Ampeg V4, maximizing headroom, needing real answers...

[gepetto33]

Hey guys,

I've seen quite a few posts in regard to this question, but nothing that correctly suits my application -

I play guitar through it, for heavy, sonic type music.

I do not and will never need power amp breakup; i use a modified tube distortion pedal that does a wonderful job at providing exactly the gain i want. I am running a 70-74 Ampeg V4 with JJ 7027's which work pretty good for the most part, but are getting tired from the amount of use they've had through the years (3+).


I am looking for a tube that can help my V4 increase clean headroom....

Are 6550's the answer?
- Have heard good things about the SED 6550's (used in a plexi)

Do they take well to guitar amps, with correct modification and biasing?

Some say yes. Some say no, it makes no difference in power. Would like a supported reason if it doesn't.

Also considering the JAN-Philips 6L6WGB as i've heard good things about the tone (i'm aware this will not increase headroom beyond the 7027's i'm currently using, but they might pack a better tone)....has anyone used these?

Have also heard good things about the JJ KT88's, in regard to use in a plexi - could my ampeg even handle these, even with modification?

Please help me shed some light on this kind of dilemma.....Thanks!

[Diablo]

The only tubes I've used in a V4 are NOS 7027a, (RCA, GE, Sylvania). You get plenty of clean headroom with these tubes. The V4 puts around 540 volts to the plates, so that's why I like to stick to NOS 7027a, which have no problem with the voltage. I've used the JAN-Philips 6L6GWB tubes in a Tweed Bassman clone, and they sound great and do give an early breakup. However, that amp has 460 volts to the plates, and I would be afraid to stick those tubes in the V4.

[gepetto33]

Right on, i didnt realize at first that the WGB's were low wattage tubes, i'll def not go for those.

Have looked around on Ebay, and my other tube stores and have only found a very expensive set of JAN Philips 7027's for like $300.

Don't really know where else to look?? I figured they would be the best sounding choice over 6550's...seems like those might darken up the sound of a v4, making it more bass amp-like.

[Steve Conner]

Help, Uncle Ned, My Amp Has 7027's!

The article says that you can stick just about any good-quality tube in an Ampeg V-series.

Don't see any reason why 6550s or KT88s wouldn't work. There will be a slight power increase, but usually not as much as you hoped for. If you had 60W before, you might have 75 or 80 with the new tubes. The reason is that the power output is limited by the transformers, as well as the tubes. The bigger tubes need beefier transformers to realise their full potential. If you want 100W out of a pair of 6550 or KT88s, you have to feed them over 600 volts.

And "clean headroom" correlates directly to the amount of undistorted output power you can get. It's the same thing.

Having said that, sometimes you can get more "umph" out of the larger tubes by loading them more heavily: connecting an 8 ohm speaker to the 16 ohm output tap.

And don't forget the extra heater current on 6550/KT88/EL34 tubes.

[Diablo]

Have looked around on Ebay, and my other tube stores and have only found a very expensive set of JAN Philips 7027's for like $300.

I avoid the tube stores because their prices are so high. I've been able to buy 'em on ebay auctions for much more reasonable prices. As Steve pointed out though, the V4 power tube sockets are wired to use either a 7027a or 6l6GC. If you buy new production tubes (JJ Tesla), save some money and just buy 6L6GC because they charge a premium for the pinout differences that make it a 7027A. The only key thing is that whatever tube you buy, it has to be designed to handle 540 volts.

[rudutch]

6L6 Types

this MIGHT work

[gepetto33]

Hmmmm, choices choices....

Honestly, 7581 tubes seem like the best combination of tone and output, but

a.) can they handle 540v
b.) can you find them anywhere

Have got the search beacon out, this is the tube im looking for.

[ThermionicScott]

On paper, a 7581 doesn't look any more capable than a 7027A. (I'm sure at least some later production tubes had the same guts for both.)

Biasing cooler can net a little more headroom, but you probably knew that.

[byrdbrane]

I've tried a lot of different 7027 tubes through my V-4. I have another custom built 7027 amp that will take any tube in the 6L6 family, just plug and play. The custom amp has a very short signal path from the guitar to the speaker, therefore you can really hear the tonal qualities of each tube that you audition through the amplifier. Because the V-4 has like 7 tubes in the preamp section and a whole lot of circuitry, you don't quite hear the same tonal qualities of the power tubes as occurs with the custom built amp. That being said, I will note that my V-4 has had some mods done by the guitar player from the Wipers. He eliminated the reverb circuit, added an extra filter cap, eliminated a couple of the rocker switches on the top, added a master volume and made the second channel a separate 1/4" send for looping through an Echoplex. Since I've had the amp I keep blowing the same tube socket and seem to get periodic voltage spikes that fry tubes and circuitry.... Trying to remember the pin number. But last night was no exception. Watched a $50 RCA 7027 flash like a light bulb and there goes the sound... threw in a Phillips and played for another hour without incident. I've replaced one of the series wired Mallory filter caps once and am getting ready to again. I suspect this to be the source of the voltage spikes that make this amp a rather high maintenance device. You can't beat the sound however. I also have a bogner Shiva and I would say I prefer the tone of the V-4, especially when using my Patrick Eggle Berlin Plus with custom wound pick ups or my Gibson ES-345, also Gibson SG VOS. When I last replaced the problematic Mallory cap it tested next to no remaining capacitance.

Now as far as the tubes with the most headroom? I would say I prefer either the Phillips JAN, which I wouldn't pay more than $50 for a single tube. Some recent RCA NOS tubes I bought proved to be garbage. The other tube that I would give an excellent rating to is the tall bottle Raytheon, if you can find any. I understand they made some tubes for RCA, but not the junkers some scam tube dealer sold me. When I contacted him about a tube that tested short, he just started shrieking at me. I'm like o.k., sounds guilty to me.

The JJ's that you mention, while performing reliably, sounded like crap, if you ask me. The Sovtek quartet I bought sounded excellent for the first 3 months and then tubes started failing quickly, but I still have one that is still in service. These were purchased shortly after they went into production, so maybe their QA/QC has improved.

At the end of the day I recommend you keep that amp stock for reliability, maybe except for having a master volume installed like the one on the back of my amp. Then you will be able to keep the preamp level down and krank the master, that will give you the additional headroom you're looking for, while sticking loyal to a tube you'll be sorry you ever thought of replacing.

[Earl Norton]

It has been discussed here before: the secret ( and it is not really a secret) to more headroom is efficient speakers not different tubes.

[byrdbrane]

Well in this particular instance I went from Krank 120 Watt 16 Ohm Eminence speakers to Jensen Jet Alnico Blackbird 100 Watt 16 Ohm speakers. I spent around $800 on the upgrade. Did this improve the sound? Not really. Was it worth spending $800? No. I think having a master volume knob installed will get the user more headroom at a reasonable cost.

[ThermionicScott]

I think having a master volume knob installed will get the user more headroom at a reasonable cost.

How would it accomplish that feat?

[byrdbrane]

O.k... I'm actually going to get off my butt and look to see where the Master Volume ties into the circuit board... Ok, for mine there is a three wire wiring harness coming off the variable resister. The knob itself is inserted onto the back of the metal chassis. (On my amp the reverb circuit has been totally eliminated so, the variable resister is mounted where the reberb lockout switch was once located) So once you get it installed you'll want to set your volume where you want it and probably keep it there. The knob on the front of your amp, previously your master volume and preamp gain then acts as your preamp gain, which you can then leave relatively low, say 50% or lower to increase your headroom. Then keep your master where it will give you the volume your looking for. I find 50% with these amps is plenty because they are so loud. In this scenario the amp keeps a really flat tone that is very unique and hard to duplicate in other amps. If you wanted more crunch another trick is to pull the two outside tubes, thus running the amp at 50 watts. I notice it breaks up a little earlier in the two tube mode and is less ear strain when one wishes to play at lower volumes. Still, I would say generally speaking the 4 tube mode is preferable. Sometimes, when short of tubes, this is also a quick easy trick to keep the rig running. Pulling the two outside tubes isn't the only configuration that works mind you.

[Earl Norton]

Please define "headroom" for us. thanks.

[crisisat22]

I am looking for a tube that can help my V4 increase clean headroom....

You are the first person I have ever heard who actually wanted to increase the clean headroom in one of these

You can try modding it for 6550's, it was commonly done when current production 7027A's were not easy to find. As someone said earlier, I would not expect a significant increase in power.

Years ago I was fighting to get my V4 to go in the opposite direction. Even with two tubes pulled it was still very loud before breakup (Kind of like the difference between a 747 and a 757 at takeoff...) I ended up replacing all the 12DW7's in spots V1 and V4 with 12AX7's. This helped the amp break up a bit better, maybe you could replace them with 12AU7's and go the other way? It would not be a direct change to the power section, but it may clean up the preamp a bit?

[g-one]

It should be mentioned that distortion in these amps can be easily due to the preamp. The first gain stage is before the volume control and a hot pickup will easily overdrive it. For clean sounds I have to run the attenuator switch at the -9 setting.

[byrdbrane]

The definition for headroom can be found at the following link, thus saving the writer some time in explaining...

A good definition I think...

http://en.wikipedia.org/wiki/Headroo...nal_processing)

[Steve Conner]

To maximize headroom, just plug your guitar straight into the FX return jack.

[byrdbrane]

headroom is the amount by which the signal-handling capabilities of an audio system exceed a designated level known as Permitted Maximum Level (PML). Headroom can be thought of as a safety zone allowing transient audio peaks to exceed the PML without exceeding the signal capabilities of an audio system (digital clipping, for example). Various standards bodies recommend various levels as Permitted Maximum Level.

also

A margin of audio safety between the current signal level and the maximum signal level possible without introducing distortion. Headroom is usually measured in decibels. When referring to a tape recorder, headroom is the difference between the standard operating level (0VU on the VU meter) and a level causing 3 percent total harmonic distortion. You can increase high frequency headroom by recording audio tape at higher speeds.