[Milsurplus] [regenrx] Re: pentagrid detector sensitivity

Thu Jan 5 21:39:18 EST 2012

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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