[Milsurplus] [regenrx] Re: pentagrid detector sensitivity

Thu Jan 5 21:51:31 EST 2012

Yes. It's a Eureka Beacon...  the ground end of the Rebecca-Eureka system.

I wonder if the destruct charge is still under the red cap?  :))

BTW, anybody got an unmodified AN/APN-2 they would like to sell? Mine has
a post-WW II mod by Canadian Aviation Electric.

-John

================

> The AN/PPN-2 is not an IFF set, it is a "pathfinder" beacon set used to
> guide in airborne troops in WWII.  A marvel of electronics engineering and
> packaging for that period of time.
> Ray
> ----- Original Message -----
> From: "Michael A. Bittner" <mmab at cox.net>
> To: <regenrx at yahoogroups.com>
> Cc: <milsurplus at mailman.qth.net>
> Sent: Thursday, January 05, 2012 8:48 PM
> Subject: Re: [Milsurplus] [regenrx] Re: pentagrid detector sensitivity
>
>
>> FWIW, the 1R5 (battery equivalent to the 6BE6) is used as a grounded
>> grid
>> UHF amplifier with grid-1 grounded and grids 2, 3 & 4 tied to the plate
>> in
>> the AN/PPN-2 IFF set.  BTW there's a PPN-2 on eBay right now with a BIN
>> price of  $2,700.00.  Also, the Hallicrafters S-72 uses the 1R5 as its
>> local oscillator in a conventional triode configuration with grids 2, 3
>> &
>> 4 tied to the plate.  Why??  What's so great about the 1R5 that it's
>> used
>> as a GG amp or an LO??  Mike, W6MAB
>>
>>
>>  ----- Original Message -----
>>  From: davidpnewkirk
>>  To: regenrx at yahoogroups.com
>>  Sent: Thursday, January 05, 2012 5:12 PM
>>  Subject: [regenrx] Re: pentagrid detector sensitivity
>>  --- In regenrx at yahoogroups.com, "kyoritsu" <rikkyograsing at ...> wrote:
>>  >
>>  > Forgot to mention a couple of experiments I did with the 6BE6 as a
>> regenerative detector.
>>  >
>>  > I tried injecting the signal on grid 3 (keeping the oscillator tank
>> and
>> grid leak on grid 1). Lyle Williams (The New Radio Receiver Handbook)
>> wrote you could inject the signal into the screen grid of a pentode
>> detector, and I wanted to see how this would work on the other control
>> grid of a pentagrid. Well, it doesn't work. Of course, it can still
>> oscillate but the only station I heard was one local AM broadcaster,
>> regardless of where it was tuned or what band. I was hoping for antenna
>> isolation.
>>  >
>>  > Also tried tying together the two control grids, 1 and 3. Sort of a
>> belt and suspenders approach to regeneration, since the two screen grids
>> are internally tied together in the 6BE6. This does work, but there's a
>> clear reduction in gain.
>>  >
>>  > So far, the 6BE6 works best with grid 3 grounded. But since it is a
>> converter tube, you could add a separate heterodyning oscillator circuit
>> in addition to the usual regenerative detector, something that was
>> suggested back in the 1930s and still comes up from time to time now.
>>  >
>>  > The 6BE6 goes into oscillation at a lower voltage than any of the RF
>> pentodes I tried. It might be a candidate for a low B+ regen. Also,
>> perhaps some of those extra grids could be put to work in space charge
>> mode.
>>
>>  Some comments on these way-cool experiments. What's unusual about your
>> using the 6BE6 as a replacement for the 6BZ6 is that grid 1 of the
>> 6BE6--which, per the 6BZ6 basing, its its control grid--is its
>> _oscillator
>> grid_. Grid 3 on the 6BZ6 is the tube's signal control grid; the 6BE6
>> specs in the RCA Receiving Tube Manual say that with the tube's grid 1
>> grounded and signal fed in at grid 3, the BE6's transconductance (7.25
>> millisiemens in this connection) is almost that of the 6BZ6 (8 mS) under
>> more or less the same operating conditions (and with its grid 3, its
>> suppressor grid, grounded). I'd be interested in learning how the 6BE6
>> operates as a regenerative detector with its grid 1 grounded and its
>> grid
>> 3 serving as its only control grid. Perhaps we can find manufacturer
>> specs
>> for the 6BE6 operating as an amplifier, with grid 1 as control and grid
>> 3
>> grounded; but the tube was designed for grid 3 to be the signal gozinta.
>>
>>  Yes, the more grids a tube has, the generally more noisy it is--in
>> small-signal operation. (Small-signal operation is when an active device
>> is operated in such a way that the incoming signal is small enough not
>> to
>> shift its dc operating point--that is, when the device is amplifying
>> linearly.) When a tube operates as an amplitude-self-limiting oscillator
>> it's in large-signal mode because its dc operating point--its dc
>> bias--has
>> shifted as a result of the presence of the signal it's generating and
>> handling. A regenerative detector operates in large-signal mode both
>> non-oscillating (it must be operating nonlinearly to "detect" AM) and
>> oscillating (in which state it amplitude-self-limits, commonly by
>> grid-cathode conduction).
>>
>>  So although it seems facile to consider that a pentagrid regenerative
>> detector might be or should be noisier than a detector with fewer grids,
>> we can't directly that from what we know about the relative noisiness of
>> tubes with differing numbers of grids operating *small*-signal.
>>
>>  Another thing to keep in mind when evaluating different tube types that
>> can be plugged into a given basing hookup is that in most screen-grid
>> detectors, only the embedded triode consisting of the tube's cathode,
>> grid
>> 1, and grid 2 does the RF amplification/oscillation. The specification
>> conveying the most significance to builders of such detectors, the
>> grid-1-to-grid-2 amplification factor (mu, pronounced mew), is only
>> rarely
>> included in tube specifications. (If "triode connnected" data is
>> available
>> for a given pentode or tetrode--"triode connected" in this case usually
>> meaning "by connecting the plate and grid 2 [screen] together"--the mu
>> reported can, per Lankford-Smith in the Radiotron Designer's Manual, be
>> taken as closely equivalent to the grid-1-to-screen mu.)
>>
>>  The variation from type to type of grid-1-to-screen mu is the main
>> reason
>> you've encountered significant regen-control-setting variation for
>> critical regeneration across the various types you've tried. The RCA
>> 6AK6
>> data doesn't include its triode-connected mu; as an example, though the
>> 6F6 pentode has a mu of 7 when triode connected. In contrast to this,
>> the
>> 6AU6, a sharp-cutoff pentode with transconductance about half that of a
>> 6BZ6, has a mu of 40 when triode-connected. So, yes, I'd expect that
>> you'd
>> have to turn up your regeneration "considerable" with a 6AK6 relative to
>> a
>> 6BZ6 or a 6BZ6.
>>
>>  That you had to turn up regeneration with the 6AK6 does not necessarily
>> mean that this tube is "worse" as a detector than the BZ6 or BE6; it
>> merely means it's different--for as I've reported earlier in this forum,
>> I
>> find that tubes with lower grid-1-to-screen mus are generally more
>> frequency-pulling-resistant in the presence of strong signals than tubes
>> with higher mus when they're all compared as oscillating detectors.
>>
>>  Best regards,
>>
>>  Dave
>>  amateur radio W9VES
>>
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