Tube type synchronous detectors

[Opcom]

The way particular IC's come into and go out of fashion, there is nothing like a gross of same-type tubes to spark the imagination and quell fears of EMP and obsolescence.

Case of 6GH8's
Case of 6J6's
case of 70L7's
3 Cases of 12BQ6's !!

to the point, some time ago, there was a discussion of this and a plethora, or even a cornucopia, of schematics, or copied articles about synchronous detectors.

These were tube construction articles, fairly old ones from before and during the beginning of SSB ham popularity, some complicated and fussy looking, some more simple.

Does anyone recall where this might have been or what topic?

Having recently borrowed an outboard sync detector (little solid state box thingie) and used it with an R-390A, I'm converted to wanting a sync detector and want to study them before deciding what to do.

I don't really need another project but I like to read and think. My boss says extracurricular reading makes me smarter at work.

[Pete, WA2CWA]

See http://amfone.net/Amforum/index.php?topic=18379.0;wap2

[Opcom]

Thanks! You using a cellphone?

[Steve - K4HX]

Specifically:

The article by Bill - W3DUQ from the September 1967 issue of 73 magazine is available at the link below.

http://www.amwindow.org/tech/pdf/w3duqsyncdet73mag1967a.pdf

[W7TFO]

A quote from W3DUQ, the author of the 73 article mentioned:

"Let's get rid of those outmoded, wideband, distorted telephone quality single sideband gizmotchies"

Nuttin' new under the sun....

73DG

[K3ZS]

I remember that article but did not realize that it was by W3DUQ.   Anyone planning on building it should try to get the demodulator tubes first.   They are hard to find.

[WQ9E]

It shouldn't be a problem to substitute some of the more readily available sheet beam tubes in place of the 7360 demodulator tubes.  7360 tube supply has dried up because of the commercial rigs that used them but other sheet beam tubes were used in consumer entertainment gear and are readily available at lower prices.

[Pete, WA2CWA]

6AR8, 6JH8, and 6ME8 are the most common, but note that they all have different pin wiring, so they are not a direct substitute for the 7360.

[w3jn]

The GE YRS-1, circa 1952 or so, is another sync detector that shouldn't be too awfully hard to copy.  There was a project in GE Ham News that was essentially the YRS-1.  The thing uses a passel of dual triodes but I don't think a 6J6 would be usable as the cathode is common in that tube (unless you wanna use each 6J6 as a single triode).

[Opcom]

A sheet beam tube moves the beam from one plate to the other, like a CRT moved the beam right to left, but has no similar anodes.

Seems like the 6J6 mentioned or any high quality dual triode could replicate the function to a degree for some purposes.

[flintstone mop]

Hey Patrick
Would there be any stability problems and-or alignment issues using tubes vs IC's and computer magic?
I realize there are some apps that tubes will out do a solid state circuit.
I wonder if anyone built Bill's circuit and how it would compare to today's Sync detector??
Would it give the Almighty Sherwood SE-3 a run for its money??

[vincent]

1929 Style Synchronous Frequency Detection:

http://www.google.com/patents?id=nzhHAAAAEBAJ&printsec=abstract#v=onepage&q&f=false 
 

[Rob K2CU]

The Kolozsy circuit looks like a direct conversion receiver with a ring demodulator for a product detector. There is no indication of how the local oscillator "locked" onto the carrier. He leaves out the detail of how the local oscillator is brought into "synchrony" (lock) with the incoming carrier.

The three sheet beam tubes that Pete mentioned, were intended for color demodulator service in TV sets and are plentiful and fairly cheap. 6ME8 - $3, 6JH8 - $4, 6AR8 - $5.

Should anyone be interested, I have created spice models for these as well as the 7360, and LTSpice schematic symbols for all. LTSpice is a free spice circuit simulator available from Linear Technologies.

I may experiment with a Tayloe mixer for the product detector since the L.O. would be at four times the carrier and less likely to get into the I.F. and juice the AGC. Now, to implement the Tayloe in hollow state.

[vincent]

Right, it is unclear how the synchronous detection occurs. It's interesting the mechanical arrangement (fig. 1) for the detection (mixing?) of the desired signal by using the coils of the speakers.
It would be interesting your Spice model for the 7360 but unfortunately I never used the Spice Simulator (my hair and beard are too white?  )

[Rob K2CU]

You are never too grey or white haired to learn about something neat, especially when it is free. Sure, LTSpice is aimed at their IC's, but they provide a pretty good set of provided models, and I will gladly share the extra goodies I have accumulated over the years. BTW, one of my associates who learned and uses LTSpice a lot is over 75. It is really good for simple things too, like filters. I used it to tutor my EE son in the workings of the TR-7, especially the front end filters.

I openly offer to help anyone who is interested in getting into using it.

[WA1GFZ]

I have a copy of a West Coast handook with a H mode mixer done with 4 triodes.
It was used as a DSB generator if I remember.
Lift the cathodes and add RCs and you get a tayloe.

LT Spice saves me a lot of time and solder, great tool

[Opcom]

Hey Patrick
Would there be any stability problems and-or alignment issues using tubes vs IC's and computer magic?
I realize there are some apps that tubes will out do a solid state circuit.
I wonder if anyone built Bill's circuit and how it would compare to today's Sync detector??
Would it give the Almighty Sherwood SE-3 a run for its money??

I can't answer that. There are too many variables. Would you agree that the main issues besides amplifier linearity is frequency stability and freedom from noise?

ICs in many cases have much better specs for stability and noise, and computers control precisely. The desire for tube gear is or a challenge to make it as good as possible. Certainly some of those designs would have been more than adequate.

I like Bill's circuit but am not going to build that one. I prefer to think about one one with a simple AFC circuit and balanced modulators.

This brings up the question of gating. Does one flip the signal polarity abrupltly at zero crossing or does one use a sinewave in a product detector?

[vincent]

Thanks for your offer of help Rob.  Actually I used a couple of programs, like the RfSim99, related to filters, and I found it very interesting and useful. What has piqued my curiosity is your model for the 7360, I'd be curious to see how it performs, as a mixer, (if this is possible) in a program, we can say virtually? I've played in the past with this mixer tube “live” connected to test instruments and in the “real world” connected to an antenna (maybe "someday" I will put a page on my website with some fresh results of these tests).

[Rob K2CU]

Besides mimicking the DC transfer characteristics of the tube, the model works in balanced modulator and mixer circuits in LTSpice. Like most spice simulations that involve RF, you have to take the results with a grain of salt. Typical inter electrode capacitance right form the RCA data book were included and you have a perfectly balanced tube. RF circuits with inductors need to have some measure of series resistance included or you may get unexpected results, even discontinuities, in the waveforms. From the 7360, models were derived for cousins 6ME8, and 6AR8. The 6JH8 is too close to 6AR8 to bother to make a model.

[Opcom]

GE Ham News 1948 vol 3 nr. 6 - has a locking oscillator adapter for AM and SSB

QST July 1948 has something similar, an exalted carrier demodulator.

These have simple AFC at best, different at least in description from the W3DUQ circuit. I'm not sure they used I and Q back then, not by name anyway.

I stand corrected, to have it all as in W3DUQ's design from "73" September 1967, or these others, means a lot of tubes.

It's all good reading but a big project and no matter how simplified it could be made it is not for a weekend, too much for around here due to other things in the works.

I'd admire it if you guys design or build such a beast though.

I could give those boxes of tubes to the YL.

[Opcom]

I confess!

I have given in to the lure of an appliance.. I ordered the rackmount version of the Sherwood Engineering Incorporated SE-3 MK IV adapter today.

This is a good decision based on the amount of time it would take me to build a similar item and the wish to try one out for SWL purposes, which I do a lot.

I asked the gentleman many technical questions in e-mail before deciding. All of them were answered well and after a phone call today I believe it will be very useful with the R-390A and/or the SX-28.

I have used the Rycom R1307A/GR with the R-390A's I.F. output. For elimination of unwanted sideband noises, It works well on AM in either SSB mode as long as the signal is zero beat, and it has an interesting AFC circuit so the BFO can be used in AM. It has no AGC but an input attenuator.
All of this is satisfactory but not at all automatic and takes some fiddling because the AFC is not a PLL and won't lock in over any wider a range than normal drift, so the fiddling comes in on round tables as there is always one person who is rockbound or a bit off. The schematic for the Rycom is a very interesting read (attached).

Once I receive the SE-3 MK IV unit I'll try it out and post in an appropriate topic.

I wish I was retired like some of the members here, with each day mine to do as I please, and I could then try building either the G.E Ham News equipment or the W3DUQ equipment, or even a combo, merged into one equipment and allowing either method of detection. Each has its own advantages. That could also be done at a parts count savings IMHO after studying both.

[vincent]

Thanks for the information and explanations. With particular reference to the 7360 as a mixer, I think these simulators are particularly useful when you vary the different parameters (plate voltage, grid, LO level, etc..) and then you can see improvement or worsening compared to the starting circuit. But I think there could be a substantial difference of measurement results between simulation and reality if one is not careful, as you suggested in your message.

Very interesting the Rycom R1307/GR receiver (and selective voltmeter), very good for VLF/LF reception and excellent as an “IF amplifier” for testing front ends. It would not be very difficult to add an AGC. Have you seen the characteristics of the audio output transformer? 

[Opcom]

This one only.. It would not be simple or cheap to replace it.

10KCT
250WV, 75mA DC
sec1 - 600 Ohm 10W
sec2 - 4 Ohm 10W
response +/-0.5dB 30C to 25KC
 (note no power bandwidth given)

The triode 6AQ5 setup can't make 10W, and the 160V B+ won't do it even if the screens were tied to + instead of the plates, but it seems like they considered that someone some day might hook the output stage to the 270V unregulated B+ and tetrode-ize it.

I'm happy with the perfect 1W or so I get!  - but the output stage's phase inverter seems a little weird, is it unbalanced?
Any more needed and I might as well use a 'shared' hi-fi amp.

It would be good to collect operating data on that stage and add it to the "triode connected beam tube" spreadsheet. The sheet has 200V and 250V data and it is very different than the 10K CT winding found in the Rycom data. - the 'book' specs go for 4K to 4.5K CT.

[vincent]

Yes, it would not easy to replace that transformer! That phase splitter seems to be a classic one, maybe not the best but it works. I sometimes connect an external speaker with very good results. This receiver has many interesting circuits, one is the product detector that uses a 7360, although not in its balanced configuration. The low internal noise generated by this receiver makes its use very pleasant. By adding a good SW converter (and an AGC) at its input (or directly to the 2215kHz IF ampli) would make an excellent general coverage receiver.   

[Opcom]

It's a boon for those with the simplest receivers too as any SW receiver with an IF in the set's range will do.

I don't know why a 7360 was chosen except might might have low noise or few irregularities where linearity is concerned. A byproduct of beam deflection rather than gridwise gating. The 7360 is very interesting.

There's also the E80T by Philips. So are there no Octals? I guess the concept was not thought practical before.

The 6BN6 is a gated beam tube, and somewhere there's a picture of its structure. It is similar in some ways to half a 7360.

The 7360 and the rest act like a display CRT, but it is a signal CRT with just two 'deflection plates', sheet beam tube.. The deflection is more nice and linear, not curved like a grid curve.

The BFO is injected to the control grid, which is decently linear in this tube. That is necessary for the linearity of deflection to be taken advantage of.

It would be very interesting indeed if there were a tube that were a 4 quadrant tube with a pencil beam instead of a 2-dimensional sheet beam tube. Then it could receive balanced input from two sources plus overall control from the grid. constellation demodulator.

Note the 7360 used in the Rycom is not fed a balanced input to its plates but unbalanced, and one plate is at signal ground, like a basic scope.. sort of a waste in some ways.  Am I right on that?

attach: 7360 compare to CRT
attach: 7360 datasheet