I'm pondering about the input stage of my 813 SE project. I need some 50V RMS with low impedance on the 813 grid. Others seem to go the single stage with a high current pentode but I would like to have triodes only. So it has to have 2 stages.
Below is what I came up with after a couple of glasses white wine. I'm probably crazy but simulation shows good result, it can drive a load of 30k in parallel with 1000pF way beyond 20 kHz and 100Vpp. Power supply is +-200V.
Am I completely nuts, or?
Below is what I came up with after a couple of glasses white wine. I'm probably crazy but simulation shows good result, it can drive a load of 30k in parallel with 1000pF way beyond 20 kHz and 100Vpp. Power supply is +-200V.
Am I completely nuts, or?
An externally hosted image should be here but it was not working when we last tested it.
It's possible to get rid of the coupling cap to the 813 if I use -300-350V but that would complicate the power supply.
Getting rid of the other coupling cap is also possible but I would have to set the grid to +85V on V2B and this baby is asked to swing 100Vpp. So I would need more + voltage, say +300V.
That would set V2B to +300V plate and -80V cathode, a bit much for the poor tube
Lowering V1A plate to -88V would only move the coupling cap to the input.
Getting rid of the other coupling cap is also possible but I would have to set the grid to +85V on V2B and this baby is asked to swing 100Vpp. So I would need more + voltage, say +300V.
That would set V2B to +300V plate and -80V cathode, a bit much for the poor tube
Lowering V1A plate to -88V would only move the coupling cap to the input.
Power:
From my junk box, two 685VAC transformers for 900VDC, a lot of different chokes. Somewhere I have a couple of junk 350-0-350VAC transformers for the +-200V supply. 6SN7 needs a 6.3V biased to around -100V so may need an extra 6.3VAC.
Need: 10VAC 5A for each 813. Perhaps rewind a couple of 80VA toroids.
I'm thinking of letting Sowter wind me a couple of boatanchors for output. 8.5k primary, 8 ohm secondary, their P-sized core, it will handle 20W at 25Hz with 90mA DC. Same core can go to 20W at 20Hz if I reduce primary to 6.5k.
this project is definitely not for the newbies!
From my junk box, two 685VAC transformers for 900VDC, a lot of different chokes. Somewhere I have a couple of junk 350-0-350VAC transformers for the +-200V supply. 6SN7 needs a 6.3V biased to around -100V so may need an extra 6.3VAC.
Need: 10VAC 5A for each 813. Perhaps rewind a couple of 80VA toroids.
I'm thinking of letting Sowter wind me a couple of boatanchors for output. 8.5k primary, 8 ohm secondary, their P-sized core, it will handle 20W at 25Hz with 90mA DC. Same core can go to 20W at 20Hz if I reduce primary to 6.5k.
this project is definitely not for the newbies!
Hey-Hey!!!,
I have a small boy, and I am gathering parts for a U-L connected PP 813. Look to another industry specializing in protection. Toddlers and Firearms comes to mind. I am going for ~700 B+ and those top caps make me nervous too. I am thinking some sort of lock and key for the AC power supply and then still excercise caution. Let's see, maybe one of those cool key type switches the moovies always portray the Nuclear weapons with...
regards,
Douglas
As to voltage being lethal, when backed by a few uF of high quality capacitor, it is ridiculously unsafe at voltages usually associated with SE EL84's.
I have a small boy, and I am gathering parts for a U-L connected PP 813. Look to another industry specializing in protection. Toddlers and Firearms comes to mind. I am going for ~700 B+ and those top caps make me nervous too. I am thinking some sort of lock and key for the AC power supply and then still excercise caution. Let's see, maybe one of those cool key type switches the moovies always portray the Nuclear weapons with...
regards,
Douglas
As to voltage being lethal, when backed by a few uF of high quality capacitor, it is ridiculously unsafe at voltages usually associated with SE EL84's.
Hi all,
If any of you have photo's / schematics /stories...about or on the 813 I would love to put them up on my 813 page.
http://home.zonnet.nl/horneman/813.htm
Regards,
Bas
If any of you have photo's / schematics /stories...about or on the 813 I would love to put them up on my 813 page.
http://home.zonnet.nl/horneman/813.htm
Regards,
Bas
Sure, I will take pics you can grab from my gallery later.
These amps will become real boatanchors
About safety, 900V on the topcap is a little too unsafe if you have kids or pets. I have old rescued ceramic topcaps but the insulation isn't fully safe. A cage over the amp would be recommended. At least covering the 813's.
Using extra insulation sleeves over cables carrying >500V is also recommended if you have quality wires, else extra sleeves at >60V.
I'm still pondering over the driver stage, 1 stage or 2. With 1 stage I would need a triode with mu > 70 or a pentode. I think this could be done with a triode and a high Gm pentode in a mu follower, pentode being the upper load. ECL86 would perhaps be a good tube but the triode is exactly the same as 12AX7 and I think that is a tube which should not swing more than a few volts. ECL82 (6BM8) could perhaps do but the pentode is a bit low in the Gm department.
These amps will become real boatanchors
About safety, 900V on the topcap is a little too unsafe if you have kids or pets. I have old rescued ceramic topcaps but the insulation isn't fully safe. A cage over the amp would be recommended. At least covering the 813's.
Using extra insulation sleeves over cables carrying >500V is also recommended if you have quality wires, else extra sleeves at >60V.
I'm still pondering over the driver stage, 1 stage or 2. With 1 stage I would need a triode with mu > 70 or a pentode. I think this could be done with a triode and a high Gm pentode in a mu follower, pentode being the upper load. ECL86 would perhaps be a good tube but the triode is exactly the same as 12AX7 and I think that is a tube which should not swing more than a few volts. ECL82 (6BM8) could perhaps do but the pentode is a bit low in the Gm department.
PL802
Hello ,
PL802 triode strapped has mu of 70 and Ra of 2.2k . Don't know what the miller capacitance is like though , probably horrendous
They're cheap and may be worth a try . Pete Millet has some interesting results on his site regarding the distortion of these and various other high gm valves
data
...maybe worth a look ?
316a
Jax said:Sure, I will take pics you can grab from my gallery later.
These amps will become real boatanchors
About safety, 900V on the topcap is a little too unsafe if you have kids or pets. I have old rescued ceramic topcaps but the insulation isn't fully safe. A cage over the amp would be recommended. At least covering the 813's.
Using extra insulation sleeves over cables carrying >500V is also recommended if you have quality wires, else extra sleeves at >60V.
I'm still pondering over the driver stage, 1 stage or 2. With 1 stage I would need a triode with mu > 70 or a pentode. I think this could be done with a triode and a high Gm pentode in a mu follower, pentode being the upper load. ECL86 would perhaps be a good tube but the triode is exactly the same as 12AX7 and I think that is a tube which should not swing more than a few volts. ECL82 (6BM8) could perhaps do but the pentode is a bit low in the Gm department.
Hello ,
PL802 triode strapped has mu of 70 and Ra of 2.2k . Don't know what the miller capacitance is like though , probably horrendous
They're cheap and may be worth a try . Pete Millet has some interesting results on his site regarding the distortion of these and various other high gm valvesdata
...maybe worth a look ?
316a
Hey-Hey!!!,
On the front end, I think that if it is balanced input, a gain of 60-80 per side will be more than adequate. This includes IT step up too. Not too much NFB is in my plans.
Maybe use a low Rp beam tube set up in 50% tap U-L with a four coil IT. Maybe a 6CB5A, or 6JS6C in a 2-3x step down, or a pair of 2A3's, driven by a pair of 12A4's....so many ways to do this.
One thing is sure, direct coupled or tx coupled to avoid the low grid circuit R that is required of this valve. At very least, LC, with a nice CT grid choke....
And then there is the PS...Hg vapour, a six-pack of 5R4's, the choke input inductor is going to be a massive...Let's build it single chassis-stereo.
regards,
Douglas
On the front end, I think that if it is balanced input, a gain of 60-80 per side will be more than adequate. This includes IT step up too. Not too much NFB is in my plans.
Maybe use a low Rp beam tube set up in 50% tap U-L with a four coil IT. Maybe a 6CB5A, or 6JS6C in a 2-3x step down, or a pair of 2A3's, driven by a pair of 12A4's....so many ways to do this.
One thing is sure, direct coupled or tx coupled to avoid the low grid circuit R that is required of this valve. At very least, LC, with a nice CT grid choke....
And then there is the PS...Hg vapour, a six-pack of 5R4's, the choke input inductor is going to be a massive...Let's build it single chassis-stereo.
regards,
Douglas
Yes, but we´re talking some serious amps here!!
I think one 6S45 would make it as a single stage driver tube, at least i it is loaded by a choke or an IT. Same goes fo EC86.
Personally I´ll go for the much gruntier 6S19 since I want to drive the 813 grid into positive voltage.
Power supply will be a hybrid Gratez bridge configuration with 2 x 6AU4GTA and some silicon per channel.
Urg...
I was going for the Hammonds but based on the latest findings here on this very board my feet went cold.
Lundahl would end up at the same cost as the offer from Sowter but the latter is encapsulated at least.
Tis hobby ain't cheap.
I have not made up my mind yet. I aimed at 850V 90mA but could go with lower current.
I was going for the Hammonds but based on the latest findings here on this very board my feet went cold.
Lundahl would end up at the same cost as the offer from Sowter but the latter is encapsulated at least.
Tis hobby ain't cheap.
I have not made up my mind yet. I aimed at 850V 90mA but could go with lower current.
#11
Hi
This is my 813 SEamp,Wish to obtain your even more ideas £¬Thank ¡£
http://www.balstudio.com/813/813page1.htm
Hi
This is my 813 SEamp,Wish to obtain your even more ideas £¬Thank ¡£
http://www.balstudio.com/813/813page1.htm
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