If you look at a few commercial ham amp designs you can see where they
skimped on the choke and bypassing. Ive been harping for years that the
primary cause of blown electrolytics in many amps is from RF coming
right down the B+ lead.
The MLA-2500, Clipperton L, DTR-2000, etc uses only 500pf as a bypass
for crying out loud! No wonder they blow filters and transformers. Add
a .0047 or .01 and do the job right. 160/80M output goes up as well.
Ive run a Clipperton xfmr at well over 1500W with no smoke in my 432
amp. The customer insisted on a Dahl so I got the original cheap.
Any amp covering 160-10 should have at least a .0047 added in parallel
with whatever is there.
Carl
KM1H
----- Original Message -----
From: "Edward Swynar" <gswynar@durham.net>
To: <garyschafer@comcast.net>; <amps@contesting.com>
Sent: Thursday, February 26, 2009 11:06 AM
Subject: Re: [Amps] Minimum Value of RF Plate Chokes
> On 26th February, Gary wrote:
>
> "...Seems that with a small choke (small inductance for the frequency)
> the
> choke is actually tuned to resonance when its reactance is a low value
> compared to load impedance.
> If the choke is too small for that band add extra input capacitance to
> the
> tuned input network on the tube side to resonate the choke..."
>
> *******************************
>
> Hi Gary,
>
> Many thanks for that FB explanation...however, in as much as it might
> make
> sense to me, I STILL can't get past the notion in my head that I
> always
> believed that a choke should be, essentially, "invisible" to the rest
> of the
> circuitry that might accompany it...
>
> By effectively changing the circuit values in a tank circuit to
> accommodate
> a less-than-perfect choke, what is the fall-out going to be to the
> operating
> parameters of the tube...? After all, we are now CHANGING computed
> values
> for specific "Q" in the tank components, to make-up for the
> shortcomings of
> the choke --- correct?
>
> Also, what would happen when the final tank circuit is off-resonance
> slightly --- will RF end-up back into the power supply?
>
> Again, I may well be missing something critical here, but by having to
> go
> through all these "gymnastics" in the values of the other parts of the
> pi-tank system, it is very obvious that the presence of a
> "sub-standard"
> choke is hardly "invisible" in the whole scheme of things, and it
> seems to
> fly in the face of a properly-designed final pi-tank network, on a
> given
> band...
>
> Help me here...!
>
> ~73~ Eddy VE3CUI - VE3XZ
>
>
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