Plate blocking cap in Alpha 76PA
|
I am doing some updating to my Alpha 76PA 3-tube amplifier.? I have switched the T/R relay to a pair of vacuum relays and changed the "relay" (AKA Send or PTT) request to send from 24 Volts to be a compatible 12 Volts for modern transceivers.? I am about to replace the original Alpha Plate Choke with a re-wound Ameritron style taller choke.
While I'm at it I have a, new-but old, Cera-Mite 5000 PF, 15 KV door-knob capacitor.? I'm planning to replace the original plate blocking capacitors with this door knob cap.? The original plate blocking cap uses dual original 2000 PF, 6 KV ceramic disk capacitors.
?
?
I've has this door knob cap a long time and I'm no longer planning on building a tube amplifier from scratch.? As you can see I've fabricated two copper straps to place the cap in the 76pa amp.? I fabricated these straps to put to door knob cap into a previous Alpha 76PA I had.? And when fastened in place it is quite sturdy and has adequate clearance from its surroundings.
?
This amplifier will be kept in my station as a back-up for my Solid State PA.? I've found SSPAs to be less tolerant of operator errors than tube amps.? But I still like the instant on and 6 meter capability in my current SSPA (403A/Flex PGXL).
What are your thoughts on this replacement other than it is overkill in this situation?
?
73,
Dave, w6de
|
开云体育Regarding replacing the plate blocking caps….if it ain’t broke, don’t fix it.? ? I blew up one of those red plate blockers by Ceramite.? It turns out that they are not rated for significant RF current, so… ? Keep the original caps would be my suggestion… ? -Chuck K1KW ? From: [email protected] [mailto:[email protected]] On Behalf Of Dave w6de
Sent: Wednesday, May 07, 2025 12:26 AM To: [email protected] Subject: [ham-amplifiers] Plate blocking cap in Alpha 76PA ? I am doing some updating to my Alpha 76PA 3-tube amplifier.? I have switched the T/R relay to a pair of vacuum relays and changed the "relay" (AKA Send or PTT) request to send from 24 Volts to be a compatible 12 Volts for modern transceivers.? I am about to replace the original Alpha Plate Choke with a re-wound Ameritron style taller choke. While I'm at it I have a, new-but old, Cera-Mite 5000 PF, 15 KV door-knob capacitor.? I'm planning to replace the original plate blocking capacitors with this door knob cap.? The original plate blocking cap uses dual original 2000 PF, 6 KV ceramic disk capacitors. ? ? I've has this door knob cap a long time and I'm no longer planning on building a tube amplifier from scratch.? As you can see I've fabricated two copper straps to place the cap in the 76pa amp.? I fabricated these straps to put to door knob cap into a previous Alpha 76PA I had.? And when fastened in place it is quite sturdy and has adequate clearance from its surroundings. ? This amplifier will be kept in my station as a back-up for my Solid State PA.? I've found SSPAs to be less tolerant of operator errors than tube amps.? But I still like the instant on and 6 meter capability in my current SSPA (403A/Flex PGXL). What are your thoughts on this replacement other than it is overkill in this situation? ? 73, Dave, w6de |
开云体育Dear Dave, ? The ‘PA makes a great project amp. ? I went with dual 3CPX800A7’s and slammed together an outboard power supply. The power supply was way heavier than the RF head. ? I replaced the blocker with a single HT58 ceramic doorknob and put in a new plate choke with a tinier heavier wire gauge and a doorknob at the bottom. ? ? Hal W4HBM |
开云体育Same here, used exactly the same type to get more capacitance on 160m as a HT bypass capacitor It exploded after a few minutes. I assume those capacitors are not suitable for RF. ? 73 Peter, DJ7WW ? ? From:
[email protected] [mailto:[email protected]] On Behalf Of Chuck Neal via groups.io ? Regarding replacing the plate blocking caps….if it ain’t broke, don’t fix it.? ? I blew up one of those red plate blockers by Ceramite.? It turns out that they are not rated for significant RF current, so… ? Keep the original caps would be my suggestion… ? -Chuck K1KW ? From:
[email protected] [mailto:[email protected]] On Behalf Of Dave w6de ? I am doing some updating to my Alpha 76PA 3-tube amplifier.? I have switched the T/R relay to a pair of vacuum relays and changed the "relay" (AKA Send or PTT) request to send from 24 Volts to be a compatible 12 Volts for modern transceivers.? I am about to replace the original Alpha Plate Choke with a re-wound Ameritron style taller choke. While I'm at it I have a, new-but old, Cera-Mite 5000 PF, 15 KV door-knob capacitor.? I'm planning to replace the original plate blocking capacitors with this door knob cap.? The original plate blocking cap uses dual original 2000 PF, 6 KV ceramic disk capacitors. ? ? I've has this door knob cap a long time and I'm no longer planning on building a tube amplifier from scratch.? As you can see I've fabricated two copper straps to place the cap in the 76pa amp.? I fabricated these straps to put to door knob cap into a previous Alpha 76PA I had.? And when fastened in place it is quite sturdy and has adequate clearance from its surroundings. ? This amplifier will be kept in my station as a back-up for my Solid State PA.? I've found SSPAs to be less tolerant of operator errors than tube amps.? But I still like the instant on and 6 meter capability in my current SSPA (403A/Flex PGXL). What are your thoughts on this replacement other than it is overkill in this situation? ? 73, Dave, w6de |
HaL Mandel