You're not. A lot of people love it. My good buddy George Biondo from Steppenwolf was very into his when he had it. Slight correction, though...it's 60w.
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Best year for Ampeg B15
- Thread starter JB1962
- Start date
Not if you run 7581A power tubes...
. I get 70 watts all day long. And that’s continuous. According to Ampeg, original power with 7027A tubes was 60 watts RMS minimum, 138 watts peak music power. Jimmy, as usual, your knowledge of all things Ampeg is spot on.
Yep, and Rick Danko was playing a fretless Ampeg AEB-1 to boot. A B-15S is a bit on the heavy side, and personally I like the Double Baffle Reflex Cabinet, 6SL7’s in the preamp, and a lighter amp. Just my take.
No it wasn't...I didn't know you could get a 10w boost in a B-15S with different power tubesNot if you run 7581A power tubes...
I had a late 70's B-15n with the ultra hi and ultra lo switches and always liked that feature, was like a little SVT, was clear as a bell, I bought it brand new.
I have one of those also, just put a D-140 in it, they are a lot louder than the B -15's, I think they're rated at 60 watts though, at least that's what mine says. They weigh a ton though and I'm still lugging SVT's around. I separate the head and the cab when I move it.
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Not if you run 7581A power tubes...
Does it take any mods to run 7581A power tubes? Is there a noticeable difference?. Are using old American tubes or something like the new Tung Sols?
I’m using the new Tung Sols. 35 watts per tube. No mods necessary (other than a bias adjustment as you would do with any new tubes). I got a nice bump in perceived volume compared to prior volume at identical settings. But my old tubes for comparison were the original 45 year-old 7027A tubes. So, they may have just been worn out. One day I may put a set of NOS 7027A tubes back in and see if the difference is really what it seemed.
Sorry to the OP. Not trying to hijack your thread. Truth told, you can’t go wrong with any version of the B15. Find the one in the best condition at the best price and dive in to the deep end. You won’t regret it!
I've got the original Magnavox tubes in mine too, it's a '78, probably about time anyway
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The price for NOS 7027a's isn't as bad as some NOS power tubes. Curious, though...if 7581a's are a replacement for 6L6GC's, you didn't have to do any pinout mods to replace 7027a's? I had always heard 7027a's were 6L6gc's with a different pinout, no?
Interestingly enough, Ampeg used Altec 421’s in the later black tolex amps and offered D-130F’s as a factory upgrade in in the Blue Check Vinyl Portaflexes. Ultimately, you want to use what sounds best for you and the JBL D-140F is a great speaker.
7581A is in the same boat, shouldn’t give you any power advantage over 7027A in the same circuit when properly biased. New sensor has a habit of just using old data sheets so the 7581A is listed as having max plate voltage of 500V while the 7027A is specified as 600V. I think the B15S uses the same power amp design as the V2/VT40 so probably around 550 plate/screen?
Here are the two available from thetubestore:
Tung-Sol 7027A Audio Tubes - www.thetubestore.com
Tung-Sol 7581A Audio Tubes - www.thetubestore.com
Visually they are very similar looking in terms of plate structure, getters, etc, and there is a $7 price difference. I'd assume there is something more to the 7027A the correlates with the higher max voltage rating they should have, but the pessimist in me wonders if they're essentially the same tube with the extra pins in the 7027A.
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7581A tubes have two less pins (1 and 6). But, it is not a problem in the B-15S circuit, as those pins are not used in any event. See this thread, which gave me the idea. Beans on Toast provides the explanation at post eight. Tung-Sol 7581A Questions
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I wouldn't know. I just use whatever my amps ask for and don't ask questions
Beans knows pretty much everything! Very good then...
Agreed! Beans and the Talkbass Ampeg Portaflex Wiki have been such a great teacher and resource for my B15 experience. You can spend hours there troubleshooting just about any issue with a B15 and leave with answers to questions you did not even know you had.
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I'm not sold on it yet, doesn't seem to be able to handle the power on cranked low notes, the original Eminence bottomed out too.
Ampeg in general didn't use the extra pins so as pointed out it's no issue swapping between the types from that perspective. Fender amps often used the extra unused pins as tie points for the grid/screen resistors so you have to be careful on those amps if you use alternate tube types. My concern was more for long term stability of the 7581A reissues in an amp that calls for 7027A voltages, but I believe Beans has been using them in his V4 for a while and I know some others have as well. I still have NOS in my V4 and B25 but might try these in the future.
Bob,
I’ve run E-140’s at over 100 watts (RMS), inside a B-15N(C) Portaflex cabinet with the head removed. There were no issues, so could be that something else is amis. I do remember that JBL’s use flat wire for
their voice coils and ocassionally a JBL will get re-coned, with the wrong kit. The wire in some of the aftermarket generic 15” speaker reconing kits isn’t always speced for a JBL. I learned this the hard way, when I had to have one of those E-140’s re-coned and they used the wrong kit.
It has been re-coned and doesn't have a silver cap like they're supposed to, maybe you're right.
The silver dust cap isn’t in and of itself an indication of a issue with the voicecoil. I’ve seen examples of D-140 ‘s with either dust cap.
