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Old 12th May 2013, 12:35 PM   #13071
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by 6L6 View Post
Good.
.....
F5 Power up bias problem - help please!
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Old 23rd May 2013, 06:53 PM   #13072
Anchan is offline Anchan  United States
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Default capacitors

Hello,
I've got almost all the parts to build an F5. Actually, I am building Juma's variation... but posting here because many more eyes.
F5 with 2SK2013/2SJ313

My question is about limiting the bandwith. I am building this amp with a lot of spare parts that I already have, including a Vicor switching supply (pretty good one.) I also live about 200m from three AM radio antennas.

Now, I haven't had a ton of problems with other equipment that I built, but I would prefer to play it safe and limit the bandwith a bit.

I've seen posting on this thread of 1-3nF across the feedback resistors R5/R8, but it seems that was mostly to prevent overshoot, more than anything.

1) What size capacitors would someone recommend across the feedback resistors and/or the input jfets?

2) Is matching/ and or specific type of cap imperative?

Forgive me if this question has been asked here, but I could not find it with a search.

Thanks
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Old 24th May 2013, 07:57 AM   #13073
AndrewT is offline AndrewT  Scotland
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If the local AM RF power is a problem then I suggest you fit both differential and common mode attenuators.
I also suggest you use good RF screening chassis.
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Old 24th May 2013, 12:49 PM   #13074
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You can tune the F5 to broadcast into the 160 and 80 meter ham bands.
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Old 24th May 2013, 02:31 PM   #13075
6L6 is offline 6L6  United States
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Quote:
Originally Posted by Anchan View Post
1) What size capacitors would someone recommend across the feedback resistors and/or the input jfets?

2) Is matching/ and or specific type of cap imperative?
In the F5Turbo article Nelson suggests 1000pF (0.001uF) from gate (before the gatestopper resistor) to output, or across the feedback resistors. You can see them if the F5T article on the V3 schematic - http://www.firstwatt.com/pdf/art_f5_turbo.pdf

I have had fatal oscillation problems with the F5T -- that cap, in addition to 680R gatestoppers, solved it.

Don't worry about type of cap, whatever you have on hand will be fine.
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Old 24th May 2013, 09:31 PM   #13076
Anchan is offline Anchan  United States
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Thanks! It was hard for me to locate that information, but there it was!


Quote:
Originally Posted by 6L6 View Post
In the F5Turbo article Nelson suggests 1000pF (0.001uF) from gate (before the gatestopper resistor) to output, or across the feedback resistors. You can see them if the F5T article on the V3 schematic - http://www.firstwatt.com/pdf/art_f5_turbo.pdf

I have had fatal oscillation problems with the F5T -- that cap, in addition to 680R gatestoppers, solved it.

Don't worry about type of cap, whatever you have on hand will be fine.
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Old 27th May 2013, 05:51 PM   #13077
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Quote:
Originally Posted by Anchan View Post
.... I....live about 200m from three AM radio antennas.
This is outside the realm of your posting, but have you considered wearing copper boxer shorts, with a good grounding strap to your left shoe's soul?

...
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Old 28th May 2013, 08:48 PM   #13078
Itsmee is offline Itsmee  England
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Quote:
Originally Posted by Anchan View Post
I also live about 200m from three AM radio antennas.
Just build a BIG loop antenna and bury it in the garden, free power
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Old 28th May 2013, 10:03 PM   #13079
Anchan is offline Anchan  United States
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Quote:
Originally Posted by CanAm Man View Post
This is outside the realm of your posting, but have you considered wearing copper boxer shorts, with a good grounding strap to your left shoe's soul?

...
Already do that... but its always been more for style than anything else
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Old 28th May 2013, 10:06 PM   #13080
6L6 is offline 6L6  United States
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Lol!!
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