Re: Building my first amplifier. Where to start?
Hsu,
Thanks for the details on the gu81m tubes. They look great too. Too pretty to be hidden. I have settled now on two gu43b tubes. Should be happy at 2kw and push to 3kw if needed.?
|
Re: Building my first amplifier. Where to start?
Hal,
When I got the transformer I did some experimenting, as you do :) . I found that if I run the outer two phases in parallel ( with one reverse polarity from memory, tbc) I could also parallel the relevent two outputs for more current at the same voltage. So we are aligned there with that thought.??
|
Re: Building my first amplifier. Where to start?
Jeff,
I have parked the idea of the triode and have ordered the tetrode boards from Dom, f1frv who has been very helpful. I am also finalising an order with Alex Ur4LL, for some gu43b tubes, capacitors etc. My plan is to run two in parallel.
I'm thinking that if I run the tubes at just below 3k ( rating is 3.2kv I think) I will have less likelihood of arcing in the tube. I also don't need every last watt out of them? Is this logic sound?
|
Re: Gi46b on 2m - Thermal drift problem
On 12/27/2023 9:51 PM, Jim VE7RF wrote:
Watch out.? You will introduce a ton of stray C on that hb teflon? plate block cap assy.....to the chassis below it.
That amounts to a bunch more anode to chassis C.
Negatory. Being HFers, we can be forgiven, perhaps, for forgetting that at V/UHF, things are different... and there are such things as "transmission lines". This is a traditional stripline plate tank, which configuration can be calculated to resonate at desired V/UHF/microwave frequencies depending upon the width, length, spacing between the line and the top and bottom ground planes, AND the thickness of the line; all of these determine the line parameters. These parameters were all determined nearly a hundred years ago by a guy named Harold Wheeler, and many articles and some books have been written since then to tell and show how to calculate transmission line parameters. My Elmer, W6GGV (SK), originally wrote an article covering the calculation and use of transmission line equations during the early '60s, then wrote equations into programs for the old HP67/97 calculators and published a series of articles in "Ham Radio" magazine just after Jim Fiske, W1HR, died around 1980 or so. Later, I adapted them to the TI-93 calculator but by then, such calculators were no longer in vogue so I never published my programs. Shortly after Hank's article was published, Brian Beezley codified the equations into a for-profit program for the home computer. Knowing the spacing, and the surface area, you can calculate out the C.? ?You can also easily measure it with an LCR meter.
No need, since it's a stripline. HOWEVER...
That hb block cap assy ( with the paper clips) is massive.
Yes, it is... the impedance of the original stripline line is no longer maintained because of the additional thickness of that humungously-thick sheet of teflon being used between the two very-thick copper plates, which thickness looks like it has been vastly increased from the original dimensions. In reality, for an anode voltage up to around 5 kV, the teflon insulation only has to be about 0.02" thick. For a pair of 4CX250Rs or 4CX300As operating from about 2.5 kV, 0.010" has proven adequate. The flashover voltage of teflon, if I recall correctly, is about 500 - 700 volts per mil (one-thousandth of an inch). As with a lumped-constant blocking capacitor (such as a doorknob), you want the voltage-holdoff capability, or in this case, teflon thickness, high enough to withstand at least double your plate voltage and preferably 3 or 4 times. But if you make it too thick in efforts to increase the breakdown voltage, then the whole line becomes too thick and the line width or length has to be changed to compensate. This becomes especially critical in the original K2RIW design which used standard 2" or 3" aluminum chassis to enclose the tank, because the shorter chassis height caused the line thickness to become a much more significant portion of the line thickness within the stripline. And BTW, this is also why these types of amplifiers do not perform properly when the top cover is left off: that top cover is actually PART of the anode tank circuit. And as a consequence, it absolutely MUST be solidly-connected to the bottom chassis walls with el mucho fasteners! A screw every 1-1/2 inches is not unreasonable; one every 2 inches is questionable and further apart is just asking for low efficiency and poor overall performance. This, of course, becomes even more important at 432 MHz. It is absolutely unnecessary to use quarter-inch-thick copper "heat spreaders" for such plate lines: they just don't get that hot. When they do, the outlet air from the tube tends to keep them cool enough that the teflon insulation is not compromised. This is an excellent argument for having the exhaust outlet located at least part-way down the chassis, rather than directly on top of the tube. Otherwise, you have absolutely NO air flow whatsoever around the plate tank; so of course, it's going to get hot with use, and probably change dimensions and thus resonance. Years ago, when I was building lots of these amplifiers using -250Rs, -300As, 8122s, and Svetlana 4CX400s, I used to use ordinary double-sided teflon PC board for my plate lines, most often 0.012" thick. I never had one fail, nor did they ever exhibit thermal instability. I also used sheets of 0.012" teflon AND G-10 fiberglass PC board to build plate bypass capacitors for 220 and 432 amplifiers. The copper thickness of that material was 1 or 2 mils; the capacitors typically were just 4 square inches large. To increase the bypass capacitance, I would sometimes use 0.006"-thick teflon sheet but when I did, I had to be extremely careful to make sure there were absolutely no burrs or sharp edges anywhere on the surfaces carrying high voltage. (I had a lot of those capacitors punch through!) I have seen half a dozen otherwise-beautifully-machined 144 or 220 or 432 amplifiers using this -RIW stripline technique that failed to work properly, most often exhibiting very poor efficiency. The cause is almost always because the builder substituted thicker materials for the original anode stripline circuit components, failing to recognize that the line impedance changed as a consequence. Another cause of such failures out-of-the-box were due to the builder substituting for the original chassis height enclosing the whole stripline, usually going to higher chassis heights such as 4" or even 6". What has to be kept in mind, when dealing with V/UHF circuits that no longer use simple lumped-constant L-C circuits, is that now, you are into the realm of the stripline... and it does not resemble our ordinary inductor-capacitor circuits at all. 73, Steve K0XP
|
Re: Gi46b on 2m - Thermal drift problem
Watch out.? You will introduce a ton of stray C on that hb teflon? plate block cap assy.....to the chassis below it.?
That amounts to a bunch more anode to chassis C.??
?
Knowing the spacing, and the surface area, you can calculate out the C.? ?You can also easily measure it with an LCR meter.
?
That hb block cap assy ( with the paper clips) is massive.
?
Jim? VE7RF
|
Re: Gi46b on 2m - Thermal drift problem
On Wed, Dec 27, 2023 at 04:08 PM, mike repinski wrote:
How can this be done?
Insert a teflon sheet or other suitable insulator between 2 copper slabs, one of which is directly on the anode. Here is mine to give an idea. It's based on plans published by YU1AW. (Ignore the paperclips! It was just a mock up to see how much metal work I'll need to do!) 
|
Re: Gi46b on 2m - Thermal drift problem
Yes, similar to a K2RIW amp.?
On Wednesday, December 27, 2023 at 07:08:22 PM EST, mike repinski via groups.io <mikflathead@...> wrote:
An even better option, if your tank is well insulated (as mine is) is to remove the blocking cap entirely
How can this be done?
On Wednesday, December 27, 2023 at 05:48:56 PM EST, John Sparkes via groups.io <vk6jx@...> wrote:
No probs. An even better option, if your tank is well insulated (as mine is) is to remove the blocking cap entirely and connect the anode directly to the tank. I used large Teflon standoff posts and thick Teflon sheet as you have everywhere, so there are no issues with HV on the tank. John
On 27 Dec 2023, at 21:02, Tim Fern <timjfern@...> wrote:
?Thanks!
I'm down with COVID right now, the junkbox has some other Ceramic button caps, I switch it out in a few days and let you know how I got on.
vy73
Tim
|
Re: Gi46b on 2m - Thermal drift problem
An even better option, if your tank is well insulated (as mine is) is to remove the blocking cap entirely
How can this be done?
On Wednesday, December 27, 2023 at 05:48:56 PM EST, John Sparkes via groups.io <vk6jx@...> wrote:
No probs. An even better option, if your tank is well insulated (as mine is) is to remove the blocking cap entirely and connect the anode directly to the tank. I used large Teflon standoff posts and thick Teflon sheet as you have everywhere, so there are no issues with HV on the tank. John
On 27 Dec 2023, at 21:02, Tim Fern <timjfern@...> wrote:
?Thanks!
I'm down with COVID right now, the junkbox has some other Ceramic button caps, I switch it out in a few days and let you know how I got on.
vy73
Tim
|
Tim and anyone interested :
Here’s looking inside the RF box. You can see the original blocking cap - just like yours ! This is a YU1AW “Lazy Builder” design. Suited my construction capabilities perfectly !
You can see the thick Teflon sheet insulation between the tune (right) and the”load” caps. I was so dumb back then, I thought I could adjust the loading like a HF triode amp. As Lou said, we all still learning about amps.
The lower pic shows the RF box inside the amp cabinet. The large blower feeding cooling air into the bottom of the RF box, Russki REW14 input and output relays, many 6A10 diodes for operating bias, toroidal filament tranny, metering, etc. are visible.
The only other stuff up I made was not using proper terminated cables for the input and output N-Type connectors. I’ll fix that soon.
Good luck with it, and let us know how you go.
Cheers,
John VK6JX
|
Tim - here’s what happened to my 2200pF blocking cap. Cracked and a little burnt. This caused ALL of the “thermal” power output drift in my 2m amp. She’s rock solid now, for complete JT65B overs. Love it !
John
|
Re: Gi46b on 2m - Thermal drift problem
No probs. An even better option, if your tank is well insulated (as mine is) is to remove the blocking cap entirely and connect the anode directly to the tank. I used large Teflon standoff posts and thick Teflon sheet as you have everywhere, so there are no issues with HV on the tank. John
toggle quoted message
Show quoted text
On 27 Dec 2023, at 21:02, Tim Fern <timjfern@...> wrote:
?Thanks!
I'm down with COVID right now, the junkbox has some other Ceramic button caps, I switch it out in a few days and let you know how I got on.
vy73
Tim
|
Re: Building my first amplifier. Where to start?
The G2 volt is 850V， yes， very large G2 current, hundreds milliampre??
? ?Hsu Steve < k0xp@...> 于2023年12月28日周四 04:08写道：
Hsu, what g2 did you use? It seems as though the GU-81M consumes
a LOT of g2 current, too...
73 & HNY,
Steve K0XP
On 12/27/2023 11:54 AM, Hsu wrote:
It seems that the GU-81M is what you want. I just
built an amplifier using a pair of FU-81/FM-8 (GU-81M/GI-8) with
output power: 1.8-14MHz, 2900W, 21-28Mhz, 2500W.grid driven, if
you only want 1KW, you can use one GU-81M on grunded-grid with a
power gain of about The GU-81M has a large
output capacitance, the plate capacitor must be replaced with a
fixed capacitor and requires a roller inductor to tune, and at
21MHz and higher, the plate capacitor C1 is replaced by the
output capacitor, as the EX8A does.?The amplifier is very quiet
and requires little to no heating time, and the tubes are very
inexpensive
? ? ? ?Hsu
desmond auld GI0UTE < desauld@...>
于2023年12月27日周三 16:32写道：
Peter,
You are of course correct. But due to the tappings I have
options to get the voltage to where I want. The rectifier and
the DC produced would be better if I settled on 3 phase, but I
prefer this to be a plan b at this stage.
Thanks des?
--
See my QRZ.com page at
|
Re: Building my first amplifier. Where to start?
Hsu, what g2 did you use? It seems as though the GU-81M consumes
a LOT of g2 current, too...
73 & HNY,
Steve K0XP
On 12/27/2023 11:54 AM, Hsu wrote:
It seems that the GU-81M is what you want. I just
built an amplifier using a pair of FU-81/FM-8 (GU-81M/GI-8) with
output power: 1.8-14MHz, 2900W, 21-28Mhz, 2500W.grid driven, if
you only want 1KW, you can use one GU-81M on grunded-grid with a
power gain of about The GU-81M has a large
output capacitance, the plate capacitor must be replaced with a
fixed capacitor and requires a roller inductor to tune, and at
21MHz and higher, the plate capacitor C1 is replaced by the
output capacitor, as the EX8A does.?The amplifier is very quiet
and requires little to no heating time, and the tubes are very
inexpensive
? ? ? ?Hsu
desmond auld GI0UTE < desauld@...>
于2023年12月27日周三 16:32写道：
Peter,
You are of course correct. But due to the tappings I have
options to get the voltage to where I want. The rectifier and
the DC produced would be better if I settled on 3 phase, but I
prefer this to be a plan b at this stage.
Thanks des?
--
See my QRZ.com page at
|
Re: Building my first amplifier. Where to start?
It seems that the GU-81M is what you want. I just built an amplifier using a pair of FU-81/FM-8 (GU-81M/GI-8) with output power: 1.8-14MHz, 2900W, 21-28Mhz, 2500W.grid driven, if you only want 1KW, you can use one GU-81M on grunded-grid with a power gain of about The GU-81M has a large output capacitance, the plate capacitor must be replaced with a fixed capacitor and requires a roller inductor to tune, and at 21MHz and higher, the plate capacitor C1 is replaced by the output capacitor, as the EX8A does.?The amplifier is very quiet and requires little to no heating time, and the tubes are very inexpensive ? ? ? ?Hsu desmond auld GI0UTE < desauld@...> 于2023年12月27日周三 16:32写道：
Peter,
You are of course correct. But due to the tappings I have options to get the voltage to where I want. The rectifier and the DC produced would be better if I settled on 3 phase, but I prefer this to be a plan b at this stage.
Thanks des?
|
Re: Building my first amplifier. Where to start?
Des,
?
Ian’s callsign is GM3SEK.
?
When I was involved in Underground Coal Mining many of the
Vehicles ran on 3 phase a.c., with stout umbilical cords connecting
To 4160, 3-Ph distribution xfmrs dragged along on skids,
With numerous outlets for 480, 960, etc.
?
Why not see if you can dismember your 3-Ph XFMR and wind the
Primaries, etc, in parallel for a 240 input and extra oomph
On the outputs?
?
Hal
|
Re: Building my first amplifier. Where to start?
I would have to disagree with the 2500V in the case of the GS35
specifically.? To get 1.5KW out, I think the Ig will be too high
at that low of a voltage.??
I ran 4300V on mine and that was very nice from a minimal Ig
standpoint although I think 3500V may be the sweet spot
compromise.? The tube spec is 3KV CCS and 6KV pulse.? Of course
with any proposed tube you want to use, getting a check with a
suitable BDV tester is going to be step one.??
An additional benefit of the higher HV::? The Soviet tubes in
general tend to be a bit less gain than the Eimac and the higher
voltage will help with the gain as well.
73/jeff/ac0c
alpha-charlie-zero-charlie
On 12/26/2023 2:15 PM, Steve wrote:
toggle quoted message
Show quoted text
First thing I'd do is copy the spreadsheet and revise the
dropped Ep to no more than 2500V, perhaps 2550 at most, then
design for that reduced value. Unless you're in a commercial
establishment, with commercial-quality mains and components, Ep
always seems to drop below our best hopes? 8-/
Steve, K0XP
On 12/26/2023 8:05 AM, desmond auld
wrote:
Hal,
Yes, one of concerns is "committing" to a tube that dries up by
way of availability.? That's why the GS35 and Gu43b are on my
radar,as they seem so plentiful.? If i do get an amplifier up
and running of my own creation i will invest in many spares to
keep on the shelf and circulate every year to keep fresh ish.?
The old 811's in my existing amp has are now getting relatively
expensive for a 65w dissipation tube,and the 572B's are out of
hand cost wise considering they are all now Chinese of
poor/average quality, so i understand the concern of going down
a dead end.??
I have spent some time today reading, and plugging in numbers
into the wonderful G3SEK spreadsheet to calculate the values of
C1, C2 and L1 in the tank circuit of an imaginary amplifier
based around two GU43b's in parallel. I have assumed some
things, obviously, like the HV will drop under load to 2700vdc
from circa 2900vdc.? I have modified the spreadsheet to have a
tab for each band, 10-80m, that i'm interested in, and also a
summary sheet with what a beginner such as myself thinks is
important.? i would be VERY grateful if those that know what
they are doing could critique my assumptions and the outputs.?
Spreadsheet attached , with summary copied in below.
Does anything look way out of wack in my assumptions, or not
practically possible in my outputs?
I went looking in my "capacitors for the big amplifier" box and
have a good section of high voltage door knobs, and two
beautiful vacuum variables, that i could use.? One is very
large, 25KV rated 15-350pf, and another is smaller 15-90 pf 40Kv
rated.? I had almost forgot i had these things!? I'm getting
quite excited. :)?
Has anyone any good links for winding tank coils with
calculations etc??
Alex from UR4LL has the GU43b tubes in stock and i am talking to
him at the moment about purchasing some along with some other
parts i may need.? He has a beautiful EImac 4cx 10,000 for sale
if anyone is interested.? I'm not man enough :)
Thanks guys
--
See my QRZ.com page at
|
Re: Gi46b on 2m - Thermal drift problem
Thanks!
I'm down with COVID right now, the junkbox has some other Ceramic button caps, I switch it out in a few days and let you know how I got on.
vy73
Tim
|
Re: [Amps] [ham-amplifiers] Fw: [yccc] Followup: KM1H
Hi John, hope you had a Merry Christmas and do have a Happy New Year.
On Wednesday, December 27, 2023, 2:21 AM, John Sparkes via groups.io <vk6jx@...> wrote: Ha ha ! We sure are, Lou ! Some of us, learn a lot from you guys. BTW, my W1QJ converted SB220 6m amp works bloody well. The Japs don’t know what’s hit them !! Happy new year to all. John VK6JX On 27 Dec 2023, at 07:58, Louis Parascondola via groups.io <Gudguyham@...> wrote:
?
We are always learning! ?
On Tuesday, December 26, 2023, 5:52 PM, Alek Petkovic via Amps <amps@...> wrote: Thanks for that information Lou and thanks to Doug for the leg work. Carl, along with Rich, Tom, Ian White, Tony King, yourself, Jim and lots of others are the ones that have fed me with knowledge, interest and enthusiasm in all things amplifiers over many, many years. 73, Alek VK6APK. On 27/12/2023 5:13 am, Louis Parascondola via groups.io wrote: > > > > Sent from the all new AOL app for iOS > <> > > Begin forwarded message: > > On Tuesday, December 26, 2023, 3:43 PM, Rudy Bakalov > < r_bakalov@...> wrote: > > > >? ? ----- Forwarded Message ----- >? ? *From:* Doug Grant < dougk1dg@...> >? ? *To:* YCCC < [email protected]> >? ? *Sent:* Tuesday, December 26, 2023 at 03:38:10 PM EST >? ? *Subject:* [yccc] Followup: KM1H > >? ? Since nobody had any direct info on Carl's status, I drove to his >? ? house and knocked on the door today, not quite sure what to expect. > >? ? Carl's ex-wife answered the door and invited me in. She announced >? ? me to Carl, who then made his way down the stairs . We had a nice >? ? visit and yakked for about a half-hour. He knew me, and even asked >? ? how my "twin" (K1AR) was doing. > >? ? He was unaware that his ham license had expired, but at age 83, >? ? sometimes events like that slip by. > >? ? So now you know "...the rest of the story". > >? ? 73, > >? ? Doug K1DG >_______________________________________________ Amps mailing list Amps@...
|
Re: Building my first amplifier. Where to start?
Peter,
You are of course correct. But due to the tappings I have options to get the voltage to where I want. The rectifier and the DC produced would be better if I settled on 3 phase, but I prefer this to be a plan b at this stage.
Thanks des?
|
Re: Building my first amplifier. Where to start?
Steve,
I haven't measured idle current of the transformer so I will do that when I dig it out from long term storage. To be fair, even if it idles absorbing a 1kw, which I doubt, I only get maybe 8 hours max per week to "ham" so it's not such a big issue.?
The 3cw 30,000 uses 1kw on the filament alone, so wasted power is all relative:) .
I take your point on rerunning the spreadsheet at reduced voltage level, so I will do that.?
Thanks des?
|
HaL Mandel