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#1
Thinking about buying another VJ, this one a V3 being a combo.

I want to mod it a bit then I wanna add a tremolo circuit. It would be the same style of trem found in the Vibro Champ and other such small Fenders.

Basically it would be a VJ but a bit more open sounding with more solid bass and a bit more "grit" here and there. It would not be so dark because of accented highs.

Here is the schem I made... (the top half is the VJ schem with mods, bottom is the tremol and power supply.)


I left out a cathode bypass switch cause there wasnt a ton of room. There would be a SPDT (On-Off-On) switch to select between a 25mF cap, 0.68mF cap and no cap. Should add a lot of versatility.

So basically VJ combo with...
Volume
Speed
Intensity
Bright Switch
Voice Switch (cathode cap)

Now the thoughts and issues...
-I am using an extra Deluxe Reverb choke I got for free...would it be alright to use?

-I was thinking about opening up the sound a bit by throwing some more voltage on the plates...maybe 82K instead of 100K.

-Whats the point in the stock 1M resistor in parallel with the 1M volume pot. This makes the control a 500K pot. I just ditched the resistor in my schem and made the pot 500K.

-Is the Intensity pot 25K or 50K?

-The B+ in the VJ is less than the Champ. In the Vibro Champ one triode (the left one) is supposed to have 170V on it and the other triode (one on the right) is directly connected to the power supply and should have 340V on it. You will notice I used a 330K resistor instead of the Vibro's 470K to try and adress this problem. I havent done the math but I "think" this will work.

Suggestions and ideas welcome.

Thanks...
Last edited by kurtlives91 at Aug 4, 2008,
#2
I can't seem to enlarge your schematic and I was very curious to see it as I am an avid VJ fan.
Where in the circuit are you putting the cathode bypass switch?

This sounds like a terrific idea. I've never played a Vibro Champ, but I had the pleasure of playing around with a Vibro Deluxe a while back and it was great.
#4
Finished a layout for this tremolo.

Its built on a terminal strip and is quite compact. There will be tons of room in the chassis.

I can post it if anyone's interested. I probably should post it to see if anyone spots an error.
#5
Please do post it. I have no intention of trying to replicate it, I have far too many other projects right now. But I am very interested in how you do it and how well it works!
#6
Well there is no reason why it wouldn't work...it should work great. Ill wait till some tube expert like SYK says its cool or what not. All I know is the trem on my Vibro Champ is amazing.

It wont be hard to implement the tremolo. Tube socket, 12AX7, 12 components, wire, foot switch jack, drill a few holes, done!

Cant get my scanner working right now but Ill try again tomorrow.
#7
If you can spare the expense maybe put in one of those cheap weber alnico signatures.
Nothing like new speakers for a cheaper amp.
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#9
An older alinco speaker like an oxford or pioneer would make this shine.
#10
Ordered the few parts that I didnt have already for this project today.

Also decided I am going to add a little "sag" to the power supply.

Still need to get a VJ combo, need to get payed at work...bah
#11
Quote by kurtlives91
Now the thoughts and issues...
-I am using an extra Deluxe Reverb choke I got for free...would it be alright to use?
check the specs on the choke to be certain it can handle the current necessary.

in a deluxe, the choke comes AFTER the supply for the plates of the output tubes.
so the current through it is just for the preamp tubes, PI and screen grids of the 6V6s.
IF it can handle the current, a choke adds a ton of filtering.
put it before the first filter cap and move A the first cap, to get the best filtering.
if it can't handle the current, just move A to the first cap.


Quote by kurtlives91
-I was thinking about opening up the sound a bit by throwing some more voltage on the plates...maybe 82K instead of 100K.
this will cost you just the tiniest bit of gain. not a big deal. since you aren't using a master volume, you will probably never drive the second stage to either cutoff or saturation before the output stage clips. but with a master volume, i might be concerned you would be biasing the second stage closer to cutoff. a less pleasant distortion.

Quote by kurtlives91
Bright Switch
look at that one again. the way you have it connected looks more like a Dim Switch.
Meadows
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#12
Ill check the specs on the choke...

I thought more voltage meant more of a "Tweed" sound if you will... Thats a crappy way of putting it but more THD and such. Bah...

Nice catch on the bright switch...what was I thinking...Ill fix that.

What do you think about the changes to the power supply?

Also that 330K resistor in the trem circuit. Will that give my plates enough power?

And finally was I correct with my thinking about ...
"Whats the point in the stock 1M resistor in parallel with the 1M volume pot. This makes the control a 500K pot. I just ditched the resistor in my schem and made the pot 500K."
#13
Quote by kurtlives91
Ill check the specs on the choke...
a must.

Quote by kurtlives91
I thought more voltage meant more of a "Tweed" sound if you will... Thats a crappy way of putting it but more THD and such. Bah...
imho, the "tweed" sound has more to do with things like the absence of a tonestack, cathode bias on output tubes, cathodyne PI, etc.

no reason to not try something different with the plate resistors, though. maybe you'll like what you get.

Quote by kurtlives91
What do you think about the changes to the power supply?
if you can get away with putting the choke in the front end, that would be great. tons of filtering and you can even use a much larger cap for the first filter if the choke comes first.


Quote by kurtlives91
Also that 330K resistor in the trem circuit. Will that give my plates enough power?
dunno. not terribly interested in trem circuits. maybe if it was ripped from a brownie ...


Quote by kurtlives91
And finally was I correct with my thinking about ...
"Whats the point in the stock 1M resistor in parallel with the 1M volume pot. This makes the control a 500K pot. I just ditched the resistor in my schem and made the pot 500K."
some people would dump both resistors and leave the pot value @ 1Meg. whatever works for you.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#14
Went downtown today and picked me up a VJ combo...

I can't remember playing or the sound of my stock VJ head so it was fun playing this little combo. Epiphone did a good job fixing the grid leak resistor issue at the input. I did not find the amp too dark or muddy stock at all. Very clear, probably the speaker mind you. This speaker really voices the amp...it plays a huge part in this combo's tone.

Very impressed with the amp stock... the amp starts to drive at about 10:30 on the volume knob. The sound was clear and defined. The overdrive was quite unique, very nasally and mean, a great blues tone. I am not sure but I think the unique overdrive tone might have been caused by the speaker distorting. Ill have to check its wattage. Anyways I really like the speaker and attribute the great tone I was getting to it, I will not be changing the speaker.

So I started doing one or two mods at a time then listening to them. The mods were to smooth out the overdrive and reduce gain at first. A bit has changed from the original schematic so Ill post a revised version at the end.

Here you can see I drilled a hole for the bright switch (top) and the voicing switch (bottom). The voicing switch is wired but not the bright switch. The voicing switch selects between a 0.68uF, 50uF and no cap on the first triodes cathode. Very unique and different tones with all the positions. I am going to change the 50uF to something higher though for more of a fat boost I think.


Still need to drill two more holes...speed and intensity controls on the front.

I also drilled the holes for the extra tube socket and the foot-switch jack (to turn the tremolo on and off). Ill probbly throw the stock EHX 12AX7 into the oscillator position (the trem tube doesn't affect tone, just functional). Then Ill probably use a Tung-Sol for the main pre-amp tube.


Got some neat old stuff today....check out those transistors, still in original packaging. Imagine going to the hardware store and picking that stuff up.
#15
Made one side of the voicing switch 220uF...much better.

Adding 220pF for the brightswitch. Seems to add a lot of noise but no brightness haha, odd.

Got the choke today...it's 9H at 120mA. I think this should be fine.
#16
Very cool build. I thought about doing one of these the moment I saw it... one knob? This amp screams for massive modifications.

It would be sweet if you could record the original tone and the modded tone to post it up. Or at least post a clip of the new sound possibilities.
All my photobucket pics are dead so no links to my guitar build threads.
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#17
My other VJ has 4 knobs on it and 2 added switches. I wanted to keep this one simple and in the vintage style.

I still have to add the tremolo circuit which then I will add two more external controls.
#18
I was thinking of just building in the distortion circuit I built, and a noise gate. (haven't designed one of those... so I'd just have to copy something else to do it)

I ended up buying the Vox Valvetronix 15 watt instead. It has awesome tones right out of the box, so I couldn't pass it up. Besides, I'm so deep into guitars right now I don't have time to be modding amps.
All my photobucket pics are dead so no links to my guitar build threads.
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#19
kurtlives91 I'm always interested in watching your work. I'm hoping to see more of your tube amp builds soon. I find tube amp builds very intriguing and I'm hoping to start my own little project in the near future (aka when I find a source for materials). I find such threads as yours to be a wealth of information about guitar electronics. Please keep up the good work.
#25
Added heater wires for the extra 12AX7 yesterday. Ever since the amp has been blowing fuses...

The first triode's grid has continuity between it and ground... I thought that was odd.

Is it possible the transformer cant handle the extra current the added tube is drawing?
#26
OK figured out why fuses were blowing...with three tubes in the fuses blows. Now with two tubes in (I tried all combos of tubes) the fuse doesn't blow.

So the heater winding of the transformers secondary cant handle the extra current the added tube is drawing.

How do I figure out what the heater winding is rated at current wise? I tried searching the net but found nothing...

How the hell did that guy who added a gain stage to his V1 do it...bah

Could I steal 9V DC off the EL84's cathode?
#27
Quote by kurtlives91
OK figured out why fuses were blowing...with three tubes in the fuses blows. Now with two tubes in (I tried all combos of tubes) the fuse doesn't blow.

So the heater winding of the transformers secondary cant handle the extra current the added tube is drawing.

How do I figure out what the heater winding is rated at current wise? I tried searching the net but found nothing...

How the hell did that guy who added a gain stage to his V1 do it...bah

Could I steal 9V DC off the EL84's cathode?



No, way too little current flows through the EL84, remember? You'll exceed the cathode current.

You've searched for the xformer part number? Does it have any ratings printed on it at all?

Have you tried a slow blow fuse? Perhaps inrush current is killing you.

It says 35 watt consumption. Power in = power out. Calculate the amount of secondary power. Maybe you are pushing it.
#28
So I thought about what you were saying about the inrush...

So with two tubes in the amp runs fine... so that's what I did. I put two tubes in then after then I added the third.... They all glow!

So then just for shi ts and giggles I turned the amp off... I then started it back up again with all three tubes in. They all glowed and worked and the fuse didnt blow.

I'm not complaining but how the hell is it the amp can handle the extra tube now?
#29
From the sewatt forums, the VJ power transformer has a 6.3v 2A heater winding. People have converted it into an 18w Lite (2x 12AX7, 2x EL84) pulling just over 2A heater current using the stock PT, with great success.
The Laney Thread are big and clever. No exceptions.
#30
How long did you leave it off? Were the tubes and xformer still warm when you turned it back on? Sounds to me like you're maxing out the transformer's current capacity, and inrush is blowing the fuse.

I'd replace the transformer, or add another one to power the extra heaters.

If you increase the secondary current, you increase the primary current. You'll probably need a thicker fuse.
#31
^thats what I thought too at first. I thought ya everything is still warm.

Now it works fine with three tubes installed...weird.

The only thing I can think of is that I used a new brand of 2A fuse.
#32
Quote by Losenger
How long did you leave it off? Were the tubes and xformer still warm when you turned it back on? Sounds to me like you're maxing out the transformer's current capacity, and inrush is blowing the fuse.

I'd replace the transformer, or add another one to power the extra heaters.

If you increase the secondary current, you increase the primary current. You'll probably need a thicker fuse.
Like I say, an extra 12AX7 is only gonna bring the heater current demand up to about 1.3A, and the capacity is 2A, so it's well within limits.
The Laney Thread are big and clever. No exceptions.
#34


SYK might have some sort of explanation, he usually does

But for me, unless it happens again, i'd leave it if all the readings are right.
The Laney Thread are big and clever. No exceptions.
#35
Finished today...tested and got no tremolo effect.

Here is the layout I made and used...


The tremolo tube voltages and the Vibro Champ voltages as per the schematic are in brackets.
1. 99V (170V)
2. -0.6V
3. 0 (66V)
6. 355 (340V)
7. 99V
8. 101V (175V)

On the original schem I made the tubes were getting power at point A. I wired it instead so they get power right after the rectifier, there is no dropping.

Any help would be great.
#40
The layout wasn't right...don't know where the error was but I mad a new one.

It works not but when the trem is turned off the intensity pot acts a volume control. Biasing gone bad I imagine.

I think positive DC component from the trem circuit is being passed to the cathode of the preamp tube and biasing it positive so that it cuts off, which doesn't change when the trem is "off" because the static DC is still present at the trem tubes' cathode and therefor, by way of the intensity pot, also present on the preamp tube cathode depending on the intensity setting.

I am thinking a cap between the pot and cathode should do it, that's what I am going to try today.
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