Loud Reissues the Ampeg V4-B using Lower Voltage 6L6GC

[bob p]

Some interesting things happening at Loud Technologies. They've filled that gap we've been talking about, between the B-15 reissue and the SVT reissue. Now they're coming out with a 100W reissue of the V4-B.

One thing that I thought was interesting is that Loud has made some changes to the amp that may make it sound a bit different than the original. The orginal used 7027A and used some really high B+ voltages. Back in the day, the anode voltage on the 7027A was in the range of 550 - 590 VDC.

Today's reissue is going to be a 6L6GC amp, and we know that 6L6GC wouldn't hold-up very long at those vintage voltages. There's been a fair amount of debate going on at other sites about whether there's any current production 7027A-equivalent tube that is really equivalent to a 7027A, or whether they're just a re-labeled 6L6GC. If they're really a 6L6GC and not a 7027 then they shouldn't be expected to last very long at the vintage-spec high voltages. I don't think that any current production 6L6GC is going to be up to the task.

My thoughts were that Loud wouldn't be able to reissue the amp in it's original form because there are no modern 6L6 tubes that would survive in the circuit. I thought that they would end up having to drop the B+ voltages considerably in order to produce a reliable 100W amp that's based upon modern 6L6GC, and if they were to do that, then the amp might not end up being a very faithful "reissue" of the original from a tonal perspective.

Of course, that's not a popular opinion to voice on the fanboy sites.

Ampeg finally admitted that they've dropped Va to around 455V. That's a drop of 100 to 150 VDC from where the old V4-B used to operate. Although the new amp will certainly be more reliable in running 6L6 at "reasonable" voltages, the question that I'd like to have answered is how much you'd expect the sound of the amp to change by the rather significant drop in B+ voltages. Based upon my experience, a 6L6GC definitely sounds different at 350V compared to 450V, so I'm thinking that a vintage amp that ran 7027A at 550-590V would sound appreciably different than a reissue that runs 6L6GC at 450V.

I'm hoping that you guys who have been refurbing/restoring/playing the vintage Ampeg gear might have some insights in this regard.

Loudthud? Anyone?

[Steve Conner]

Higher plate voltage requires a lower idle current so as not to exceed the plate dissipation. This means more crossover distortion.

Tube crossover distortion is not like the solid-state kind that simply adds an annoying fizzle to the signal. It's spread over a much wider range of signal amplitudes, giving the stage less gain for small signals than large ones. The effect is somewhat like an expander. I always felt that it made the sound "harder" and exaggerated the dynamics.

Anyway, I guess my point is that lowering the supply voltage will do the opposite of this. But not necessarily as they could lower it and still bias the tubes cold.

[bob p]

Harder, edgier, and more dynamic is what I think of at the higher B+ voltages, while softer and mushier is what I think of when you drop B+ by 100V or more. I've been thinking that the lowered B+ voltages would reduce those hard/edgy characteristics in the new reissue amps, but rather than leading off the discussion with an assumption like that, I thought I'd ask for peoples' opinions. (I didn't want to start off the thread with a comment that might get the fanboys to start throwing rocks at me.)

It'd be interesting to hear the opinions of the guys who have compared the real vintage amps and the reissues when they finally become available. I'm thinking that there are going to be some parallels between the sonic differences that I expect between the new/old V4-B, and that they should be similar to the sonic differences between the high voltage BF Fenders to the lower voltage BF Fenders. After all, 100 to 150V of B+ is a pretty significant change.

[jazbo8]

Was the OPT Ra-a changed as well (perhaps lower than the original)?

[bob p]

Ampeg says the reissue Ra-a is 2200 for a quad, which is comparable to 4400 for a pair of 6L6. That puts them on the flat plateau of the Ra-a characteristic's power curve, where movement from side to side doesn't really change anything significant.

yeah, we all know that the OPT doesn't really have it's own impedance, just a ratio.

[nashvillebill]

This reissue V4B has gotten 33 pages of discussion over on Talkbass 2013 Ampeg V-4B 100W Reissue - TalkBass Forums

[bob p]

I noticed that thread. Lots of opinions, but virtually zero technical content, and the guys who had technical concerns tended to be dismissed by the people who like pretty pictures.

[nashvillebill]

Oh, there's some nice photos on that Talkbass thread. Layout looks nice. Ra is indeed 2200 according to the Ampeg guy who posted on the thread towards the end. They confirmed plate voltages too. And gave specs for heater current for the PT, it's almost enough for 6550's.

edit:

Here's the quote from Ampeg:

More info from our engineer:

You can note to the one dude that I over-rated the transformer to handle 5.6A @ 6.3VAC. It is not ideal to overload it with 6550s, but it is not as dramatic as he made it out to be. Honestly, I forgot when I was thinking about it.

In regards to the primary difference not being a big deal, I disagree. We auditioned different primary values in the initial stages of design right around 20% and found there were performance and tonal differences. 2200 sounded and performed better, which is why we are using it.

Plate voltage is 445VDC and this amp is fixed bias, not cathode.

Oh and they also said there is a bias adjust pot.

[bob p]

> almost enough for 6550s

Yes, they over rated the filament transformer windings for 6L6, but they fell about 800ma short of being adequate for 6550s or EL34 or KT77. (IMO that was a stupid oversight.) I've wondered why they just didn't keep the voltages high and run 6550 (like 1/3 of an SVT) instead of dropping the voltages and running with a quad of 6L6. but that's another question entirely.

I'd really like to hear peoples' opinions about how the big drop in B+ changes the feel of the amp. I'm thinking that it's going to feel different to someone who's used to an old V4-B, but that doesn't mean it will be a bad amp, just a different amp.

[soundguruman]

Some interesting things happening at Loud Technologies. They've filled that gap we've been talking about, between the B-15 reissue and the SVT reissue. Now they're coming out with a 100W reissue of the V4-B.

One thing that I thought was interesting is that Loud has made some changes to the amp that may make it sound a bit different than the original. The orginal used 7027A and used some really high B+ voltages. Back in the day, the anode voltage on the 7027A was in the range of 550 - 590 VDC.

Today's reissue is going to be a 6L6GC amp, and we know that 6L6GC wouldn't hold-up very long at those vintage voltages. There's been a fair amount of debate going on at other sites about whether there's any current production 7027A-equivalent tube that is really equivalent to a 7027A, or whether they're just a re-labeled 6L6GC. If they're really a 6L6GC and not a 7027 then they shouldn't be expected to last very long at the vintage-spec high voltages. I don't think that any current production 6L6GC is going to be up to the task.

My thoughts were that Loud wouldn't be able to reissue the amp in it's original form because there are no modern 6L6 tubes that would survive in the circuit. I thought that they would end up having to drop the B+ voltages considerably in order to produce a reliable 100W amp that's based upon modern 6L6GC, and if they were to do that, then the amp might not end up being a very faithful "reissue" of the original from a tonal perspective.

Of course, that's not a popular opinion to voice on the fanboy sites.

Ampeg finally admitted that they've dropped Va to around 455V. That's a drop of 100 to 150 VDC from where the old V4-B used to operate. Although the new amp will certainly be more reliable in running 6L6 at "reasonable" voltages, the question that I'd like to have answered is how much you'd expect the sound of the amp to change by the rather significant drop in B+ voltages. Based upon my experience, a 6L6GC definitely sounds different at 350V compared to 450V, so I'm thinking that a vintage amp that ran 7027A at 550-590V would sound appreciably different than a reissue that runs 6L6GC at 450V.

I'm hoping that you guys who have been refurbing/restoring/playing the vintage Ampeg gear might have some insights in this regard.

Loudthud? Anyone?

Just another cheap Chinese imitation.
There are so many good amps to buy and use, why bother with Chinese pseudo-ampegs anyway?

[bob p]

Thanks for that analytical, fact-based, unbiased contribution to the thread.

[soundguruman]

Thanks for that analytical, fact-based, unbiased contribution to the thread.

Don't be sad Bob, there are still really good amps, made and supported in USA. (just the opposite of what you're looking at here...)

[jazbo8]

IMO, lower plate voltage with higher current is not the way to go, I would rather run the new tubes with higher plate voltage (even above spec) and lower current (perhaps using a OPT with higher primary impedance as well).

[bob p]

jazbo8, it sounds like you and I share the same concerns -- that the lower voltage is going to result in an amp that behaves differently/sounds differently. The old V4-B operating at those "obscene" voltages made it very much a rip-off-your-face type of amp. It was a monster. Unfortunately, there are some serious problems that have to be dealt with when trying to reissue an amp like this one, and those are the kind of concerns that might have led the designer of the reissue amp to dramatically change the amp's operating parameters. Will those sorts of compromises result in a dramatic change in the characteristic/feel of the amp? I think so. I think that the result might well be a neutered amp. But rather than jumping to conclusions I'd rather address the technical concerns and lay a technical foundation for finding the right answer.

The first problem relates to finding tubes that can handle those voltages.

The old amps ran 7027A at those really high voltages of 550-590 VDC, and those kinds of voltages have historically been a death sentence for a 6L6GC. If we set aside the idea of sourcing NOS 7027A and look at modern tubes only, we do have the option of the new JJ 7027A. It's rated for Ua=500v in pentode mode:

http://www.jj-electronic.com/pdf/7027.pdf

Of course, there are widespread doubts about whether the new JJ 7027 is really up to the standards of an old 7027A. Quite a few people have expressed concerns that it's actually nothing more than a re-labeled 6L6GC:

http://www.jj-electronic.com/pdf/6L6%20GC.pdf

(And then there is the question whether any of the european/asian/chinese tubes are really the equivalent of a 6L6GC, or just another re-branded tube.)

Looking at data sheets for the two JJ offerings, things do look very much the same. The inter-electrode capacitances are slightly different, but the rest of the specs look the same. (I haven't tried to compare the plate characteristics).

This naturally brings up the question of whether the new JJ 7027 will hold up in the vintage Ampeg amps. Knowing that would be a very helpful data point in assessing how to build a V4-B clone/reissue. I'm really hoping that some of the guys who know the vintage Ampegs will chime in with a good answer.

[g1]

Are they intending it to be true to the original sound wise? If so, I agree that it probably won't with that much difference in the B+. But maybe it is to be a modern take on an old classic, more of a "tribute" than a clone, like the new Camaro's or such. I just saw the info on the '68 silverface reissues, Princeton, Deluxe, and Twin. They've made a few changes (bassman tonestack on one channel, vib. and reverb on both channels, reduced neg. feedback etc.) but look very much the same as the originals. So maybe Ampeg is doing something similar here?

The old amps ran 7027A at those really high voltages of 550-590 VDC, and those kinds of voltages have historically been a death sentence for a 6L6GC.

Those voltages are fairly conservative compared to what some Musicman amps run 6L6's at. . I'm sure there are Musicman amps out there that are running with modern 6L6's. Lot's of 6V6 and 6BQ5 amps run at plate voltages way beyond max., Fender didn't care much for observing max. plate voltage ratings either. As seems to be generally agreed, it's not so much the plate voltage that causes problems, but the dissipation (and screen currents). I think a lot of the problems with tube failure in Ampeg V series amps is bias related. How many Ampeg V series amps out there have had adjustable bias installed? How many are trying to use the "magic" 70% figure? Stock they were biased around 55%, actually more like 50% if we believe the original 7027's were 35W tubes. So biasing correctly and changing to 1K screens will really help the lifespan of modern tubes in these amps.

Of course, there are widespread doubts about whether the new JJ 7027 is really up to the standards of an old 7027A. Quite a few people have expressed concerns that it's actually nothing more than a re-labeled 6L6GC:

New issue 7027's are 6L6's repinned for 7027 pin out. I have been following the 7027 issue since the first new versions (Sovtek) came out. They (New Sensor) acknowledged this to me at that time (sorry I no longer have that fax ).
The only difference between original 7027A's and 6L6's were the pinout and the max. plate & screen voltage and wattage specs. 600Vplate, 500V screen and 35W. The plate characteristic curves are identical.
The new 7027's are no longer rated that high, rather exactly the same as their 6L6's.
So, for new issue 7027's, if all the specs are exactly the same, it's a 6L6 with 2 extra pins connected, right?
But don't take my word for it, Bob at Eurotubes should know, and here's what he says on his website: "The JJ 7027A is actually the same tube internally as the JJ 6L6GC. However the JJ 7027A is wired just like a traditional 7027A and is a drop in replacement for any amp using 7027A's. Older Ampeg amps using 7027A's can use either the JJ 7027A or the JJ 6L6GC with no modification whatsoever. Using the JJ 6L6GC's will just save you a few bucks."
So why would anyone even bother to make a 7027 replacement then? Because some amps have the sockets wired up so 7027's will work but 6L6's won't. You can either rewire the sockets, or use 7027's.
Ampeg, however has the sockets wired so they will work with either 6L6 or 7027's.
You noted that the only difference in the JJ spec. sheets for the 2 tube types was some interelectrode capacitances. A closer look shows those involve g1. This is because they have connected an extra pin (#6) to it, the extra lead length affects the capacitance.

This naturally brings up the question of whether the new JJ 7027 will hold up in the vintage Ampeg amps. Knowing that would be a very helpful data point in assessing how to build a V4-B clone/reissue. I'm really hoping that some of the guys who know the vintage Ampegs will chime in with a good answer.

As you probably know from various threads, JJ seems to be problematic lately. For a while they were recommended for these amps, but lately they seemingly have lots of QC issues. Except the ones from Eurotubes .
If you are planning a clone/build, then like I mentioned before, conservative bias (like stock) and up the screen resistors to 1K's. FWIW, I have 2 almost bone stock (masters added) V4's (not B's). And also a VT22 (chopped to head) in the family. All stock bias circuits. Power tubes VOS, some Sovtek "7027's" and JAN 5881/6L6WGB. Of the three amps, none have had problems going through output tubes, actually I'm amazed how long they last.
Sorry for the long winded reply and going on about the 7027's, but as I said, I've been following the issue a long time.
Looking forward to hearing more about the V4B re-ish.