el84 driver tube, with less the 5ma current
hello people,
i'm refurbishing an old amp.
it is a push pull el84. it was completely down, so i kept only the trannies and the chassis.
the only problem: the power trannie puts out : 140vdc at 0.19a dc; in the original scheme there was a voltage doubler, so you end up with something like 320vdc (or a bit lower) at 90ma.
i need 80ma for the el84, left with 10ma for the drivers.
in the orignial scheme there were 5 * ecc83, each probably at 2ma.
but i don't wanna use the phono stage or the ecc83 as a driver. Can anybody help me on choising a decent driver that can live with 5mA per channel.
thanx a lot
greetings
hello people,
i'm refurbishing an old amp.
it is a push pull el84. it was completely down, so i kept only the trannies and the chassis.
the only problem: the power trannie puts out : 140vdc at 0.19a dc; in the original scheme there was a voltage doubler, so you end up with something like 320vdc (or a bit lower) at 90ma.
i need 80ma for the el84, left with 10ma for the drivers.
in the orignial scheme there were 5 * ecc83, each probably at 2ma.
but i don't wanna use the phono stage or the ecc83 as a driver. Can anybody help me on choising a decent driver that can live with 5mA per channel.
thanx a lot
greetings
well people, i don't think this problem has to be solved, but if it is, that is nice too;
i have this transfo, and i could not believe it was capable of putting out this small amount of Amps.
i have found an old "simple rule". it states the power of an transfo.
it says that
the height (in cm) of the iron plates * the width of the iron leg that goes into the windings : this number has to be taken to the power of 2 and then you have the power.
and then multiplied by 0.64.
in my case:
hight of the plates : 4cm
width of middle leg : 3 cm
(4*3)²*0.64 = 92watt.
having a
6v at 0.3 amp
6.3 at 4 amp
140v at ???? amp
the core will saturate at 140v with 0.463 Amp. which is a lot more then the 0.190 A which is written on it.
so i wonder: i have seen nice designs for a EL84PP, they use all sorts of drivers, but most of the time they need a bit more then a few mA, so even if this trannie is designed to give 140v at 190ma, how bad will it be to draw 220ma ?
i think a good measurment of the power rating of a trannie is the heat it is dissipating ?
am i a bit right on my thoughts ?
thanx
i have this transfo, and i could not believe it was capable of putting out this small amount of Amps.
i have found an old "simple rule". it states the power of an transfo.
it says that
the height (in cm) of the iron plates * the width of the iron leg that goes into the windings : this number has to be taken to the power of 2 and then you have the power.
and then multiplied by 0.64.
in my case:
hight of the plates : 4cm
width of middle leg : 3 cm
(4*3)²*0.64 = 92watt.
having a
6v at 0.3 amp
6.3 at 4 amp
140v at ???? amp
the core will saturate at 140v with 0.463 Amp. which is a lot more then the 0.190 A which is written on it.
so i wonder: i have seen nice designs for a EL84PP, they use all sorts of drivers, but most of the time they need a bit more then a few mA, so even if this trannie is designed to give 140v at 190ma, how bad will it be to draw 220ma ?
i think a good measurment of the power rating of a trannie is the heat it is dissipating ?
am i a bit right on my thoughts ?
thanx
Yes I would say this could be a very good way to go. This design gets the best out of small output transformers and delivers very convincing bass. The Gingertubes amp uses ECL86's which is OK because the ECL86 contains a derated EL84. The triode section is half of a ECC83, so you should be able to build a nice little amp with the valves you already have. The amp is called the "Baby Huey".
Shoog
hello,
i have red about baby huey,
still a few problems
1)i have old opt, so no ultralineair, it is gonna be triode or pentode;
2)maybe a bigger problem, the el84 are biased at 38ma, so i need around 160ma at 300v for this amp.
if i follow the instructions on the power trannie i can only get 95ma at 350V. (with a doubler). but that' is almost twice as much. maybe a tad to much.
could they be tammed down to 25ma ? or do i loose all the potential then ?
i have red about baby huey,
still a few problems
1)i have old opt, so no ultralineair, it is gonna be triode or pentode;
2)maybe a bigger problem, the el84 are biased at 38ma, so i need around 160ma at 300v for this amp.
if i follow the instructions on the power trannie i can only get 95ma at 350V. (with a doubler). but that' is almost twice as much. maybe a tad to much.
could they be tammed down to 25ma ? or do i loose all the potential then ?
dude,
If the original amp was PP EL84 the the power tranny will cope fine with the Baby Huey circuit. The fact that you will be using only 2 12AX7s (1 for each channel) instead of 5 means that you have 5.6 Watts less load on the heater winding and that will allow you to draw another 20mA or so from the High Voltage without any problems. As the Output Trannies do not have Ultralinear taps, you will probably be better off running the EL84s in Pentode mode and increasing the global feedback a bit. You could run Triode Mode without any global feedback but that will give only about 5 watts output compared with 15 watts in Pentode Mode.
Other designs to look at for inspiration / guidance are SY's "Red Light District" (EL84 PP Pentode Mode) and Eli's "El Cheapo" (Triode mode).
Both of these designs have been posted in this forum - do a search.
Cheers,
Ian
If the original amp was PP EL84 the the power tranny will cope fine with the Baby Huey circuit. The fact that you will be using only 2 12AX7s (1 for each channel) instead of 5 means that you have 5.6 Watts less load on the heater winding and that will allow you to draw another 20mA or so from the High Voltage without any problems. As the Output Trannies do not have Ultralinear taps, you will probably be better off running the EL84s in Pentode mode and increasing the global feedback a bit. You could run Triode Mode without any global feedback but that will give only about 5 watts output compared with 15 watts in Pentode Mode.
Other designs to look at for inspiration / guidance are SY's "Red Light District" (EL84 PP Pentode Mode) and Eli's "El Cheapo" (Triode mode).
Both of these designs have been posted in this forum - do a search.
Cheers,
Ian
gingertube said:
Oh, but what a sweet 5 W it can be.
Also Poindexter's Music Machine http://audiotropic.netfirms.com/Projects/machine1.html
dave
then_dude said:
Original amp did not used UL taps, the damping introduced by local feed back makes it superfluous.
http://www.dissident-audio.com/PP_ECL86/Page.html
300V at EL84 plates and screens is already quite high and your tranny does not seem to be able to deliver more than 27W, definitly too lo for 4 x EL84.
Also check for its ability to feed the heaters, near 4 amps at 6.3V.
Yves.
the orginial amp was an el84pp.
i can deliver 4 amps at 6.3v, and 0.3amp at 6v.
i'll give it a try. but i will need more then 20ma extra. the heat will be my guide; in these dark times.
so am i right by stating that the gobal power of the trannie may not be suprassed, but you can use the power that is not used on a winding for another ?
if so, maybe i'll buy a cheap 6.3 transformer, to take off the 6.3 windings.
i have looked already at all these designs,
1-the baby huey : a very nice scheme
2-the 6v6 poindexter machine (which is also a candidate cause it needs not a lot power for the heating, so i can use the extra power for the B+)
3-red district: looked at, looks nice: but just like all the designs: to much current on the B+ (but i'll try)
4-el cheapo.
maybe, i'll buy some power resistors, and hook them up, see what the power supply does. if it goes super hot, i know it is not for me. and will step back to a design with a less current draw.
thanx everybody
i can deliver 4 amps at 6.3v, and 0.3amp at 6v.
i'll give it a try. but i will need more then 20ma extra. the heat will be my guide; in these dark times.
so am i right by stating that the gobal power of the trannie may not be suprassed, but you can use the power that is not used on a winding for another ?
if so, maybe i'll buy a cheap 6.3 transformer, to take off the 6.3 windings.
i have looked already at all these designs,
1-the baby huey : a very nice scheme
2-the 6v6 poindexter machine (which is also a candidate cause it needs not a lot power for the heating, so i can use the extra power for the B+)
3-red district: looked at, looks nice: but just like all the designs: to much current on the B+ (but i'll try)
4-el cheapo.
maybe, i'll buy some power resistors, and hook them up, see what the power supply does. if it goes super hot, i know it is not for me. and will step back to a design with a less current draw.
thanx everybody
then_dude said:the orginial amp was an el84pp.
i can deliver 4 amps at 6.3v, and 0.3amp at 6v.
i'll give it a try. but i will need more then 20ma extra. the heat will be my guide; in these dark times.
so am i right by stating that the gobal power of the trannie may not be suprassed, but you can use the power that is not used on a winding for another ?
if so, maybe i'll buy a cheap 6.3 transformer, to take off the 6.3 windings.
<snip>
thanx everybody
Testing with load resistors is going to give you an optimistic result unless you rectify and filter ahead of the load resistors because of the sinusoidal load currents with resistors - the actual load is very non sinusoidal and has considerably higher pk currents and results in much more heating in the windings.
One thing to be aware of is whether or not the stated load current is AC or DC - post rectification. If DC then this particular issue goes away. (I probably need to re-read your earlier posts, but don't have much time now..)
Your assumption may not be a safe one, it will depend on how the transformer was originally specified, sometimes the dcr of the high V secondary will be too high to allow additional current to be drawn safely as it is not just the overall heating that counts, but the heating in individual windings and their thermal resistance to ambient. (You may be within the va rating of the transformer and still exceed the power an individual winding may safely provide - usually evidenced when the winding insulation fails and the winding shorts.) The above is a bit long winded.. Sorry..
How about a sweet little El84 SE amplifier using this transformer? In that case you can comfortably stay within the rating of the transformer. Do you need the additional power?
Good luck..
thanx a lot kevinkr,
i know that i cannot draw the complete power of the trannie out of the B+ line.
i'm a ware of it.
i have not got any power resistors lying around.
but i thought of something else. the original push pull puts out 40watt stereo: that means 10 watt for each el84. if that is at 300volt: it has to be at least 33ma per tube. not taken losses and preamp tubes, the trannie is capable of much more than written on it.
so the scheme of the push pull (a trio w-41) needs at least 150ma at 300v. while the trannie says: 190ma dc at 140v. strange.
can anyone help on this one ? is my calculation of mA correct from the 20 watt bassis ?
if so: the baby huey or the machine 6v6 are maybe my favorites. if it is a 10k opt then the 6v6 machine can be taken otherwise the baby huey looks the winner.
ps: i don't need to much power; i'm gonna put it after a full range fostex 93db. i think 5 watt should be enough, don't like loud music.
i know that i cannot draw the complete power of the trannie out of the B+ line.
i'm a ware of it.
i have not got any power resistors lying around.
but i thought of something else. the original push pull puts out 40watt stereo: that means 10 watt for each el84. if that is at 300volt: it has to be at least 33ma per tube. not taken losses and preamp tubes, the trannie is capable of much more than written on it.
so the scheme of the push pull (a trio w-41) needs at least 150ma at 300v. while the trannie says: 190ma dc at 140v. strange.
can anyone help on this one ? is my calculation of mA correct from the 20 watt bassis ?
if so: the baby huey or the machine 6v6 are maybe my favorites. if it is a 10k opt then the 6v6 machine can be taken otherwise the baby huey looks the winner.
ps: i don't need to much power; i'm gonna put it after a full range fostex 93db. i think 5 watt should be enough, don't like loud music.
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