The turns ratio is only ~12.7, which is pretty low, what is the secondary commonly loaded with, 8 Ohms?
Probably a mistake, I would expect something on the order of 8K plate to plate.
Also I have had good results with 6P14P-EV running at up to 430V as long as you don't exceed plate or screen dissipation ratings. The JJ EL84 I have tried under these conditions red plated very quickly. Most Japanese and American designs from the early 1960s run the 6BQ5 and later 7189/A at well over 400V B+ (HH Scott, Fisher, Realistic amps I have looked at.) Dissipation also well beyond the design rating of the tube, they worked fine, but most modern replacements don't.
At lower voltages the amp will perform pretty poorly.
Roger Modjeski designed (and still makes) an EL84 amplifier that runs over 700V on the plates, screen voltage is quite low. The amp in question is this one:
http://www.ramlabs-musicreference.com/rm10mk2.html
It's been in continuous production for several decades, and actually sounds quite good - surprisingly the very high power claims are met in testing. (I tested one long ago)
http://www.ramlabs-musicreference.com/rm10mk2.html
Also I have had good results with 6P14P-EV running at up to 430V as long as you don't exceed plate or screen dissipation ratings. The JJ EL84 I have tried under these conditions red plated very quickly. Most Japanese and American designs from the early 1960s run the 6BQ5 and later 7189/A at well over 400V B+ (HH Scott, Fisher, Realistic amps I have looked at.) Dissipation also well beyond the design rating of the tube, they worked fine, but most modern replacements don't.
At lower voltages the amp will perform pretty poorly.
Roger Modjeski designed (and still makes) an EL84 amplifier that runs over 700V on the plates, screen voltage is quite low. The amp in question is this one:
http://www.ramlabs-musicreference.com/rm10mk2.html
It's been in continuous production for several decades, and actually sounds quite good - surprisingly the very high power claims are met in testing. (I tested one long ago)
http://www.ramlabs-musicreference.com/rm10mk2.html
Jaap: but proven design is one
In this monoblock after rectifers i placed a 1uf cap instead of both 33uf 75k 33uf 75K
then the two 330uf in series with the 2 x 75k
Need the primairie voltages for a new trafo and their mA
Any hint...?
the two 60v pin 2 and 5 are connected green wire
Have no idea of their mA nor function
Quote Rongon ...Is that Stingray amp really using a +420V plate supply for fixed bias EL84's? I'd think that would melt standard Russian 6P14P tubes.
....Yes i measured one myself cause did not believe it as well..
This monoblock looks built as the stingray has tw 12AT7 instead of one and a 6414...
Perhaps the JJ EL84 can work with that high a B+ and yield a reasonable service life.
I'd rather reduce the B+ to 325V or so, and have a wider variety of EL84 type tubes to choose from.
ECC81 = 12AT7. 15mA plate current would put it way over max plate dissipation. Are you sure it's supposed to take 12AT7?
35mA each EL84 at 320V plate-cathode looks exactly right.
.....Yes 12AT7 definitely two
....Yes i measured one myself cause did not believe it as well..
This monoblock looks built as the stingray has tw 12AT7 instead of one and a 6414...
Perhaps the JJ EL84 can work with that high a B+ and yield a reasonable service life.
I'd rather reduce the B+ to 325V or so, and have a wider variety of EL84 type tubes to choose from.
ECC81 = 12AT7. 15mA plate current would put it way over max plate dissipation. Are you sure it's supposed to take 12AT7?
35mA each EL84 at 320V plate-cathode looks exactly right.
.....Yes 12AT7 definitely two
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Has anyone looked at the output on Roger's amp at full power? Is there any crossover distortion?
In my Scott 299 I run the tubes at <20mA per tube. If Max keeps the voltage where it is I would at least maybe lower the bias a bit so it runs cooler.
From what was explained this amp seems to not sound good and is also is running extremely hot.
In my Scott 299 I run the tubes at <20mA per tube. If Max keeps the voltage where it is I would at least maybe lower the bias a bit so it runs cooler.
From what was explained this amp seems to not sound good and is also is running extremely hot.
Quiescent current would be measured across the 10R cathode resistor. e.g. Vk=350mV .350/10= 35mA
Deduct the screen current (3mA-5mA) and multiply by the plate voltage, that's your plate dissipation. You can figure out the actual screen current by measure the voltage across the 100R screen resistor.
Basically adjust the bias (-24v, make more negative) until you read 250mV across the 10R cathode resistor.
explain a little further
one monoblock is still running on a variac -180v- which give a Anode voltage of 356 v
I changed the resistors for the v of the 12AT7 so they are on the same voltage as before..
Problem is of course the bias voltage too low
On 356v the EL84 sounds much more musical - open and relaxed and is leaving me room to listen to music instead of a wall or mass of sound.....too unrefined and more like a blow or punch.
If i lower the variac can listen to the EL84 on a 330v as well for a short while only of course and on the 330V EL84 anode v. is musical as well
But need two new trafo's ( cause problably this one is alsoo little browned)
So try to figure out the primairie voltages and its mA's
and why on Pin 2 on pin 5 -see pic of trafo are there 60v ...mA its mA is .....could be....?
And there is only 13v for rectifiers of bias - to ask for f.e. 24 v directly Pin 3 and pin 4 primary side and a not known mA as well..
--Okay know now thanks can i take 2x 10mA as spec for the new trafo famousMB..?
one monoblock is still running on a variac -180v- which give a Anode voltage of 356 v
I changed the resistors for the v of the 12AT7 so they are on the same voltage as before..
Problem is of course the bias voltage too low
On 356v the EL84 sounds much more musical - open and relaxed and is leaving me room to listen to music instead of a wall or mass of sound.....too unrefined and more like a blow or punch.
If i lower the variac can listen to the EL84 on a 330v as well for a short while only of course and on the 330V EL84 anode v. is musical as well
But need two new trafo's ( cause problably this one is alsoo little browned)
So try to figure out the primairie voltages and its mA's
and why on Pin 2 on pin 5 -see pic of trafo are there 60v ...mA its mA is .....could be....?
And there is only 13v for rectifiers of bias - to ask for f.e. 24 v directly Pin 3 and pin 4 primary side and a not known mA as well..
--Okay know now thanks can i take 2x 10mA as spec for the new trafo famousMB..?
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Thanks - take that along good info -
but not possible now 250-300mV is needed but have to go to the original set up and am not gonna do it cause think will cause further damage
(Have been too hot as well -can see it - so have to be carefull not my own mono's and have one still playing so need to preserve)
Could alsoo be that previous owner had 4 ohm speakers so ....do not know its history but has been....
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With the amp off the variac you were getting 250mV-275mV at the cathodes. Can you increase the bias voltage to get 200mV? There is plenty of voltage there so you can always change around the resistors to get more bias voltage.
If you are set on lowering anode voltage then do it by means of secondary and not the variac on the primary. The variac is lowering your heater and bias voltages.
If you are set on lowering anode voltage then do it by means of secondary and not the variac on the primary. The variac is lowering your heater and bias voltages.
...yes the heather voltages are too low as well....need 2 new trafo's
cannot get 200mV on the cathodes now.... around 139mV 125 120 117 mV 4 El84
Any idea about the mA of the 2 60v --Pin 2 and Pin 5-- green wiring - primairy side ..? they are there but have no clue about there being
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+1, something is not quite right with the turns ratio.
Very good illustration of why the concern about the "high" anode voltage is over-blown, as long as the maximum anode dissipation isn't exceeded, the tubes should be fine.
@max29 - so your amp is like the Stingray, except it is cathode biased, correct?
the psu is very likely...and yes cathode biased
Difference:
Trafo itself: 155v and 175v on the primary side -Pin 1 and Pin 6 - instead of 315v on the Stingr. -
so did not measure two HT paralled at all .... maybe they were paralled but changed in the course of on-going over heating ..anyway 330v made the 440-430 anode voltage
Capacitors resitors: stingray shows : 330uf 75k 330uf 75k 330uF 75k 330uf 75 -i changed to 1uf paperinoil and 460uf 75 k 460uf 75k-.
this monobl. was when i got it here: 33uf 75k - 33uf 75k 330uf 75k 330uf 75K -i changed to...see above
think the stingray came much later then this one but the kept a lot of the overall layout and voltages...
Same bias v : both -24 and simular smoothing strategy after the 4 recties
Difference:
Trafo itself: 155v and 175v on the primary side -Pin 1 and Pin 6 - instead of 315v on the Stingr. -
so did not measure two HT paralled at all .... maybe they were paralled but changed in the course of on-going over heating ..anyway 330v made the 440-430 anode voltage
Capacitors resitors: stingray shows : 330uf 75k 330uf 75k 330uF 75k 330uf 75 -i changed to 1uf paperinoil and 460uf 75 k 460uf 75k-.
this monobl. was when i got it here: 33uf 75k - 33uf 75k 330uf 75k 330uf 75K -i changed to...see above
think the stingray came much later then this one but the kept a lot of the overall layout and voltages...
Same bias v : both -24 and simular smoothing strategy after the 4 recties
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there i need new trafo's - like to lower the anode voltage of the El84 as well -- (cause much more musical - not need/want power ..95db speakers he has - but refinement music openess more easy- relaxed way of listening so to say...)
For this way of producing music need to know (best ideal) anode voltage, heather v, bias voltage of the El 84's (as my second layer)
Can even change the voltage to the 1st and 2d 12AT7 cause...that might be a step further but any ideas and experience very welcome so we can share
For this way of producing music need to know (best ideal) anode voltage, heather v, bias voltage of the El 84's (as my second layer)
Can even change the voltage to the 1st and 2d 12AT7 cause...that might be a step further but any ideas and experience very welcome so we can share
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Sorry if you already stated but what is the EL84 cathode resistor value? I thought this was a fixed bias amp with current sense cathode resistors.
When you measured the secondary pins 1 and 6 why do you have two measurements(155, 175)? Did you measure each pin in reference to ground? You want to measure directly across pin 1 and 6. 155+175=330
When you measured the secondary pins 1 and 6 why do you have two measurements(155, 175)? Did you measure each pin in reference to ground? You want to measure directly across pin 1 and 6. 155+175=330
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A: 10ohm parralled with a 100uf
B: yes in reference to ground...not correct....?
each single measured
C: yes 330v both 155 & 175v
If go for 330-340 Anode v El84 need .....230 220 ...? Two of 115 or ....?
- Heathers have a own seperate line
- Bias has 2- Pin 3 and Pin 4 - now 13v very low - smoothing has to get it up a lot - ....prefer different.
F.e. take schottkey as recties and so leave the extreme spikes out
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The power tubes are running hot because their bias voltage is not negative enough.
Just turn the four bias trimpots to minimal and plug the amplifier in the wall.
Adjust your meter to one test point and adjust to 0,2V to start with. Do all four and play some music. If your EL84 are suitable there should be no red glow.
There still can exist some issues like shorted coupling caps, thats why you should do a few DC measurements.
Just turn the four bias trimpots to minimal and plug the amplifier in the wall.
Adjust your meter to one test point and adjust to 0,2V to start with. Do all four and play some music. If your EL84 are suitable there should be no red glow.
There still can exist some issues like shorted coupling caps, thats why you should do a few DC measurements.
An externally hosted image should be here but it was not working when we last tested it.
Your amp isn't cathode biased, it's fixed adjustable. i.e. You can make it as negative as you want to get the current through output tubes down, the amp will run cooler.
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