Crate V5 - very low volume

[Aerostoon]

I picked up a Crate V5 amp and the volume is quite low, even on 10 you can talk over it. It does overdrive quite a bit it just is not loud at all.
My first thought was a bad tube. I swapped in a new 12AX7 and an EL84 tube one at a time and there was no change. I tried a different 8 ohm speaker and it wasn't any louder. I pulled the chassis and took a good look over the circuit board and all the wiring. Every thing looks fine. I did an internet search for any Crate V5's with low volume. Not one showed up.
Does anyone have any ideas. Maybe a failed bias resister?

[Jazz P Bass]

Crate V5 Schematic

You need to take some very basic voltage measurements.

12AX7: Pin 1 (plate) & 3 (cathode) Pin 6 (plate) & 8 (cathode) (all volts dc). Pin 4/5 & (heater- volts ac)

EL84: Pin 7 (plate), Pin 3 (cathode), Pin 9 (screen) (all volts dc) & pin 4-5 (heater- volts ac)

These voltages are the static, no signal voltages that set up each tube to operate properly.

If the static voltages check good, then a 100mv signal can be injected into the input jack to test the dynamic signal voltages.

[Aerostoon]

Thanks Jazz P Bass, I will check and record the results. Thanks for the schematic as well

[Fragger]

Informative thread talking about modding the V5, you might pull out some gems.

thefret(DOT)net/showthread.php/9379-Crate-V5-mods-anyone?

[Aerostoon]

I have the chassis pulled out and thought I would check R7 and R16 as they are located in the Center of the tube socket pin connections. R16 measured 217K which is very close but R7 measures 9.48K which is far off of 220K. Could this be the cause of the amps very low volume? The resister band markings are identical between R7 and R16. It is red/red/yellow/gold. 220k 5%.

I will check the voltages suggested above next.

[The Dude]

R7 is in parallel with R27. Since R27 is 10K, you are primarily measuring that resistor since it's resistance is much lower. In many/most circuits, you need to unsolder one side of a resistor to get accurate readings.

[Aerostoon]

I feel a bit silly but I did learn something. Thanks for your reply!

[The Dude]

Just an FYI:

Resistors don't lower in value. That is the clue. When a resistor fails or is bad it will go towards open or raise in value and is caused by excessive current draw by something else. When a resistor is bad, it is normally an indication that something else is shorted. The only time I've seen a resistor lower than its marked value is when I worked for a manufacturing facility and we got a batch that was marked wrong.

[Aerostoon]

Ok, I finally got back to this project after being pulled away by some household tasks. I made a mistake and wrote down pin 7 of the 12AX7 tube so I will have to check that pin tonight.

12AX7:
Pin 1 (plate) 187 VDC
Pin 3 (cathode) 1.59 VDC
Pin 6 (plate) 189 VDC
Pin 8 (cathode) I had pin 7 written down so I need to check this one tonight.
Pins 4 & 9 (heater – volts ac) 0 VAC ( I couldn’t get any voltage reading on this one)
Pins 5 & 9 (heater- volts ac) 13.7 VAC


EL84:
Pin 7 (plate) 341 VDC
Pin 3 (cathode), 64 MVDC
Pin 9 (screen) (all volts dc between pin and chassis ground) -296 MVDC
pins 4 & 5 (heater- volts ac) 6.5 VAC

[pontiacpete]

It looks like you are missing voltage on the el84 cathode, should be something there , maybe 10vdc
And the screen should be positive voltage not negative, maybe your leads were reversed on your DMM.

correction you should have high voltage on that screen not milli volts.
Maybe there's something not connected with R17 or bad parallel cap. ?

[52 Bill]

Or R18 has come unsoldered or gone open.

A few of your voltage readings seem off. It may be the problem with the amp or just mistaken readings. Please read dc voltage to ground at pin 3 and pin 9 of the EL84 power tube.

Also read dc voltage to ground from pin 5 of the 12AX7 tube.

[Aerostoon]

I measured pin 5 to ground on the 12AX7 and it was 13VDC;
Pins 3 and 9 each to ground doesn't show any DC voltage?

I will have to pull the circuit board to inspect the solder joints.

[eschertron]

I measured pin 5 to ground on the 12AX7 and it was 13VDC;
Pins 3 and 9 each to ground doesn't show any DC voltage?

I will have to pull the circuit board to inspect the solder joints.

I'm with 52 Bill on something fishy with R18.

While it's still in one piece you can probe R18, volts DC to ground on each end and then volts DC from one end to the other. If both ends of R18 to ground read close to B+, then probe pin 9 of the EL84 socket to ground (as you've done before). You can have the tube in or out for this measurement.
With power off and HV discharged, check continuity from the legs of R18 to where they should be connected. One side, pin 9 of the socket. The other, B+ (pick it up at R25, perhaps). Tell us what you find.

[Aerostoon]

One side of R18 is 334 VDC and the other is 0? There is 0 VDC at pin 9.

[eschertron]

One side of R18 is 334 VDC and the other is 0? There is 0 VDC at pin 9.

Did you measure across R18? If you did, and got "no voltage", then I suspect if you power off and remove the circuit board, you will find R18 is failed open. This is assuming you probed the actual leads on R18 while testing. I find it hard to believe that a 3W resistor would burn up, but then why did they make it 3W? Outrageous.

I don't know if it's possible that the screen is actually grounded out and not causing horrible secondary effects; haven't seen that one yet.

You are looking for an open circuit path where there should be continuity (or appropriate resistor value). Do your continuity checks and verify what's really connected to what, and where the open circuit is.