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 5th November 2008, 06:07 PM #21 Banned   Join Date: Sep 2005 Kevin, Yes, with the 211 the voltage gain and swing since to be ok Using the 845: Ri=1700 u=5.3 with 11K5 (LL1620 con.B) we have Rout=1700/(38*38)=1.2ohm good to drive any loudspeakers to get 10Vrms on 8ohm (Pout=10*10/8=13w) you need Vg=10*38/5.3=72v Using the 211: Ri=3800 u=12 with 11K5 (LL1620 con.B) we have Rout=3800/(38*38)=2.6 too high to drive normal loudspeakers with 23K(LL9202 con.B) we have Rout=3800/(53*53)=1.35ohm to get 10Vrms on 8ohm (Pout=10*10/8=13w) you need Vg=10*53/12=44v but the 211 at 530Vrms on anode will be linear like the 845 at 380Vrms ? Probably it is true using the 211 and 23K transf. at higher plate voltage near 1200v With a 23K the bias current necessary is low so only 60mA will be enougth So is true that the 211 give less problem as input swing but it need higher power supply voltage to get same power and this mean more difficult to find good components with 1500Vdc like the capacitors. For a more precisious calculation add internal resistance of transformers (prim. and sec.).
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Join Date: May 2007
Hi,
Maybe this is a little far out, but why not make a Lundahl transformer coping with more current by adding an opposite current through the secondary? This to get rid of the capacitor and still get enough inductance. If 4:3,5 doesn´t give enough gain, one could go 3,5:4.
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 5th November 2008, 06:40 PM #23 Banned   Join Date: Sep 2005 Using the 6HV5A is very difficult use interstage transformers because these need an inductance value about 100H and 25-30ma of dc current
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Quote:
 Originally posted by audiodesign Kevin, Yes, with the 211 the voltage gain and swing since to be ok Using the 845: Ri=1700 u=5.3 with 11K5 (LL1620 con.B) we have Rout=1700/(38*38)=1.2ohm good to drive any loudspeakers to get 10Vrms on 8ohm (Pout=10*10/8=13w) you need Vg=10*38/5.3=72v Using the 211: Ri=3800 u=12 with 11K5 (LL1620 con.B) we have Rout=3800/(38*38)=2.6 too high to drive normal loudspeakers with 23K(LL9202 con.B) we have Rout=3800/(53*53)=1.35ohm to get 10Vrms on 8ohm (Pout=10*10/8=13w) you need Vg=10*53/12=44v but the 211 at 530Vrms on anode will be linear like the 845 at 380Vrms ? Probably it is true using the 211 and 23K transf. at higher plate voltage near 1200v With a 23K the bias current necessary is low so only 60mA will be enougth So is true that the 211 give less problem as input swing but it need higher power supply voltage to get same power and this mean more difficult to find good components with 1500Vdc like the capacitors. For a more precisious calculation add internal resistance of transformers (prim. and sec.).
Good analysis, and I actually need the higher source impedance because of the way my speakers were designed.. Will probably run something like 12K opts. I plan to run at something like 1.1 - 1.2KV in all likelihood and have access to the high voltage components required.
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 5th November 2008, 06:58 PM #25 Banned   Join Date: Sep 2005 Paolo, the 6HV5A have low microphonic effect if I tapping the bulb, I can hear a little tic on speaker but very low
 5th November 2008, 07:05 PM #26 diyAudio Member     Join Date: Jun 2004 Location: big smoke I found the 6HV5A eats voltage and really starts singing over 1kV. __________________ Ears aren't microphones.
 5th November 2008, 07:11 PM #27 diyAudio Member     Join Date: Feb 2005 Location: roma Hi Andrea, as I mentioned you, the best result I got is with 6H30, parallel ( are easy to select for similar sections), with a Tango NC20 interstage at 20 mA of Ia; the swing is 185 Vrms/530 Vpp ( at less than 2% of distortion. The Va is about 250 Vdc. I am close to the limit but the tube is really strong. Another tests http://www.multitask.it/845/1403-1Kh...15vin-nc20.jpg at this addres there is a FFt with 6BX7 and NC20 (another test) with 20mA at 1KHz, 3% THD; Vout about 130 vrms. at 20 hz the result is good. http://www.multitask.it/845/1403-1Khz-50mA-nc20.jpg at this link there is a FFT with the same setting but with 50mA of Ia; the 3% of THD is at 150 Vrm at 1KHz, but at 20 hz it is very bad. http://www.multitask.it/845/1403-1Kh...-5vin-nc20.jpg athis link is the same circuit with 20mA of Ia , 5 Vin, 40 Vout, 1 KHz; the IIIrd is low. Bye Walter
 5th November 2008, 07:12 PM #28 diyAudio Member   Join Date: Aug 2004 Location: Italy Oh very thanks Andrea, a precious information ! Cheers, Paolo
 5th November 2008, 07:19 PM #29 Banned   Join Date: Sep 2005 Walter, 6H30 or many other tubes have no enougth voltage gain to create a real two stages amp. You probably use the amp with a pre-ampl so this mean 3 stages.
 5th November 2008, 07:41 PM #30 diyAudio Member     Join Date: Feb 2005 Location: roma Andrea, if you use the Sowter 8540, 1:4; loaded with 50k you have 3K of input impedance; this will help. This means that with a G of 8 with 6H30 ( I have to check on my notes), with a Vin 2 volt (normally output for a preamp) we have 8 volt on input of 6H30 and 64 volt at the ouput of this stage. Bye Walter

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