Re: Artificial centre tap for GG 3CX1200
I forgot to put in these RF
Parts door-knob links
?
?
Dave, w6de
?
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From: [email protected] <[email protected]>
On Behalf Of Dave w6de via groups.io
Sent: 3 December, 2023 00:58
To: [email protected]
Subject: Re: [ham-amplifiers] Artificial centre tap for GG 3CX1200
?
Ceramic Disk Capacitors are used as RF bypass capacitors in RF circuitry--that is to short RF to ground.?
And Capacitors can be also used to block DC and low frequency current form passing through them. How to use the in your situation is described below.
?
Use a set of High Voltage Ceramic disk capacitors, wired from each of the two filament leads to ground—this will allow the high frequency RF to pass through and block the low frequency
AC filament voltage..?
-Disk ceramic Capacitors are also used in High Power Tube Amplifiers as a DC blocking capacitor to Pass through only the RF from the plate to the PA plate circuit and then the antennas
system.?
-Since this works in the plate circuit and it will work in the ground/common circuit too.?
-I am not certain about the voltage requirement for this filament grounding circuit.?
Look at the Filament transformer’s insulation value.?
You aren’t going to need much higher voltage for the capacitors than that.
?
Turns out, high voltage disk capacitors are becoming hard to find:?
I found this at RF Parts:
?
0.01 micro farad @ 2KV
-Assuming you will use a 0.05 microfarad capacitance value you will need 10 of these to make your filament grounding system.?
Double than quantity if you need a high voltage of 4KV.
-Alternate choice but more expensive are doorknob capacitors.?
While these might be awkward to mount a capacitance above 2000pf may work for you, these will certainly work and look impressive.?
You are going to need one of these door-knob capacitors for your amplifier plate circuit too.---just buy 3 and you’ll be set :>).
?
A capacitance of?
0.05 microfarad will present only 3.8 Ohms (2 x 1.8) resistance to the RF signal at 1.8 MHz even lower resistance as the frequency goes up.?
But will present 106K Ohms (2 x 53K) ohms to the 6.3 volts 60 Hz AC voltage.?
Use this calculator to determine alternate capacitance values if you desire:
?
73,
Dave, w6de
?
?
?
Hi, I've been trying to gather parts for a 3CX1200D7 build. I had trouble locating a sufficient filament transformer. Tube requires 6.3V @ 25A. Ended up finding one for 6.3V @ 28A - Would like to have more overhead but thought it would
be the best I'd find, and only $50 brand new! Perfect!
BUT In my haste to complete an order of needed parts, I wasn't paying close enough attention. It turns out that it doesn't have a CT. (it's dual secondary - parallel is
6.3V@28A and series is 12.6V@14A) - D'oh!
Now what... when I used to play with guitar/audio amps, a semi-common thing to do would be to take a pair of low value resistors, put one end of each to each end of the filament winding, and ground the joint in the middle for a fake CT. Unsure how this will
affect a cathode bias.
I've also heard of using the secondary winding of a totally separate transformer that
does have a CT, and using it in parallel across my filament winding, then using that transformers centre tap. Further, I've heard of using a pair of diodes, each anode to each end of my
filament winding and tie the cathodes together in the middle... or maybe that was t'other way around... either way I dunno about this either.
Anyways, obviously the best way forward would be to actually use a proper transformer, but since I can't find one and I already made this oopsie... I'm wondering what the next-best-way forward is? :)
Thanks :)
|
Re: Artificial centre tap for GG 3CX1200
Ceramic Disk Capacitors are used as RF bypass capacitors in RF circuitry--that is to short RF to ground.?
And Capacitors can be also used to block DC and low frequency current form passing through them. How to use the in your situation is described below.
?
Use a set of High Voltage Ceramic disk capacitors, wired from each of the two filament leads to ground—this will allow the
high frequency RF to pass through and block the low frequency AC filament voltage..?
-Disk ceramic Capacitors are also used in High Power Tube Amplifiers as a DC blocking capacitor to Pass through only the RF
from the plate to the PA plate circuit and then the antennas system.?
-Since this works in the plate circuit and it will work in the ground/common circuit too.?
-I am not certain about the voltage requirement for this filament grounding circuit.
?Look at the Filament transformer’s insulation value.?
You aren’t going to need much higher voltage for the capacitors than that.
?
Turns out, high voltage disk capacitors are becoming hard to find:?
I found this at RF Parts:
?
0.01 micro farad @ 2KV
-Assuming you will use a 0.05 microfarad capacitance value you will need 10 of these to make your filament grounding system.?
Double than quantity if you need a high voltage of 4KV.
-Alternate choice but more expensive are doorknob capacitors.?
While these might be awkward to mount a capacitance above 2000pf may work for you, these will certainly work and look impressive.?
You are going to need one of these door-knob capacitors for your amplifier plate circuit too.---just buy 3 and you’ll be set :>).
?
A capacitance of?
0.05 microfarad will present only 3.8 Ohms (2 x 1.8) resistance to the RF signal at 1.8 MHz even lower resistance as the frequency goes up.?
But will present 106K Ohms (2 x 53K) ohms to the 6.3 volts 60 Hz AC voltage.?
Use this calculator to determine alternate capacitance values if you desire:
?
73,
Dave, w6de
?
?
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From: [email protected] <[email protected]>
On Behalf Of va3dxv via groups.io
Sent: 1 December, 2023 18:57
To: [email protected]
Subject: [ham-amplifiers] Artificial centre tap for GG 3CX1200
?
Hi, I've been trying to gather parts for a 3CX1200D7 build. I had trouble locating a sufficient filament transformer. Tube requires 6.3V @ 25A. Ended up finding one for 6.3V @ 28A - Would like to have more overhead but thought it would
be the best I'd find, and only $50 brand new! Perfect!
BUT In my haste to complete an order of needed parts, I wasn't paying close enough attention. It turns out that it doesn't have a CT. (it's dual secondary - parallel is
6.3V@28A and series is 12.6V@14A) - D'oh!
Now what... when I used to play with guitar/audio amps, a semi-common thing to do would be to take a pair of low value resistors, put one end of each to each end of the filament winding, and ground the joint in the middle for a fake CT. Unsure how this will
affect a cathode bias.
I've also heard of using the secondary winding of a totally separate transformer that
does have a CT, and using it in parallel across my filament winding, then using that transformers centre tap. Further, I've heard of using a pair of diodes, each anode to each end of my
filament winding and tie the cathodes together in the middle... or maybe that was t'other way around... either way I dunno about this either.
Anyways, obviously the best way forward would be to actually use a proper transformer, but since I can't find one and I already made this oopsie... I'm wondering what the next-best-way forward is? :)
Thanks :)
|
Re: Need Help with Amp Supply LK500ZC
You should not be getting any grid current reading.
Alek, VK6APK.
On 3/12/2023 6:11 am, John Roland
wrote:
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Adrian and all
I sent a similar reply a few hours ago, but it doesn't show up, I
assume it's lost.? And if not I hope the 2 versions are
consistent.
I measured the voltage across the 2 terminals of the big zener.
? key down 9.3 volts
? key up? 9.1 volts
Individual Tube Idling Currents Keyed, no input signal
Rear Tube:? Plate: 40 ma? Grid 10 ma
Front Tube Plate; 60 ma??? Grid: 18 ma
All readings drop to 0 when unkeyed.
Cheers ? /John
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Re: Need Help with Amp Supply LK500ZC
Adrian and all
I sent a similar reply a few hours ago, but it doesn't show up, I assume it's lost.? And if not I hope the 2 versions are consistent.
I measured the voltage across the 2 terminals of the big zener.
? key down 9.3 volts
? key up? 9.1 volts
Individual Tube Idling Currents Keyed, no input signal
Rear Tube:? Plate: 40 ma? Grid 10 ma
Front Tube Plate; 60 ma??? Grid: 18 ma
All readings drop to 0 when unkeyed.
Cheers ? /John
|
Re: Artificial centre tap for GG 3CX1200
For a few years now, I've been using Antek toroids for my
"custom" transformers: ? Where necessary,
I've bought a suitable low-voltage unit and rewound it for my
requirements. Since the secondaries are always wound on the
outside even on toroids, turning one of their standard
transformers into one that fulfills your exact needs is simply a
matter of unwinding all the external tape and kapton insulation,
then carefully unwinding the low voltage winding in question, then
rewinding as appropriate.
Before starting the process, I check the volts-per-turn ratio by
winding ten or twenty turns of ordinary hookup wire on the toroid
then applying power and measuring the voltage. You can easily do
this while applying an appropriate load to the existing or your
"new" winding. Thus, I used one of these:
as the basis for a
7.5VAC/21.5A 3-1000Z filament transformer, installing my own
center tap while at it. The price of their toroids is extremely
reasonable, especially considering all the hassle involved in
finding, buying and perhaps modifying a standard iron lamination
E-I transformer. Antek even has a 1500 VA 950-volt high voltage
transformer that can become an excellent basis for a voltage
doubler, high voltage power supply:
?
(Unfortunately, that is their largest and highest-voltage
transformer.)
An interesting bit of trivia is that the high voltage
transformers used in the Alpha 8410 (which uses a pair of
4CX1000As or 4CX1500Bs) appear to be a pair of 1500VA toroids
"wound" together to form a single unit; I've been wondering
whether they might actually be a pair of those 950-volt units
mentioned above... Several years ago, I bought a pair of the 950
volt units and used one of them to built a compact high voltage
power supply for my Heath HA14 amplifiers; the core hardly even
gets warmer than lukewarm even at 700W output in CW contests.
After rewinding several of the low-voltage units, you develop a
technique of easily unwinding the outside kapton and other
insulation layers then unwinding the copper wire while keeping it
straight and unmarked, then rewinding the wire and insulation as
necessary. It's gotten to the point where I was able to modify
that 12V toroid mentioned above into my desired 7.5VCT/21.5A?
transformer within a little more than four hours, including
rewinding all the kapton and insulation tape back onto the core.
And I just can't beat the prices. Shipping is also reasonable.
Everything I've bought so far was in stock but you can easily
check for stock status on their web site.
I am not an Antek owner or stockholder, nor do I have any other
affiliation with the company or its owners/stockholders, other
than that of a very satisfied customer.
Steve, K0XP
On 12/2/2023 11:40 AM, va3dxv wrote:
On Fri, Dec 1, 2023 at 04:27 PM, HaL Mandel wrote:
In fact,
HARBACH may just have the perfect item in
stock, or would
be able to wind up something in a heartbeat.
Well friend, I'm not sure if a dollar is worth the same to you as
it is to me :) Keep in mind also; Something that you can get for
two hundred bucks is going to be triple that for me, once I factor
in shipping, import tax, exchange rate, etc...? I didn't pay more
than a hundred bucks for any other part of this build including
the vacuum variables! The xfrmr I got is new and it was fifty
bucks, which is about what I'd expect to pay for the "correct" one
at a hamfest, so until that happens I'll have to make it work :)
Though I didn't know Harbach was still in the game. Hammond has a
suitable 30A listed in their Peter Dahl list but it's custom
order. If I really like how the amp turns out I might contact
them.
--
See my QRZ.com page at
|
Re: Artificial centre tap for GG 3CX1200
On Fri, Dec 1, 2023 at 04:27 PM, HaL Mandel wrote:
In fact, HARBACH may just have the perfect item in
stock, or would be able to wind up something in a heartbeat.
Well friend, I'm not sure if a dollar is worth the same to you as it is to me :) Keep in mind also; Something that you can get for two hundred bucks is going to be triple that for me, once I factor in shipping, import tax, exchange rate, etc...? I didn't pay more than a hundred bucks for any other part of this build including the vacuum variables! The xfrmr I got is new and it was fifty bucks, which is about what I'd expect to pay for the "correct" one at a hamfest, so until that happens I'll have to make it work :) Though I didn't know Harbach was still in the game. Hammond has a suitable 30A listed in their Peter Dahl list but it's custom order. If I really like how the amp turns out I might contact them.
|
Re: Alpha Amp Group Still Active??
Strange.? When I access my 8100 via a USB port, it responds to commands from a terminal program instantly.? I wonder if you've tried accessing the 8410 from a terminal program???
|
Re: Artificial centre tap for GG 3CX1200
And if we simply ground one of the terminals of the 6.3V transformer, what happens?
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Re: Artificial centre tap for GG 3CX1200
Dear ‘1200 Builder,
?
When dealing with Heavy Iron it is not wise to
Jury-Rig.
?
Save for the ability to purchase the right iron.
?
In fact, HARBACH may just have the perfect item in
stock, or would be able to wind up something in a heartbeat.
?
Hal Mandel
W4HBM
|
Re: Artificial centre tap for GG 3CX1200
A 6.3 VAC @3A ?CT transformer will work just fine.? That’s what I used ? -Chuck K1KW ? ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of va3dxv
Sent: Friday, December 01, 2023 5:07 PM
To: [email protected]
Subject: Re: [ham-amplifiers] Artificial centre tap for GG 3CX1200 ? On Fri, Dec 1, 2023 at 11:58 AM, Chuck Neal wrote: Yes I have done this and it works very well. Ahh that's good to hear, Thanks! Any idea on whats needed of the required transformer? I'm kind of thinking that as long as the winding can handle the DC current, and doesn't have a huge DC resistance, then it's probably ok? Like a 12V 1A maybe?
I'll poke around and see how easy it would be to add a CT, didn't really consider that at first, but yeah. Thanks Guys.
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Re: Need Help with Amp Supply LK500ZC
The clue is surely in the grid current reading. It should be zero with no drive.
73, Alek VK6APK.
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On 2/12/2023 5:49 am, Adrian Fewster wrote: I had asked for that. what is the same result for each tube on its own with the other removed ?
Also voltage across zener keyed and unkeyed ?
73
vk4tux
On 2/12/23 06:47, John Roland wrote:
Someone asked about idling current.? With no drive but the amp keyed I'm seeing about 80 ma? plate current and about 30 ma grid current.? Both meters drop to 0 when unkeyed.
|
Re: Artificial centre tap for GG 3CX1200
On Fri, Dec 1, 2023 at 11:58 AM, Chuck Neal wrote:
Yes I have done this and it works very well.
Ahh that's good to hear, Thanks! Any idea on whats needed of the required transformer? I'm kind of thinking that as long as the winding can handle the DC current, and doesn't have a huge DC resistance, then it's probably ok? Like a 12V 1A maybe? I'll poke around and see how easy it would be to add a CT, didn't really consider that at first, but yeah. Thanks Guys.
|
Got an 80B here and I am having meter issues. The swr and power meter were not working properly and I put in a new op amp on the meter board and I also changed out the 2 2n3904's going to the op amp.
Now the meters are at full scale. At this point its over my head. Was wondering if anyone had any ideas.? The grid and plate meter is fine and the amp puts out bear a KW. I am just using me external meter for the time being.
Tia
Dave N8DC
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Re: Need Help with Amp Supply LK500ZC
Adrian and all
I measured the voltage across what I believe to be R6 in the 1988 power supply schematic or R1 in the 1983 schematic.? It is visible in the 4th picture I sent yesterday evening (PST) in the upper right corner of the 4th picture down as a large 100k resistor attached to the large zener diode.
? I hooked up my tranceiver output to the dummy load but left the relay connected to the amplifier and keyed and unkeyed the transceiver in RTTY mode.? Amp in XMT mode.?? Transmitter unkeyed, the voltage across the resistor was around 44.5 volts.?? Keyed, the voltage was a few millivolts.??
Someone asked about idling current.? With no drive but the amp keyed I'm seeing about 80 ma? plate current and about 30 ma grid current.? Both meters drop to 0 when unkeyed.
XYL insists I clear the 300 foot driveway of the foot of snow that fell last night so I'll be away for the next few hours.
/John
|
Re: Artificial centre tap for GG 3CX1200
Quote: “I've also heard of using the secondary winding of a totally separate transformer that does have a CT, and using it in parallel across my filament winding, then using that transformers centre tap.” ? Yes I have done this and it works very well.? Using the resistors for a fake CT will add a variable bias as the cathode current varies which will hurt the IMD performance.? Also as suggested, you might be able to make your own CT.? Try probing the secondary winding with a DVM fitted with a pin to see if you can find the ? voltage point.? I have also done this and found a CT at a very easy point to get to between the two layers of the secondary at the physical end between the two layers. ? -Chuck K1KW
?
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From: [email protected] [mailto:[email protected]] On Behalf Of va3dxv
Sent: Friday, December 01, 2023 1:57 PM
To: [email protected]
Subject: [ham-amplifiers] Artificial centre tap for GG 3CX1200 ? Hi, I've been trying to gather parts for a 3CX1200D7 build. I had trouble locating a sufficient filament transformer. Tube requires 6.3V @ 25A. Ended up finding one for 6.3V @ 28A - Would like to have more overhead but thought it would be the best I'd find, and only $50 brand new! Perfect!
BUT In my haste to complete an order of needed parts, I wasn't paying close enough attention. It turns out that it doesn't have a CT. (it's dual secondary - parallel is 6.3V@28A and series is 12.6V@14A) - D'oh!
Now what... when I used to play with guitar/audio amps, a semi-common thing to do would be to take a pair of low value resistors, put one end of each to each end of the filament winding, and ground the joint in the middle for a fake CT. Unsure how this will affect a cathode bias.
I've also heard of using the secondary winding of a totally separate transformer that does have a CT, and using it in parallel across my filament winding, then using that transformers centre tap. Further, I've heard of using a pair of diodes, each anode to each end of my filament winding and tie the cathodes together in the middle... or maybe that was t'other way around... either way I dunno about this either.
Anyways, obviously the best way forward would be to actually use a proper transformer, but since I can't find one and I already made this oopsie... I'm wondering what the next-best-way forward is? :)
Thanks :)
|
Re: Artificial centre tap for GG 3CX1200
Still another easy way out is to unwind those heavy windings and
put in your own center tap. There can't be more than 20, 25 turns
of wire per 6V winding?? Transformer secondaries are always wound
on the outside, meaning modifying them is very easy.
Steve, K0XP
On 12/1/2023 10:56 AM, va3dxv wrote:
Hi, I've been trying to gather parts for a 3CX1200D7 build. I had
trouble locating a sufficient filament transformer. Tube requires
6.3V @ 25A. Ended up finding one for 6.3V @ 28A - Would like to
have more overhead but thought it would be the best I'd find, and
only $50 brand new! Perfect!
BUT In my haste to complete an order of needed parts, I wasn't
paying close enough attention. It turns out that it doesn't have a
CT. (it's dual secondary - parallel is 6.3V@28A and series is
12.6V@14A) - D'oh!
Now what... when I used to play with guitar/audio amps, a
semi-common thing to do would be to take a pair of low value
resistors, put one end of each to each end of the filament
winding, and ground the joint in the middle for a fake CT. Unsure
how this will affect a cathode bias.
I've also heard of using the secondary winding of a totally
separate transformer that does have a CT, and
using it in parallel across my filament winding, then using that
transformers centre tap. Further, I've heard of using a pair of
diodes, each anode to each end of my filament winding and tie the
cathodes together in the middle... or maybe that was t'other way
around... either way I dunno about this either.
Anyways, obviously the best way forward would be to actually use a
proper transformer, but since I can't find one and I already made
this oopsie... I'm wondering what the next-best-way forward is? :)
Thanks :)
--
See my QRZ.com page at
|
Artificial centre tap for GG 3CX1200
Hi, I've been trying to gather parts for a 3CX1200D7 build. I had trouble locating a sufficient filament transformer. Tube requires 6.3V @ 25A. Ended up finding one for 6.3V @ 28A - Would like to have more overhead but thought it would be the best I'd find, and only $50 brand new! Perfect!
BUT In my haste to complete an order of needed parts, I wasn't paying close enough attention. It turns out that it doesn't have a CT. (it's dual secondary - parallel is 6.3V@28A and series is 12.6V@14A) - D'oh!
Now what... when I used to play with guitar/audio amps, a semi-common thing to do would be to take a pair of low value resistors, put one end of each to each end of the filament winding, and ground the joint in the middle for a fake CT. Unsure how this will affect a cathode bias.
I've also heard of using the secondary winding of a totally separate transformer that does have a CT, and using it in parallel across my filament winding, then using that transformers centre tap. Further, I've heard of using a pair of diodes, each anode to each end of my filament winding and tie the cathodes together in the middle... or maybe that was t'other way around... either way I dunno about this either.
Anyways, obviously the best way forward would be to actually use a proper transformer, but since I can't find one and I already made this oopsie... I'm wondering what the next-best-way forward is? :)
Thanks :)
|
Re: Need Help with Amp Supply LK500ZC
One picture clearly shows the the CT bias resistor and the zener diode being switched by a relay (blue)mounted on the center wall. ?The PC board which looks like a relocation of the ALO board might be doing some detecting of swr or something that might shut down??the ptt? or something. ?Bug it sure doesn’t look transistor bias switching with the wiring I see over to the blue relay. He’s got a radio Dan?gizmo with a coax going onto it. ?I’m wondering if that senses RF and triggers the relay PTT line, ? This is definitely one for my memoirs. ?Just when you thought you’ve seen it all something comes along and takes the cake. ?Engineers build?amplifiers and hams cone along and try to make it better. I could fill up a 55 gallon drum of modifications I ripped out of amps. ?With no documentation it gets costly to spend the time to figure out what some?? screwdriver happy ham had in his brain. Jeez
On Friday, December 1, 2023, 12:39 AM, John Roland <johnroland51@...> wrote:
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Re: Need Help with Amp Supply LK500ZC
What I think Lou is saying is...... the cut off bias isn't being applied on RX....( cuz of lousy bias relay contacts on RX)...... hence the tubeS are sucking normal idle current.? BUT if that was the case, the plate current meter would be indicating normal idle current.? ?Now that the amp seems to be functioning ok...... what is the normal idle current ????? (keyed, but NO drive applied).?
?
With normal idle current, how much idle current is there...and what is the loaded B+?? ?Knowing that, simple calc to determine idle anode dissipation.?
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Re: Need Help with Amp Supply LK500ZC
|
Floyd - K8AC
HaL Mandel