW, you wouldn't happen to have a schematic for an Ampeg Bassamp 835 would you? I can't find one anywhere.

soundmasterg · Post by **soundmasterg** » Tue Aug 17, 2004 8:48 am

Hi Bob. No, I don't have one of those schematics unless it is in the latest Groove Tubes book with the cd. None of my other books list that one. you may check with the guy who wrote the Ampeg book. He seems to have a lot of stuff himself, or at least he knows where you can find it.

rictified · Post by **rictified** » Wed Aug 18, 2004 2:36 pm

Thanks Greg, I think that is going to be a hard one to find, I can find virtially no information on it or any of the Bassamps except in the Ampeg book and there isn't much there either.

soundmasterg · Post by **soundmasterg** » Thu Aug 19, 2004 9:16 am

Hi Bob. I've never heard of it myself....I must have skimmed that section in the Ampeg book. I'm sure if he included something in there about it, then he must have some info on it, or he might know where to direct you. Bill Moore is his name. You may also post a message on Ampage about it. There is a guy there named Ray Ivers who is really knowledgeable about Ampegs...he may reply to your post.

rictified · Post by **rictified** » Thu Aug 19, 2004 7:44 pm

I got it going tonight, the old pull it apart and put it back together again and it works trick, I love that, haha! It's got a bad connection somewhere in the preamp, I've isolated it to the preamp tube, probably a bad connection to the socket, I'll tear it apart again tomorrow. I've tried Ampage and nothing, would still be nice to have one, if you have the Ampeg book there's the exact one in the Ampeg Mountain, #73, they say it's a 1960 and it may be, the guy I bought it from said it was a 58. But whatever year it is it's really cool, is constructed like a little SVT, separate pre-amp and everything, and sounds great. Even has a voltage regulater tube for some reason. Came with EL37's, big bucks for those, luckily 6L6's work also.

rictified · Post by **rictified** » Thu Aug 19, 2004 7:50 pm

Eureka! I just figured it out, it's gotta be one of the heater wires on the pre-amp tube socket, because if I get a false connection the sound dies out slowly instead of immediately stopping, and that also explains why it took me so long to find it, it would have to be connected long enough for the tube to heat up before it would begin to work work.

soundmasterg · Post by **soundmasterg** » Fri Aug 20, 2004 8:39 am

Thats pretty strange Bob. Those EL37's are really nice tubes, and you're right...worht a lot of money. You may try some EH7591A's in there instead of the 6L6's....I hear they sound better....but of course you would have to rewire the sockets too.
I had an interesting problem with the 200S I just rebuilt. I was going to play it at a jam...hooked it up and turned it on to warm it up. When I flicked the standby switch, there was an internal arc and it went completely dead! After I got it back home, I opened it up and found out that I had neglected to solder one connection on the aux power switch, so it was just making mechanical contact and must have worked loose enough to arc and carbonize the wire! I rewired it again and ditched the aux power jack since it is only 2 prong and it works great again. Not bad for my first rebuild I guess...only missing one solder joint.

rob · Post by **rob** » Fri Aug 20, 2004 8:44 am

Bob, there's an Ampeg shop not too far from me. Visit them online at www.fliptops.com
Maybe they can dig up a schematic for you. Or maybe not, depending on how old it is.

rictified · Post by **rictified** » Sat Aug 21, 2004 7:17 am

Thanks Rob, I already checked with them, it's late 50's early 60's. It's so old it has an input for the crystal mic'ed Ampeg pickups they used to make for uprights which is where they got their name. It actually sounds good with the 6L6's in it, they are old GE's but are at about 20% on the tester, so they gotta go. The problem is I don't know where to set the bias. Maybe I can figure it out from the curves in the tube books. I've forgotten to soldier things before also, I always double check now, I don't like those surprises.
I rewired an SVT for 117V a few weeks ago, (had put a new standby switch in in Lima) and on the first gig the standby switch broke, good thing it broke in the on position because I was about an hour from home with no spare.

soundmasterg · Post by **soundmasterg** » Mon Aug 23, 2004 10:09 am

Bob, as far as biasing that amp, you can just use the formula for whichever tube you intend to use. Say you are using the SED 6L6GC, which has a plate dissipation of 30w. So figure out your plate voltage, then measure the plate current, and set your current for between 60% to 70% of that 30w dissipation max value.
An example: The 200S I worked on recently had 565v plate, and I set it for 41ma. 565*.041= 23.165W of dissipation. The max for a 6550 is 35w, so 70% of 35 is 24.5, and I'm under that so its a safe setting and it is where it sounds best with those tubes.
If that amp you are messing with is cathode biased, you may want to run it a little on the cooler side. If you have a bias king its really easy to bias it this way. If not, then you would have to wire up some 1 ohm resistors to ground from the cathode of each power tube and probably go with a cathode resistor for each tube rather than share it between a pair as many amps are set up. Does that help?