Mixer

[N4LTA]

I am in the process of building a 262 Khz IF strip as previously discussed and plan to put the Mixer on the same modular chassis. I am leaning towards a 7360 beam tube but I am open for other suggestions. Is the 7360 state of the art for vacuum tubes or is there a better solution?

Thanks

Pat
N4LTA

[w3jn]

A Pullen (two triodes) gives a sheet beam tube a run for its money.

I'd go with a 6JH8 instead of the 7360.  It's a dirt cheap TV tube that's very similar (different basing though).

You'll need to play with the LO level to get the best performance.  Push-Pull LO injection on the deflection plates, with good balance, will null any feeedthru, just like a DBM.

[KM1H]

NOS 7360's still show up in the under $10 range in old stashes. At least all the characteristics are well known and documented in decades of mixer use.

The comments Ive seen over the years on the TV set versions dont seem to include sufficient design info for Plug n Play. Maybe I missed them.

The Pullen is excellent and the 6ES8 is the best of the non exotic tubes as well as not expensive and its documented in mixer use. The 6DJ8/6922 is a close second and many other dual triodes will give good performance, even a 6J6.

Do a Google on Pullen Mixer and there is a bunch of info.

John, I thought you were in transit? Are they giving you a new Suburban?

Carl
KM1H

[N4LTA]

I have a couple of 7360s and ordered three 6JH8s.

Would you use the same circuit in the BFO mixer or is that overkill?

Pat
N4LTA

[W1VD]

Some info on 7360 dynamic range vs. LO injection level should you decide to go that route...

http://www.w1vd.com/SS-1R.html

(scroll down to 'Examination of 7360 LO Injection Level')

[w3jn]

Naw, I'm here in SV-land, Carl.  No g-ride for me - I shipped a Cadillac CTS but until it gets here I'm bumming rides and riding the bus.

To the topic:  Carl;s right about the 6ES8.  It's one of the few variable-mu triodes, and you can apply AVC to the input grid for even better dynamic range.

[WA1GFZ]

Enjoy the view John greek women are hot

[KM1H]

Thats cuz they braid their armpits   At least in the early 80's the last time I was there!

My #2 son is married to a civilized one and they will probably be making weekend trips to Athens, Rome, etc if his transfer to the embassy in Dubai comes thru in December.

Enjoy your time there John, dont dissapear from the forums.

Carl
KM1H

[k4kyv]

Naw, I'm here in SV-land, Carl. 

Have you brushed up on your Greek?

I was there for a couple of short visits back in the 70's.  Nearly got run over by a bus one time in Athens.  At that time they would let you freely crawl all over the Acropolis and explore.  I understand that since then, they noticed that the thousands of tourists scrambling over it every day was eroding away the stone, so now it is off limits to the public and you have to view everything through a fence.

Regarding the 7360's, someone sent me three n.o.s. ones a few weeks ago, but the parcel came open in transit and the only thing that arrived here was the empty box with no contents.  I recall having to run 7360 filaments off DC to avoid hum in the output.

[N2DTS]

What are you going to do with the receiver? What is important?

In my homebrews, I used a 6be6 mixer, with a 6c4 LO.

It seems very quiet, very tolerant of LO injection levels, does not load the LO down, does not seem to distort at high signal levels, I cant find any problem with it.

With the antenna disconnected, there is NO noise from the receiver.
I run all the tubes off 150 volts or less, which might help keep the noise low.

I did lots of experiments with various mixers and LO's, and the simple circuits I ended up with seem to work best.

I did not try the beam tube mixers though, as I dont have the tube.
 
I suggest experimenting before the design is final, I learned a lot on the first receiver I built.
There are lots of designs out there, but you have to go with what you can get to work well.
I had no luck with triode mixers or multi winding LO coils.

Brett
N2DTS

[w3jn]

Don - nope, no greek for me.  Most speak at least some English.

As a contrast to some countries I've visited, Greeks are very tolerant of foreigners.  Last nite at the supermarket, I was in line, and the vegetable weighing lady (you bring your produce to her for weighing/pricing, there being no scales at the checkout) was yelling and gesticulating at every person in line in succession.  When I got to her she asked me something in greek, and I said "I'm sorry?" - she then gave me a big smile and asked from which bin I had gotten the bananas, and thanked me politely.  Then she went back to yelling at the guy behind me 

[KM1H]

Sounds just like my daughter in laws family John   They are loud, gestulating, and fun to be around. Sorta like Italians but using an incomprehensible language.

Growing up around Italians in Brooklyn I had a pretty good language understanding by the time I went there.

I did the Acropolis crawl up the the side and thru the brush in the early 60's one of the many times the USN pulled into Pireaus. That was long before any serious preservation or restoration started.

Carl
KM1H

[N4LTA]

Pretty much a dedicated 75 and 40 meter receiver for mostly AM but I probably will put in a product detector. I am going to build it in modules. I already have started the Audio - dual EL84s with a 12AT7 Phase inverter and first preamp and probably another 12AX7 for an Infinite impedence detector and amp.

[N2DTS]

Then you might look at my receiver design, in electric radio 176 and 177 (January and Febuary 2004).
It was very easy to get working, a number of people have built it and had it work.

No special parts, nothing seems critical, very good fidelity as far as I can tell.

Brett

[w3jn]

An infinite impedance detector is great.  The only "but" is that to take full advantage of the properties of this detector, you should use a separate, amplified AVC stage.  That is, lightly capacitively tap off the plate of the last IF (10-20 pF or so), to a 6BA6, whose plate circuit has another IF xformer.  Detect the AVC off the secondary of this xformer.

By doing this, and putting a pot in the cathode of that 6BA6, you can (1) independently control the AVC characteristics of the receiver and (2) eliminate any capacitive loading on the audio detector stage.  This will give you very nice low-distortion audio detection.

In my HB I learned the hard way that trying to use an infinite impedance detector and AVC detector off the same xformer will give audio distortion at high modulation levels due to the capacitive loading of the detector circuit.

Carl - I'm finding I need to work on my gesticulating skills to survive here 

[N4LTA]

N2DTS

I don't have those issues of the magazine - Is the radio posted or available anywhere?

Pat
N4LTA

[N2DTS]

I will send you some info.
I should have included it with the IF transformers.

Brett

[WU2D]

75 and 40M? Why not use up more of those 12AT7s? It will make a fine tube for both HFO and Mixer and with the second sections, you get buffering. Here is a typical Pullen circuit. There are better lower noise tubes like the 6ES8 but really any 12AT7 or 12AU7 would do a good job on the low bands.

Mike

[KM1H]

Some have even used octal dual triodes as Pullens in WW2 Super Pros up to 18 mc. I might have to give that a try in a SX-28 and see how high they can be pushed.

With all dual triodes, except the 6ES8, there will be a need for something besides  IF stages on the AVC line. This means a controlled RF amp even if set for near unity gain.

Ive never evaluated signal handling with a Pullen connected directly to the antenna. Rapidly varying input levels may have pulling effects on an unbuffered LO.
The 7360 for sure doesnt like reactive loads which was a major complaint against the SS-1R at the time.

Carl
KM1H