9 pin remote cuttoff pentode for IF

[N4LTA]

Was there a good 9 pin remote cutoff tube for IF work similar to the 6BA6 , 6BJ6, 6BZ6  ect?

Thanks,

Pat
N4LTA

[KM1H]

There are a small few that have that pentode along with a triode section Pat. I remember discussions on it but not the details.

Carl

[N4LTA]

Thanks Carl


I was afraid that was the case.

The reason that I was looking was that I am building an IF strip to experiment with on a PC Board (I have some 262 Khz PC type IF transformers) and 7 pin sockets with shields for PC board use are impossible to find. I was hoping for an equivalent 9 pin as Belton makes a very nice shielded 9 pin PC socket. Maybe I'll have to build it on a small chassis.


Pat
N4LTA

[w3jn]

6EH7.   It's a frame grid tube with gobs of gain, so be careful with bypassing, lead dress, etc.

[N4LTA]

Yes - I had seen that one but was a little "scared" of it because of the high gain. I have some of them.

I may give it a try.

Thanks,

Pat
N4LTA

[KJ4DAQ]

I know one Europian tube,  EF89 used for IF.  It is a remote cut-off pentode.

73

KJ4DAQ

[Radiohead]

Also the EF80 and the EF184 (more gain) is populair here, used as first stage for a DDS or PLL amplifier.

[w3jn]

Meh, you can bias it to whatever gain you need.   Use some unbypassed resistance on the cathode, that'll provide some degeneration. 

If this is gonna be part of a complete RXer at some point, you'll prolly need two AVC loops - one for the RF, and one for the IF.  Not a big deal though.

[WD5JKO]

  I have been bit by too much RF amp gain before. This happens when the bandwidth of the RF amp passes a signal outside the IF passband such that the IF detector never sees the signal since the IF amps have much narrower selectivity response. This means the RF amp(s) run at full gain (no AGC from off freq BIG signal) which overloads the crap out of the first mixer stage. This causes blocking.

  A couple of ways around the problem include adding a second AGC loop where the 1st mixer input is sensed, and AGC action from it derived, and increasing the dynamic range of the RF stage(s) and the 1st mixer stage.

  The RCA AR-88 receiver is a good example where a strong signal 20 Khz away from center can completely block the receiver...like a squelch. Those 6SG7 RF amps overload the heck out of the 6SA7 mixer.

Jim
WD5JKO

[KM1H]

I like the way the SX-28 handled the front end with both a seperate AGC loop and bypassing the 2nd RF stage on the 2 lower bands. By 1940 standards it was a hard radio to beat.

Id have to say that the AR-88 decided on 2 RF stages primarily for image rejection and gave little thought to gain distribution. Reducing the gain of the second stage should help. Either with resistor changes or putting in a slug such as a 6SS7. Changing the uber noisy 6SA7 to a 6SB7Y will drop the noise considerably on 20M and up. I had an 88 in the 70's but wasnt overly impressed and sold it quickly.

OTOH, the RCA RBB and RBC is damn near bullet proof and it might help to study their circuit.

Carl
KM1H

[N2DTS]

Is this for a homebrew receiver?
What is it going to be used for?

I see no need for any RF amplifiers below 20 meters with a good antenna.

My simple homebrew design seems as good as the flex 5000 and better then anything else I tried, on AM, on 160 to 40 meters.
High Q circuit into the mixer, then right into the filter.

I can TX 700 watts 5 to 10 KHz away and dont see it on the scope monitor on the IF!

Noise is very low, no antenna, no noise at all.

Weak signals might be a little more readable on the homebrew than the flex (phaze noise?)

I suspect it could be pushed to 20 meters fine, but never tried it.

I also suspect people tend to overdesign receivers.

Brett

[N4LTA]

This is for the IF amp - Not the RF amp.

The receiver will have no RF amp initially.

I made a custom PC pad design for a 7 pin socket that I think can accomodate a solder type pin socket with a shield and I have layed out a strip with two 6BA6s  initially. The IF can are 262 Khz PC type cans.

I may go with a frame grid IF a little later

The mixer is a Pullen and the detector is a infinite Z type  - all are on individual PC modules.

So far I have built and tested the Audio amp and preamp    - An EL34 with a 6C4 - and the preselector and the VFO.

The VFO is a 12AT7 with a cathode follower.

The Pullen is built but not tested as is the infinite Z detector.

It is just a little modular play project to how individual things fit together

[w3jn]

Cool!

You might try a separate amplified AVC channel and detector.  You'll need anohter 6BA6 and another 262 IF xformer.  Tapp off the primary of the last IF xformer with a 50 pF cap or so to the grid of this 6BA6, plate circuit is the primary of the new 262 xformer.  Then hang a 6AL5 off the secondary for the AVC detector.

This will help keep the infinite impedance detector infinite impedance, with no capacitive loading.  You'd be tossing away many of the advantages of the imfinite impedance detector if you detect the AVC off the same secondary.

One reason the SX-28 and R-390/390A sound so good is because they have separate amplified AVC channels/detectors.

[N2DTS]

Sounds like a really fun project!
I really like the idea of building it on circuit boards in modules.
I never tried that, but it seems like a very good idea, and easier to work on/build/change.

I don't like circuit board mount tube sockets, in older stuff they could be problems, but good work in building would eliminate that problem I suppose.

Since I built my RX's for hifi, I used broad band 455 KHz IF transformers for car radios I think, and let the kiwa filter do the filtering. They work like mechanical filters, maybe better, and the IF does not roll off the bandpass, or change it.

It seems pointless to me to try and get the IF cans to generate the bandpass filtering.

I have been thinking about building a CW rig, which would need a seperate AGC takeoff before the bfo.
I was thinking to split the IF after the mixer, one strip would go to the detector, the other to the agc circuit.
For AM, you don't need to do that, but might for CW.
I dislike audio derived agc on CW!

With all the experimenting I will have to do, I should build things on circuit boards in sections.
Not that I have to etch the boards though....

Receivers are REALLY fun to build!

Brett

[KM1H]

You might try a separate amplified AVC channel and detector.  You'll need anohter 6BA6 and another 262 IF xformer.  Tapp off the primary of the last IF xformer with a 50 pF cap or so to the grid of this 6BA6, plate circuit is the primary of the new 262 xformer.  Then hang a 6AL5 off the secondary for the AVC detector.

This is one area Id cheat as the 6AL5 is not a good detector diode IMO. A 1N34, 60, 270, and other germaniums are more sensitive. Schottky diodes are another choice such as the ubiquitous 1N5711.

Carl
KM1H

[N2DTS]

Carl,
Why do you need sensitivity for the agc detection?
I put 2 diodes in series for a delayed agc response, I did not want the agc to kick in till it had to...

Brett