Jump to content
Gibson Brands Forums
Sign in to follow this  
fleetlin49

Vjr V3 Mods???

Recommended Posts

"Besides, the voltage lowering mod is based solely on a theory. Theories are fine in laboratories but real life is something else. Your theory has not (maybe even cannot) be proven true in a V3..."

 

This is an asinine statement Steven. All tubes are designed to be run within certain voltages ranges for optimum performance....and when you run them beyond those limits you will more than likely experience a short lived tube. That's not theory...that's a fact. I would also like to point out for those who may not know it.....when power tubes fail they often take other components with them. That's one of the main reasons why getting the voltages set right and adding a screen grid resistor to amps without them is highly recommended. The screen grid resistor is there to protect other components.

 

I would like to Echo ET's post and recommend that anyone considering modding a valve jr(any version)...head over to sewatt.com for some straight talk from a diverse group of players,modders and Electrical Engineer's as well.

Share this post


Link to post
Share on other sites
"Besides' date=' the voltage lowering mod is based solely on a theory. Theories are fine in laboratories but real life is something else. Your theory has not (maybe even cannot) be proven true in a V3..."

 

This is an asinine statement Steven. All tubes are designed to be run within certain voltages ranges for optimum performance....and when you run them beyond those limits you will more than likely experience a short lived tube. That's not theory...that's a fact. I would also like to point out for those who may not know it.....when power tubes fail they often take other components with them. That's one of the main reasons why getting the voltages set right and adding a screen grid resistor to amps without them is highly recommended. The screen grid resistor is there to protect other components.

 

I would like to Echo ET's post and recommend that anyone considering modding a valve jr(any version)...head over to sewatt.com for some straight talk from a diverse group of players,modders and Electrical Engineer's as well.[/quote']

 

I did NOT know that a power tube can take other components with it on its way out! Thanks! seriously.

 

(though I suppose I should just toss that up to your own observations that should in no way affect my own amp or anyone elses amp for that matter and do nothing on my end to prevent loss of components...)

Share this post


Link to post
Share on other sites

actually a wayward tube will do damage to a lot of others in the amp.. resistors are first; followed by the transformers...

We keep putting up the rant about the spec's of the EL84 but I did not want to qoute already known VJ posts so I started googleing...

 

Here is a data sheet on the El84:

http://www.hifitubes.nl/weblog/wp-content/ei-el84.pdf

 

All data sheet list Va on pin 7 as 300vdc, so the VJ in stock trim is 325vdc to 335vdc.

All parties on the VJ forums I've been on for 2+ yrs now all state the EL84 sounds best at 315vdc, which by the data sheet is still high.

 

Here is another test:

http://www.netads.com/~meo/Guitar/Tubes/Miles/el84-1.html

Tech Notes

According to the RCA tube manual, a single 6BQ5 (EL84) can produce up to 5.7 watts, with 10% THD. The design center maximum ratings were 300 volts on the plate, 65mA cathode current, and 12 watts static plate dissipation.

Share this post


Link to post
Share on other sites

We do not judge anyone that is willing to be on a quest for tone and can assume the risks set out in the safety guidelines.

-----------

 

that's not really true., people being what they are. But it's the general idea. And the best place on the web to learn to mod your vj.. and other amps as well.

Share this post


Link to post
Share on other sites
actually a wayward tube will do damage to a lot of others in the amp.. resistors are first; followed by the transformers...

We keep putting up the rant about the spec's of the EL84 but I did not want to qoute already known VJ posts so I started googleing...

 

Here is a data sheet on the El84:

http://www.hifitubes.nl/weblog/wp-content/ei-el84.pdf

 

All data sheet list Va on pin 7 as 300vdc' date=' so the VJ in stock trim is 325vdc to 335vdc.

All parties on the VJ forums I've been on for 2+ yrs now all state the EL84 sounds best at 315vdc, which by the data sheet is still high.

 

Here is another test:

http://www.netads.com/~meo/Guitar/Tubes/Miles/el84-1.html

Tech Notes

According to the RCA tube manual, a single 6BQ5 (EL84) can produce up to 5.7 watts, with 10% THD. The design center maximum ratings were 300 volts on the plate, 65mA cathode current, and 12 watts static plate dissipation. [/quote']

 

oh I was not disputing anything layboomo said, the parenthetical statement was just for fun. just want to be clear on that.

 

thanks for those links I will read away soon.

Share this post


Link to post
Share on other sites

The ironic thing about much of this discussion Steven is that we both genuinely have valve jr owners best interests in mind......I don't doubt that for a minute.

Share this post


Link to post
Share on other sites

I really love my version 3 AFTER FOLLOWING THE ADVICE OF THE S2 INFO AND THE NICE AND VERY HELPFUL PEOPLE AT SEWATT. When I first brought it home I didn't much care for it at all. But now, I can't stop playing it and every time I turn it on I'm simply amazed at the tone and feel. You guys are wasting your time responding to this guys criticism. He'll never admit when he's wrong no more than GM will. I read the old treads, he was ignorant too. There's always one person that has to try to spoil something that starts out fun and informative. Keep doing what your doing and enjoy your hobby. I appreciate your generous sharing of your knowledge and experience and I know that many others do too.

Share this post


Link to post
Share on other sites
We do not judge anyone that is willing to be on a quest for tone and can assume the risks set out in the safety guidelines.

-----------

 

that's not really true.' date=' people being what they are. But it's the general idea. And the best place on the web to learn to mod your vj.. and other amps as well.

 

[/quote']

Twang: you called me on that one for sure.. guess it was your 4th build that did it to me... sorry buddy.

I know your 5th will fly...

Share this post


Link to post
Share on other sites
There's always one person that has to try to spoil something that starts out fun and informative. Keep doing what your doing and enjoy your hobby. I appreciate your generous sharing of your knowledge and experience and I know that many others do too.

 

Don't worry Tarts. Never underestimate the sheer power of amp mod addiction! Trolls will always come and go, but when up against an addiction like this (no clinics, no treatment, and no hope of a cure), the trolls either get addicted or fall by the wayside. Sad, but true. :-k

 

Me? I dunno. I've sorta developed this thing for seeing amps naked, so I guess I keep coming back for the amp porn. O:)

 

Gil...

Share this post


Link to post
Share on other sites

ET.

It was a build full of stupid mistakes.

 

my fifth build will scare you.

 

It does me, anyway.

Share this post


Link to post
Share on other sites

WOW! I've been gone for a week and look what happened..........anyways I suppose I should have chosen my "word" more carefully. I should have said "recommended" not "essential".

 

I've already changed my tubes out for JJ's. She sounded much better after that. And I swap between the JJ and the EH depending on the mood I'm in. Sounds like I'm going to be biassing the amp soon. I suppose I should be a little more specific. Does the Hammond OT sound better than the stock one? what are the diferrences? Thats my big first question.

 

I'm a customizer/modder at heart. If there is a way to make it better, I find it and do it! Hence the reason none of my cars or guitars are stock! Heck, just about everything I own is modified in some way. I definately ain't the type to drive a fully restored [-X Ford Model A! That thing would be chopped, channeled, lowered, and burnin' rubber within a damn week!!!!

 

So Steve, you have fun in that stocker but don't be supprised when I blast past in my hot rod blasting rock n roll with a hot little looker on my side.

Share this post


Link to post
Share on other sites

I understand what Stevie is saying. I love my V3 combo. I don't mod anything normally. I do remodeling all day long and when I get home I DON'T WANNA MOD STUFF. The VJ is a great amp and a lot of people who are thinking of getting one are getting the idea it's crap without a lot of extra work - NOT SO. They are buying BlackHearts because they don't wanna have to solder... I think Epiphone made a winner with this lil' baby. I tryed out the BH's when they first came out and I'm still an Epiphone Man! Some guys MOD - some don't. I don't, and I don't see any reason to. With my Korg Toneworks pedal I can dial in almost any sound I want - I'm a happy camper. Thanks Epiphone for making a sweet lil' 5-watt amp and not RIPPING ME OFF on the price.

Share this post


Link to post
Share on other sites
WOW! I've been gone for a week and look what happened..........anyways I suppose I should have chosen my "word" more carefully. I should have said "recommended" not "essential".

 

I've already changed my tubes out for JJ's. She sounded much better after that. And I swap between the JJ and the EH depending on the mood I'm in. Sounds like I'm going to be biassing the amp soon. I suppose I should be a little more specific. Does the Hammond OT sound better than the stock one? what are the diferrences? Thats my big first question.

 

I'm a customizer/modder at heart. If there is a way to make it better' date=' I find it and do it! Hence the reason none of my cars or guitars are stock! Heck, just about everything I own is modified in some way. I definately ain't the type to drive a fully restored [-X Ford Model A! That thing would be chopped, channeled, lowered, and burnin' rubber within a damn week!!!!

So Steve, you have fun in that stocker but don't be supprised when I blast past in my hot rod blasting rock n roll with a hot little looker on my side.[/quote']

 

The hammond ese is a slight improvement over the stock version 3 and it's recommended if you might want to try octal power tubes down the line. The version 3 is essentially a modded amp of sorts out of the box as it includes many of the mods recommended for the earlier versions. If you have specific questions about specific mods I recommend you head over to sewatt.com as many threads here seem to end up in a to mod or not to mod discussion and it sounds like you already decided to.

Share this post


Link to post
Share on other sites

Man, I got to remember not to leave this site for a week at a time! I bought it because I heard all the modded ones and thought they sounded great. Then I found out I had the V3 and all the stuff Epi changed. I want a screamer, man!

Sewatt here I come!! thanks layboomo, see you on the other side.

Share this post


Link to post
Share on other sites

I'm a customizer/modder at heart. If there is a way to make it better' date=' I find it and do it! Hence the reason none of my cars or guitars are stock! Heck, just about everything I own is modified in some way. I definately ain't the type to drive a fully restored [-X Ford Model A! That thing would be chopped, channeled, lowered, and burnin' rubber within a damn week!!!!

 

So Steve, you have fun in that stocker but don't be supprised when I blast past in my hot rod blasting rock n roll with a hot little looker on my side.[/quote']

 

You heathen b'! Don't ruin a classic! What's wrong with building a T rod, or '32 A from scratch using a TIG, chromemoly tubes and fiberglass?

Share this post


Link to post
Share on other sites
So Steve' date=' you have fun in that stocker but don't be supprised when I blast past in my hot rod blasting rock n roll with a hot little looker on my side.[/quote']

Me? No, I'm a public transit person..., and you'll never believe how hot the co-eds are on the A train (at least not until your hot rod fines, license suspensions, and gas bills force you to see who's riding in (& on) what.

 

Hit every BLUE NOTE baaaby..., I'm going to play on:-"

Share this post


Link to post
Share on other sites

"hot rod fines"??? fines for what? As long as there is a DOT inspection and it PASSES, I won't be fined. Especially if I serenade the DOT inspector with my Lp Jr. and my hot, little Valve Jr! (need to keep it guitar centered)

 

=D> I see, your a tree hugging hippie. You have fun with that. At least I'll be able to take those "hot the co-eds" somewhere besides that A train! lol

Share this post


Link to post
Share on other sites

On correcting the voltages, I've found that specifically redoing the power supply and bias to match the tubes up with normal operation works wonders for distortion. For example, B+1 is 340V; the maximum rating of the EL84 is 300V on the plate and 300V on grid 2 (screen). RC-30 gives 250V on both for Class A1 typical; you should probably bias the amp to get 250V on the plate, and also use a screen resistor to reduce B+2 to 250V.

 

I find that the VJR's power supply works great for a 6V6GT power tube in Class A1 at 12% THD (total harmonic distortion); see RC-30 page 387. The 340V B+1 can supply 315V to the plate; you can drop to 225V at the screen from after B+3. There you go, instant 6V6GT beam power tube amp. For 8% THD you can use 250V/250V (4.5W) or 180/180 (2W).

 

As for that 12AX7, 293V? RC-30 page 415 shows a max of 330V, so 293V should be good. This means you could use smaller plate resistors if you like; though I'd say raise B+3 and keep those plate resistors as-is because they're in the signal path. 293V at pins 1 and 6 is good.

Share this post


Link to post
Share on other sites
...

I find that the VJR's power supply works great for a 6V6GT power tube in Class A1 at 12% THD (total harmonic distortion); see RC-30 page 387. The 340V B+1 can supply 315V to the plate; you can drop to 225V at the screen from after B+3. There you go' date=' instant 6V6GT beam power tube amp. For 8% THD you can use 250V/250V (4.5W) or 180/180 (2W).

 

As for that 12AX7, 293V? RC-30 page 415 shows a max of 330V, so 293V should be good. This means you could use smaller plate resistors if you like; though I'd say raise B+3 and keep those plate resistors as-is because they're in the signal path. 293V at pins 1 and 6 is good.

 

[/quote']

 

Don't be surprised to find upwards of 400v on the plate of a 12ax7 in a Fender Super Reverb. Think it might've been the Trem tube, but don't remember now.

 

Anyway, my old Crate VC508 had about 270v on the plate of it's el84, and when using the loop input directly compared to the loop input of one of my last semi-stock (power & bias adjusted) V3 VJrs with 310v on the plate, there was just no contest. The Crate couldn't even come close to keeping up. And yet, the stocker was blown away by my twin Funk 47's (el84/Hammond 125DSE) that I still use post-processor as stereo power amps. The Hammonds are simply better to my ears. YMMV

 

I've got 350v on the plate of the 6V6 in my Beast Jr with a 125ESE, and it sounds freeking scary awsome. And it absolutely blows the doors off my Funk 47's. Go figure! =D>

 

Gil....

Share this post


Link to post
Share on other sites

 

Anyway' date=' my old Crate VC508 had about 270v on the plate of it's el84, and when using the loop input directly compared to the loop input of one of my last semi-stock (power & bias adjusted) V3 VJrs with 310v on the plate, there was just no contest.

[/quote']

 

I've got 350v on the plate of the 6V6 in my Beast Jr with a 125ESE' date=' and it sounds freeking scary awsome. And it absolutely blows the doors off my Funk 47's. Go figure! :-

[/quote']

 

What about the screen grid?

 

This is probably review for you, but let's get a little deeper into the subject. A diode emits free-floating electrodes from the (heated) cathode, creating a space charge that gets sucked away by the positive anode; a triode adds a (cold) control grid between the two to control the flow, isolating the negative space charge via a negative grid and allowing more current flow as the grid becomes positive. This works for recto tubes (1 way current flow diode) and preamps (low current triode using a grid to control current flow).

 

The 6V6 is a beam tetrode (pin 1 is the metal shell, or nothing in 6V6GT; an EL34 pentode hooks Pin 1 to the suppressor). In a tetrode, we add "Grid 2," the screen grid. The screen grid G2 reduces the inter-electrode capacitance between the control grid G1 and the plate from several pF to 0.01pF or less. G2 is less positive than the anode by a little, and much more positive than the cathode; because of this, the G2 attracts cathode electrons (again, more when G1 is more positive and less when G1 is more negative), serving only to accelerate them towards the plate. This means more current flow is possible!

 

If you raise the screen grid above the plate (say 300V plate 310V screen) you have a problem, it starts capturing electrons. If you lower the screen grid (say 300V plate and 215V screen instead of 250V), it starts limiting current flow and can cause distortion. At a point it can sound nice; at a point it can sound nasty; and I believe the tube is most linear with the screen grid just barely more negative than the plate (correct me if I'm wrong). The OT makes a big difference too; load has an effect.

 

Here's an EL84 data sheet to look at. 250V and 250V produces less third order harmonic distortion than 250V and 215V... (which is in general good, though not always, depends on what you want to happen)

 

http://www.mif.pg.gda.pl/homepages/frank/sheets/010/e/EL84.pdf

 

Also gil check out the last page of this 6V6 data sheet, the chart shows you distortion versus the load resistance (OT impedance is close.. it's reactive though, changes with frequency, etc).

 

http://www.mif.pg.gda.pl/homepages/frank/sheets/127/6/6V6.pdf

 

The point is you can do a lot to tune the tube to what you want it to do; for me, getting them into some good operating ranges did wonders.

Share this post


Link to post
Share on other sites

Absolutely. Screen voltage can tune the tube if you care to play with it. With the screen grid tied to the plate voltage, you have triode mode. Some data sheets for EL34s have g2 at a higher voltage than the plate. But when it's below plate voltage, max power and magic happens for guitar amps. You can even make it springy or stiff by tweaking the difference of plate to screen voltage. And don't forget chokes!

 

My point is that it's really an awfully big ballpark we get to play in. You certainly don't have to go above or beyond the manufacturer's specs. But you can. Even the too-high plate voltages that are found in all versions of the stock VJr wouldn't be so bad if the bias was a little cooler to compensate. But there is still that 10k wide voltage spread between the plate and screen in the stockers. Hammond OT's drop less voltage between B1 and the plate than a stock OT, so I use a 2.2k 3w in R12, plus a 1k 1w safety resistor in series to the screen grid. That's still a little stiff, but I like it and I setup my filter caps high to add even more punch. I think maybe a 1k in R12 and a 500R safety resistor would get the voltages almost even, and give more "bloom" to the picking dynamics, but that might be into triode mode territory for the stock OT. Anyway, the 300v maximum ceiling on the screen grid is the real limiting value. That's generally my target and everything else swings around that. Swamping the rail is like boppin' ferrets in a box... push one down, another pops up. Anyway, R10 at 1.2 or 1.3k gets things nice and close, and good and warm for maximum power output. I like it loud. O:)

 

Oh yeah, here's the data sheets I use cuz they're for the tubes I generally use.

http://www.jj-electronic.com/pdf/EL84.pdf

http://www.jj-electronic.com/pdf/6V6.pdf

 

Gil...

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...