1330 kHz and 8340 kHz

[W0EP]

I am examining a 13-tube homebrew receiver.  It uses the small 7-pin tubes.
It looks like a single conversion.

The bandswitch is labeled for 80/40/20/15/10.

I see two crystals in conjunction with a switch marked "sideband - upper/lower"
and the two crystals are marked 1330 and 8340.

Is there any "magic" in the 1330 and 8340 frequencies?

I think my next step is to measure the output of the bfo to try to
figure out what the IF frequency is.

Just wondering about their choice of 1330 and 8340.

[AC5UP]

I see two crystals in conjunction with a switch marked "sideband - upper/lower" and the two crystals are marked 1330 and 8340.

That is a bit odd... Usually the crystals will be within a 3 to 5 KC spread. The 8340 I can appreciate as there are plenty of YaeCommWood's with an 8.3xx MC IF so the filters are easy to come by, but the 1330 KC crystal? Very odd choice and few designs will intentionally use an AM BCB frequency in a heterodyne scheme.

I think my next step is to measure the output of the bfo to try to figure out what the IF frequency is.

Or... If you have a signal generator and a 'scope or RF voltmeter, sweep the generator through the IF and at some frequency you should see a large increase in the output level. An IF strip is essentially a fixed-frequency receiver........

[W0EP]

Thanks!

I don't see any other filtering in the IF other than a couple
of stages of IF transformers and amps.

The audio amp seems to work.  Going to explore the IF as you
described, see if I can figure it out. 

[W4OP]

The freqs seem odd but not the math.
The IF would be (1330+8340)/2= 4835KHz  and the  het oscillator would then be  3505KHz.

This is the same scheme the Heathkit HR-20 used.
Their sideband oscillators were 4010 and 13990 yielding a 9MHz IF and a 4990KHz het oscillator

Dale W4OP

[W0EP]

Measured the BFO tonight. 

It adjusts from 82.7kHz to 85 kHz.

Injected a 7100 kHz signal in the antenna port, followed it through
first couple of stages, but it get's lost before the IF cans.  More
investigation required.

[N3QE]

Whenever I've seen crystals labeled things like 1330 and 8340, they tend to be surplus from VHF public service radios of the 50's/60's/70's. The actual fundamental frequency is related in a complex way (overtone, multiplication and IF offset) to the marked frequency.

If the last BFO is 85kHz and 13 tubes, then almost certainly at least a double conversion receiver, maybe with converters on the front for some bands (making it triple conversion on those bands.)

[N2EY]

I am examining a 13-tube homebrew receiver.  It uses the small 7-pin tubes.
It looks like a single conversion.

The bandswitch is labeled for 80/40/20/15/10.

Pictures, please? Tube lineup, description of size, type of tuning dial and number of gangs in tuning cap and bandswitch?

I see two crystals in conjunction with a switch marked "sideband - upper/lower"
and the two crystals are marked 1330 and 8340.
 

In other posts you measured the BFO as 85 kHz and mentioned lots of IF cans.

I suspect this rx is actually a double-conversion design loosely based on W6TC's HBR series, but using IF cans from ARC-5 receivers and bandswitching.

The HBRs had a tunable-oscillator front end that converted the ham bands down to a fixed first IF of 1600 kHz, to get good image rejection. Then there was a conversion to 100 kHz to get good selectivity. The HBRs were very popular in their time, and there are still hams building and using them, and variants of them.

The IF of the 3-6 MHz ARC-5 receiver is 1415 kHz and the IF of the .19-.55 MHz ARC-5 receiver is 85 kHz. The difference between the two is....1330 kHz! The sum is 1500 kHz, which may be what's actually inside the holder marked "8340" if it is FT-243 type.

73 de Jim, N2EY

[W0EP]

Thanks for all the advice.  This thing has some indications
of having worked  (dial calibration marks, etc.) but
also has loose ends.  So it may have been an unsatisfactory
attempt.  Makes an interesting puzzle!

Tube line up and  signal path (as far as I can tell so far)

 (underside, part 1 http://w0ep.us/radio_stuff/unkown_rx/GEDC0205.JPG )

<antenna>

Slug tuned coils selected by bandswitch along with a
one-section air variable (about  1 in. dia, knob labelled "antenna")
It appears that some coils are not attached.

<6au6>

More bandswitched coils.  Some small air-variables in this
neighborhood but they are not connected to anything!

<6cs6>  

nearby is a <6ak5> and some slug tuned
coils also bandswitched.  I believe this is the LO.

Single section air-variable cap on the top deck, a bit larger
in dia. (1.25" ?) and about 2 inches long (20 plates?)
which is attached to gear drive and main tuning.

IF can

<6be6>

IF can

1330 and 8340 crystals attached to
a switch marked for USB/LSB nearby
is a <6ak5>

IF can

<6cb6>

IF can

 (underside part 2  http://w0ep.us/radio_stuff/unkown_rx/GEDC0206.JPG )

<6t8>
    output to headphones

audio xfmr (I think it is not even connected)

<6aq5>

In the neighborhood of the 6t8 is a 6c4 and a
1'x1' can shaped thing.  from that collection comes the
BFO signal, loosely coupled by wire twisted in
near that last IF can.

<6au6> with a 100 kHz crystal which appears
to inject calibrator signal into the front end.

Tubes left over that I don't yet know the function of:  <12au7> <6ak5>

And there is a 5y3gt rectifier tube.

 (topside http://w0ep.us/radio_stuff/unkown_rx/GEDC0213.JPG )

The front panel is nicely painted with factory-type lettering.

 (front http://w0ep.us/radio_stuff/unkown_rx/GEDC0218.JPG )

Controls on the front --
knobs look like from a xxxxBC-348xxxx (correction, BC-312),
arrows and sometimes word printed on knobs
(left to right)

ANTENNA
SIDEBAND (upper/lower)  (knob says "crystal" and has an arrow)
Band switch  (80M 40M 20M 15M 10M)
R.F. GAIN
A.V.C. (switch: up-HIGH/down-LOW)
C.W. OSC  (switch: up-ON / down-no marking)
AUDIO  (integral power on/off switch)
PITCH
CALIBRATE (switch: no markings)
SQUELCH (integral switch)
PHONES (jack)
DIAL/SET  (little knob up near the dial which shifts
the rotating thing a bit left or right)

There is an s-meter in the upper left which is a Triplet meter
with pencil marks "s-9", "+20", "+40" on the meter dial.

Main tuning knob is in the center.  slide-rule dial with single,
narrow window and a turning mechanism actuated by the band switch
(mechanism is disconnected due to dial cord break).  Paper
cover on the turned cylinder has pencil marks with ham-band
type numbers.

I will try to get some pictures. (added picture links to this post)

Injecting a signal in the antenna I can follow it through the
coils and bandswitch.  It gets lost near the sideband switch.
But I'm not sure if I have the main tuning set correctly to receive.
I'll have to work on that some more.

With phones plugged in, I can get some sound if I
max the audio gain.  I'm thinking it is self oscillation.
Otherwise, no static or shoosh noise at all.

I don't know for sure that the tubes are in the right sockets,
but this is where I found them.  All tubes tested ok in
my ancient and dodgy tube tester. All tubes have bayonet-type
shields except rectifier.

Chris

[N3QE]

Looking at the wiring around the bandswitch... may have been built with some optimism about adding all those bands someday, but I don't think they're all there.

Check LO and BFO for oscillation on various bands/sideband selection. Could be done with a scope, counter, or just another HF radio.

[N2EY]

This thing has some indications
of having worked  (dial calibration marks, etc.) but
also has loose ends.  So it may have been an unsatisfactory
attempt.  Makes an interesting puzzle!

It appears to be a project that was never finished. Or maybe it was finished but then was cannibalized.

Tube line up and  signal path (as far as I can tell so far)

 (underside, part 1 http://w0ep.us/radio_stuff/unkown_rx/GEDC0205.JPG )

<antenna>

Slug tuned coils selected by bandswitch along with a
one-section air variable (about  1 in. dia, knob labelled "antenna")
It appears that some coils are not attached.

<6au6>

More bandswitched coils.  Some small air-variables in this
neighborhood but they are not connected to anything!

6AU6 is first RF stage. The intent was probably to have the first tuned circuit adjustable (hence the front panel control) but not the second. This may not have worked so well, and been a reason the design was abandoned.

<6cs6>  

nearby is a <6ak5> and some slug tuned
coils also bandswitched.  I believe this is the LO

Single section air-variable cap on the top deck, a bit larger
in dia. (1.25" ?) and about 2 inches long (20 plates?)
which is attached to gear drive and main tuning.

6CS6 is first mixer, 6AK5 is LO, big cap is tuning.

IF can

<6be6>

The first IF is almost certainly 1415 kc. Those IFTs are from ARC-5/Command sets (WW2 surplus). The 6BE6 is the second mixer, converting 1415 kc. down to 85 kc.

IF can

1330 and 8340 crystals attached to
a switch marked for USB/LSB nearby
is a <6ak5>

IF can

<6cb6>

IF can

 (underside part 2  http://w0ep.us/radio_stuff/unkown_rx/GEDC0206.JPG )

<6t8>
    output to headphones

audio xfmr (I think it is not even connected)

<6aq5>

In the neighborhood of the 6t8 is a 6c4 and a
1'x1' can shaped thing.  from that collection comes the
BFO signal, loosely coupled by wire twisted in
near that last IF can.

<6au6> with a 100 kHz crystal which appears
to inject calibrator signal into the front end.

Tubes left over that I don't yet know the function of:  <12au7> <6ak5>

Two stages of 85 kc. IF. The xtals provide sideband selection as mentioned before. The 6T8 is probably combination BFO and product detector. The can underneath is the BFO coil from an ARC-5

And there is a 5y3gt rectifier tube.

 (topside http://w0ep.us/radio_stuff/unkown_rx/GEDC0213.JPG )

Clearly based on the HBRs but with a lot of different ideas. The tubes are common 1950s TV types, probably chosen because they were on hand.

The rx doesn't match any published design I know of. It has some strong and some weak points. The major problem is that you don't have any documentation at all.

If it were mine, I would do one of two things:

1) Tear it down for the parts. Lots of goodies on that chassis.

or

2) Trace out the entire receiver schematic as wired. Then see how much sense it makes, and if missing bits can be replaced to make a working receiver.

If it is determined to restore it, I'd start with the power supply, getting it working right first. Then the last audio stage, getting it right, and working towards the antenna.

Your choice

73 de Jim, N2EY

[W0EP]

That is a whole lot of good info!

Thank you very much.  I really appreciate the help from this group.

Chris
w0ep

[W0EP]

I made a bit of headway with this.

I found that the LO was not putting out anything.
I used my sig gen to produce the proper freq for 40 meters
and I was able to receive signals.  (It helped quite
a bit when I  realized I should use hi-z headphones.)

Now I am looking at this LO circuit.

Here are the connections to the tube socket:

1 - RF choke, about 250 volts
2,3,7 - gnd
4 - filament voltage
5 - to bandswitch (resonant parts)
6 - 30 pf cap to different place on bandswitch (other side of resonant parts)
  and 10k resistor to ground and a 25pf  cap to the next stage.

There is a 6ak5 in this socket and I finally realized
that the plate of a 6ak5 is on pin 5.  So, the
RF choke is going into the grid.  That definitely
doesn't sound right.

How do I figure out what tube is supposed to be here?

I'm thinking it would probably have plate on 1,
cathode on either 2 or 7, filament btwn 3 and 4
and grids on 5 and 6  (and the unused of 2 or 7)

Or.. I could change the wiring around to match the 6ak5




Any idea which 7-pin tube they were using

[AC5UP]

The 6C4 has most of what (I think) you're looking for and was popular as a local oscillator... http://www.nj7p.org/Tube4.php?tube=6c4

Just because there was a remote cutoff Pentode in that socket doesn't mean the correct tube is a remote cutoff Pentode. Almost all of them have the plate on Pin 5 and you want the plate on Pin 1. The 6C4 is essentially half of a 12AU7 in a seven pin Noval socket with pins 1 and 5 tied to the plate and Pin 6 to the grid.

Another common local oscillator tube was the 6BA6 or 6AU6, but they have almost the same pinout as a 6AK5.

[W0EP]

Good call!

I found a 6C4 in my tube collection and gave that a try.
It works!

Three settings of the bandswitch seem to work.
With those settings the LO produces:

  Low  --  High    || +1415   1st IF   
12639 -- 12926   || 14054 -- 14341       
  2234 --  2601   ||  3649 -- 4016       
  5767 --  5976   || 7172 -- 7391     

A question:  If the LO is at 12639
and the IF is 1415, that could get me either
14054 (+) or   11224 (-).  I think my only frequency-limiting
components are the front end tuned circuits and the
IF coils.  Am I right in concluding that those front-end
tuned circuits are the thing which select 14054 instead
of 11224?

I have the receiver working, in a fashion.  The RF
gain control is terrible, and there is brown stuff
coming out of the large multi-cap can.  And some black
beauties in there which probably are just taking up space.

I guess the next step would be to make a list of all the
caps I'd need to replace.  Then I can see what it will
cost and whether I want to go there.

 

[AC5UP]

Good call!

I found a 6C4 in my tube collection and gave that a try. It works!

Whoa..................       Won't do that again this year!