Re: [Amps] Serious design stage

[R.Measures <r@somis.org>]

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

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

 They are both AB1-capable tetrodes and both have a 7.5v filament.  
The 8171 was very common in AM, and FM broadcast service until 
transistor amps with combiners began to take over the market -- which 
is probably why 8171s are currently plentiful.  The 8171/ 4CX10,000D 
will dissipate up to 12kW and deliver about c. 1.1 S-units more signal 
at the Rx end than a 4-1000A - using the same HV supply.    And, when a 
smaller stick is appropriate, by simply turning down the microphone 
gain, an 8171 will deliver 1200 pristine watts pep in Class A.
-  The 8171's anode-screen ceramic insulator emits an erie blue light 
during Tx due to electrons missing the anode and striking the 
insulator.  (The accelerated cathode electrons bump into Al2-O3 atoms, 
knocking their electrons into a higher orbit.  When the electrons slow 
and fall back to their original orbit, they emit blue light.)   
However, to see this phenomenon, a clear Mylar film window needs to be 
glued in a cutout in the fiberglas chimney, and a viewing window added 
to the amplifier.
  An added benefit of the power level available from an 8171 is that 
under certain propagation conditions, the observed signal gain at the 
Rx-end is 2 to 3db greater that the P-gain measured at the Tx-end.  I 
know this sounds crazy, and I used to think it was until after I sold 
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 
> transmitter shack then it is to the street.

  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 
> > > stage of a 4-1000A linear.  The power supply, because of its size is 
> > > to be external and connected by a cable.
> > >
> > > In the first design I was going to bring the 6500VDC power through a 
> > > cable to the linear.  But then it occurred to me that since the main 
> > > reason for the separate supply was the size...which is MOSTLY the 
> > > 12KVA transformer I am using.  It might be safer to just make the 
> > > transformer external and have the rectifiers and filter capacitors 
> > > in the transmitter case thus allowing the only the transmission of 
> > > AC, at a lower potential, (using a voltage doubler circuit) in the 
> > > cable.  Thus, by just turning off the input power I could eliminate 
> > > the potential on the cable instantly...or almost so...while the 
> > > filter capacitors which are the biggest danger would be in the 
> > > transmitter cage and would be connected to shorting circuits 
> > > 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 
> > > seen it done.
> > >
> > > Any comments???
> >
> >
> > ?  Jim -- I see it as a sound idea provided there is room for the 
> > filter capacitors in the RF unit.  However, a 12kva transformer would 
> > be more suitable for an 8171 than an 8166/4-1000A.  Switching to such 
> > would not require a larger chassis since either tube requires c. 8" x 
> > 8" of chassis space.  Advantages with the 8171 are a simpler tuned 
> > input circuit, a quieter blower, and 6x the peak emission.   If you 
> > have a 4" deep chassis, Peter Dahl makes a 7.5v, 75A filament 
> > transformer that will fit in a 4" chassis.   On E-bay, I've seen 
> > 8171s go for c. $300.
> >
> > cheerz
> >
> > > _______________________________________________
> > > Amps mailing list
> > > Amps@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/amps
> > Rich Measures, AG6K, 805.386.3734.  www.somis.org/
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
Rich Measures, AG6K, 805.386.3734.  www.somis.org/

_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps