Where to measure bias?

[FourT6and2]

The CCV is slightly different from my other amps. Just arrived today. Put all the tubes in, tried to bias it up. Plate voltage was reading super low, around 230 volts. I replaced the power tubes with a brand new set of Ruby EL34 BHTs I have laying around and that seemed to do the trick. Plate voltage is now reading 520 volts. But I'm not getting any bias reading off the tube pins. I notice there's no resistor to ground off pin 1 and 8. So that may have something to do with. It's not like my Marshalls where I can just stick a probe on pin 1 to measure the bias.

So where do you measure the bias on this thing?

And is 520 volts on the plates still too low? Shouldn't it be up around 550 or something?

 

[FourT6and2]

Ugh.

Looks like I'll have to buy a bias meter that has socket probes. I hate using those things. All my other amps have the 1 ohm resistors between pins 1, 8 and ground. So I can just measure the bias in mV at pin 8. The CCV doesn't have this. Huge inconvenience. Looks like I'll have to wait another week or so before I can see how this things sounds.

Might as well get some new preamp tubes and SED power tubes while I'm at it.

 

[Anonymous]

The CCV is slightly different from my other amps. Just arrived today. Put all the tubes in, tried to bias it up. Plate voltage was reading super low, around 230 volts. I replaced the power tubes with a brand new set of Ruby EL34 BHTs I have laying around and that seemed to do the trick. Plate voltage is now reading 520 volts. But I'm not getting any bias reading off the tube pins. I notice there's no resistor to ground off pin 1 and 8. So that may have something to do with. It's not like my Marshalls where I can just stick a probe on pin 1 to measure the bias.

So where do you measure the bias on this thing?

And is 520 volts on the plates still too low? Shouldn't it be up around 550 or something?

There is a switch on the back of the amp for high output/low output that will affect the plate voltages also if the amp is biased insanely hot like one of mine was when it first arrived then that can pull the plate voltages down lower.

when my ccv arrived it was reading 85 ma per tube and the plate voltage was at 520 volts until I lowered the cathode current draw to around 47ma per tube the plate volts then read 550v ish

 

[FourT6and2]

The CCV is slightly different from my other amps. Just arrived today. Put all the tubes in, tried to bias it up. Plate voltage was reading super low, around 230 volts. I replaced the power tubes with a brand new set of Ruby EL34 BHTs I have laying around and that seemed to do the trick. Plate voltage is now reading 520 volts. But I'm not getting any bias reading off the tube pins. I notice there's no resistor to ground off pin 1 and 8. So that may have something to do with. It's not like my Marshalls where I can just stick a probe on pin 1 to measure the bias.

So where do you measure the bias on this thing?

And is 520 volts on the plates still too low? Shouldn't it be up around 550 or something?

There is a switch on the back of the amp for high output/low output that will affect the plate voltages also if the amp is biased insanely hot like one of mine was when it first arrived then that can pull the plate voltages down lower.

when my ccv arrived it was reading 85 ma per tube and the plate voltage was at 520 volts until I lowered the cathode current draw to around 47ma per tube the plate volts then read 550v ish

The guy I bought it from said he biased it a little cold to be safe (38mA). And I measured plate voltage with the power switch in both high and low positions. But, I replaced the power tubes and now it's reading 520 volts. So that seems about right.

In any event, I still can't bias it until I get a meter that plugs into the sockets. But I'm having some other issues with the amp, so it will have to go in for repairs anyway.

 

[Anonymous]

The CCV is slightly different from my other amps. Just arrived today. Put all the tubes in, tried to bias it up. Plate voltage was reading super low, around 230 volts. I replaced the power tubes with a brand new set of Ruby EL34 BHTs I have laying around and that seemed to do the trick. Plate voltage is now reading 520 volts. But I'm not getting any bias reading off the tube pins. I notice there's no resistor to ground off pin 1 and 8. So that may have something to do with. It's not like my Marshalls where I can just stick a probe on pin 1 to measure the bias.

So where do you measure the bias on this thing?

And is 520 volts on the plates still too low? Shouldn't it be up around 550 or something?

There is a switch on the back of the amp for high output/low output that will affect the plate voltages also if the amp is biased insanely hot like one of mine was when it first arrived then that can pull the plate voltages down lower.

when my ccv arrived it was reading 85 ma per tube and the plate voltage was at 520 volts until I lowered the cathode current draw to around 47ma per tube the plate volts then read 550v ish

The guy I bought it from said he biased it a little cold to be safe (38mA). And I measured plate voltage with the power switch in both high and low positions. But, I replaced the power tubes and now it's reading 520 volts. So that seems about right.

In any event, I still can't bias it until I get a meter that plugs into the sockets. But I'm having some other issues with the amp, so it will have to go in for repairs anyway.

sorry to hear that...
520 Plate Voltage does seem low and if the amp is biased at 38 ma per tube then I would think that you should see 550-560 plate voltage in the high power position and about 460 plate volts in the low power position.

can I ask what are the issues with the amp that it needs repair ?
good luck with it

 

[steve_k]

Just clip one probe to the chassis or a ground lug and the other probe to pin 5 for bias current. You got to have it in full power, not half. PV can be read from pin 3. I know you know this, but make sure you are in DCV mode and that your DMM can handle the voltage.

 

[FourT6and2]

sorry to hear that...
520 Plate Voltage does seem low and if the amp is biased at 38 ma per tube then I would think that you should see 550-560 plate voltage in the high power position and about 460 plate volts in the low power position.

can I ask what are the issues with the amp that it needs repair ?
good luck with it

Keep in mind plate voltage and B+ varies depending on the voltage coming into the amp from the mains. It will never be a hard and fast constant number. You could read 550 volts at home and 520 volts at your practice space and then 560 volts at a gig. Unless you're using a power conditioner of course.

The other issues with the amp are a number of the switches on Channel 1 don't seem to be working.

I will say this, though. Having built a number of amps myself and having seen what good electronics work looks like... this CCV is one of the WORST built and constructed amps I've ever seen. Cold solder joints. Leads held in place on top of pot lugs by solder, rather than going through the eyelet/lug. Why would anybody do that? There was even a zip-tie holding some wires in place. But whoever built the amp accidentally caught the edge of the zip tie around a capacitor coming off the PCB and bent it.

This is a first-run CCV that was built by that electronics company that Brad and company used initially. I can see why they decided to go to Metro instead. But it looks like the people who built this one had never attempted to solder before.

Just clip one probe to the chassis or a ground lug and the other probe to pin 5 for bias current. You got to have it in full power, not half. PV can be read from pin 3. I know you know this, but make sure you are in DCV mode and that your DMM can handle the voltage.

I use a high-quality Fluke meter. Hmmm... not getting any sort of bias reading when I do that. My meter just shows zero. Usually I measure bias off Pin 8. But the CCV has no 1 ohm resistors bridging pins 1 and 8, to ground. Setting the meter to VDC should give me a negative reading at Pin 5, which would be the bias voltage. But that's not what I'm getting. Something's not right.

EDIT: I also noticed the power transformer gets SUPER hot. I know this thing is pushing 500+ volts. But my Super Lead, which runs just as high a voltage, (and uses the same transformer from Mercury) doesn't even get warm.

 

[RedB4Black]

The CCV is slightly different from my other amps. Just arrived today. Put all the tubes in, tried to bias it up. Plate voltage was reading super low, around 230 volts. I replaced the power tubes with a brand new set of Ruby EL34 BHTs I have laying around and that seemed to do the trick. Plate voltage is now reading 520 volts. But I'm not getting any bias reading off the tube pins. I notice there's no resistor to ground off pin 1 and 8. So that may have something to do with. It's not like my Marshalls where I can just stick a probe on pin 1 to measure the bias.

So where do you measure the bias on this thing?

And is 520 volts on the plates still too low? Shouldn't it be up around 550 or something?

There is a switch on the back of the amp for high output/low output that will affect the plate voltages also if the amp is biased insanely hot like one of mine was when it first arrived then that can pull the plate voltages down lower.

when my ccv arrived it was reading 85 ma per tube and the plate voltage was at 520 volts until I lowered the cathode current draw to around 47ma per tube the plate volts then read 550v ish

The guy I bought it from said he biased it a little cold to be safe (38mA). And I measured plate voltage with the power switch in both high and low positions. But, I replaced the power tubes and now it's reading 520 volts. So that seems about right.

In any event, I still can't bias it until I get a meter that plugs into the sockets. But I'm having some other issues with the amp, so it will have to go in for repairs anyway.

sorry to hear that...
520 Plate Voltage does seem low and if the amp is biased at 38 ma per tube then I would think that you should see 550-560 plate voltage in the high power position and about 460 plate volts in the low power position.

can I ask what are the issues with the amp that it needs repair ?
good luck with it

This was my amp. Whenever I biased it, using a bias-rite, I'd get a PV of around 540. It's going in for repairs as some of the switches don't seem to be working properly on channel 1. They were fine before I shipped as I tested the amp when I installed the tubes prior to packing and I packed it very well - it does not appear from looking at the box that it sustained any major hit. So basically, I'm not sure if something got jarred loose in the shipment. We've reached an accord on how to handle getting it fixed up.

 

[FourT6and2]

Yep. No worries. Shit happens. Matt has been great to work with.

 

[JerryP]

Just clip one probe to the chassis or a ground lug and the other probe to pin 5 for bias current. You got to have it in full power, not half. PV can be read from pin 3. I know you know this, but make sure you are in DCV mode and that your DMM can handle the voltage.

Can't measure bias current like that. That will only give you the bias voltage which tells you nothing about the bias setting. Probably like -38v or somewhere around there. That's how Peavey sets up their test points on their amps, to read bias voltage.
Jerry

 

[FourT6and2]

That's what I thought.

 

[steve_k]

Is that an original or a production model? Seems like the bias meters will also read plate voltage with the amp on standby as well. Memory is drawing some blanks, but seems like there was an issue using a meter.

 

[FourT6and2]

First-run production I think.

 

[Anonymous]

Is that an original or a production model? Seems like the bias meters will also read plate voltage with the amp on standby as well. Memory is drawing some blanks, but seems like there was an issue using a meter.

A bias rite will work just fine with an original ccv or 1st production run ccv when the amp is turned on...

 

[FourT6and2]

You shouldn't be able to read any high voltage in the amp at all, when in standby. In standby, only the heaters are getting power. At least that's they way it should be. Maybe the MIDI board, too. But definitely not the tubes' plates, screens, etc. So I don't see how you can read bias voltage with the amp in standby...

 

[LP Freak]

You shouldn't be able to read any high voltage in the amp at all, when in standby. In standby, only the heaters are getting power. At least that's they way it should be. Maybe the MIDI board, too. But definitely not the tubes' plates, screens, etc. So I don't see how you can read bias voltage with the amp in standby...

 

[dawnofdreamx97]

You shouldn't be able to read any high voltage in the amp at all, when in standby. In standby, only the heaters are getting power. At least that's they way it should be. Maybe the MIDI board, too. But definitely not the tubes' plates, screens, etc. So I don't see how you can read bias voltage with the amp in standby...

the ccv standby switch does not work like a standard marshall standby. There is voltage on the tubes even in standby....

 

[FourT6and2]

Weird. What's the point of the standby switch in the CCV, then? Is it just a mute switch?