AMPEG B25,WOW!

[sunnfever]

I got the B25 I posted on a few days ago and it is one cool amp. Sounds so different from sunn stuff. It did have all the mods mentioned in the earlier post that includes a bias control wired inside. This thing sounds ANGRY! Turn it up past half and it snarls at you like Sid Vicous on steroids! Sunn and Ampeg were so on top of their engineering game! The cab needs new drivers for sure though. Sounds better through the sunn 2x15 or my home built single 15. AWESOME!!!

[JoeArthur]

I got the B25 I posted on a few days ago and it is one cool amp. Sounds so different from sunn stuff. It did have all the mods mentioned in the earlier post that includes a bias control wired inside. This thing sounds ANGRY! Turn it up past half and it snarls at you like Sid Vicous on steroids! Sunn and Ampeg were so on top of their engineering game! The cab needs new drivers for sure though. Sounds better through the sunn 2x15 or my home built single 15. AWESOME!!!

What's your point? and why ain't you posting this on some ampeg forum?

Ampegs do sound different primarily because their preamps are "current starved".  Some people like that sound, others don't.  Sunn users would be among those that "don't".

[sunnfever]

My point was to generate a response or responses from anyone who might have one of these in their gear collections and might have any thoughts,ideas or comparisons between the sunn stuff and said ampeg or even the cabs that I mentioned as well. I have seen plenty of posts mentioning other brands or technical questions that relate to other gear and they seem to get friendly and helpful responses. While your "current starved" info was  an appreciated piece of knowledge, whats with the undercurrent of hostility?   Are "amp tramps" not welcome in "sunn people" town? Sheesh!

[Soundmasterg]

I don't mind the Ampeg comments myself, and have a vintage SVT myself, and like it. If you wanted more info about the Ampeg, then an Ampeg forum would certainly be able to provide that better than a Sunn forum, but then I'm sure you realize this. The B25 is a good sounding and reliable amp, and certainly gives a different sound than a Sunn does. The way I look at it is that each amp/guitar/bass, etc, is just a tool, and they all have different places where they shine. Glad to see you're happy with your purchase.

Greg

[sunnfever]

It was a trade and I also got a Coliseum 300 in the deal! I do post questions here that aren't just looking for the usual "tech fix" or "Where can I get this?" type answers. I just thought since the B25 was from that general era that the older and wiser here would have some perspective on it and it's relation to the gear of the time(which would obviously include sunn.) Perhaps the mods on it were done by an owner that wanted it to sound more sunn like?J/k I dig it anyway and can't wait to get a sorado that is on the way so I can A/B them. It is certainly a different animal and that  was very apparent when I plugged in!

[Isaac]

Ampegs do sound different primarily because their preamps are "current starved".

What does this mean? Technically, in a nuts and bolts (or resistors and capacitors!) sort of way.

[JoeArthur]

Ampegs do sound different primarily because their preamps are "current starved".

What does this mean? Technically, in a nuts and bolts (or resistors and capacitors!) sort of way.

Take the first input stage of a B25 as an example.  There is a 5.6K cathode resistor and a 270K plate resistor.  Take the voltage drop across these resistors and divide by the resistance, you'll get something like 0.4 milliamp of current.

Other amps, such as the Fenders and Sunns will use a 1.5K cathode with a 100K plate, typically giving between 1.0 and 1.5 milliamp current.

This doesn't mean one is bad and the other is good, just that the results will be different.  Distortion characterists and headroom changes because the tube is biased differently and covers a different portion of the curve.

Sound is certainly subjective and hard to describe. Generally (very) the lower current operation can be crisper and cleaner sounding at low levels, can feature less headroom and can get fuzzbox sounding when pushed.  Higher current can sound warmer at lower levels with higher headroom and can get muddier sounding at higher levels.

Of all the amp makers, I think Marshall probably experimented more than others, mixing various current operation stages together... like during the early 70s when they split the cathodes of their input stage, and even more variation with the JCM 800 series.

[sunnfever]

Those were the facts that I had hopes of my original thread generating! If you'll allow me one more question and I will speak of this interloping Ampeg no more , I mentioned this thing had a mod to except 6550's(I imagine because of the scarcity of 7027 tubes) and had an 8ohm output intalled along with a bias adjustment added,but without doing anything to the preamp section I am figuring it still retains its original tonal flavors? Is that right?

[Isaac]

Thanks, Joe. Exactly what I wanted to know.

[JoeArthur]

Those were the facts that I had hopes of my original thread generating! If you'll allow me one more question and I will speak of this interloping Ampeg no more , I mentioned this thing had a mod to except 6550's(I imagine because of the scarcity of 7027 tubes) and had an 8ohm output intalled along with a bias adjustment added,but without doing anything to the preamp section I am figuring it still retains its original tonal flavors? Is that right?

7027a tubes were great tubes, but you are correct... they are harder than heck to find.  There are two popular conversions to less scarce tubes - one to EL34 and the other to 6550.  IMHO... if you want to retain the original tone, the 6550 conversion would certainly be the best - both 6550 and 7027a tubes are more "hi-fi" than EL34s.  A bias adjustment addition would be better than swapping resistors to get the tubes to bias, so that is a good thing.

I don't know what you mean about the 8 ohm output.  If I remember correctly, the B25 did have switching output jacks for extension speaker use that would switch taps on the secondary side of the output transformer.  What speakers are you using?

I guess I'm trying to decide if someone thought that a different output transformer was required for the tube conversion (it's not)... or if the installation of different speakers caused a rewiring of the secondary side.

[sunnfever]

I am trying to find info on this amp but ampeg forums pail to the sunn forum. If you want, I will better explain myself when I come home from work and have a spare moment to figure this thing out. Never enough time for my toys, especialy an unfamiliar one. Hope to hear from you later.

[Soundmasterg]

7027A's weren't very much different than a true 6L6GC, and in some circles, people say they were exactly the same. (Ned, formerly of Triode Electronics among others seems to hold this view) There were recently several makers of a 7027 type (EI, Sovtek) but it appears only Sovtek is making one now, and I don't know if it is a true 7027 or not , or there are a couple (JJ and Winged C/SED) 6L6GC types that would hold up fine in the Ampeg circuit. You can get them from www.tubesandmore.com for a reasonable price.

If you want to do one of the conversions, than the 6550 sub is a better one for sure. The 6550 as a tube lasts longer and is stronger than an EL34, and it also generally sounds better for bass too. If it was me, I would use 6L6GC's.

The best source for Ampeg questions would be the book about Ampegs, and the two guys who wrote the book. I can't recall their names right now, but do a search and you'll find it. Another good source is Jess Oliver, who probably designed the thing while he was at Ampeg. He's in the New York area somewhere but you can email him too.

The founder of Ampeg hated distorted sounds and he insisted that any amps built while he was at Ampeg wouldn't distort, which is one reason why they have the low current thing going on in the preamp. Sure it ends up distorting a different way, but it is harder to distort a low current stage than it is to distort a high current one like the Fenders use.

I like the Ampeg sound for certain things, and the Sunn sound for certain things...and on bass, even solid state or direct can sound good too depending on what you're going for.

Greg

[sunnfever]

The cab is a B25b cab with two non descript 8ohm squareback speakers that look pretty shaby. New drivers are in order. I wish I could post pics here but my computer skills are second only to my feeble bass playing ability!  I will describe the back of the amp. Left to right as follows:3 amp fuse,ac outlet 500 hundred watts max,standby switch,hum balance adjustment,1/4extension amp output. Below hum balance is a 1/4speaker output. Below extension amp output is an 1/4extension speaker output. Along bottom is script that denotes which tubes should go where. Left to right:5AR4,7027A,7027A,7199,12AX712AX7. The 7027a's were replaced with Philips ECG 6550's. Pres look like Sovtek and Groove Tubes. From what I have read the B25 was paired with a 16 ohm cab. The person I traded with to get it said that the extension speaker out was wired for 8ohm. If the B25 were used originaly in conjunction with a 16 ohm cab then if you used the extension speaker out at the same time wouldn't that have to have been a 16 ohm cab also to stay within impedence paramaters?                                                                                                      Jess Oliver is supposed to be part of a site called fliptop but I have had trouble accessing it. And if the the original owner of Ampeg hated distorted sound then the engineers snuck this one behind his back! Halfway up it is not what my ears would term as "clean". Thanks to all of you for your input on this most "unsunn" of vintage amplifiers. I am surely getting as good of information here as anywhere else. This thread has generated great and much appreciated feedback!

[JoeArthur]

7027A's weren't very much different than a true 6L6GC, and in some circles, people say they were exactly the same. (Ned, formerly of Triode Electronics among others seems to hold this view) There were recently several makers of a 7027 type (EI, Sovtek) but it appears only Sovtek is making one now, and I don't know if it is a true 7027 or not , or there are a couple (JJ and Winged C/SED) 6L6GC types that would hold up fine in the Ampeg circuit. You can get them from www.tubesandmore.com for a reasonable price.

If you want to do one of the conversions, than the 6550 sub is a better one for sure. The 6550 as a tube lasts longer and is stronger than an EL34, and it also generally sounds better for bass too. If it was me, I would use 6L6GC's.

The best source for Ampeg questions would be the book about Ampegs, and the two guys who wrote the book. I can't recall their names right now, but do a search and you'll find it. Another good source is Jess Oliver, who probably designed the thing while he was at Ampeg. He's in the New York area somewhere but you can email him too.

The founder of Ampeg hated distorted sounds and he insisted that any amps built while he was at Ampeg wouldn't distort, which is one reason why they have the low current thing going on in the preamp. Sure it ends up distorting a different way, but it is harder to distort a low current stage than it is to distort a high current one like the Fenders use.

I like the Ampeg sound for certain things, and the Sunn sound for certain things...and on bass, even solid state or direct can sound good too depending on what you're going for.

Greg

7027As do seem to have the same operating characteristics as 6L6GCs.  Especially if you don't consider the "other connections" to the grids (IIRC I think it's the control and screen grid connections that are available (also) at different pins).  From this perspective and assuming the wired pins are checked for compatability, the 6L6GC could be a push-in swap.

(BTW... I'd also check the wired pins for either a EL34 or 6550 replacement - ya never know since production was always subject to change without notice!!)

But there is another aspect that isn't revealed by operating characteristics - and yes, I do think most 7027A tubes available today are nothing more than re-labled 6L6s.

From about 1977 through 1981 I (me myself... my Model T was used by the bass player) used two similar amps - one was a Twin Reverb and the other was a VT-22.  I played through both - the Twin Reverb was more of a "monitor" amp - closer to the bass player on the opposite side of the drums.  The VT-22 was always behind me and (as a result?) driven harder.

Every 9-12 months I needed to replace the output tubes in the Twin (6L6GC).  I never replaced the output tubes in the VT-22 (7027A).  In fact, the way I knew I had to replace the Twin's tubes... was when it couldn't keep up with the VT-22.

So while I do agree they are VERY similar spec wise, the 7027As had to have been better built.  I don't know how, I only know they lasted.

Maybe that's why a push in replacement of 6L6s is not usually recommended (although certainly possible) for 7027As.  Meaning, the 6550 has a better chance of equaling the useful life.  But that doesn't explain the EL34 replacement recommendation - which does have a shorter life than the 6L6 (IMHO).