I have several 8000 TUBES.
Has any one built an amp using the 8000?
Has amplification factor of 16.5
I hope to run them Push pull at about 800 volts.
Not sure best impedance transformer to use? I have a 5k Plate to plate 100 watts.
Has any one built an amp using the 8000?
Has amplification factor of 16.5
I hope to run them Push pull at about 800 volts.
Not sure best impedance transformer to use? I have a 5k Plate to plate 100 watts.
That's a sweet tube! It will be a pain to work with, but a rewarding pain at that.
It's a little more onerous than just using powerdrive, you need a directly coupled driver that can deal with grid current, but it also needs to swing below 0V.
800V/150mA will get those plates nice and hot.
The issue that you're going to have with something like this is that you'll run out of room on the positive swing pretty easily unless your load impedance is nice and high. 10K PP transformer should give you something useful, but your driver will have to swing from +80 to -80, with about 40mA of grid current peak at the +80 end and 0mA of grid current on the -80 end. Powerdrive can do this, as can a directly coupled cathode follower, just be sure there's a negative supply sitting under it so you can get what you need out of the driver. If you have to use the 5K transformer, you're going to be more on the B side of class AB.
Plan on using some feedback on this amp for sure! Look at the Altec 811 push-pull for some visual assistance. Plate to plate feedback from 8000 to the tube behind the grid driver is a nice option that doesn't get all wacky from OPT phase shift.
A cathode feedback winding is worth considering. You're going to need an output transformer wound for high voltage anyway, so what's an extra winding at that point.
As always, GNFB from speaker out to driver will get you some help too.
This will be a very powerful push-pull amp, I would recommend having your winder use the largest core they have. If you don't need the power, you could always go SE 🙂
It's a little more onerous than just using powerdrive, you need a directly coupled driver that can deal with grid current, but it also needs to swing below 0V.
800V/150mA will get those plates nice and hot.
The issue that you're going to have with something like this is that you'll run out of room on the positive swing pretty easily unless your load impedance is nice and high. 10K PP transformer should give you something useful, but your driver will have to swing from +80 to -80, with about 40mA of grid current peak at the +80 end and 0mA of grid current on the -80 end. Powerdrive can do this, as can a directly coupled cathode follower, just be sure there's a negative supply sitting under it so you can get what you need out of the driver. If you have to use the 5K transformer, you're going to be more on the B side of class AB.
Plan on using some feedback on this amp for sure! Look at the Altec 811 push-pull for some visual assistance. Plate to plate feedback from 8000 to the tube behind the grid driver is a nice option that doesn't get all wacky from OPT phase shift.
A cathode feedback winding is worth considering. You're going to need an output transformer wound for high voltage anyway, so what's an extra winding at that point.
As always, GNFB from speaker out to driver will get you some help too.
This will be a very powerful push-pull amp, I would recommend having your winder use the largest core they have. If you don't need the power, you could always go SE 🙂
5K plate to plate is low. 10K is better and 15K -20K is even better but hard to wind with wide bandwidth. This tube is basically a bigger brother to the 211 tube, they are similar in operating points... The 211 is probably a bit more linear because of the way the electrodes are spaced in relation to each other. The tube will work better at over 1000v B+, like the 211.
GM70 may be a better tube for the operating conditions you want to use and they can be bought relatively cheap still.
GM70 may be a better tube for the operating conditions you want to use and they can be bought relatively cheap still.
It is not too shabby in SE A1, _if_ you can wind 23K with audio bandwidth suitable to a monster build.
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8000
Thanks all for the advise;
I will get 10k out transformers, what current would be needed?
I have built several 811A pp amplifiers using the Grampian circuit record cutting amp, never tried the Altec but have the circuit. The Grampian 811A uses 2.5k output transformer I have an original c core output transformer from a Grampian C core 9 kilo’s
Recently, I bought some GM70’s and sockets need to get the power transformers and push pull out put transformers.
Would the Tube Labs mosfet drive work with the 8000; I have never tried it with the 811 amps the 6bl7 with 600 volts works well, so easy to make. Would a negative supply for the 6BL7 work?
Phil
Thanks all for the advise;
I will get 10k out transformers, what current would be needed?
I have built several 811A pp amplifiers using the Grampian circuit record cutting amp, never tried the Altec but have the circuit. The Grampian 811A uses 2.5k output transformer I have an original c core output transformer from a Grampian C core 9 kilo’s
Recently, I bought some GM70’s and sockets need to get the power transformers and push pull out put transformers.
Would the Tube Labs mosfet drive work with the 8000; I have never tried it with the 811 amps the 6bl7 with 600 volts works well, so easy to make. Would a negative supply for the 6BL7 work?
Phil
Attachments
The DC current rating isn't as big of a deal as the power handling and bandwidth. I'd be looking at 100W rated transformers with a much HF bandwidth as you can get.
A 6BL7 cathode follower directly coupled to the grid of the 8000 will work nicely.
A 6BL7 cathode follower directly coupled to the grid of the 8000 will work nicely.
Thanks audiowize
I was going to order a 100 watt toriod from Toriody in Poland they work very well used in the 811A and KT88 amps. He always wants to know the max current draw.
Thanks Phil
I was going to order a 100 watt toriod from Toriody in Poland they work very well used in the 811A and KT88 amps. He always wants to know the max current draw.
Thanks Phil
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