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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Your bypass C's posted by drlowmu on April 11, 2007 at 07:33:24:
"220 uF across 750 ohms is .96 HZ !! Unnecessary."The -3db point of that stage is 1.13hz so that stage will be flat down to 11.3hz (a first order filter needs a decade from the -3db point to get back to flat). Designing for 8hz will leave you with a response that is not flat until 80hz.
The formula is, bypass cap value in uf = 1000000/ 6.28 * F3 * r
r = (RK * rk) / (RK + rk)
rk = (RL + RP) / (mu + 1)
RK = value of cathode resistor
RP = plate resistance of tube
RL = value of plate resistor
Mu = Mu of tube
F3 = the 3db down point of the filter"I'd do about a 25 uF high quality film cap across the 750 ohm input stage's Rk,"
That will leave him with an response that does not reach flat until
110hz."and a 8-10 uF high quality film cap across the 2A3 stage's 3,200 ohm Rk."
A 10uf cathode resistor bypass cap will leave the output stage not reaching flat until 300hz.
"Normally, seek to obtain under 8 HZ, in the 4-8 HZ range is OK,"
As I said, if the filter has a -3db point of 8hz the circuit will not be flat until 80hz.
Tre'
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Follow Ups
- Re: Your bypass C's - Tre' 14:25:06 04/11/07 (11)
- Re: Your bypass C's - dave slagle 06:29:43 04/12/07 (9)
- Re: Your bypass C's - Tre' 09:51:58 04/12/07 (8)
- Re: Your bypass C's - dave slagle 10:29:50 04/12/07 (3)
- Re: Your bypass C's - mqracing 10:45:47 04/12/07 (2)
- also consider.... - mqracing 10:51:25 04/12/07 (1)
- Re: also consider.... - drlowmu 13:48:58 04/12/07 (0)
- Re: Your bypass C's - mqracing 10:28:34 04/12/07 (3)
- Re: Your bypass C's - Tre' 18:01:48 04/12/07 (2)
- Re: Your bypass C's - mqracing 18:37:42 04/12/07 (1)
- My bad - Tre' 19:11:32 04/12/07 (0)
- Re: Your bypass C's - drlowmu 16:02:33 04/11/07 (0)
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