[Milsurplus] [regenrx] Re: pentagrid detector sensitivity
Michael A. Bittner
mmab at cox.net
Thu Jan 5 21:57:39 EST 2012
Interesting! I guess the reason for setting different pulse codes with the code wheels on the set is to enable distinguishing one path from another.
In any case, why use a pentagrid converter as a triode?? Mike, W6MAB
----- Original Message -----
From: Ray Chase
To: Michael A. Bittner ; regenrx at yahoogroups.com
Cc: milsurplus at mailman.qth.net
Sent: Thursday, January 05, 2012 6:39 PM
Subject: Re: [Milsurplus] [regenrx] Re: pentagrid detector sensitivity
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
>
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
More information about the Milsurplus
mailing list