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Re: [Amps] Henry 2K-3 PS Mod

To: "Kevin LaHaie" <>, <>
Subject: Re: [Amps] Henry 2K-3 PS Mod
From: "jeremy-ca" <>
Date: Fri, 21 Mar 2008 17:53:03 -0400
List-post: <">>
----- Original Message ----- 
From: "Kevin LaHaie" <>
To: <>
Sent: Friday, March 21, 2008 3:37 PM
Subject: [Amps] Henry 2K-3 PS Mod

> Hello
> I am planning to convert the stock P/S in my Henry 2K-3 to a purely
> capacitor filter primarily to increase the HV, but in addition some way
> that capacitor filters are better for SSB.

I have no idea where you ever got that idea. Capacitor filters do one thing 
and that is cost less to manufacture.

My other, newer Henry's (2K
> Classic X and 3K Classic X Mark II) still use the choke filter design,
> albeit with higher voltages, and never had a complaint!
> My current plan, after reviewing the supply, would be to merely removing
> the choke, and the .1uf 7500v resonating capacitor across it, to provide
> a standard capacitor filter.  The stock capacitor is an oil filled 20uf
> unit rated at 5000v.  The stock bleeders are 3, 20k 100 watters in
> series across the output.

The bleeders set a minimum current draw when the amp is in standby and 
permit the choke to provide a critical inductance to keep the HV from 
soaring.  That is a part of the excellent voltage regulation of the amp.

> I am seeking 4 pieces of advice
> 1. What changes to the biasing is necessary with the higher plate voltage

None probably, there will be a slightly higher idle current but in SSB or CW 
service the difference in dissipation is meaningless.

> 2. Is there enough 'headroom' with the 5kv rated cap, or should I use a
> higher voltage rating.  Never a bad idea, but curious if it's too close
> to max HV.

More than enough headroom.

> 3. Is 60kohms too little resistance for the bleeder in the capacitor
> filter design? I would like to 'cool down' the heat the amp makes at
> idle, and without the bleeders playing a big part in the regulation
> aspect of a choke filter, perhaps this value could be increased?

The sole purpose will then be to bleed off the HV when the amp is shut off. 
Something around 250-500K would be a good compromise between dissipation and 
discharge time. If you go too high then high value caps will recharge on 
their own and you could get a nasty surprise.

> 4. I have read that it's good practice to place a high value composition
> resistor across the wirewounds in case they open as a backup to bleed
> the cap.  What value would be recommended?

I cant envision any value carbon comp being used. First they are not rated 
for 3500V, second do the math for wattage required at any value that would 
accomplish anything.

> Thanks, any opinions?

Yes, leave it alone. Unless you use a very high value of C the regulation 
will suffer and so will your SSB signal. You will also have a higher AC 
ripple on your signal with just 20 uF which may or may not be audible.

Id also suggest measuring the DC resistance of the xfmr secondary and see if 
it is even suitable for a fat C only. For some reason I dont have it noted 
in my manual.

Also the comment about instability is a very real issue with that amp.


> 73 Kevin K7ZS
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