This is a project that can be a great lesson learning opportunity.
After all, how hard can it be? Ha ha.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 10/10/19 4:08 PM, Jim Thomson wrote:
Date: Thu, 10 Oct 2019 11:38:25 -0400
From: Roger D Johnson <n1rj@roadrunner.com>
To: amps@contesting.com
Subject: Re: [Amps] Tips For Winding a Plate Choke
<A simpler alternative is to switch another choke in series for the lower
<frequencies. This is quite simple to do. Think of two chokes in series
<with a capacitor connected to the junction of the chokes. A relay grounds
<the other side of the cap on the high frequencies thereby effectively
<removing the lower choke from the circuit.
<73, Roger
## That trick was used by asi,,and its forerunner company.
50uh + 135uh. Both chokes used on 160m. 50uh choke used
on 80-10m.
## Both chokes in series cant be used on 80m...... u will get
fireworks and huge arcs across the junction point....and also
fried relay contacts.
## Buddy tried 135uh + 50 uh...and also 170uh + 50 uh.
Same deal, both in series can only be used on 160m only.
Since the HB amp was 160-15, final config was 135uh + 70 uh.
## One other important note, 3 x 1 megohm 3 watt mofs in series
are wired between relay contact and chassis. ... IE: cold end of cap.
THEN the junction cap
is in DC block mode. With the spst-NO mech relay energized, the
Cap is now RF grounded...as well as DC grounded Without the 3 x
megs in place, u will get
arcs across the open contacts when relay de-energized. Reason is cuz
of the leakage R across the cap.... even HEC HT-57 15 kv types.
## we tore our hair out trying to figure it out. In desperation, we
noticed
Alpha used the same 2 x choke config + junction cap...... but used
spare contacts on bandswitch
instead of a relay. Alpha used 3 x 1 meg, 1/2 watt Carbon comp
resistors in series.....wired in parallel with
contacts. Cold side of cap is dc grounded on low band....and RF + dc
grounded on high bands. So we ripped
off the alpha resistor concept..... which works.
## another method Is 2 x chokes, big and small.... with bottom of each
choke fed with B+. Bypass caps
at base of each choke. A spst vac relay with COM wired to anode. NC
wired to top of 1st choke.
NO wired to top of 2nd choke. Be careful with this config ! Vac
relay will have B+ plus peak RF voltage
on its contacts. When tube is driven full bore, the RF voltage
developed in the tank circuit is AC.....and will
backfeed through the plate block caps.....and superimpose itself onto
the anode. Total peak V will be a little
bit less than double the loaded B+ voltage. The advantage is.... each
choke can be optimized. IE: 200-300 uh
for 160+80m for choke one......... and 50uh for choke two. The
drawback is... the spst vac relay has to be able to
withstand the B+ and the rf peak voltage. RF voltage rating of vac
relays drops like a rock as freq increases.
## The ameritron choke....if u cant make it fit.... is the cheap and
easy way out....even if a few turns have to be
removed from the bottom...as in martins 30m band issue.
## 2 x ameritron chokes... WELL spaced apart..with separate B+ and
bypass caps at base of each choke.... and each top separately
wired to anode.... will also work. aluminum bar acrosss the tops of a
pair of 15 kv HEC bypass caps. Choke mounted on top side
of al bar...dead center. Used for amps that require up to 3A of
plate current. Then u can use 8 kv for B+.
Jim VE7RF
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|