[Amps] Serious design stage

[R.Measures]

On Apr 21, 2004, at 7:43 AM, Jim Isbell wrote:

> Two reasons for the 4-1000A:
>
> a) I already have it with socket etc.
>
> b) Its the coolest looking tube in the world and part of this project,=20=

> maybe 85%, is to create a linear that will cause ooohs and aaaahhs=20
> from the onlookers as they view the 4-1000A and the 866's  lit up=20
> behind the window in the front of the cabinet.

=F0  If you are after oohs and aahs from those who are not=20
amplifier-savvy, A 4-1000A or a 2000T is ideal.
>
> I have never seen an 8171...are they similar??

=F0 They are both AB1-capable tetrodes and both have a 7.5v filament. =20=

The 8171 was very common in AM, and FM broadcast service until=20
transistor amps with combiners began to take over the market -- which=20
is probably why 8171s are currently plentiful.  The 8171/ 4CX10,000D=20
will dissipate up to 12kW and deliver about c. 1.1 S-units more signal=20=

at the Rx end than a 4-1000A - using the same HV supply.    And, when a=20=

smaller stick is appropriate, by simply turning down the microphone=20
gain, an 8171 will deliver 1200 pristine watts pep in Class A.
-  The 8171's anode-screen ceramic insulator emits an erie blue light=20
during Tx due to electrons missing the anode and striking the=20
insulator.  (The accelerated cathode electrons bump into Al2-O3 atoms,=20=

knocking their electrons into a higher orbit.  When the electrons slow=20=

and fall back to their original orbit, they emit blue light.)  =20
However, to see this phenomenon, a clear Mylar film window needs to be=20=

glued in a cutout in the fiberglas chimney, and a viewing window added=20=

to the amplifier.
=F0  An added benefit of the power level available from an 8171 is that=20=

under certain propagation conditions, the observed signal gain at the=20
Rx-end is 2 to 3db greater that the P-gain measured at the Tx-end.  I=20
know this sounds crazy, and I used to think it was until after I sold=20
the original "Plywood Box" and I heard it on the air.
http://www.somis.org/Pbox.html
>
> Two reasons for using the 12KVA transformer:
>
> a) Its here and weighs "a ton".
>
> b) I dont want to move it far enough to sell it and its closer to the=20=

> transmitter shack then it is to the street.

=F0  An 8171 would not require moving this transformer.
>
> rlm wrote:
>
>>
>> On Apr 20, 2004, at 11:29 AM, Jim Isbell wrote:
>>
>>> After collecting parts for most of a year I am in the serious design=20=

>>> stage of a 4-1000A linear.  The power supply, because of its size is=20=

>>> to be external and connected by a cable.
>>>
>>> In the first design I was going to bring the 6500VDC power through a=20=

>>> cable to the linear.  But then it occurred to me that since the main=20=

>>> reason for the separate supply was the size...which is MOSTLY the=20
>>> 12KVA transformer I am using.  It might be safer to just make the=20
>>> transformer external and have the rectifiers and filter capacitors=20=

>>> in the transmitter case thus allowing the only the transmission of=20=

>>> AC, at a lower potential, (using a voltage doubler circuit) in the=20=

>>> cable.  Thus, by just turning off the input power I could eliminate=20=

>>> the potential on the cable instantly...or almost so...while the=20
>>> filter capacitors which are the biggest danger would be in the=20
>>> transmitter cage and would be connected to shorting circuits=20
>>> controlled by the safety switches on the lid of the transmitter.
>>>
>>> There must be some reason this is not a good idea as I have never=20
>>> seen it done.
>>>
>>> Any comments???
>>
>>
>> ?  Jim -- I see it as a sound idea provided there is room for the=20
>> filter capacitors in the RF unit.  However, a 12kva transformer would=20=

>> be more suitable for an 8171 than an 8166/4-1000A.  Switching to such=20=

>> would not require a larger chassis since either tube requires c. 8" x=20=

>> 8" of chassis space.  Advantages with the 8171 are a simpler tuned=20
>> input circuit, a quieter blower, and 6x the peak emission.   If you=20=

>> have a 4" deep chassis, Peter Dahl makes a 7.5v, 75A filament=20
>> transformer that will fit in a 4" chassis.   On E-bay, I've seen=20
>> 8171s go for c. $300.
>>
>> cheerz
>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>> Rich Measures, AG6K, 805.386.3734.  www.somis.org/
>>
>>
>
>
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>
>
Rich Measures, AG6K, 805.386.3734.  www.somis.org/