Ampeg V4 Club

[coreyfyfe]

Oh, and BTW, there's nothing on pins 1 and 6 on these new reissue 7072A tubes, which would have been connected to the control and screen grids on the originals...

That's because they're 7581As not 7027As. Still in the 6L6GC family, but if you ordered the new 7027As you got the wrong tubes. Or you've uploaded the wrong pictures?

The tubes store has listings for both, are they selling one as the other? They look pretty similar but there's a $7 difference...

www.thetubestore.com - Tung-Sol 7027A Audio Tubes

www.thetubestore.com - Tung-Sol 7581A Audio Tubes

 

[beans-on-toast]

I wouldn’t be surprised if the Tung-Sol 7027A and 7581A are basically the same tube. You can see connection differences in the images between the base and the plate.

 

[coreyfyfe]

I wouldn’t be surprised if the Tung-Sol 7027A and 7581A are basically the same tube. You can see connection differences in the images between the base and the plate.

Wouldn't surprise me at all if they were the same internal structure with the 7027A labeled version just having those extra pins. The post above the tubes/boxes are clearly labeled 7581A while DaveO said they were 7027A, as I said I hope he didn't pay for one and get the other. They'll work in the amp (as you already know) but the are supposed to be distinct offerings.

 

[Joth]

You could try moving the 47K power tube grid stopper resistors onto the tube socket but I doubt that it would make a difference.

I've found that bad solder joints are common in these amps. The amps run so hot and over time it takes a toll. Reflowing all the joints on the boards helps. The tube sockets can have gunk between the terminals under the sockets. I use pipe cleaners soaked in a cleaner to get under there and clean.

I did install twisted heater wires because it irked me the way that they did it. Same goes for vintage SVT's.

I don't know how accurate the service manual bandwidth specs are. They seem more than a little optimistic.

In my 78 V4B, which drove me crazy and was parked up for years because it would go into a low freq sub sonic oscillation now and then when hitting hard notes (the speakers looked like a heart beating). I recently got the idea of moving those 47k stoppers off of the board and directly onto the sockets, and that cured the problem finally. It now has a fresh new life and is out on loan to friends recording an album as I write.
I did something of a service video on a recent V4 fixup and mention this and a few things here

 

[beans-on-toast]

In my 78 V4B, which drove me crazy and was parked up for years because it would go into a low freq sub sonic oscillation now and then when hitting hard notes (the speakers looked like a heart beating). I recently got the idea of moving those 47k stoppers off of the board and directly onto the sockets, and that cured the problem finally. It now has a fresh new life and is out on loan to friends recording an album as I write.
I did something of a service video on a recent V4 fixup and mention this and a few things here

Thanks. Good to know that moving the resistors made a difference. It is best to have them at the tube socket. For the power tubes, the signal level is higher so it should be less of a problem having a longer wire between the resistor and the socket. The routing is important. But you’ve shown that moving the resistors resolved the issue.

The wire routing in the original layout was neatly tucked down against the chassis. In an original V4B, they ran side-by-side, straight down from the board, they turn and run flat against the chassis over to the tube sockets. When the wires cross any other wires they do so at ninety degrees. The original wire layout of the amp was very neat. This can help in limiting oscillations.

Sometimes I find that the wire layout in these amps has been messed up by well meaning techs and that can it can cause problems.

 

[beans-on-toast]

Wouldn't surprise me at all if they were the same internal structure with the 7027A labeled version just having those extra pins. The post above the tubes/boxes are clearly labeled 7581A while DaveO said they were 7027A, as I said I hope he didn't pay for one and get the other. They'll work in the amp (as you already know) but the are supposed to be distinct offerings.

I just noticed that the top of the tube in the image is silk screened 7581A. They must be 7581A’s.

 

[mrpackerguy]

I just picked up a mint condition USA built V4BH. At home I'm running it though an Acme Series III B2 and because it is such an inefficient cab, it's just a terrible combination - the V4BH doesn't feed that cab NEAR enough wattage that the cabinet craves and needs, and my wife's not complaining upstairs with it cranked (doesn't take much to get her yelling down "Turn it down!!"). And anything past 2:00 on the gain and master overdrives it through the Acme B2. For gigs, I'll be running it with my Berg AE212 - much more efficient cab and should provide plenty of stage volume without distortion (it's in the band trailer 60 miles away).

My question is, the 212AV is well known as a great mate with the V4s. But the 212AV looks so dang awkward to haul around. Can anyone chime in on its portability?

 

[coreyfyfe]

My question is, the 212AV is well known as a great mate with the V4s. But the 212AV looks so dang awkward to haul around. Can anyone chime in on its portability?

I have a pair of the 112AV cabs and a custom 2x12 of fairly similar dimensions to the 212AV, so not exactly what you're looking for, but the 2x12 is pretty easy to carry/move. Grab the side handles and lift. Or bear hug if need be. Not so big that it's hard to move in doorways and such, not too heavy. You could always add wheels if you wanted, I usually just plop my cabs on top of my rolling road case for my amp and move them that way.

 

[daveobieone]

I just noticed that the top of the tube in the image is silk screened 7581A. They must be 7581A’s.

You know how sometimes you get something in your head, and you are SO sure about it, that you don't even look at the numbers on the tube or the tube box...DUH...That's what I did. I was so sure I had ordered 7027's, that I didn't even notice that I was installing 7581A's. Very sorry about the confusion. What a bone-head I am sometimes!

Here's the good news...
The new issue Tung Sol 7581A's (yes that IS what they are) turn out to be some wonderful tubes in the V4B! Distortion is very low (after a bias tweak, see below), and power at clipping is over 100 watts. The amp stays below 1% distortion till you get right up near the clip point.

A few details...
I installed 10 ohm 2 watt metal film cathode resistors, which I hand matched. Of course, that meant flying a cathode common buss across the output tubes for everything to connect to...but it worked out well. I also cleaned up some of the overly long wires, and put some decent twist on the filament wires from the power transformer while I was at it.

The new Tung Sol 7581A tubes ran really frigidly cold at first power-up. Only running about 8 watts at idle. There was a fair amount of cross-over distortion, and harmonic distortion was pretty high. It was clear that the bias was needing adjustment for these. The good news is, they were all within a few tenths of a watt of each other. The matching on this set was perfect.

To pull down the bias, I experimented with a few different fixed value resistors in parallel across R49 the 75K shunt resistor after the rectifier. It turns out that a 470K across R49 dropped the bias voltage enough to run the new Tung Sol's at about 50% of the 35 watt rating, or about 17 watts at idle. At that point, the amp performs really well, and the tubes should last a very long time. I plugged in slightly used (but still above 5000) set of GE 6L6GC's, and they were running at about 70% with the same bias set-up. So, I can carry a spare set, and just drop them in if needed at a gig or rehearsal.

Next time I'm in there, I'll try to have a suitable pot to install, so future adjustment will be easy.

BTW, on your suggestion Beans, I did re-solder all the tube socket connections...both power tubes, and on the boards. Some of them looked really crummy on close inspection with a magnifier and strong light. No more static when wiggling around the smaller tubes now.

Bottom line is...
These new production Tung Sol 7581A tubes are great in our V4B amps, BUT, you WILL need to tweak the bias to get the most out of them.

After I get some $ coming in, I will likely order a set of the 7027A tubes to see how they match up to the 7581A. My guess is, they are likely the same tube, perhaps with a different base that includes the additional pins.

 

[beans-on-toast]

You know how sometimes you get something in your head, and you are SO sure about it, that you don't even look at the numbers on the tube or the tube box...DUH...That's what I did. I was so sure I had ordered 7027's, that I didn't even notice that I was installing 7581A's. Very sorry about the confusion. What a bone-head I am sometimes!

Here's the good news...
The new issue Tung Sol 7581A's (yes that IS what they are) turn out to be some wonderful tubes in the V4B! Distortion is very low (after a bias tweak, see below), and power at clipping is over 100 watts. The amp stays below 1% distortion till you get right up near the clip point.

A few details...
I installed 10 ohm 2 watt metal film cathode resistors, which I hand matched. Of course, that meant flying a cathode common buss across the output tubes for everything to connect to...but it worked out well. I also cleaned up some of the overly long wires, and put some decent twist on the filament wires from the power transformer while I was at it.

The new Tung Sol 7581A tubes ran really frigidly cold at first power-up. Only running about 8 watts at idle. There was a fair amount of cross-over distortion, and harmonic distortion was pretty high. It was clear that the bias was needing adjustment for these. The good news is, they were all within a few tenths of a watt of each other. The matching on this set was perfect.

To pull down the bias, I experimented with a few different fixed value resistors in parallel across R49 the 75K shunt resistor after the rectifier. It turns out that a 470K across R49 dropped the bias voltage enough to run the new Tung Sol's at about 50% of the 35 watt rating, or about 17 watts at idle. At that point, the amp performs really well, and the tubes should last a very long time. I plugged in slightly used (but still above 5000) set of GE 6L6GC's, and they were running at about 70% with the same bias set-up. So, I can carry a spare set, and just drop them in if needed at a gig or rehearsal.

Next time I'm in there, I'll try to have a suitable pot to install, so future adjustment will be easy.

BTW, on your suggestion Beans, I did re-solder all the tube socket connections...both power tubes, and on the boards. Some of them looked really crummy on close inspection with a magnifier and strong light. No more static when wiggling around the smaller tubes now.

Bottom line is...
These new production Tung Sol 7581A tubes are great in our V4B amps, BUT, you WILL need to tweak the bias to get the most out of them.

After I get some $ coming in, I will likely order a set of the 7027A tubes to see how they match up to the 7581A. My guess is, they are likely the same tube, perhaps with a different base that includes the additional pins.

I run the 7581A’s in my ‘74 V4B and am very happy with them. Same story, the tube store did a good job at matching. When you get the adjustable bias in place, it will be a lot easier to experiment with the bias setting.

Good news re the static issue. This can also be caused by any loose tube socket contacted. Retensioning the socket terminals if necessary solves that. Sounds like you are fine though.

BTW, we all manage to do boneheaded things. Don’t get me started on that.

 

[Mastermold]

...
My question is, the 212AV is well known as a great mate with the V4s. But the 212AV looks so dang awkward to haul around. Can anyone chime in on its portability?

The 212AV is very portable. It's not heavy, nice size at just a little larger than a single 15 but smaller than a 410, and has nice recessed side handles for and easy loading in/out. It's the cabinet I use most often with my SVTs for small venues and has become my most used all purpose cabinet. And most important, it sounds great! Here's a photo I've posted around here a few times:

 

[mrpackerguy]

I just picked up a mint condition USA built V4BH. At home I'm running it though an Acme Series III B2 and because it is such an inefficient cab, it's just a terrible combination - the V4BH doesn't feed that cab NEAR enough wattage that the cabinet craves and needs, and my wife's not complaining upstairs with it cranked (doesn't take much to get her yelling down "Turn it down!!"). And anything past 2:00 on the gain and master overdrives it through the Acme B2. For gigs, I'll be running it with my Berg AE212 - much more efficient cab and should provide plenty of stage volume without distortion (it's in the band trailer 60 miles away).

My question is, the 212AV is well known as a great mate with the V4s. But the 212AV looks so dang awkward to haul around. Can anyone chime in on its portability?

I went and got my Berg AE212 from the band trailer and Oh what a difference! Much louder, virtually no breakup until the gain is pushing 3:30 O'Clock. Should be very usable at the gig and I can have my boost pedal as standby. It's amazing what 10 db further north in cabinet efficiency can do with 100 tube watts. Acme 93 Berg 103. I still love my Acme, though for certain situations, especially jazz. But I think this proves to me the Acme Low B2 Series III is not a good match for the V4s.

 

[beans-on-toast]

The 212AV is very portable. It's not heavy, nice size at just a little larger than a single 15 but smaller than a 410, and has nice recessed side handles for and easy loading in/out. It's the cabinet I use most often with my SVTs for small venues and has become my most used all purpose cabinet. And most important, it sounds great! Here's a photo I've posted around here a few times:


View attachment 2886450

That Kay bass is so cool. Any problems with feedback at higher levels. It can be a problem with hollow body instrument.

 

[Mastermold]

That Kay bass is so cool. Any problems with feedback at higher levels. It can be a problem with hollow body instrument.

Yes I have to keep my fingers on it at all times during a song else I become Jimi Hendrix !

 

[beans-on-toast]

Yes I have to keep my fingers on it at all times during a song else I become Jimi Hendrix !

If the pickup is not sealed such as epoxy encased, dripping a layer candle wax on the back of the pickup case can dampen vibrations. The back of the pickup case can act like a drum and the wax adds enough weight to stop it. This is not the same as a potted pickup where the wax is on the coils.

I’ve found that in cases like you described where the strings start to vibrate if you aren’t holding them, this has helped. My old Hofner is one example. Originally it came stuffed with a bedsheet to dampen the top but it affcted the charisteric tone of the instrument. The wax allowed me to remove the sheet and solve the problem.

 

[daveobieone]

Ok...I've been playing through this old (but new to me) Magnavox-era V4B now for the past several weeks with my 10 piece horn band.

I've been playing bass since the mid-1960's, through everything from a Sears 150 watt solid-state (my first bass amp), to Fender Dual-Showman's, to Kustom K-200's / K-400's, to my recent Mesa D800/Subway stack...and a whole lot in between. I have never been SO satisfied with my tone as I have been in the past few weeks using this V4B! I really look forward to rehearsal/recording sessions with my band now. The tone is just something I can't get out of my head, and I can't wait to pick up my bass, and hear it again. Even with the tone set nearly flat (mid and bass at 1:00), and no ultra switched in, the tone is just wonderful. No pedals needed...I just plug straight-in. All the guys in my band have been raving about it too, and they don't usually have much good to say about the sound of anything.

What I can say for sure is, I wish I had found this tone 45 years ago!

The V4B does have two drawbacks however... First, the 60 pound weight of the thing. With my old-guy back, it's about all I can do to pick it up. Second, the amp just really isn't loud enough for the larger gigs this band plays. It's enough for our rehearsal studio space, but for the larger venues (usually without PA support for bass) it wouldn't be enough. This band plays really loud!

I'd never want to part with the V4B for rehearsal and recording...The sound is so wonderful, but for me, it's just not practical for gigs....BUT, I want that sound at gigs too!

So, after reading through about 60 favorable reviews, I bought one of the Ampeg SCR-DI pedal things. My thought was, I'd put this ahead of my Mesa D800/Subway stack, and maybe I could get somewhere close to the glorious new tone I've discovered from the V4B at gigs. I'm NOT dumping on the Mesa...it does sound very good, and it's really powerful, but it just doesn't quite have that "magic" that the V4B has.

The Ampeg pedal hasn't arrived yet, but I wanted to ask...Has anyone else here gone down this road? What settings have you found to work well with the SCR-DI that work for you? I'm guessing maybe Jimmy has played with this pedal a bit...perhaps others as well.

Thanks!
Dave O.

 

[beans-on-toast]

That feeling when you plug in and you have that smile on your face. You just know, this is it. The weight is an issue, carts and some help lifting makes it workable.

The nice thing about the V4B is that you can push both the pre and power amps hard enough to get that on-the-edge sound. It can be more difficult with a way more powerful amp. But that’s why I have an SVT as well.

 

[jumbodbassman]

my V4B with a squareback is the sound i still strive for 45 years later. The V4B with a full array of speakers cabs can get pretty loud. i have a SCR DI - it does do a V4B for me.

 

[JimmyM]

Ok...I've been playing through this old (but new to me) Magnavox-era V4B now for the past several weeks with my 10 piece horn band.

I've been playing bass since the mid-1960's, through everything from a Sears 150 watt solid-state (my first bass amp), to Fender Dual-Showman's, to Kustom K-200's / K-400's, to my recent Mesa D800/Subway stack...and a whole lot in between. I have never been SO satisfied with my tone as I have been in the past few weeks using this V4B! I really look forward to rehearsal/recording sessions with my band now. The tone is just something I can't get out of my head, and I can't wait to pick up my bass, and hear it again. Even with the tone set nearly flat (mid and bass at 1:00), and no ultra switched in, the tone is just wonderful. No pedals needed...I just plug straight-in. All the guys in my band have been raving about it too, and they don't usually have much good to say about the sound of anything.

What I can say for sure is, I wish I had found this tone 45 years ago!

The V4B does have two drawbacks however... First, the 60 pound weight of the thing. With my old-guy back, it's about all I can do to pick it up. Second, the amp just really isn't loud enough for the larger gigs this band plays. It's enough for our rehearsal studio space, but for the larger venues (usually without PA support for bass) it wouldn't be enough. This band plays really loud!

I'd never want to part with the V4B for rehearsal and recording...The sound is so wonderful, but for me, it's just not practical for gigs....BUT, I want that sound at gigs too!

So, after reading through about 60 favorable reviews, I bought one of the Ampeg SCR-DI pedal things. My thought was, I'd put this ahead of my Mesa D800/Subway stack, and maybe I could get somewhere close to the glorious new tone I've discovered from the V4B at gigs. I'm NOT dumping on the Mesa...it does sound very good, and it's really powerful, but it just doesn't quite have that "magic" that the V4B has.

The Ampeg pedal hasn't arrived yet, but I wanted to ask...Has anyone else here gone down this road? What settings have you found to work well with the SCR-DI that work for you? I'm guessing maybe Jimmy has played with this pedal a bit...perhaps others as well.

Thanks!
Dave O.

My typical setting with the SCR-DI is about the same as what I use on most Ampeg gear with that EQ...bass and mids 2:00, treble 9-10:00. But it's important to note that there are plenty of settings available on it and most all of them sound good unless you lower the bass response too much.

Also, new V4B's weigh 40 lbs

 

[peterpalmieri]

Ok...I've been playing through this old (but new to me) Magnavox-era V4B now for the past several weeks with my 10 piece horn band.

I've been playing bass since the mid-1960's, through everything from a Sears 150 watt solid-state (my first bass amp), to Fender Dual-Showman's, to Kustom K-200's / K-400's, to my recent Mesa D800/Subway stack...and a whole lot in between. I have never been SO satisfied with my tone as I have been in the past few weeks using this V4B! I really look forward to rehearsal/recording sessions with my band now. The tone is just something I can't get out of my head, and I can't wait to pick up my bass, and hear it again. Even with the tone set nearly flat (mid and bass at 1:00), and no ultra switched in, the tone is just wonderful. No pedals needed...I just plug straight-in. All the guys in my band have been raving about it too, and they don't usually have much good to say about the sound of anything.

What I can say for sure is, I wish I had found this tone 45 years ago!

The V4B does have two drawbacks however... First, the 60 pound weight of the thing. With my old-guy back, it's about all I can do to pick it up. Second, the amp just really isn't loud enough for the larger gigs this band plays. It's enough for our rehearsal studio space, but for the larger venues (usually without PA support for bass) it wouldn't be enough. This band plays really loud!

I'd never want to part with the V4B for rehearsal and recording...The sound is so wonderful, but for me, it's just not practical for gigs....BUT, I want that sound at gigs too!

So, after reading through about 60 favorable reviews, I bought one of the Ampeg SCR-DI pedal things. My thought was, I'd put this ahead of my Mesa D800/Subway stack, and maybe I could get somewhere close to the glorious new tone I've discovered from the V4B at gigs. I'm NOT dumping on the Mesa...it does sound very good, and it's really powerful, but it just doesn't quite have that "magic" that the V4B has.

The Ampeg pedal hasn't arrived yet, but I wanted to ask...Has anyone else here gone down this road? What settings have you found to work well with the SCR-DI that work for you? I'm guessing maybe Jimmy has played with this pedal a bit...perhaps others as well.

Thanks!
Dave O.

The new V4b is a bit lighter and with a couple different cab set ups it goes way louder the. Needed.