RCA 6146 Tube

N2CQR's Mighty Midget Receiver

Here you have Bill Meara N2CQR Mighty Midget pictures and comments.

Before and after...

Bill used an old Heathkit 'sixer' transceiver cabinet and chassis to host his receiver. Here you have a similar one ('twoer'), side by side with his MMRX.

MM operating position

MMRX with a Heathkit DX-60B and VF-1, with a Radio Shack speaker. Note intercom used for 'around the house' listening.

Parts layout

Here you have the MMRX parts layout.

Here you have some messages Bill sent to the Glowbugs List about his MMRX:

Date: Sun, 14 Jun 1998 02:26:10 -0400
From: Bill Meara
Subject: GB Might Midget RX report

With new telescopes they have 'first light' so with homebrew receivers I guess we should call it 'first sigs.'

This evening I received signals with my homebrew Mighty Midget receiver. I'd had some trouble getting the crystal filter circuit to work properly, so I temporarily put a 455 kc IF can in the circuit in place of the filter (the can itself plugged in to the two adjacent FT-243 crystal sockets - fit like a glove!). I'll eventually get the filter working, but the quick switch did the trick and allowed me to got to bed happy in the knowledge that the radio works. Special thanks to James, W5LWU, who donated the crystals. 455 kc rocks are getting hard to find. One crystal company wanted 75 dollars a piece to make them for me! Ouch!

RX works FB. Not enough audio for a speaker, but 80 CW and 75 phone sounded especially good through HB circuits.

73 de N2CQR
Bill Meara, Falls Church, Virginia

Date: Sun, 28 Jun 1998 15:45:12 -0400
From: Bill Meara
Subject: GB More Mighty Midget RX News

Solder melters:

I guess you know you are becoming a fanatical homebrewer when even Field Day can't pull you away from the workbench!

Here's the latest on my Mighty Midget RX project. This receiver is really FB!. I've been amazed by the stability. After a very brief warm up period, I can leave it tuned to rag-chew roundtables on 75 or 40 for hours without having to re tune. It's got all the sensitivity needed on these bands: I can hear the band noise!

Without the crystal filter, selectivity is, of course, not so great but the two 455 kc IF cans do an adequate job for phone. Last week I bought a couple of 455 kc filters (one Toyo, one Collins) on the net. I also found some 455 kc crystals. During the next week or so I will be doing some cut-and-try experimentation with various filter arrangements and will report results to the group. I'm also thinking (a little) about an outboard Q multiplier.

BTW, this morning I came across an article in the February 1963 issue of CQ describing the pioneering crystal filter work of J.J. Lamb. Lamb wrote QST articles in the August 1932 and March 1933 QSTs describing how to achieve single signal results with one crystal and a variable cap.

Frequency coverage is great!. With a little pruning of the oscillator coils (wound on pill bottles!) I now have coverage from 3558-3992 kc and 7030-7593 kc. The tuned circuits in the RF amp and mixer grid circuits don't really allow for a 'peak' at the low end of 80. I could fix this by adding a bit of capacitance, but I'm not really planning on using this RX for CW so I won't bother.

I have had some trouble getting the two ganged tuned circuits to track properly. The two section variable cap I'm using is missing the little screws for the trimmers, so I just experimented a bit with external trimmers of similar values. I found I could get good tracking on one band, but not both. I suspect the inductances of the hand-wound coils are not close enough for good tracking. I decided to optimize for 40. 75/80 still sounds great.

I notice some 'mixer pulling' of the H.F. oscillator when I swing the cap in the RF amp and mixer grids. But this is no big deal.

On really strong SSB sigs, it seems like I don't have enough BFO energy to properly demodulate. I suppose I could put coupling cap between the BFO and the IF amp, but instead I just back off the RF gain a bit and everything comes out just fine.

I thought about putting another stage of AF amplification in there, but the Sixer chassis is getting a bit crowded and I decided not to push my luck - too much AF gain on too small a chassis might cause the kind of feedback trouble that I've completely avoided on this project. The RX works fine with headphones, and for speaker operations I just plug in one of those computer speakers with an internal AF amp. Works great!

Parts that I've noticed are hard to come by: 455 kc IF cans (AES is out of them!) and of course 455 kc crystals.

One final note: When involved in a project like this, its a lot of fun to browse through the radio magazines of the era. It is amazing how many tips and ideas you can pick up by doing this.

I hope the other MM projects are going well.

73 de N2CQR
Bill Meara, Falls Church, Virginia

Date: Sun, 12 Jul 1998 14:01:23 -0400
From: Bill Meara
Subject: GB Mighty Midget on the air!

I solved my muting problems with the Mighty Midget Receiver. In addition to lifting the RF gain control completely off ground, I now also lift the cathode of the IF amplifier off ground. As you can imagine, this seriously reduces the receiver's gain!

I matched the RX up with a DX-60B (cobbled together from two hamfest-acquired junkers) and got on 40 this weekend. First QSO was on 7010 CW with W8DAN in Xenia, Ohio. Then today I got on AM (I have a crystal for 7295) and worked Jim, N8ULN. It was a real thrill to use the little receiver for a for-real AM phone QSO.

Operating flexibility will hopefully be improved when I get my VF-1 VFO going. My version looks like it was put together by a demented soldering school drop-out! The bright side is that by tearing it down and putting it back together again, I'll experience (sort of) the joys of Heathkit building.

I hope all the other MM RX projects are going well!

73 de N2CQR
Bill Meara, Falls Church, Virginia

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