Thanks to Dan N5AR.
After his order there were 6 remaining.
I just ordered two.
So there are four remaining.
73
Ivan
WK1W
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of
amps-request@contesting.com
Sent: Monday, October 21, 2013 12:00 PM
To: amps@contesting.com
Subject: Amps Digest, Vol 130, Issue 58
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When replying, please edit your Subject line so it is more specific than
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Today's Topics:
1. Re: 200-ohm tank and "un-un" in HF amp design? (Roger (K8RI))
2. Re: ?200-ohm tank and "un-un" in HF amp design? (peter chadwick)
3. Re: 200-ohm tank and "un-un" in HF amp design? (Jim Barber)
4. Re: 200-ohm tank and "un-un" in HF amp design? (Peter Voelpel)
5. Re: 200-ohm tank and "un-un" in HF amp design?
(Manfred Mornhinweg)
6. Re: 200-ohm tank and "un-un" in HF amp design? (Vic K2VCO)
7. Alpha 77dx switch (Dan Hearn)
8. Re: Alpha 77dx switch (Paul Christensen)
----------------------------------------------------------------------
Message: 1
Date: Mon, 21 Oct 2013 02:00:34 -0400
From: "Roger (K8RI)" <k8ri@rogerhalstead.com>
To: amps@contesting.com
Subject: Re: [Amps] 200-ohm tank and "un-un" in HF amp design?
Message-ID: <5264C302.7080309@rogerhalstead.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
On 10/20/2013 8:54 PM, Carl wrote:
> All 3 of the Command Tech amps 1/2/3 tubes used a single toroid
> switched for 40, 80, and 160 followed by the balun. It was the
> switched pi net toroid that caused problems.
> On the 6M amp they also use a balun.
>
> When Palstar bought the line they went to 3 seperate toroids and kept
> the balun.
>
Is Palstar still building amps?
73
Roger (K8RI)
> Ive worked on several of all models from both companies and havent had
> a balun problem but none were used for RTTY that Im aware of.
>
> Carl
> KM1H
>
------------------------------
Message: 2
Date: Mon, 21 Oct 2013 10:32:27 +0200
From: peter chadwick <g8on@fsmail.net>
To: amps@contesting.com
Subject: Re: [Amps] ?200-ohm tank and "un-un" in HF amp design?
Message-ID: <17807976.2771382344347662.JavaMail.www@wwinf3708>
Content-Type: text/plain; charset=UTF-8
>The touted higher harmonic suppression of a PI-L is mainly a myth.....a
>plane jane PI is more than ample for harmonic suppression.<
As a Class AB stage has a second harmonic component of plate current only
6dB down on the fundamental, what sort of Q do you run in the pi network to
get the extra 37dB of suppression needed to meet the FCC regulations or the
extra 44dB needed elsewhere?
73
Peter G3RZP
------------------------------
Message: 3
Date: Mon, 21 Oct 2013 02:31:49 -0700
From: Jim Barber <audioguy@q.com>
To: amps@contesting.com
Subject: Re: [Amps] 200-ohm tank and "un-un" in HF amp design?
Message-ID: <5264F485.7070704@q.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Just to clarify, I used 1.6 for "K", which in Ian's spreadsheet is in the
middle of the range for AB:
Single 8877
4KV
625mA
60% efficiency
"K" factor of 1.6
= 4000 ohms plate load impedance.
Jim W7RY: You're correct about the EP dropping some under load, of course.
My transformer is 3KV 2A CCS, (admittedly overkill for this
example) filter is 32uF, only enough bleeder current for safety. 4KV seemed
like a comfortable estimate, since the (unloaded) peak voltage will be
around 4.2KV .
Vic: Thanks for the link regarding the constant current curves.
I most definitely will look into that, and may post back if I find something
worthwhile.
To summarize, the consensus seems to be a simple PI with padding cap(s)
switched into the low-Z end on 160 meters. Since in this case the main tank
inductor(s) are a 3uH "transformer" inductor followed by a large
square-wound 24uH roller, I'll actually need to switch in both additional L
and C. I can get 5KV 10A Kilovac relays cheaply enough; even with wacky
tuning and load SWR considerations those should do the job at the low-Z end.
Thanks es 73,
Jim N7CXI
On 10/20/2013 9:56 PM, Vic K2VCO wrote:
> Don't believe the 1.8.
>
> I found that this is far from the correct value for the 4CX1000A.
> Maybe it's closer for triodes like 8877s, maybe not.
>
> See
> <http://www.granta.g4axx.com/Linear_design_notes.php3>
> for an example of how to determine the load impedance from the the
> constant current curve for the tube. Here's an 8877 datasheet which
> contains those curves:
> <http://www.g8wrb.org/data/Eimac/3CX1500A7.pdf>
>
> On 10/20/2013 1:37 PM, Jim W7RY wrote:
>> Jim...
>>
>> To figure the plate load impedance:
>>
>> RP = EP / 1.8 X IP
>>
>> 1.8 = K factor for class AB1 (Changes with ZSAC) RP = Plate
>> Resistance EP = Plate Voltage IP = Plate Current
>>
>>
>> 1.8 X .65 Amps = 1.17
>>
>> 1.17/ 4000 = 3418 Ohms plate load impudence.
>>
>> Your actual voltage will more likely be 3800 with a .65amp load which
>> brings the load down to 3250 Ohms.
>>
>>
>> Better to just switch in some loading padders with your bandswitch.
>>
>> See the last 8 years of the ARRL handbook for the K8RA amplifier
>> using the 3CX1500D7 tube.
>> There are some great examples there.
>>
>>
>> 73
>> Jim W7RY
>>
>>
>> On 10/20/2013 8:28 AM, Jim Barber wrote:
>>> 1500 watts
>>> 4kV, 625mA
>>> Single 8877 at around 4000 ohms plate impedance in AB2.
>>>
>>> Tnx,
>>> Jim N7CXI
>
------------------------------
Message: 4
Date: Mon, 21 Oct 2013 13:34:37 +0200
From: "Peter Voelpel" <dj7ww@t-online.de>
To: <amps@contesting.com>
Subject: Re: [Amps] 200-ohm tank and "un-un" in HF amp design?
Message-ID: <E1D32362103346C1A10C6665F016C348@amateurfunk>
Content-Type: text/plain; charset="iso-8859-1"
I don?t believe that the anode voltage drops to zero volts at 625mA anode
current.
4KV voltage swing in your calculation is probably too high.
73
Peter
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Jim Barber
Just to clarify, I used 1.6 for "K", which in Ian's spreadsheet is in the
middle of the range for AB:
Single 8877
4KV
625mA
60% efficiency
"K" factor of 1.6
= 4000 ohms plate load impedance.
------------------------------
Message: 5
Date: Mon, 21 Oct 2013 13:36:18 +0000
From: Manfred Mornhinweg <manfred@ludens.cl>
To: amps@contesting.com
Subject: Re: [Amps] 200-ohm tank and "un-un" in HF amp design?
Message-ID: <52652DD2.3060701@ludens.cl>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hello,
it should be remembered that the values of loading capacitance, tuning
capacitance and the inductance of the tank coil not only depend on
impedances and frequency, but also on Q. The designer has a wide degree of
control over these values.
For example, if we need to match 4000 ohm to 50 ohm, on 160 meters, and we
have a loading capacitor of just 1000pF, and we don't want to add capacitors
in parallel, we can pick a Q of 10. This leads to 215pF tuning capacitance
(including tube and stray capacitance), a 35.8uH coil, and 882pF of loading
capacitance.
If that's still too high, just let's decrease the Q to 9.5. That gives us
204pF, 37.2uH, and 645pF.
Still too high? Use Q=9. Then we get 194pF, 38.4uH, and just 272pF of
loading capacitance!
In practice this would be done by tapping the tank coil at a spot where the
Pi circuit tunes up with the loading capacitor at the center of its range,
into a dummy load. Regardless of how much maximum capacitance that capacitor
has! That will give us the best matching range possible for real antennas
with non-perfect SWR. Of course, the smaller the loading cap is, the
narrower this tuning range becomes.
The actual penalty of having a very high plate impedance is that we cannot
use a lower Q. With 4000 ohm, we cannot go below a Q of 8.89.
This makes tuning a bit touchy, and we need a VERY good tank coil to get
acceptable losses. The loss depends on the ratio between the natural
(unloaded) Q of the components, mainly the coil in practice, and the loaded
Q. If the coil has a natural Q of 300, which is typical, and we are running
it at a loaded Q of 10, it will loose one thirtieth of the total RF power.
At 1500 watts, that's 50 watts heating the coil, which may be a problem.
If the plate impedance instead is just 2000 ohm, the minimal Q we can use
is 6.4, in practice we might use 8 or so. That way the loss is a bit lower,
and tuning is a bit broader.
Of course we cannot go too low with the loaded Q, because that will increase
harmonic output to an unacceptable level. Old handbooks say that actually we
shouldn't go lower than Q=10 or so.
On the highest bands, the problem is another one: All that tube capacitance
and stray capacitance forces us to use a Q higher than we would like! For
example, on 10 meters with a 4000 ohm plate, a Q of 10 would need a tuning
capacitance of just 14pF. Good luck finding a tube, and a construction
method, that keeps the tube and stray capacitance lower than this! Likely
that capacitance will be higher, forcing us to use a higher Q. If the total
tube and stray capacitance, plus the minimal capacitance of the tuning cap,
is 40pF, we need to use a Q of 30 (or higher). At Q-30, the coil becomes
only 0.83uH. With a natural coil Q of 300, we would have 150 watts of loss
in that little coil! That's why many amps use coils wound from thick, broad
silver plated copper strip for the high bands. Absolutely highest possible
natural Q of that coil is a strict need! And of course tuning gets much more
touchy than on the lower bands.
For these reasons, most amplifiers don't use the same loaded Q on all bands.
They use higher Q on the higher bands, to accomodate the tube and stray
capacitances, and lower Q on the lower bands, to keep the tuning and loading
caps from growing too much, and to allow the use of smaller loading coils.
High Q coils for low frequencies are large.
Well, that was a quick burst of antique tube technology, from my side.
Since it's monday morning, I hope I may be forgiven. Now I switch back into
2013.
Manfred
========================
Visit my hobby homepage!
http://ludens.cl
========================
------------------------------
Message: 6
Date: Mon, 21 Oct 2013 08:12:04 -0700
From: Vic K2VCO <k2vco.vic@gmail.com>
To: amps@contesting.com
Subject: Re: [Amps] 200-ohm tank and "un-un" in HF amp design?
Message-ID: <52654444.9060804@gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Right. I said maybe and maybe not. I also included a link to the
constant-current curve for the 8877 so he can find out for sure.
On 10/20/2013 10:16 PM, Jim W7RY wrote:
> Ummmm... He's using an 8877.
>
> 73
> Jim W7RY
>
> On 10/20/2013 9:56 PM, Vic K2VCO wrote:
>> Don't believe the 1.8.
>>
>> I found that this is far from the correct value for the 4CX1000A.
>> Maybe it's closer for triodes like 8877s, maybe not.
>>
>> See
>> <http://www.granta.g4axx.com/Linear_design_notes.php3>
>> for an example of how to determine the load impedance from the the
>> constant current curve for the tube. Here's an 8877 datasheet which
contains those curves:
>> <http://www.g8wrb.org/data/Eimac/3CX1500A7.pdf>
>>
>> On 10/20/2013 1:37 PM, Jim W7RY wrote:
>>> Jim...
>>>
>>> To figure the plate load impedance:
>>>
>>> RP = EP / 1.8 X IP
>>>
>>> 1.8 = K factor for class AB1 (Changes with ZSAC) RP = Plate
>>> Resistance EP = Plate Voltage IP = Plate Current
>>>
>>>
>>> 1.8 X .65 Amps = 1.17
>>>
>>> 1.17/ 4000 = 3418 Ohms plate load impudence.
>>>
>>> Your actual voltage will more likely be 3800 with a .65amp load
>>> which brings the load down to 3250 Ohms.
>>>
>>>
>>> Better to just switch in some loading padders with your bandswitch.
>>>
>>> See the last 8 years of the ARRL handbook for the K8RA amplifier using
the 3CX1500D7 tube.
>>> There are some great examples there.
>>>
>>>
>>> 73
>>> Jim W7RY
>>>
>>>
>>> On 10/20/2013 8:28 AM, Jim Barber wrote:
>>>> 1500 watts
>>>> 4kV, 625mA
>>>> Single 8877 at around 4000 ohms plate impedance in AB2.
>>>>
>>>> Tnx,
>>>> Jim N7CXI
>>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
------------------------------
Message: 7
Date: Mon, 21 Oct 2013 08:18:03 -0700
From: Dan Hearn <n5ardxcc@gmail.com>
To: "Amps@contesting.com" <Amps@contesting.com>
Subject: [Amps] Alpha 77dx switch
Message-ID:
<CAHU7KERmwJtc_xqVNpLqozWc0fJBOuV3tE8jw6sScHbx34-Zmg@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
I just ordered 2 of the 4 pushbutton switch units used in this amp from
Mouser.
They show 8 units left in stock. Switchcraft 67041K-506.
Dan, N5AR
------------------------------
Message: 8
Date: Mon, 21 Oct 2013 11:33:22 -0400
From: "Paul Christensen" <w9ac@arrl.net>
To: <Amps@contesting.com>
Subject: Re: [Amps] Alpha 77dx switch
Message-ID: <0358C5F9252240F5BAF9718ACC5C0854@btgpc>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
Dan,
A quick price check shows that's roughly the same price I paid through
Newark back in 1998. It's nice to know many of the OEM parts are still
available for an amp that dates back to the '70s. There are few OEM parts
on the Alpha 77 series that cannot be obtained today - or easily
substituted.
Paul, W9AC
----- Original Message -----
From: "Dan Hearn" <n5ardxcc@gmail.com>
To: <Amps@contesting.com>
Sent: Monday, October 21, 2013 11:18 AM
Subject: [Amps] Alpha 77dx switch
>I just ordered 2 of the 4 pushbutton switch units used in this amp from
> Mouser.
> They show 8 units left in stock. Switchcraft 67041K-506.
>
> Dan, N5AR
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
------------------------------
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