Crate V5 mods... anyone?

[jim p]

My second V5 modification is changing from EL84 to 6V6GT for the output tube. So far with the exception of taking out the 9 pin socket and replacing it with an octal socket the only change is value of cathode resistor R17 to 380 ohms. I am looking into the value of the screen resistor R18 and may increase it to 5 to 10 k ohms. If someone was into a total rebuild with a 6V6 instead of an EL84 you gain 300mA of heater current capability so you could have two 12AX7 tubes and a 6V6GT output tube within the limits of the power transformer. With that you could have input stage, cathode follower driven tone stack, gain stage, volume stage and output tube. Now will start on adding reverb to this amp and maybe a Weber AlNiCo 10S speaker if it will fit.

[Tomko]

Jim P
Thanks for the good suggestions. I will give them a try. Unfortunately, both the vol. and tone pots have failed mechanically- be careful with them. I can't get in touch with Loud Tech. Anyone know where else I can get them? So the amp is down until I get some new pots. I don't think I tried the stock Sovteks after the mod but I believe I tried a different 12AX7. I had the same results- no headroom. I tried a 12AY7 to lower the gain to get more headroom. Maybe it's the Tesla EL84. So I will proceed with the stock Sovteks after I get some new pots. Thanks again.

[rock_mumbles]

Hi Tomko, as far as your lack of clean headroom.

What mods have you done, you said you took out the op amp circuit, changed the 1.5K to a 47K and the 4.7K on the EL84 to a 47K, is that all you have done?
Did you leave R11 (1M) resistor to ground after the input resistor and remove R2 (100K)?
What I did to clean up one of my Valve Juniors was to decrease the value of the resistor to ground between the two triodes of the 12ax7.
Where did you put the tone stack and volume control? Did you put the volume control in place of R7 the 220K to ground into the second triode?

I know a lot of questions...

[Blaze]

Is this any good for $180.00 ?

http://guitars.musiciansfriend.com/p...ead?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/....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]

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]

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]

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]

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.