The AM Forum

I'm thinking about building a version of one of Crosby's HBR receivers, with some modifications.
I'm trying to decide if it is worth using a gated beam mixer tube (7360 or similar) or to go with
the 6ES8 version of the Pullen mixer that I've seen used in the 75A5. Or even some 6J6s since
they've been multiplying in my cellar for decades...  I keep vacillating between going whole
hog, by then I keep thinking simple and cheap has some merits too, especially since the parts
are totaling around $75,456 in 1959 dollars. ;D

So, I need someone to talk some sense into me, I am not sure the outlay and work for
the 7360 is going to buy me all that much in dynamic range or noise figure?  Anyone
try both in set and can share their experiences?

Pete  k1zjh

Hello Pete

Can only speak to the 7360. I've spent the last six weeks restoring a Squires Sanders SS-1R (no rf amplifier, 7360 first and second mixers, i-f filter, i-f amplifiers, etc) to peak operating condition and making receiver dynamic range measurements. I'm in the process of writing a web page on the results.

On 40 meters (only) the receiver is single conversion so that provides a convenient look at the performance of a single 7360 mixer all by itself. The receiver has no rf amplifier so the progression is antenna, front end filter, 7360 mixer, i-f filters, i-f amplifiers, detector and audio.
 
As built by Squires, the LO to the 7360 was about 6V p-p...RCA recommends 10V p-p to the deflection plate. The measurements below are for the stock receiver with 6 V p-p and other levels using an external HP8640B and amplifier as the LO.

Stock (6V p-p):
MDS: -136 dBm
Blocking (20 kHz): 120 dB
Two tone (20 kHz): 89 dB

HP8640B (10V p-p)
MDS: -138 dBm
Blocking (20 kHz): 129 dB
Two tone (20 kHz): 94 dB

HP8640B (14V p-p)
MDS: -138 dBm
Blocking (20 kHz): 132 dB
Two tone (20 kHz): 94 dB

Note the good noise floor right into the mixer. The front end filter is simple and ingenious. It's a combination parallel tuned at the operating frequency and series tuned trap at the image frequency network and exhibits very low loss - thus the good noise floor. Image rejection is a lackluster 60 - 70 dB or so, though. Have a feeling, but haven't measured it, that the relatively unsophisticated i-f filters are responsible for the two-tone dynamic range topping out at 94 dB.   

Hope this info is of some use.

Jay 

   

 

   

Man that is quiet. I bet you could drop a 20 dB pad ahead of the radio on 40 meters.

Nice to see the great progress you made with the SS-1R. Some great information. Now you need a SS-1V  :D

Pete, I'ma gonna give ya the same answer I gave ya on ARF  ;D ;D

One other problem is that Crosby used the second harmonic of the LO on the higher bands
to reduce drift problems in the HBR receivers.  I can see how that might work with a 6BE6 mixer,
but I suspect the Gated Beam mixer wouldn't work in that application..

Pete

Jay, a couple of things since I spent a fair amount of time with a SS-1R at Sam Harris' place when he was evaluating it when it was new.

-  MDS isnt as important on 40, what is it and the images at 10M?

- Simulate a real world antenna with varying VSWR's up to 3:1 or so.

- Hook it up to a multiband antenna during a lot of activity.

Our experience was that performance dergaded rapidly from a pure 50 Ohm load as that simple filter wasnt up to the task. There were several others that tested those receivers back then with similar results and the writeups may have survived.

The best I could do with a 6GM6 and 7360 in a 75A4 was a 10M NF of a hair over 6dB showing the consequences of the added switching as well as a less than ideal LO level. For all but those rare and extra quiet 10M days it is sufficient and out hears any SS rig I own without using an external 1dB NF preamp.

My current experiences with a 6ES8 Pullen are most encouraging and I expect to finalize and publish the data later this summer. It does require attention to LO level and isolation as well as careful reading of all of Pullen's notes. A 6GM6 RF amp will result in a 10M NF in the 2dB range using an input tuned circuit, one at the output of the 6GM6 and another at the 6ES8 input. Coax connected as Im building modular for ease of experimenting.

Carl
KM1H

Carl

Is this a variation of the Pullen mixer that ran in ER for the 75A4 a while back?

Pete

I put a pullen mixer in my SuperPro. Now the original 6L7 had two stages of RF ahead of it and I suppose these helped to overcome the noise!

I did not go crazy, I was simply going to use a 6SL7 dual triode but I found aan octal in metal like your 6J6 with a common cathode the 6SC7 and used that.

I have no data other than to say it works great and is not noisy.

Mike WU2D

Carl

First, I'm not portraying the SS-1R as an example of good or bad receiver design...just reporting on the measurements I've made. 

The MDS on 10 meters (in stock form with starved LOs) is -135 dBm. I'd expect this to improve some with proper LO level as it did on 40 meters.

Image rejection measured somewhat >60 dB on all bands...thus my 'lackluster' comment.

Yes, the manual does indicate that the receiver is expecting something close to 50 ohms.

Until my recent measurements on the 7360 I had no idea what dynamic range performance to expect. A search of the literature and the internet turned up nothing in the way of hard numbers. How about the Pullen? Are there any dynamic range measurements for that circuit? How can one make an informed comparison without this information? Sensitivity and image rejection are only part of the equation.

 

 

 

Having had a SS-1R for about 16 years, this receiver wants a reasonably resonant antenna for the frequency range you want to receive. Long wires, random length of wire thrown out the window, or antenna impedances with lots of reactance don't work well at all with this receiver. Even multi-band type antennas can be a problem with this receiver depending on the design.

Jay, that is exactly what started this. I can't find any references for any measurements on
this mixer after weeks of searching. It all seems to be subjective observations so far.

Pete :)

Pete, that ER article was copied from a 1967 QST. Here is much of the available info on the Pullen.

http://www.mines.uidaho.edu/~glowbugs/receivers.htm

looks like a single ended mixer with low Z lo source. Not high performance looking to me in 2008

Agree completely Jay about measurement data. Since W2VCZ was a very respected DXer, author, and engineer Id have to believe he understood IMD and how to measure.

But as you know its not easy to compare apples and oranges. Im far away from the IF strip and filtering part of my project and Im not quite ready to hack up the 75A4 again. :)

Perhaps there is a cheap and simple receiver that those interested can purchase and implement the Pullen as well as several different beam deflection tubes. Then share and compare the info.

The various Heath's come to mind as well as the Kenwood R-599 but Im sure there are other choices that wont break the bank.




Mike, interesting about the 6SC7 but I dont know its 10M capability which of course doesnt concern a Super Pro. It has a pretty low transconductance.

Ive used a 7F8 Pullen in a S-40B, with just swapping out sockets, which has been a test bed for several projects and it actually allows 10M signals to be heard! However I havent worked on the LO or RF amp as yet so no real numbers are available but the 7F8 was used quite a bit up thru the FM band.

Carl
KM1H

Jay,
Correct me if I'm wrong but nobody really measured IMD before the early 70's when solid state receivers appeared.

It was understood and measured at least for the USN as far back as WW2. In the 60's and 70's the high end commercial marine radios had some of the best IMD performance of the time. Racal and Rhode Schwarz were European leaders.

Hams had tried to interest the manufacturers but got mostly lip service. Drake responded somewhat but it was aftermarket development that made the R4C a great contest radio.

It wasnt until the 80's that the contesters mustered enough clout to force the issue. I remember sitting in a lab on several Saturdays in the early 80's when YCCC members brought in their latest rice boxes for IMD and phase noise measurements. There were some pretty savy RF engineers in the club and they constantly came up with improvements. Then shared info with other clubs and finally the ball got rolling.

Another BIG problem was the ARRL who didnt want to run meaningfull tests for many years being afraid of offending the advertisers.

Carl
KM1H

i worked on a ship board preselector in a rack so they must have been quite interested in IMD but hams were later. on of the masters Rob Sherwood

Time to set the record straight...

Measurements on amateur receivers began in earnest in the mid 70's with work done by Wes Hayward  (July 75 QST article) in conjunction with Doug DeMaw and myself at ARRL. The new measurement technique spawned 'receiver wars' between the three of us as well as a couple Murphy's Marauders contest ops - Fred Lass, K2TR (CX-7) and Dave Pietrezewski, K1THQ (R4C). Also involved early on with visits to the ARRL were Rob Sherwood (R4C) and Frank Carcia, WA1GFZ (SB-303). 

This link http://www.w1vd.com/receiverspecs.pdf (http://www.w1vd.com/receiverspecs.pdf) is an interesting original document (circa 1977) of early receiver measurements made at ARRL. Note my old call sign - WA1LNQ - changed to W1VD in late 1977. I made all receiver measurements at ARRL up until my departure in 1980.

The addition of receiver testing in product reviews came about in an orderly fashion once Hayward, DeMaw and myself were sure we had the technique and equipment perfected and the tests were truly representative of 'on the air' receiver performance.       

YCCC (or any other club) had nothing to do with forcing ARRL to print receiver tests in product reviews. Note that the first product review to contain receiver dynamic range tests was the Yaesu FT-901DM in November 1978 QST. This significantly predates anything that YCCC might have been doing in the 80s.

 

   

A day in heaven way back when. A pair of URM25s and a combiner. I worked on that SB303 for a year to bring the dynamic range from 67 to 86 db. When Jay first tested it for me and showed me the test method I had too much gain in the first IF. Later my boss an old Radar guy Howard Bleam let me use the lab stuff for further testing. 
I think the CX7 is still quite an RX.
Then synthesizers showed up and we all learned about close in phase noise.
Again last night with my new computer running 4 %  horsepower the RA6830 pulled AM signals out of the noise better than the SDR.

Jay, I dont read anywhere that I claimed the YCCC forced the ARRL to do anything. In fact, once the manufacturers started coming around they went directly to the user for new product suggestions and improvements. Not to say that the end result was always that great ;D

It was a result of many clubs and individuals pooling resources. Im sure you remember some of the discussions at Dayton.

It was also rather recently that the ARRL revised their procedure to include close in IMD testing; I dont remember exactly when.

My own involvement was using Pin diodes in the front end switching of the TS-940's. Initial testing was quite positive but I got a lot of noise from "experts" who claimed the cheap general purpose diodes were fine. A chance phone conversation with Ulrich Rhode, who ordered regularly from RK, turned things around as he had the clout to deal with the manufacturers as well as irrefutable test proof.

I also proved that Pin's in the TX path reduced the broad band residual noise which had been a problem for me when using the 940 to drive VHF/UHF transverters.

Carl
KM1H

Do you remember what you did to the 303?  There are still zillions of SB and HW rigs in use and Im sure a few would like the info.

As far back as I can remember Sherwood was preaching gain equalization and Ive followed that advice.

Carl
KM1H

I homebrewed everything between the output of the RF amplifier and IF filter.
The first IF was replaced with a tracking amplifier tuned by VVC diodes. They were tuned by a 10 turn pot geared to the main tuning shaft. Double balanced mixers. Cascaded IF filters and a third set between the IF output and detector. In the end the shielding between stages limited the performance. 86 dB of dynamic range back then wasn't that bad. Heck I think the FT102 is no better. fc

P.S. The new ARRL dynamic range test is bogus to hide rice box close in phase noise problems.  S5 noise floor get real

Carl...just want to dispel any notion that advertisers were exercising influence over advertisement acceptance or product review content...at least through 1980...no idea what policies may have changed, though, after that.

Back to the original question of this thread...

Perhaps what is needed here is a mixer 'test bed' so that various tube mixer configurations can be tested and characterized for noise figure, conversion gain or loss, blocking dynamic range and two tone IMD. Just thinking out loud here...a small chassis, tube sockets, some sort of input and output matching to 50 ohms etc., connectors in and out and for the HV and bias. External adjustable power supplies (like the small HP units) would provide convenient testing under a variety of conditions. The underside of the chassis would have terminal strips to support the required components for each mixer type that could be wired up quickly in a temporary fashion. An HP8640B/amplifier could be the LO. 

I'd be interested in taking on the project as time permits...and probably have most everything in terms of parts and test equipment required. What say...comments, circuits, suggestions?           

 

Carl...just want to dispel any notion that advertisers were exercising influence over advertisement acceptance or product review content...at least through 1980...no idea what policies may have changed, though, after that.

I have no idea what actually went on especially in the executive offices. Just what Ive heard from a few former members in the T&E area back in the 80's and 90's.

Back to the original question of this thread...

Perhaps what is needed here is a mixer 'test bed' so that various tube mixer configurations can be tested and characterized for noise figure, conversion gain or loss, blocking dynamic range and two tone IMD. Just thinking out loud here...a small chassis, tube sockets, some sort of input and output matching to 50 ohms etc., connectors in and out and for the HV and bias. External adjustable power supplies (like the small HP units) would provide convenient testing under a variety of conditions. The underside of the chassis would have terminal strips to support the required components for each mixer type that could be wired up quickly in a temporary fashion. An HP8640B/amplifier could be the LO. 


We are thinking similar. I have all the necessary lab equipment here including a HP-8970A


I'd be interested in taking on the project as time permits...and probably have most everything in terms of parts and test equipment required. What say...comments, circuits, suggestions? 

As time permits is the key. Ive been poking along on 2 receiver projects for about 6 months now in between work that generates a profit and some AM rig building.

Id suggest we work thru a full set of beam deflection tests with all the available tubes and in all configurations. Im a bit concerned with linearity in some of the less well known tubes.

The same with the Pullen but there is a much larger tube selection plus at least 4 sockets.

Carl
KM1H

How about 4 triodes in an h mode mixer

Carl, Frank

Sounds like we're all pretty well set up for the task. Have 8970B/346A setups here as well. Could be a very interesting project to finally put some hard numbers to previously subjective test results. Fall/winter project? 4 triodes in H mode? Single & double balanced 7360s? Pullen? What else? Would be nice to have multiple 'labs' working on this project to spread out the workload.   

 

Has anyone compared the performance of the 7360 vs the (then) cheaper 6AR8's and similar TV beam-deflection tubes?

The last time I worked with the 7360 (late 70's) they made about the best front-end mixer available in terms of noise and dynamic range.

I have several of the tubes on hand that I bought brand new back then, plus a handful of 6AR8's.  Plans were to build a receiver with no rf stage ahead of the mixer, just passive tuned circuits, feeding the 7360 which would work directly into the selectivity filter.  Got sidetracked from the project, but may get back "round tooit" some day.

One thing I recall was that the 7360 was very sensitive to a.c. hum induced by the filament current.  I would recommend running the filament off DC, just as I do my 12AX7 microphone pre-amp stage.

Sorry guys I'm stuck in the solid state world and SDR. H mode mixers are hitting iP3 of 50 dB these days. Gain distribution is the bigger deal after phase noise.
.....But it is interesting reading..
My next big project is the PDM modulator for the 75 meter final I spent the spring making the chassis with a drilled and tapped heat sinks.

Anybody can play with SS and SDR, just plug in the numbers ;D  It takes real men to do it with hollow state :P

Having worked up to 75 GHz before retiring Im happy to be actually seeing what Im working on again.

Memory tells me that the 6AR8 was a real dog and pulled off the market. Of course all the NIB ones are still available since there is no replacement market. Perhaps someone has more info.

Jay, Id keep it to the two types for now as Im sure there will be a lot of interesting discussions, "arguments", changes, and whatever. Save other circuits for the next stage.

I like to prototype dead bug style using PC and perf board stock. Im also a big fan of toroids and use a military TS-671C Q meter to evaluate and optimize. It is very much equal to the HP-4342A as far as comparable results.

Winter sounds like a good time, its not that far off for NH.

Meanwhile we need a list of all the candidate tubes. The Pullen will have a rather large list and I suspect the 7 and 9 pin miniature will generate the most interest. Ive been playing around with many older styles as a matter of curiosity as to how they perform using modern circuits and components.

Carl
KM1H

Hey Carl,
If you can't see the spark it is magic at any frequency

I got this reply on a usenet forum, and figured I'd share it. Anyone care to comment on how DC balance could have been achieved with this scheme?  Anyone have a copy of this RSGB publication????????

Pedro
---------------------------------------------------------------------------------------------------------

Back in the 1960's, Pat Hawker, G3VA reported (Amateur Radio
Techniques, Pat Hawker G3VA, 3rd ed, RSGB, p83) that Brian Booth,
G3SYC (SK ca. 2003), had used the 6JH8 beam deflection valve instead
of the 7360. Brian compared the two devices:
i) 6JH8 has a good deal more linear transfer characterisitic
ii) 6JH8 operates with the deflector plates at 0 volts, ie unnecessary
to bias to plus 25 Volts as per the 7360
iii) roughly similar transconductance 4400micromhos vs 5400micromhos
for the 7360
iv) 6JH8 has double the anode dissipation (3 watts)
v) then as now the 6JH8 is significantly cheaper.

The final comment was that Brian had used the 6JH8  as a receiver
mixer and also successfully as a mixer in transmitter circuits.

HTH and 73

John  KC0G

Carl

Guess I'll head off in the sheet beam direction since I've already been testing the 7360. Maybe you can  take the Pullen? Started pulling parts last night for the 'test bed' ... but that doesn't mean it will get underway anytime soon.

Pete

Couldn't find the curves for the 6JH8. Did see curves for the 6ME8 and it looks like that tube is set up for 75 VDC on the deflectors...and appears to handle bigger signals. Guess if one of the tube variants was designed for 0 VDC you could adjust one deflection plate slightly above or below 0 VDC.

So far my list of tubes to test includes: 7360, 6AR8, 6HW8, 6JH8 and 6ME8. What others need to be on the list?

 

Maybe this is it Pete:
See attachment
Info came from a German forum:
http://www.circuitsonline.net/forum/view/48065/2

That will be fine Jay as Im already involved with the Pullen.

Here is a pass at some suitable tubes. Im listing the older versions as possible easy retrofits to existing radios.

7 pin miniature: 6J6

9 pin miniature: 6ES8, 12AT7, 6DJ8/6922, 6BK7/6BQ7/6BZ7, 6JK8, 6JL8

Octal: 6SN7, 6SC7

Loctal: 7F8

Other suggestions welcome, I know there are lots of other 9 pin out there.

Carl
KM1H

HI Carl,

It's a great idea to come up with a list, but it could easily become overwhelming. One thing you might consider is to have multiple samples of each type part number decided to be tested. We have all had experiences with individuals that perform better than others of the same type.

May I also suggest that you consider picking a representative from each of the four triode types, Low mu, medium mu, high mu, and variable mu, and compare them on that basis? The 6J6 is a case to also consider as it has the common cathode. You might also select from a common base diagram, such as the 12AT7/12AU7 base diagram. Then you can make quick comparisons with minimal circuit changes. One would expect the low mu types to have the better dynamic range.

If you have access to a transistor curve tracer, you might consider using it to get some transfer curve data from tested tubes. I have a unit that provides steps in gate voltage for FET testing. Such a tester could easily be used with for tubes as it goes to at least 150 V. I am feeling inspired to make up a static test rig for this.
My curve tracer works with an external scope, so I could use ti with the Linksys PC scope. Hmmmm.


If I understand it correctly, the circuit description of the Pullen mixer explains that it depends upon different mu at different plate voltages, and the plate of the mixer stage is run at low voltage, around 60 VDC. This would suggest that the variable mu type might be best, though rarer to find.

You might also consider adding a pentagrid converter tube, like the good ole' 6BE6 for comparison. As I remember, the RCA Radiotron Designers handbook had a good section on mixers. It was concerned with noise performance of mixers and used a derived input resistance to compare noise performance. Tubes like the 6BE6 had high resistance and thus high noise. Triode mixers were described as having low resistance and lower noise.

The study could be expanded to include pentodes, and consider remote cut off vs. sharp cutoff, screen injection with low screen DC voltage, such as how a screen voice modulator works.

Another technique form the past is reducing filament voltage of the mixer tube. This could be tried out with the 12AT7 family types. Starve the mixer section filament.

Frank, the H bridge idea is interesting. The upper pair would need a separate filament transformer. One problem is that triodes are not a good switches as enhancement FETs. There were some dual triodes developed for computer work where they were used in switching applications.

Rob,
All 4 switches in an H mode are referenced to ground.
H mode isn't new. I saw a SSB generator in the west coast handbook using 4 triodes. No they won't saturate like a FET but have a large voltage swing.fc

Might as well add the 6SL7 to the list. Finding a use for those orphan TV
tubes is always worthy :)

Jay, some reports on what you find to be the best parameters for setting up those tubes would
be helpful as well. The anecdotal information on the web is all over the place, especially for
the operating voltages for the deflection electrodes!

Pete

Pete

Yes, the information in print and on the internet is somewhat lacking.

Planning a wide range of tests. The 'test bed' will be set up with all voltages adjustable as well as plate load impedance, cathode resistance, LO level etc, etc. The 6XX8 tubes appear to have significantly different characteristics than the 7360. Should prove interesting to look at just the mixer by itself on the spectrum analyzer and noise figure meter. Identifying peak performance when changing parameters or tube type should be much easier this way...as opposed to measuring them through an entire receiver with the fairly cumbersome sensitivity and dynamic range measurements.

Going to try to get to the project sooner than later and will note results here. Please post progress on your receiver as well!

 

Thats how Ive been doing it with Pullen and other mixers. Once Im satisfied with the circuit and record the data I then hook up the mixer as an ordinary converter but with an output attenuator for zero gain to a reciever with known IMD. The R-390A makes a nice shack warmer for this ;D

6SL7 added Pete. Im sure those audio octals will make it well up into the HF range and maybe even 10M. Many, myself included, prefer to keep some of the more collectible BA's at least looking original. For now Ive been using the 6SB7Y in place of the 6K8 and 6SA7 in some sets to bring the noise down about fourfold. Its certainly helped my BC-312N on 17M!

Carl
KM1H

Yeah the 6SL7 was the original tube for the Pullen that was suggested in the Souping the SuperPro articles. I only used the 6SC7 cause it was metal and I would not have to shield it. For miniatures, you have a great list. I would say the 6J6 would be a good baseline to test from since it might warrant an R390 spin. How would a 6J6 Pullen compare to a 6C4?

Mike WU2D