Biasing a Jose

[glip22]

You really know calling is not the way to reach him. BTW what is your PV in this Jose amp you haves in your possession?

It is a 50 watt JCM 800 and the plate voltages are 500 volts

Thats high PV for a 50 watter. Probably has nice headroom. Maybe its a replaced PT. If it were my amp I would bias the hottest EL34 of the pair around 33ma. 6550s about the same. In a Marshall with 6550 you do not use 35 watts as your PD. The OT is designed for EL34 and does not have the impedance to operate 6550 efficiently. Plus the 6550 takes less on the screens than the EL34. Mark doesn't do anything special to restrict the screen voltages in any of his amps. He and I did speak about this when I had my CCV, He just likes to bias hotter although when he biases an amp he does it by ear without a meter most of the time.

 

[LP Freak]

You really know calling is not the way to reach him. BTW what is your PV in this Jose amp you haves in your possession?

He's got a Jose modded PV? Interesting.

PV= plate voltage

Oh.

500w PV....that's not too common.

 

[H3000]

You really know calling is not the way to reach him. BTW what is your PV in this Jose amp you haves in your possession?

It is a 50 watt JCM 800 and the plate voltages are 500 volts

Thats high PV for a 50 watter. Probably has nice headroom. Maybe its a replaced PT. If it were my amp I would bias the hottest EL34 of the pair around 33ma. 6550s about the same. In a Marshall with 6550 you do not use 35 watts as your PD. The OT is designed for EL34 and does not have the impedance to operate 6550 efficiently. Plus the 6550 takes less on the screens than the EL34. Mark doesn't do anything special to restrict the screen voltages in any of his amps. He and I did speak about this when I had my CCV, He just likes to bias hotter although when he biases an amp he does it by ear without a meter most of the time.

Yes its High for a 50 watter but its a later JCM 800 and its not the first I have seen with plate voltages that high and the other JCM 800 50 watters I have had that exhibited the same High plate voltages were from the same era 1983-1985 so maybe marshall started using a different spec mains transformer during that era.
the amp has EL34 winged C in it and it sounds really good ,it sounds like a really good marshall should
the mains/power transformer and output transformer and choke are all original and its one of the last JCM800 series that would of been produced that still has the circuit board attached to the pots by flying leads instead of the later version that directly attached the circuit board to the pots

The amp has raised some other questions in my mind about the cameron Jose modded marshalls.
so maybe you could help me out with some more info please or anyone else who reads this and has owned Jose mods in the past

This Jose takes boost pedals upfront really well and although the amp does not need any help in the gain department it still benefits from a very gentle clean boost mainly from the standpoint of changing the playing feel and for adding different tonal coloration
so my question is this..... this particular Jose amp has no bright switches and works great with pedals so would you know if the Jose versions that actually have the bright switches will also work well with pedals upfront ?
I ask because the various CCV that I have owned in the past did not work well with pedals at all compared to this Jose and I wondered if that could be due to the bright switches/bright caps in the CCV

I would still love to know for definite how the CCV can be biased to such a high bias of 90% and not cook the tubes but I have a feeling its going to remain unanswered
do you think it is maybe just the winged c tubes that can take the punishment I mean 90 % should really push the tubes to the point of redplating and meltdown and yet the CCV can take it all day long and I know there are lots of other CCV owners that also bias their CCV that hot without any problems such as premature tube failiure or tonal problems.
anyway.... for now I will bias the amp conservatively at 70% and err on the side of caution
but I am not brave enough to set the bias by ear just yet...

 

[PWE Amplification]

Check your wall voltage. I bet it's around 125v, that's why you are getting 500volts on the plates.

 

[H3000]

Check your wall voltage. I bet it's around 125v, that's why you are getting 500volts on the plates.

My wall voltage is 240 volts

 

[PWE Amplification]

Check your wall voltage. I bet it's around 125v, that's why you are getting 500volts on the plates.

My wall voltage is 240 volts

Didn't realize you were not in the US. My point, which would apply anywhere, is that the ACTUAL voltage at the socket may not be what it's supposed to be and may be a little high.

 

[H3000]

Check your wall voltage. I bet it's around 125v, that's why you are getting 500volts on the plates.

My wall voltage is 240 volts

Didn't realize you were not in the US. My point, which would apply anywhere, is that the ACTUAL voltage at the socket may not be what it's supposed to be and may be a little high.

I have checked my wall voltage due to having a issue with a 60 watt MKIIC+ boogie and sometimes it varies a little during different times of the day but but not much more than a couple of volts but then that is nothing unusual for the uk.

I have a bone stock unmodded 1979 100 watt JMP 2203 here and that reads 490 volts on the plates.
and I also have a bone stock unmodded 1979 50 watt JMP 2204 here that reads 390 volts on the plates
I would think that the JCM 800 has High plate voltage because of the Mains transformer that marshall used during that era or maybe they changed the circuit ...
it was not that long ago I sold an bone stock unmodded late 1984 JCM 800 2204 that also had plate voltage of 500 volts... that was a very aggressive sounding amp compared to my 50 watt JMP 2204

 

[Rocknrollamps]

To the original question---Did you notice if it has a standard rectifier string or a bridge rectifier.

 

[thickwood]

start at 70% and listen then go 65% and let your ears tell you .
90% is hogwash for a push pull amp,tubeacide is a crime !

 

[H3000]

start at 70% and listen then go 65% and let your ears tell you .
90% is hogwash for a push pull amp,tubeacide is a crime !

It is Not hogwash at all....
not if you are using a cameron CCV and there are plenty of others here on this forum who have owned and still do own CCV-100 that have been sent out biased at 90 % MPD.

just do a search on this forum and read the threads ,I ran my own CCV biased at 90 % with the same set of tubes for almost a year and then I sold it to a friend who is a forum member with the same set of winged c in it and he kept it and the tubes still did not need changing
the only time the CCV amp did not sound right was when I experimented with the bias and dropped it down to 60%-70% and then it sounded thin and bright and ratty...

I have understand the 70% MPD rule for biasing
and when I got my first CCV and realised it was biased so hot I panicked and yet when I enquired and read the threads here it became clear that the CCV will safely bias that hot ,I dont know how it does it safely but it just does.....

so before you call hogwash on something take a look around maybe do a search on the threads as there are plenty of people on this forum who have owned and who are still CCV owners with their amps biased in the 90%

I was talking with Dan Gower over the weekend and he told me it is just down to the winged c tubes being able to take higher than 500 v on the plates and screens

 

[50MkII]

FWIW, there are other current production power tubes able to withstand that PV. I have 3 of Mark's Jose amps. The following readings were based on how Mark dialed them in. One he had biased around 42-44 with a quad of JJ6CA7 and PV of 459-461. Pretty hot but sounded good for that tube. Another with Svetlana EL34 (not winged C's) between 35-38 with PV between 460-463. The CCV's PV is hotter than any of my Jose's. Ear + Eyesight = best bias setting.

 

[H3000]

FWIW, there are other current production power tubes able to withstand that PV. I have 3 of Mark's Jose amps. The following readings were based on how Mark dialed them in. One he had biased around 42-44 with a quad of JJ6CA7 and PV of 459-461. Pretty hot but sounded good for that tube. Another with Svetlana EL34 (not winged C's) between 35-38 with PV between 460-463. The CCV's PV is hotter than any of my Jose's. Ear + Eyesight = best bias setting.

Thanks for the info
Thats good to know at least now I know I dont have to be checking to see if the amp is modded to take the voltages as it is just down to the right tubes

I have my second Cameron Jose arriving from James Lugo this morning so I will use Ear+ Eyesight = best biasing as a formula
cheers

 

[TrueTone500]

90% is obviously harder on the tubes, but if you've got a stout quad of glass - indulge! It would seem 90% is part of the 'secret sauce' when it comes to Cameron amps. My Cameron modded amp was set close to 90%, and I wouldn't have changed a thing about that amp.

 

[H3000]

90% is obviously harder on the tubes, but if you've got a stout quad of glass - indulge! It would seem 90% is part of the 'secret sauce' when it comes to Cameron amps. My Cameron modded amp was set close to 90%, and I wouldn't have changed a thing about that amp.

I definitely prefer the sound of the Jose with the tubes running hot and I have now had a set of wing C in the amp running at 90 % for nearly 5 months and they are still going strong and the amp still sounds ABSOLUTLEY F,ing incredible and I never get bored of playing it.
is it possible to have a 5 month honeymoon ?
I know 5 months is not really a true test of tubes lasting but if they last awhile longer I will definitely be more than happy with running them this hot

 

[glip22]

90% is obviously harder on the tubes, but if you've got a stout quad of glass - indulge! It would seem 90% is part of the 'secret sauce' when it comes to Cameron amps. My Cameron modded amp was set close to 90%, and I wouldn't have changed a thing about that amp.

I definitely prefer the sound of the Jose with the tubes running hot and I have now had a set of wing C in the amp running at 90 % for nearly 5 months and they are still going strong and the amp still sounds ABSOLUTLEY F,ing incredible and I never get bored of playing it.
is it possible to have a 5 month honeymoon ?
I know 5 months is not really a true test of tubes lasting but if they last awhile longer I will definitely be more than happy with running them this hot

Thats cool. It is possible to have a five month Honeymoon as long as she still swallows after you marry her.

 

[TrueTone500]

90% is obviously harder on the tubes, but if you've got a stout quad of glass - indulge! It would seem 90% is part of the 'secret sauce' when it comes to Cameron amps. My Cameron modded amp was set close to 90%, and I wouldn't have changed a thing about that amp.

I definitely prefer the sound of the Jose with the tubes running hot and I have now had a set of wing C in the amp running at 90 % for nearly 5 months and they are still going strong and the amp still sounds ABSOLUTLEY F,ing incredible and I never get bored of playing it.
is it possible to have a 5 month honeymoon ?
I know 5 months is not really a true test of tubes lasting but if they last awhile longer I will definitely be more than happy with running them this hot

Here's a topic on biasing you may find interesting...

http://www.marshallforum.com/workbench/ ... rrent.html

 

[the grimbrewer]

catastrophic tube failure sucks and how often do you want to change tubes. Output transformers ain't cheap either. 500volts is pretty smoking for a 50 watter. 70% sounds safe to me

 

[H3000]

90% is obviously harder on the tubes, but if you've got a stout quad of glass - indulge! It would seem 90% is part of the 'secret sauce' when it comes to Cameron amps. My Cameron modded amp was set close to 90%, and I wouldn't have changed a thing about that amp.

I definitely prefer the sound of the Jose with the tubes running hot and I have now had a set of wing C in the amp running at 90 % for nearly 5 months and they are still going strong and the amp still sounds ABSOLUTLEY F,ing incredible and I never get bored of playing it.
is it possible to have a 5 month honeymoon ?
I know 5 months is not really a true test of tubes lasting but if they last awhile longer I will definitely be more than happy with running them this hot

Here's a topic on biasing you may find interesting...

http://www.marshallforum.com/workbench/ ... rrent.html

WOW ! thanks very much for pointing that out thats an awesome piece of info that REALLY explains a LOT

So in the past when I have been using a bias meter and used the 70 % rule I have actually been unknowingly just applying the calculation to plate dissipation ONLY because that is what the bias meter is actually doing . whereas cathode current which is what my bias meter measures is actually both plate and screen and the bias meter is missing out 8 watts from the screens in the calculation !
so Jon wilder is actually stating that 90 % when using a bias meter is actually ONLY 70 % of screen and plate and the 70 % rule is meant to be applied screen AND plate NOT just plate.

It would seem apparent from what Jon Wilder is saying that its crucial that this ONLY actually applies to when someone is using a bias meter that is measuring cathode current.
so 70% cathode current is for plate AND screens combined but my bias meter applies the 70% to plate only WTF !
I have been doing the 90% thing with my bias meter for quite awhile now and have done it with a few CCV and an aldrich and my Jose and it obviously works very safely and it sounds great and does NOT cause premature tube failure and I have been given numerous reassurances by my friend Dan gower in the past that it is safe to do this when measuring with my bias meter but after reading your link to Jon Wilder of Wilder Amplification it NOW makes sense to me as to WHY it works.
and if I correctly understand Jon wilders comments he is saying when I set my bias at 90% using my bias meter I am in fact only actually biasing my amp at 70% of screen and plate but my meter is telling me its 90% because its applying it to plate only.

 

[Equ1nox]

60-65%. It will depend on your plate voltage(s). Figure 32mA for EL34s. Nothing more unless you like more headroom and burning up tubes, I can tell you Marks amps are dirty and nasty and the need for headroom is not a prime requisite.

 

[H3000]

60-65%. It will depend on your plate voltage(s). Figure 32mA for EL34s. Nothing more unless you like more headroom and burning up tubes, I can tell you Marks amps are dirty and nasty and the need for headroom is not a prime requisite.

The point is it depends on HOW you are taking the readings.
From what I read re Jon wilders comments the 70 % rule holds true but NOT if using a bias meter as the bias meter is reading cathode current which is actually plate and screens combined so a reading that indicates 90 % MPD on a bias meter is ACTUALLY 70% MPD.

The Cathode current reading is plate and screen combined.
Plate 25watts + Screen 8watts = 33watts so when the formula for 70% MPD is applied to 25 watts per tube it shows as 90% but when you apply the formula to 33 watts which is what the cathode current reading us based off then its 70% MPD

And THAT would explain why when I got my first CCV=100 and slapped my bias meter on it to take a bias reading it showed me that it was biased at 90% MPD or so I mistakenly thought.
It showed that because after taking the reading of plate voltage and current I did the calculation based on 25 watts which would be fine if it was plate current but its not its cathode current... so when using a bias meter that takes a cathode current reading the calculation needs to be based on 33 watts .
THIS is the thread where Jon Wilder explains it. this was pointed out to me by Rig-Talk member TrueTone500
http://www.marshallforum.com/workbench/ ... rrent.html