Crate V5 mods... anyone?

[amptweaker]

I would suspect that tantalum as your noise source.
I wouldn't worry too much about the high screen voltages as long as you use the stock Sovtek. These tubes look identical to the 6P14P and folks are using theme as 7189 subs. Besides, the 300 volts is a design center value for the 6BQ5.

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 R16 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.

[jim p]

I would suspect that tantalum as your noise source.
I wouldn't worry too much about the high screen voltages as long as you use the stock Sovtek. These tubes look identical to the 6P14P and folks are using theme as 7189 subs. Besides, the 300 volts is a design center value for the 6BQ5.

I am not looking for maximum gain from the EL84 so moving the screen grid to what looks to be it's proper location works for me. I have it connected to a triode/pentode switch anyway. I was using the tant to try to stop the noise by paralleling the cap already in circuit with no effect. Believe it to be the cap after the choke it has started to quiet so the dielectric is self healing. If I get a chance will swap the 47uF cap moving it to the input to the choke. But I have reverb drive and recovery and triode/pentode switch hardwired to the pcb so it makes that more of a job.

[amptweaker]

I'm doing a lot of testing on my V5 before I start to mod.

One of the first things I did was to measure and then calculate the impedence of the output transformer.
It's about 3K at 8 ohms.

I thought this was a bit low, and checked the data on the EL84.
A look at the Rodenhuis book confirmed it was (he uses 4.5 to 7 k).

Feeding the grid of the EL84 with the signal generator and using a dummy loads, i scoped it out. The cathode was 14.3volts at idle.

With the load at 8 ohms I got a 10vpp signal that had very noticible second harmonic distortion.
That is only 1.5 watts!
Increasing the input signal caused the bias to increase (rectification effect).
Nearly 17 volt on the cathode when the other side of the wave began to round at near 17.5vpp out. (4.78 watts into 8 ohm)

Testing at a 16 ohm load, the waveform was much more linear up to 22.5 vpp with less than 1.5 volt increase on the cathode. (4 watts at 16 ohm).
Increasing the input signal gave more symetric clipping (3rd harmonic).

I hope that I have shown that depending on the flavor of distortion you prefer, it is ok to use either an 8 or 16 ohm speaker.
As for raw wattage you will lose a bit with the 16 ohm speaker, but if the 16 ohm speaker is more efficient than the 8 ohm you will gain it back in perceived loudness.

I don't think the stock speaker was designed to be efficient much less handle 30 watts...
(I could smell the voice coil burning when i hooked it up to a 25 watt amp to break it in!)

[amptweaker]

I am not looking for maximum gain from the EL84 so moving the screen grid to what looks to be it's proper location works for me.

I noticed the unused tap at R25 and R26 too.

Never know what kind of whackyness you'll find in a Crate.

Took a look at the screen grid while driving it hard and it does turn cherry red...

[jim p]

Thanks for the info about C3 and R16 in post #111.



I have bypassed the op amp and have replaced C2 with a 0.022uf 715 Orange Drop which feeds into an 18 watt LiteIIb volume and tone control which then connects back to R7.

I just removed C8 on a friends V5 and wow did that clean it up, nice bright cleans at lower volumes that break up with higher volumes and harder attack, now it dimed is about the same gain as my amp on two or three. Since we both like more of a blues/classic rock sound, it's a lot better amp cleaned up.

The series cathode resistors sound really interesting. I could see that something between the bypassed gain level and the unbypassed gain level could be really useful. Would you "mess" with the gain on the first triode instead of the second? Why?? We were looking at a Princeton schematic so we removed the second bypass cap (I know that there's no cathode bypass cap because of the negative feedback in the princeton.) Would you still use the same bypass cap value, a 2.2uf like stock on the first triode?

Thanks again!

Replacing C2 with a lower value should have increased the highs out of the amp (C8 being a high pass component) but this is dependent on the tone stack you have. Can I find a schematic for your tone stack on the web?
Removing C8 is interesting that should increase the high frequency range of the tube (reduce gain equals reduced Miller capacitance) but you probably now increase the setting on the volume pot thus the input resistance and are back to where you started in that regard. But having no bypass will add degenerative feedback so maybe the tube is more stable.
On the split bypass if you use it on the input triode and know you do not want to overdrive the amp you could set it for unbypassed this would lower the gain so no overdriving the tube. Also lower gain is lower Miller capacitance so you won’t loose the highs when plugged straight into the guitar from that. The tube response may also be a bit more stable from the feedback. Some people are posting that they are changing to a 12AY7 or 12AT7 for lower gain this may work just as well for them.
Then if you want to overdrive the input triode you would bypass the cathode resistor for full gain on the input triode. So you just need to connect the ground lead of the bypass capacitor to ground through a switch.
Also some unbypassed resistance in series with the cathode might make things more stable from the feedback it would provide I have to search to see if that has been done.
On the bypassing of the second triode it would just be to reduce overall gain to remove it, except as before it might provide stability. One thing that may or may not be a problem is both triodes share the same decoupling I think this is why you can get signal through the amp with the volume all the way down. Without the tone stack the signal from the first tube would be 180 degrees out of phase with the second but with it? So I am not sure that this may not be a problem?

[Songman68]

Step by step modifications done to Crate V5 amp

1) Remove the amplifier from cabinet. First remove speaker jack then the six screws holding back cover of amplifier then with amplifier upside down remove four screws two on each side of cabinet that hold amplifier chassis in cabinet. (Note: you may want to enlarge the holes slightly in sides of cabinet and on back cover to make reinstallation and future removal easier)

2) If you haven’t already done so (you do have this unplugged right?) get out a dc voltmeter the highest voltage in the amplifier is approx. 320 volts DC measure from chassis to R25 should be 0 to 15 volts if so you are safe. This amplifier has a bleeder resistor R25 so supplies should drop after power down.


3) Remove preamp (12AX7) and power tube (EL84 6BQ5) put them some where you wont break them.

4) Next remove knobs on front panel may require flat blade screwdriver and a thin piece of wood to work against to prevent scratching front panel. The pots are D shaft type walk then off gently. Then remove nuts holding pots and ¼ inch jack on front panel.


5) Now make note of all the connections to the PC board because you are going to remove them. If you have a digital camera now is a good time to use it. Also if you print out the schematic note wire color and location on it. The faston connectors J4 J5 J1 and J2 may be hard to remove don’t break them of pcb by working them back and fourth.

6) Next remove the six screws that hold PCB into chassis and take it out. (hope you are putting parts someplace you wont loose them)

PC Board modifications
(See attached pictures of mods and changes to schematic also pic DSCF0947.jpg in previous post is the pre emphasis mod the tone mod is incorrect in that post tie unused side of pot in tone control to wiper not ground or unconnected up to you)

1) You are going to be removing approx 10 parts. You will need solder, solder wick, soldering iron, needle nose pliers and desoldering tool. In manufacture the compnet leads have been bent so desolder a componet lead then straighten it before removing or you may damage PCB plated feedthrough.

2) This modification will use the two Op Amp stages for an input buffer and small gain to over come loss due to pre emphasis circuit that will be added. Desolder and remove volume pot from PCB. Next remove R13 this makes IC1-A a unity gain buffer. Remove C26, C24 and C27 replace C24 with a 47nF 50-100 volt poly cap.C24 sets the low frequency limit at input to the amplifier with 47nF this is approx 125 HZ 3db down (for more bass use 100nF). In the place of C27 install a 33k ¼ watt resistor this equals a gain of 1.22 for IC1-B (want to keep gain low so first stage tube will clip before the Op Amp with overdrive).


3) Pre emphasis circuit For the tone control to be able to cut, boost and be set for flat response the high frequencies need to be boosted first. So C25 needs to be removed if you want replaced or use it again for this mod. Install one lead of a 100nF 50-100 volt cap into plated hole (via) that is connected to pin 7 of IC1 in the second hole of C25 insert lead of 33k ohm ¼ watt resistor with a 10nf capacitor accost it then connect the other lead of the 33k resistor to the second lead of the 100nF capacitor. If you want full treble brighter you can lower value of R2

4) Tone stack and volume control Here we will put volume control after tone stack and first tube stage so you will be able to overdrive input tube and still control volume. Remove C5 C6 C28 and C4 Change C6 to a 22nF 50-100volt poly capacitor. (Here a lower value cap will raise where the tone control will cut the highs higher value will lower it.) Now the volume control remove R15 and R27 using the volume pot removed from the board you will need to bend the leads 90 degrees towards the back of the pot to attach 1 ½ inch wires to the three terminals of the pot. Also need to insulate PCB were pot was attached to prevent shorting (three layers of electrical tape works) looking at the front of the pot as use to be connected to the PCB the right side terminal connects to the plated hole C28 that connects to R29 the center terminal (wiper) connects to the plated hole of R27 that connects to R7 and control grid (pin 2) of the 12AX7. The last terminal goes to the plated hole of R27 that goes to ground. (note be careful the leads soldered to pot do not short to metal back shell of pot no sound out of amp)

5) Oscillating power tube in testing the amplifier found output did not clip symmetrically and oscillated when clipped. Based on the tube data sheets the cathode biasing is to high in value. Change R17 to 270-300 ohms 2-5 watt or parallel the 330 5 watt with another 1.5k ohm 2 watt (270 ohms)


6) That’s it now put it back together and be careful around high voltage always follow one hand rule working on tube amplifiers. The one hand rule is make sure other hand and body are not tied to ground other hand does all the probing. So tie meter or scope ground to the chassis ground then do all your measurements.

Other tweaks
From the way this amplifier is set up it may have had gain, tone and volume controls?
And they took the volume control out instead of the gain control so if you add a third 250k pot across TL01-B same as in the stock schematic this will be a gain control you should add a 27k resistor in series to set minimum gain at unity (1).

Lowest frequency amplified the stock value of C24 is to low 3db down at approx 270Hz the value in the mod is 47nF for 125Hz if you want you can go bigger 100nF but this may increase that annoying 60 Hz hum we have all come to love.

On the pre emphasis mod you can change the value of R2 to increase or decrease the brightness of the maximum tone. Higher value for R2 (stock 100k) will reduce the maximum lower value increase it. If you lower the value you may want to increase the gain in the Op Amp stage to offset the loss.

Tone control pot from my results the tone is flat at the 9 o’clock position so if you use a 100k (125K) pot for the tone control this will move it to the 12 o’clock position.
Changing where the tone control operates you can reduce the value of C6 to raise or lower where the tone control operates but you should change the value of the cap in the pre emphasis circuit also (10nF across 33k ohm).

It may be my lack of skills but I tried all of this and for some reason it didn't work right. I had really low volume and really bad distortion with the amp wide open.

[deafelectromark]

It may be my lack of skills but I tried all of this and for some reason it didn't work right. I had really low volume and really bad distortion with the amp wide open.

\

It sounds like a lot of work to me, and I am an electronics technician. One of the main problems with doing a mod is to do them one at a time so you can see where you had success, or worse- catastrophe. If you put the amps (modded and unmodded) side by side, you should hear a big difference in the sound of each. But the question remains--exactly what circuit mod made the most improvement (happiness divided by dollars).
There is nothing wrong with taking a cheap and amp making it better and learning how all the parts relate to each other and to learn electronics. The fact that you are a member of the FRET is indicative of your passion to tinker and improve.
There is so much information on the websites about this stuff, it is hard to just say, " I want it to play loud and clean". It can't and it wont. Clean sound needs efficient speakers and/or powerful amps to keep them from distorting. You can play clean and soft- you are staying withing the amps power levels. If you need 50 or more watts for clrean and loud ya gotta go big. Dirty and small and reasonable levels for today's living is easy. Look at how many amps there are out there that sound good and can be made much better; but then you are getting into higher price level where a more expensive amp is really what you wanted and you needed in the FIRST PLACE. That is why I limit expenditures on small amps. Sure I could add hundreds of dollars to get all the best parts and the best circuit, But it still will sound different than someone's amp and cost more that a 'better amp'.
I have a saying on 18watt- Tone is subjective!
Mark

[jim p]

Thanks for the info about C3 and R16 in post #111.




I have bypassed the op amp and have replaced C2 with a 0.022uf 715 Orange Drop which feeds into an 18 watt LiteIIb volume and tone control which then connects back to R7.

I just removed C8 on a friends V5 and wow did that clean it up, nice bright cleans at lower volumes that break up with higher volumes and harder attack, now it dimed is about the same gain as my amp on two or three. Since we both like more of a blues/classic rock sound, it's a lot better amp cleaned up.


Thanks again!

I found a schematic for the amplifier that has the tone control that you have used I think. This is 500k log pot for tone 500k log for volume 500 pF at top of tone stack 10nF at bottom is that correct? In the schematic for the amp it is in it is input to a long tail pair or differential amplifier whatever you prefer to call it which most likely has less gain (need to work out gain for it) then the second triode you are connected to. First did you use the same values for the pots and caps? If you used the 250k pots in the amp the cap values will need to double. Also to offset the greater gain in this amp may need to reduce signal across this tone stack and volume control. If the mod was in the amplifier that you removed C8 on and it improved that backs that assumption. So you could put a resistor in series with the volume control and tone stack to reduce the signal across it. Another thing you could try is to reduce the signal at the grid of the EL84 by increasing R31 probably will need to remove or reduce C3 if you do that

[jim p]

It may be my lack of skills but I tried all of this and for some reason it didn't work right. I had really low volume and really bad distortion with the amp wide open.

What tools do you have to work with do you have a DMM, scope, signal generator ect. If you just have a meter can give you locations for ohmeter tests to see if things are wired correctly.
One quick possable problem is the volume pot shorted to it's self or the PCB if you have no insulation or the insulation on the PCB is broken. I had that happen once to me after having the board in and out to make a change.

[deafelectromark]

What tools do you have to work with do you have a DMM, scope, signal generator ect. If you just have a meter can give you locations for ohmeter tests to see if things are wired correctly.
One quick possable problem is the volume pot shorted to it's self or the PCB if you have no insulation or the insulation on the PCB is broken. I had that happen once to me after having the board in and out to make a change.

The most irritating thing that I have to deal with when making changes are cold solder joints (looks good but nothing gets through) and solder bridges that I make when I solder close to adjacent traces and the sound goes to lala land. I agree with JP that using only a meter should find all but the worst problems (like oscillations, grumbly hums, wolf tones and all that stuff- you really need a 'scope to see inside the circuit and pinpoint where the problems start).
Another very frustrating issue is much like what JP said, shorted or open parts, or parts that don't have the value printed on them in color code. Remember that some parts have a silver band or gold or on the end making them 1/10 or 1/100 of the color code value. Putting in a 0.3 ohm resistor is far from 3 ohms and things will get nasty and 'look OK'.
Dirt and corrosion has me scratching my head in most of the problems that I work on. Tarnish, rust, salty bridges, intermittent pots, and controls (switches) are almost ALWAYS the first thing that I check now and save myself from hours of 'exploratory surgery' and part replacement. Don't forget that the people who sell the parts and the manufacturers make mistakes and it can make you go loony when you put in a 'correct value part' and it still doesn't work and you spend hours looking elsewhere. New parts are always OK? No they are not. Even switches have been faulty- the least complex of the parts you use. Caveat Emptor!
Mark

[rock_mumbles]

I found a schematic for the amplifier that has the tone control that you have used I think. This is 500k log pot for tone 500k log for volume 500 pF at top of tone stack 10nF at bottom is that correct?

Yes that is the volume/tone control I used. I got the amp working like I want it today, I put a 150K resistor between C2 and the volume pot and a 470K from the volume pot side of the 150K to ground (effectively have a 250K volume pot). Now the amp works fine! BTW, I have removed C3.

Now I can have the second split cathode resistor bypassed on the first triode and have an on-off-on switch hooked up on the second triode to have full bypass (most gain) no bypass (lowest gain) or partial bypass (medium gain).

Now I'm pretty much OK with the amp, it's a nice little portable combo amp. It's not quite as powerful or quite as good sounding as my modded Valve Junior but I paid more for the Valve Junior Hammond 125ESE output transformer and mod kit than I paid for the V5.

Thanks again

[jim p]

Well I am working on my third V5 think I may do a full make over to a 6V6GT output tube and two 12AX7 for overdrive and cathode follower driven tone stack and reverb(op amp drive and recovery). Probably just make it a head instead of a combo amp. The 6V6 conversion saves you enough heater current to add the second 12AX7.
I looked at the turns ratio again and saw in another post that the impedance for a 8 ohm speaker to be a 4 to 5 k ohm plate load is wrong, that looks to be right. I measured it before and came up with 20:1 but talked myself out of it but that is what I am seeing now. For what it is worth the reflected impedance is the turns ratio squares times the load (20X20 = 400 X 8 ohms = 3200 ohms). Going by the Mullard data sheet you want 4.5 k to 5.25k at the plate approx 24:1 turns ratio. On the up side the triode mode is looking for a plate load of 3.5k so this transformer is good for the triode mode which is your lowest distortion mode if you are in to that sort of thing. But this is a single ended output and harmonic content is suppose to be what you are looking for if not you should go push pull or solid state. From what I see at the plate with a scope the distorted portion of the waveform is when the tube is off which is flyback time. When the tube turns off it is the magnetic field of the transformer collapsing that is going to drive the load think of it as a flywheel or water wheel the tube spins it up then stops and it keeps going for a while. But the speaker is a load on this so the less load the longer it spins so a 16 ohm speaker is less of a drag then an 8 ohm speaker. But a 16 ohm speaker is not a 16 ohm speaker and an 8 ohm is not 8 ohms either, that is there nominal or average impedance. So bottom line what are you looking for? A single ended output is suppose to give you second harmonic distortion for that fat sound if you undampen the output with a higher impedance you will reduce it and increase the third harmonic. Another thing to keep in mind a resistor is not a speaker to get a more realistic load you can do what I did and stuff the stock speaker in a box or Ted Weber makes a load that is a speaker with no cone.
Also looked at the cathode bias on this amp but I first moved the screen grid from its connection to J4 over to junction of R25, R26 and C16 where it should be. From testing on this tube the cathode resistor should be 270 ohms that resulted in a plate current of 38mA screen grid current of 4mA with approx 315 volts across the tube for 12 watts at the plate.
Has anyone thought of converting there amp over to being a RAT, if you remove the c and e from crate on the front of the amp you get a well centered RAT on the front. Or maybe you like that sleeper stock look.

[jim p]

Instead of running the ground lead of the capacitor used for switchable cathode bypassing back and fourth through the chassis I think it may be better to use a nmos fet switch. This way there should be less chance of noise pick up and you keep the ground loop tight around the cathode resistor. I have attached a schematic that shows the basic set-up. I may also use this same circuit to parallel the output tube cathode bias resistor when switching between triode and pentode mode. In that case I will use a four or five pole double throw switch for isolation from the screen grid connection with a two pole switch I think a high voltage arc might occour within the switch. The BS270 fets in the schematic are available from Mouser electronics for 19 cents each.

[jim p]

Yes that is the volume/tone control I used. I got the amp working like I want it today, I put a 150K resistor between C2 and the volume pot and a 470K from the volume pot side of the 150K to ground (effectively have a 250K volume pot). Now the amp works fine! BTW, I have removed C3.

Now I can have the second split cathode resistor bypassed on the first triode and have an on-off-on switch hooked up on the second triode to have full bypass (most gain) no bypass (lowest gain) or partial bypass (medium gain).

Now I'm pretty much OK with the amp, it's a nice little portable combo amp. It's not quite as powerful or quite as good sounding as my modded Valve Junior but I paid more for the Valve Junior Hammond 125ESE output transformer and mod kit than I paid for the V5.

Thanks again

I calculated the gain of the differential pair used as a phase splitter and it should be approx 26. That is close to the same gain as the second triode without cathode bypassing in the V5 (gain 25). One thing about the Lite II that looks wrong is that the plate load resistors are equal values in the phase splitter. From what I have read and simulated the plate load resistor on the input tube (R6) should be approx 20% smaller then the other plate load resistor to have equal amplititude signals. Anyway the V5 overall gain should be the same as the Lite II with the input triode bypassed and the second triode unbypassed.

[larryx]

Hello folks,
Well I'm just another confused and frustrated Crate V-5 owner. I like alot of V-5 owners am looking for some (simple) mod instructions. Not the long winded ones written by technological geniuses. I'm talkin about something the average guitar player who can read tab and paint by numbers can do! I'm getting tired of reading about Jonnie Multimeter and his triumph over bypassing the op amp section and making his personal CrateV-5 an all tube circuit. While the rest of us dread the day we bought one! How about someone with this knowledge sharing some easy to understand mods. Information like what resister and capacitors do we change? R-? and C-?. And what values do we change them to? Alot of us guitar players are just looking for a solution to get a good sound out of our V-5's. Is anyone willing to put together some ((easy to understand directions)) for making these amps worth owning ? Most of the info out there is way to difficult to understand. I CAN HEAR THE AMEN BROTHER!, COMING FROM THE NON TECHY GUITAR PLAYER CROWD OUT THERE ON THE FRET!!!

Many Thanks to who ever steps up!!!

[SciHi]

...Well I'm just another confused and frustrated Crate V-5 owner...

I spent the last couple days playing around with a v5, I recently completed extensive mods to my crate v18 and figured the v5 would be a piece of cake. BUT the v5 is pretty screwed up. As bad as people said the v18 sounded, it was just a couple of resistors and capacitors away from great sounds. The v5 however, is a trainwreck, and not in a good way. There are no really simple fixes because, #1 it doesn't have a volume control and #2 it doesn't have a working tone stack. So those two things need fixed before you can worry about any small tweaks here or there.

What is currently called volume is a gain on the opamp. It is fine to have it there, just don't ever turn it up! The amp needs a volume control, preferrably between the two tube stages of the preamp. So you either pull the existing tone pot, fix the gain on the opamp as suggested by Jim P, or pull the pot and totally bypass the opamp totally, running the input to the first stage of the preamp tube. Your option, you get to choose. Jim P does give step by step instruction so you can keep the opamp working and move the volume control to the correct place. If you want to try and locate another pot on the amp somewhere, then you could add it for volume control and leave the gain on the opamp (this is more like the earlier models of this amp). So that is a third option to fix the "no true volume control."

To fix the tone stack, Jim P has step by step instructions and they are about the easiest. But many different one knob tone stacks, such as the tweed could be adopted. You could even add 2 (or 3) pot tone stacks by using dual pots, such as Verne A. posted on HC for the Palomino 8, a close cousin to this amp. Pick your favorite, or follow Jim P step by step instructions for the simplest. Once these two major problems are fixed, then you can start simple resistor and cap changes to voice the amp to your liking.

The amp I played with was modded by Rock_Mumbles. He jumpered the opamp, used a modified liteII tone stack, and added switchable cap bypass on v1b cathode. Real nice mod, very close to a well modded VJ. Maybe we can shame Professor Mumbles in posting his modified schematic drawing...

[rock_mumbles]

Hello folks,
Well I'm just another confused and frustrated Crate V-5 owner. I like alot of V-5 owners am looking for some (simple) mod instructions...

Like Scihibmxer posted, unfortunately the Crate V5 is not as easy to mod as some other amps I've modded in the last year, you won't gain much by just changing out a resistor or cap like other amps. We both thought - a nice little combo amp for a decent price, only 5 watts so it won't make quite as much noise in the house as the 18 watt amps, it's a 2 tube amp should be no problem to modify.
I probably spent about 10 hours working on my V5 last week (I was on spring break), so I am also "Confused And Frustrated"
My response to the V5 after the initial mods (bypassing the op amp and adding in the volume/tone control) "what the heck is up with you???" I spent way too much time for very little progress. I finally have the amp so it's OK as a test amp for guitars and pedals.

So...

What kind of guitar do you play??? (my modded V5 is OK with my Tele but doesn't sound very good at all with my brother's Dimarzio humbuckers, it would need to be throttled back for humbuckers)

What do you want your amp to do??? (you have to remember it's a simple 2 tube amp so do you want some cleans with breakup or completely overdriven - for complete overdriven sound listen to 777funks modded amps he sells on ebay, they are a one-trick pony)

In my opinion the speaker has to be replaced, what kind of speaker are you thinking about??? (the Weber Sig 10 or Sig 10S are good sounding reasonably priced speakers)

The things I have done that I could help you with is an easy way to:
(a) bypass the op amp and correct the input jack. (this involves removing the volume pot )
(b) remove the stock tone stack, and move the volume control and add a simple one knob tone control into the circuit where the stock tone stack was.
(c) deal with the amp's gain, if it has too much gain for you.

I wouldn't work on the amp unless you have some spare 16mm pots (and some new knobs handy) it's really easy to mess up the pots desoldering and soldering them. I help out at a friends music store so I have access to lots of parts and a good solder station, volt meters etc., so when I burned out the volume pot soldering the ground wire on, I just got another one out of the parts drawer.

You'll also need a couple of caps for the new tone stack three or four values of resistors and maybe a new 400V capacitor that goes in the circuit before the volume/tone stack.

Again, I can help you with the mods I have done, but anything else is just a guess. If you're interested, I'll put up a mod layout and parts list.

[jim p]

The most basic mod you can do that should have a significant change to the amp (with exception of replacing the speaker) is to use the tone pot for a volume pot and keep the volume pot for a gain control. I posted a list of components to remove and replace for this and how to jumper the tone pot to the control grid of the second triode for a volume control. I could draw up a small schematic to show what the changes are if someone wants. But a basic thing you may need to know is how to read a schematic and I will guess you might be able to read about just that subject on that thing they call the WEB. If you don’t know about something here open a new tab and Google it. Where do you find those tabs you have been using eh? So Google resistor, capacitor, and inductor heck you can find sections of college courses on electronics on this web thing.
Anyway doing the tone to volume control mod you do not have to remove the pots so no chance of damage to them. Other amps out there do not have a tone control so? The gain op amp set up in this amp is better then the Crate VC508 because that only had +/- 7 volt supplies which may not have been enough headroom to prevent clipping in the op amp before the tube.

[Tomko]

So you can decrease the voltages on the EL84 by increasing the cathode bias resistor? I'm still over 330 volts on the plate and screen grid but the amp works fine. I see the cathode bias resistor for the EL84 is R17, 330 ohm, 5 watt. What would you increase it to to get the voltages below 300v?
Also, you keep saying increase R16 to 10K but it is already 220K. Is this a typo, mistake or what? You're confusing me- easy to do.