Crate V5 mods... anyone?

[Tele-Dave]

Would like to post a marked up schematic...............

Please Do. looks like a good mod.

[jim p]

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).
ERROR Value of C24 should be 100nF lowest frequency from guitar is 82Hz.


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.
ERROR Should go with 100nF lowest frequency from guitar is 82Hz

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).

[tunghaichuan***]

Cool, thanks for posting that. The Best Buy near me has these for $100, I may have to pick one up and try the mods.

Have you tried adding additional capacitance to kill some of the 60hz hum?

tung

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 180 ohms 2-5 watt or parallel the 330 5 watt with another 330 ohm 2 watt (165 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).

[jim p]

When I was talking about 60 Hz hum I meant pick up from the guitar not in the amplifier. The amplifier has 1 H choke pi filter and DC filament voltage on the 12AX7 its quiet compared to the Valve Jr combo I have.

[jim p]

Posted pictures of close to final modification of Crate V5 I bought. The vector board is the reverb drive and recovery amplifiers. Replaced the stock (crap) speaker with a Webber ceramic 10S for 38 bucks with shipping. The reverb tank is a Accutronics box with Ruby OEM guts (2 spring) from a Crate V33H. On the back pannel is the reverb pot and pentode/triode switch. May do a better job of running the RCA lines to reverb in future. I see the Crate V5 is 85 bucks at Best Buy dot com with in store pick up so the shipping is free.

[Tele-Dave]

Posted pictures of close to final modification of Crate V5 I bought. The vector board is the reverb drive and recovery amplifiers. Replaced the stock (crap) speaker with a Webber ceramic 10S for 38 bucks with shipping. The reverb tank is a Accutronics box with Ruby OEM guts (2 spring) from a Crate V33H. On the back pannel is the reverb pot and pentode/triode switch. May do a better job of running the RCA lines to reverb in future. I see the Crate V5 is 85 bucks at Best Buy dot com with in store pick up so the shipping is free.

Can you post schematic changes and step by step for these mods?

Question on previous mods. In step 2 of board mods where you remove C26 C24 and C27, C24 and C27 are replaced with other components but C26 is not. Is this left open or is it jumpered? If not jumpered then I assume it is O.K. to remove R28 since it is not connected to anything?

Also I want to have Gain and Volume setup. Can I just leave existing pot connected in its place on board and use another pot for the volume mod such as you have it? I understand that I will have to lift a leg on pot or cut trace on board to put in 27k resistor in series with pot. Is this right?

Thnx---Dave

[jim p]

Yes if you want you can remove R28 without C26 it has no function. If you want gain and volume CW1 the 250k pot accost TL01-B can be used as a gain pot. In that case do not install a resistor in the location of C27. You may to set a minimum gain by putting a 10k resistor in series with the 250k gain pot. If you search the web or call Crate for a VC508 schematic this will give you an idea of the gain, tone and volume set-up. I don't like the values of capacitance they used for the 508 also the low supply rails on the op-amp (+7 -7). This amp is better in the fact you have +/- 15 volts (more within limits if you reduce R19 and R20) for the op-amp a 1 Hennery choke in the plate supply and DC filament supply on the 12AX7. Bad thing is they took out the wrong pot to remove the gain function did not change bandwidth for a 10 inch speaker (more bass) and used a crappy speaker.

[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]

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

[lute760]

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).
ERROR Value of C24 should be 100nF lowest frequency from guitar is 82Hz.


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.
ERROR Should go with 100nF lowest frequency from guitar is 82Hz

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).

I just picked up a V5 for 20 bucks at a yard sale and wanted to try your mod,but the attachments seem to be gone.Can you repost them?

[jim p]

I found the mark up and picture to go with the no op amp modification that is part of posting #168. Here are links to them http://i1020.photobucket.com/albums/...dification.jpg http://i1020.photobucket.com/albums/...nschematic.jpg I would call or e mail Crate to get a PDF of the schematic for the amp. All the postings that now have no attachments are almost worthless, like a car repair manual with no illustrations, but it is what it is.

As always the stock speaker is junk and the output transformer is really a 16 ohm output. For more ideas on amp mods with postings you can try Sewatt

PS without the op amp to get a treble boost change the first cathode bypass cap C1 to a 470nf minimum voltage rating 16 volts.

[Infernie]

Hi Guys,

I have just laid my hand on a stock Crate V5 for a cheap price. I'm going to order a new speaker and some new tubes but i want to go even further with the modding. That's how i found this thread.

I've skimmed through the pages and decided the first thing i want to do is the Gain/Volume control mod of post #147. I hope i can find some pictures somewhere or else it will be a bit tough to do.

I've yet to decide wheter to do the no op-amp mod of post #168 or not. I don't know what i will gain with it? How does it influence my sound?

One more question: are there any mods i can try to get a good warm clean sound? I mean a sound like used in this clip:Youtube: Slow dancing in a burning room or a bit more crunchy like this: Youtube: Lenny - SRV.

Anyone knows if this is possible with this amp and a stratocaster? What should i do after i did the gain/volume control knob mod? I plan to build a tubescreamer so my amp should do a good clean sound i guess?

Thanks in advance and i owe you much if you can answer my questions.

Keep on rocking!

*EDIT*

I found an interesting mod online. I tried to make the scheme out of it.

This is the orignial link: CLICK
This is my scheme: CLICK

Do you guys think this will work out and how will it work out soundwise?