Hello kooltubes, glad to hear it worked first time. That's one of the nice things about a long-tailed pair with CCS tail, you can adjust the operating point so easily...
Gday.
I`ve been reading up on that amp. to,
and find it very interesting.
Schematic plz. kooltubes.🙂
I`ve been reading up on that amp. to,
and find it very interesting.
Schematic plz. kooltubes.🙂
Hello Mark_titano and GeirW,
I've first built the Bevoy valley amp (schematic in Morgan jones book) Ecc88 (input) Ecc88 (concertina phase inverter) + traditional PP EL84... I couldn't fit the choke on the recycled chassis, for lack of space.
I didn't like the sound and got rid of the input stage and phase inverter and replaced them with a simple differential input/driver using ECC99 biased at 21ma per tube using, a CCS, courtesy of EC8010; the schematic is somewhere in the previous pages of this thread.
The anode resistors are 14.7k (for better or worse)😕
As it is I am still experimenting with the CSS to find the best operating point that would suit my taste.
I am a newbie like you, and still at kindergarden 😀
IMHO, the differential input/driver sounds much better than the concertina; meaning it has more substance.
I cannot take any credit for the design; this amp being some other people's original ideas...but I will keep you posted!
Cheers
I've first built the Bevoy valley amp (schematic in Morgan jones book) Ecc88 (input) Ecc88 (concertina phase inverter) + traditional PP EL84... I couldn't fit the choke on the recycled chassis, for lack of space.
I didn't like the sound and got rid of the input stage and phase inverter and replaced them with a simple differential input/driver using ECC99 biased at 21ma per tube using, a CCS, courtesy of EC8010; the schematic is somewhere in the previous pages of this thread.
The anode resistors are 14.7k (for better or worse)😕
As it is I am still experimenting with the CSS to find the best operating point that would suit my taste.
I am a newbie like you, and still at kindergarden 😀
IMHO, the differential input/driver sounds much better than the concertina; meaning it has more substance.
I cannot take any credit for the design; this amp being some other people's original ideas...but I will keep you posted!
Cheers
kooltubes said:
Hi kooltubes...maybe this discussion can help you 😀
http://db.audioasylum.com/cgi/m.mpl?forum=tubediy&n=43611&highlight=ccs&r=&session=
Good design...or not?
Mark
Hi mark_titano,
The circuit seems to be easy to implement in any EL84 PP amp; why don't you build it and tell us how it sounds🙂
The circuit seems to be easy to implement in any EL84 PP amp; why don't you build it and tell us how it sounds🙂
Because I will built this one 😀
http://www.vacuumstate.com/images/PP-1C.gif
I'm waiting for the output transformers...lundhal 1682PP
Mark
http://www.vacuumstate.com/images/PP-1C.gif
I'm waiting for the output transformers...lundhal 1682PP
Mark
kooltubes said:
That's a tricky question. If you don't, then the output stage tends to act like a differential pair and is self-balancing (only to a very limited extent because of the low value of the tail resistor). Unfortunately, when you go into Class B and one valve switches off, an unbiased shared cathode resistor causes increased distortion. If you replace the shared resistor with a CCS, the output stage only works sensibly in Class A. Typically, the first 5W of a push-pull EL84 is in Class A, and the rest is in Class B.
I'd bypass the resistor.
Thanks
The output stage is triode connected with a common cathode resistor which is bypassed at this moment.
I will build a pair of your CCS to experiment on the output stage as well.
Cheers
The output stage is triode connected with a common cathode resistor which is bypassed at this moment.
I will build a pair of your CCS to experiment on the output stage as well.
Cheers
I assume you mean a stereo pair, you only want one per output stage. The upper transistor will need to be beefier.
EL84 PP triode-connected
Hello,
I have got a biasing issue with the EL84 triode-connected in push pull
The output transformer is 9K
The data sheets do not seem to agree on the bias current for the EL84 triode-connected in push pull driven in class A.
What is the correct value? 48ma or 72 ma? Is it a shared cathode resistor?
Mullard suggest a 150R common unbypassed cathode resistor for a 10K output transformer. My transformer is 9K, how do I calculate the cathode resistor?
I am getting confused there but it's part of the fun.
For those interested in a DC coupled amp have a look at this:
http://www.wdehaan.demon.nl/el84dc.html
Cheers
Hello,
I have got a biasing issue with the EL84 triode-connected in push pull
The output transformer is 9K
The data sheets do not seem to agree on the bias current for the EL84 triode-connected in push pull driven in class A.
What is the correct value? 48ma or 72 ma? Is it a shared cathode resistor?
Mullard suggest a 150R common unbypassed cathode resistor for a 10K output transformer. My transformer is 9K, how do I calculate the cathode resistor?
I am getting confused there but it's part of the fun.
For those interested in a DC coupled amp have a look at this:
http://www.wdehaan.demon.nl/el84dc.html
Cheers
Re: EL84 PP triode-connected
That is cool... i've been thinking of something like that, but Class A and with a lower B+ (based on available iron))... i have a ton of ECC85s, be nice to use some up.
dave
kooltubes said:
That is cool... i've been thinking of something like that, but Class A and with a lower B+ (based on available iron))... i have a ton of ECC85s, be nice to use some up.
dave
Optimal idle current depends on the B+ and the plate to plate load. The RCA Tube Manual gives a great explanation of how-to-do-it.
SY said:
I finally found a copy of that (50 cents 🙂) and just read that section (and will have to read a few more times and then get out my triode connected EL84 curves)... info i've seen no-where else.
dave
Thanks Sy,
I have that book and never knew all I need was there. Now that I have learned to draw loadlines for output stage, I guess it's real fun!
Triode connected EL84, push pull; Output TX: 9K, tubes are biased @ 23 ma; I am using a shared bypassed cathode resistor.
BTW, what is the simple way to balance the voltages on the ECC99 differential input using EC8010 CCS design?
I have about 3 volts difference between the anode, since the grounded grid triode is fed from the input triode.
Cheers
I have that book and never knew all I need was there. Now that I have learned to draw loadlines for output stage, I guess it's real fun!
Triode connected EL84, push pull; Output TX: 9K, tubes are biased @ 23 ma; I am using a shared bypassed cathode resistor.
BTW, what is the simple way to balance the voltages on the ECC99 differential input using EC8010 CCS design?
I have about 3 volts difference between the anode, since the grounded grid triode is fed from the input triode.
Cheers
I need help... 
I think that I will go for one of these designs:
http://www.wdehaan.demon.nl/mono/mono/el84dc.html
http://www.artimusica.nl/wim/dc_coupled_amp.pdf
The question is...which one? The one that uses the ecc85+half ecc88 as constant current source seems pretty good, simple, provides a good stability and is easy to adjust (designer's words...).
I don't know the ecc85 at all, any feedback? Are they a good solution in a long-tailed pair driver stage?
Ouput transformers: suitable transformers are Amplimo VDV 8020, Hammond 1608, 1650f, some Sowters ecc. The schematic shows the amlimo but I'll buy an hammond 1608 because I want to spend not so much for this first attempt. The 1608 has 4-8-16 ohm taps, while the amplimo has only 5 ohm. Which tap must I use for the negative feedback with the hammond?
Power supply...with that design I'll go for dual mono amp, because seems good only for this purpose. I'm wrong? 🙂
Mark
I think that I will go for one of these designs:
http://www.wdehaan.demon.nl/mono/mono/el84dc.html
http://www.artimusica.nl/wim/dc_coupled_amp.pdf
The question is...which one? The one that uses the ecc85+half ecc88 as constant current source seems pretty good, simple, provides a good stability and is easy to adjust (designer's words...).
I don't know the ecc85 at all, any feedback? Are they a good solution in a long-tailed pair driver stage?
Ouput transformers: suitable transformers are Amplimo VDV 8020, Hammond 1608, 1650f, some Sowters ecc. The schematic shows the amlimo but I'll buy an hammond 1608 because I want to spend not so much for this first attempt. The 1608 has 4-8-16 ohm taps, while the amplimo has only 5 ohm. Which tap must I use for the negative feedback with the hammond?
Power supply...with that design I'll go for dual mono amp, because seems good only for this purpose. I'm wrong? 🙂
Mark
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