Crate V5 mods... anyone?

[Blaze]

Is this any good for $180.00 ?

http://guitars.musiciansfriend.com/product/Crate-V-Series-V33H-33W-Tube-Guitar-Amp-Head?sku=487052

 

[SciHi]

Is this any good for $180.00 ?

I had a v33 head, they have some issues stock but lots of work has been done on mods over at HC, ppwatt, and TGP. Dvnator has a website with his mod, Verne Andru has a thread on HC http://acapella.harmony-central.com/showthread.php?t=2118282 and wagdog and Steeve A (blueguitar.org) have versions of a slo mod for the v33. Cleans are good stock, overdrive channel needs work. Then with the mods, both are great.

 

[Blaze]

Standard




Modded

 

[Tomko]

Rock Mumbles
The answer to your first question is basically yes. I left in R10 (now 47K) and R11 (1 meg) and went straight into pin 7 V1B. R1 and R2 were bypassed/removed. From there out of pin 6 to Marshall 18 watt basic vol/tone circuit. Not sure if I came back in at R7 for grid load to V1A pin 2 or bypasssed R7 and went straight to pin 2. Could that be my problem? Is the vol/tone stack providing grid load and I don't need/want R7? Or do I need R7? I think now that I bypassed R7. It's been several days now and I don't remember or have the chassis with me. Only other change was R31 from 4.7K to 47K. I think I did that to try to get some headroom. Any help is appreciated. I might try changing R7 from 220K to 100K as you suggested if it's not bypassed. I did get some pots on order yesterday so hopefully it won't be to long.

 

[rock_mumbles]

Hello again Tomko,

It depends on your volume pot set up, R7 dumps some signal to ground to prevent you from overdriving the next triode, the 220K stock R7 in the V5 is already a pretty small value compared to some "normal" values, but that depends on the "grid resistor" in the circuit before it.

As a quick test, put a 500K resistor across your volume pot #1 to #3 terminals, sending signal to ground around your volume pot and see if your signal gets cleaned up any.

 

[Tomko]

Rock Mumbles
You got me thinking. R7 is the grid load resistor for the next triode. I wired in at R7 going to ground so it's still in the circuit. Classic designs all use the vol pot for the grid load to the second stage so it looks like I'm doubling up. What do you think? I think R7 should be removed and I should go straight into the next triode from the vol pot. What do you think? Vol pot is 250K. The first triode grid load resistor is R11 (1 meg). New pots are on the way. Thanks for the help.

 

[SDW]

would anyone be willing to mod my V5? i'd try to do it myself but i lack the tools / ability to read schematics

 

[jim p]

screen grid resistor value

On the amp I have I am reading a screen grid voltage of over 300 volts and all the data sheets rate the EL84 for a maximum voltage of 300 volts anyone have an idea on this. For now I have increased the screen grid resistor R18 to 10k dropping the voltage by 40 volts to 285 so 5k would put it right at 300 volts. This change also lowered the tube gain lowering the plate current also.
The other thing I have going is some white noise I replaced the ceramic cap C3 with a 500 pF mica paralleled C15 with 80uF, paralleled C9 with a 47uF tant and tried two other EL84 tubes but still have it. Anyone else have this experience?
The other amp I have that has a 6V6GT as the output tube is so quiet I think I am only hearing the dc filament voltage on the output tube so may try changing it to DC.

In looking over the schematic again I think the real problem with the screen grid voltage is it is connected to the wrong location. It should be connected to the junction of R26, R25 and C16 I have not made this change yet but will and post the results.

 

[goonrick]

Hello all, new to the board. Great discussion here on this little amp.

My question is, what could we expect if we simply did away with the opamp section and made it all-tube. There's still tons to change out in the tube sectioin (moving the volume after the tone control, tweaking the cathode bias resistor, et al).

Since I normally get my drive from a stompbox, what could I expect were I to simply mod R1 and R2 values and jumper over from where R10 used to be?...

 

[goonrick]

On the amp I have I am reading a screen grid voltage of over 300 volts and all the data sheets rate the EL84 for a maximum voltage of 300 volts anyone have an idea on this....

Could we simply adjust R24 to bring the entire voltage down just a touch? I'm tempted to try to bring the entire voltage down to around 300V. Would there be any problems with doing that? Couldn't we experiment by putting a resistor in series with R24 (starting with 1 Meg) and determining the effects on voltage that way?

 

[jim p]

to just jumper past op amp

The idea of just jumpering past the op amp in basic form just remove R2 and C25 jumper from R 11 to R1 would still need a volume pot. Without adding a volume control the input level will be the volume not sure you will like that. If you want to throw away the volume pot or use it as gain pot you can convert the tone pot to a volume pot then have no tone control.

 

[jim p]

To lower plate supply voltage

If you convert the B+ supply to a choke input filter by removing C14 this will drop the supply voltage down to approx 275 volts. I would not mess with R24 it is just in the amp to pull the supply down with power off to help prevent death due to shock. So the change would be to cut the positive of C14 out and connect it to the positive side of C15.

 

[goonrick]

The idea of just jumpering past the op amp in basic form just remove R2 and C25 jumper from R 11 to R1 would still need a volume pot. Without adding a volume control the input level will be the volume not sure you will like that. If you want to throw away the volume pot or use it as gain pot you can convert the tone pot to a volume pot then have no tone control.

Yeah, I would still put the volume pot in place of R15 and R27. What would you imagine the tone control being like if left alone, spare swapping C28 out for a smaller cap?

 

[goonrick]

If you convert the B+ supply to a choke input filter by removing C14 this will drop the supply voltage down to approx 275 volts. I would not mess with R24 it is just in the amp to pull the supply down with power off to help prevent death due to shock. So the change would be to cut the positive of C14 out and connect it to the positive side of C15.

Effectively placing C14 in parallel with C15 after the choke, right? I just want to be perfectly clear before I start hacking on this little amp.

 

[jim p]

RE: Choke input

Yes you will be paralleling C15 with C14 a switch instead might be neat you would get two power output levels.

 

[goonrick]

Thanks, Jim. You're a wealth of information.

 

[jim p]

screen grid connection wrong

The screen grid resistor is attached to the wrong location on the PCB it should be on the other side of R25 (junction R25 R26 and C16). This will lower the screen grid voltage closer to (right at) its maximum rating of 300 volts. Best if you have the pcb out is to also replace R25 with a 7.5 to 10 k ohm resistor (approx 4ma across R25).

 

[jim p]

gain and volume mod

Another way to modify the amp would be to use the tone pot for a volume pot and the volume pot for a gain pot. This involves no cuts just jumpers and removing components with one being replaced (C24)
1) Remove PCB from chassis
2) Remove R13 C26 C24( to replace with 47nf for more bass or keep as is if you wish) C6 C5 C4 and R27
3) Replace C24 with a 47nf
4) Jumper junction of C6 C5 and CW2 (tone pot) to junction of R27 and R15
That’s it now the volume pot will control the gain of 2nd stage op amp for overdrive and the tone pot will control the volume.

 

[Big K]

Outstanding information!!!! But it makes my head hurt and tempts me to switch from coffee to vodka this morning with all the electrical theory.. I thought being able to solder effectively enough to swap out switches, pots and pickups made me feel like a genius when it all works but you amp modder guys are on a whole nother level :master: :master: :master: :master:
Thanks for all the shared information!

 

[tunghaichuan]

Just as a heads up, I got the new flyer from Guitar Center with the V5 priced at $79. My flyer came with a 10% off coupon, so the V5 is a pretty good deal from GC right now. :AOK:

tung

 

[jim p]

Use for stock speaker

What to do with the stock V5 speaker? Now I hope you aren’t going to sell it to someone so why not use it as a testing load for the amplifier. I put one of those cheep ¼ inch cables on it packed some fiberglass around it and put it in the box the amp came in. So now instead of just looking at the output with a resistor as a load I have a speaker instead. There is quite a difference in the waveforms on the scope between the resistor and the speaker. With a square wave you can see overshoot with the speaker you do not see with a resistor. Also you won’t drive everyone crazy (cats, dogs and neighbors)

 

[jim p]

supply voltage with choke as input

Has anyone made the supply a choke input yet, just want to know exact voltage they are getting at C15+. I may want to make the same mod on one of my amps. This would also free up Junction of C16 R26 and R25 as the decoupling for the second triode. Also if the voltage is low enough can leave the screen grid connection stock.
Found with the volume control after the tone stack at minimum you still get signal at the output of the amp. I think this is due to not having separate decoupling on both the first and second triode. So being able to move R6 to the other side of R26 would cure this as long as it is not used for the screen grid.

 

[goonrick]

Has anyone made the supply a choke input yet, just want to know exact voltage they are getting at C15+. I may want to make the same mod on one of my amps. This would also free up Junction of C16 R26 and R25 as the decoupling for the second triode. Also if the voltage is low enough can leave the screen grid connection stock.
Found with the volume control after the tone stack at minimum you still get signal at the output of the amp. I think this is due to not having separate decoupling on both the first and second triode. So being able to move R6 to the other side of R26 would cure this as long as it is not used for the screen grid.

Haven't done it yet, as I'm waiting on some components to ship. I'll be sure to post what voltages I get when I do though.

 

[goonrick]

Jim,

I did the choke input mod and am getting 296V at C15 plus. Is that about what we were shooting for?

 

[jim p]

voltage with choke input

Around 295 volts sounds right it should have been close to peak with the capacitor input (240 rms x 1.4 = 335 volts). With the choke that would drop to 335 volts X 0.89 approx 295 volts.
Do you have both tube operating? Should check to see if choke is running hot at all. I ran a simulation and the power in the choke is higher then the stock Pi filter but should just run warm to touch?
Were you looking to lower the voltage below what you now have?

 

[timothymegg]

V5 newby

I just got this little guy. The speaker sounds pretty bad but, I hooked it up to a 412 cab and it sounds much better. I would like to do some of the mods posted on here but, I can't decide between deafguy and jp? Jp is more defined but, the deafguy mod seems easier and more class A without an opamp. Any comments? Also, anyone have any experience with adding a triode switch and how to do it? One last thing, does this amp need to be biased?
Peace,
Timothy

 

[jim p]

Tone stack for all tube

Haven’t made this mod myself but have simulated it with vacuum tube models and a jfet model. If you go without the op amp the tone control is just a treble cut no boost. The op amp was the treble boost (pre emphasis). This circuit has C501 a 1nf across a 330k ohm resistor that gives you a boost when the tone pot is at full treble. You can change the operating point by changing the values of both C501 and C502 keep the ratio at 1 to1.5 ( 1nf and 1.5nf) or maybe 1to1 (1nf and 1nf) I would stay in the range of 1nf lowest value used 3-4nf highest value Lower value equal to higher frequency operating point , higher value moves it towards the bass end.

 

[jim p]

fear of op amps

The op amp used in this amplifier is in almost every stomp and effects box made. It is cheep and the specifications are fine, this stuff is AM radio frequency response realm 5 kHz max (modern op-amps go into the gigahertz range). The input impedance is higher then the 12AX7 so it will not rob the high frequencies from you pickups if you are going straight in. Once you put a box between the amp and the guitar you are not all tube. With the circuit as is or with the changes I have posted you also have a cap in series to help cut out the 60Hz that the guitar is picking up( also you can reduce bass if you want). The op amp also provides the treble boost for the tone control to work as both treble cut and boost. I have kept the gain of the op amp to a minimum so with overdrive the first stage tube will be clipping not the op amp.

But still some will prefer to have no solid state components in there signal path so I have posted a tone stack to use with the op amp removed.
Remember the people that first designed guitar amplifiers in some cases were TV and radio repairmen so it is not an exact science and nothing to get hung up about. But what they did created the sound we have come to love. Wonder how things would be if the transistor existed before the tube?

PS If you look at the schematic for the Fender Hot Rod Deluxe this op amp is used in four locations Line out, Line in, reverb drive (poor choice for that) and reverb recovery. Line out and line in are in the signal path.

 

[rock_mumbles]

Which mod ???

I would like to do some of the mods posted on here but, I can't decide between deafguy and jp? Jp is more defined but, the deafguy mod seems easier and more class A without an opamp. Any comments? Also, anyone have any experience with adding a triode switch and how to do it? One last thing, does this amp need to be biased?
Peace,
Timothy

Hello Timothy,
The bottom line the amp will sound like a "real" tube amp when converted, stock they sound like ... (you know). Take your time and study the V5 layout and the mods and pick one. The "all tube" mod will be simpler and you will end up with a simple two tube guitar amp, if you do jim p's mod you will have more stages (and in effect more sound/tone manipulation) in the preamp.

I've just started to do an "all tube" mod to my V5 with a simple tone stack and volume control where the stock tone stack is placed. I want to do it without cutting any traces, by removing components and soldering new connections onto existing component pads (it could be converted later to something different if I wanted to change it). When I get done I intend to post a color coded "mod" layout that shows the parts to remove and how to connect the new components.

EDIT: I changed the above wording, because I think people could take my intention in the original statement in a wrong way, Sorry guys I should have been more careful with what I posted.

As far as your question regarding biasing, what I think you are asking is if the amp needs to be have the bias adjusted when the output tube is changed, the answer is no. The V5 is a cathode biased SE (single ended) amp (as are most small two tube amps) and as such does not have an adjustable bias, so you just pull one tube out and plug in another. That does not mean that the bias is correct out of the box, one of the "correction" mods for Epiphone Valve Juniors is to replace the EL84 cathode resistor with a larger value so the tube is not pushed quite so hard.

 

[goonrick]

I ended up doing an amalgam between the two mod types and am pretty happy with the results. I bypassed the op-amp stage and made a typical two tube amp. I also followed jp's recommendations on tweaking the output section and power supply and the amp is running stably and sounding damn good.

I would say the all tube mod gives you less to work with in the way of preamp tones, but it does the screaming tube amp thing very well when driven with an overdrive pedal. I was shooting for a small amp that would do an acceptable job of copping a big amp tone and I got it. The one downside, and this may be inherent to all amps of this size, is that there's not a lot of clean headroom and so you're not really going to get inspiring clean tones from the amp. That's okay with me because I've got other amps that do the clean thing very, very well (Lab Series L5, DI's, etc.).

I set out from the beginning to have an amp that would conjure some class A tube mojo in a small and relatively low volume package. I'd say I got it. I will also really enjoy capturing the overdriven tones on recordings. It sounds nothing short of excellent for what it is.

BTW, I ended up switching a bunch of tubes (12AX7s, 12AT7, etc.) and settled on the 12DW7. It's an AX front triode and an AU second triode. You can get a currently manufactured DW at eurotubes and I highly recommend it. It brought out the best of my lil' killer.