The AM Forum

Hi,
I'm working on my Hammarlund BC-779 It is unusual in that it has a chromed and stamped chassis. I have recapped everything not hidden inside a box. I have reception on 2.5 to 5mc and 5 to 10 mc , noises on 1 to 200 and 200 to 400khz but I just get hiss / rush on 10 to 20 mhz. Is there any stations on that band? If one of the coils were bad in the tuner box would I still have the rush noise?
I have a signal generator and will dig deeper next week.
One last question, why do hams speak in meters and the radios are marked in khz and mhz? 5mhz and about 60 meters?
For some reason I get much better signal if I connect a wire to the grid cap of the 6K7 (V2) than connecting to the antenna terminals.

Frequency, meters, cycles,seconds are metric units. Wavelength in meters, i.e., 40m band ~ 7,000,000 cps. (cycles per second). Or 7000 kHz, 7.0 mHz

Most electrical units are "metric". You'll hear that following into hamspeak.

Ham radio jargon sticks - you'l hear someone say QSL for 'yes', QTH for location, which comes from Morse transmission over the air; some other common terms are from telegraph jargon.

Some non-North American receivers have the wavelength scale on the dial.

AND THERE'S the classic " we've always done it that way".



Put your signal generator on 10Mc, and connect some wire to the receiver input. Signal trace and see where / if the signal goes byby

 WWV transmits on 2.5, 5, 10, 15 and 20 Mc. You should be able to *copy*  it .

Good luck,
KLC

Thank You!

Well, you may NOT be able to copy WWV.

Depends on where you are and what time of day.

PLUS what antenna you have.

There are foreign broadcast/shortwave broadcasters on bands between 9mHz and
14mHz.

14mHz is the "20 meter" ham radio band. You should hear CW and SSB there.
Some are quite strong.

The best thing is to put the receiver in the "CAL" position. It does have a "CAL"
position/mode? Or use a signal generator. You can buy them as "DDS" units online
very inexpensively. They're a PIA to operate, but they will make signal. Likely
you will want to attenuate their output for receivers that run inputs in the uV
(microvolt) range.

                         _-_-bear

It does not have a CAL position, I have a signal generator(Heathkit IG-42) I rebuilt a couple of years ago, and a digital Grundig SW radio for calibration.
I will get to that next week.

Calibration on a radio like this is going to be "sloppy", not to worry!

UH-Oh! Checking things out before aligning it, I opened the band switch to find this! has anyone replaced a slider in the middle of the cams? If I remove the rear nut on the cams.. are the cams keyed to the shaft?
If I have to, I can cut the divider / support to get a replacement slider in, because If the cams get out of time all hope is lost.
Also how does the frequency window separate from the scale?

SWL Scott said:I don't know but I would be referring to the service/technical manual often. I hope you have one.

That is not in the TM11-4054 repair manual I have, I have not seen any manual showing inside the tuner box, except the coils underneath.

Don't sweat it, man.  I'll send along a complete coil/varicap/switch unit from one of my widows.

You'll have some other parts coming as well.

I may have a manual with that unit overhaul, will check.

73DG

A care package! awesome, I was trying to figure out how they made this, if the cams are not keyed, there must have been some kind of jig to set them up.
and the window , scale may have been riveted together, it's hard to tell.
I'll contact in PM, when you are ready, with a list, and payment info.

I'll need your top freq range; 20 or 30 Mc?

73DG

10-20mc

For future information, the cams do have a sequence that can be duplicated if the cams are taken apart, each cam lines with the high point on the 5 sided shaft, in each group 1st on the first point, second on the second,(clockwise)(from the front) etc...So not impossible to put back together, if taken apart after all. learning something new every day it seems.

While you have it torn down to the point where it i now, check the coils for continuity especially the RF front end coils (coils nearest, electrically, to the antenna). These are prone to opening up, due mainly to static build up or nearby lightning strikes on the antenna. The result will be the receiver working fine on some bands and deaf on other bands.

Will measuring across the antenna terminals while switching bands work?
When a coil is open, will it sound normal but no stations, or silent?
I think I will end up removing the tuner box in the end to do things properly, also as a dress rehersal for the dismantled SP-10

I have to put this in storage until I get parts.
To be continued...

I'm going to take the cam out of the SP-10 and use it for parts, as this unit is otherwise intact and working

It doesn't. Unless you carefully drill the rivets.
I've done this.
Replaced with brass nuts and screws. I think they're #3 size.

Not something to do with a hand drill, imo - not impossible, but care
and the proper cutting bit is essential.

Why do you want to separate?

Is the plastic bent?  :-\
Ask me how I know...

There is a fix for the bent plastic dial.
I've done this.

Repairing the broken "guillotine" switch part?

Should be fairly easy!

Maybe. A bit depends on something I don't recall - what the phenolic part slides in?

Guides of some dimension??

BUT, if there is any clearance, you can take some strips of bare fiberglass PC board
material and epoxy it to bridge the two pieces. If you do it both sides, should last forever!

IF the surface space available is thin, build it as one or more strips of PCB material
on edge laminated together. Thickness being whatever will it need to be in order
to clear the guides. But you will get height off the surface, which adds strength. So
maybe 3/16" standing perpendicular to the phenolic pieces, as the bridge/repair.

You'll need to clamp the whole thing carefully, and use slow set epoxy - slight abrasion
and cleaning of the phenolic surface, clean with alcohol first.

                     _-_-bear

Another set of cams from another model must have identical cam positions, or the
radio will not work properly.

I wanted to separate the window from the scale to clean it, and try to bleach out the dark spots. and paint the window disk.
Repairing the slide in the switch would not be easy unless I could buy phenolic material, the sides of the slide is a precision fit in raised areas of the walls, also fiberglass pc board is abrasive on the exposed edges.
besides the cam assembly would have to come apart, as the steel dividers prevent moving the slides off the cam.
Theoretically I could slot the steel divider and remove to avoid disassembling the cams, I am not sure what keeps the cams in their positions, and I want to avoid getting them out of time.
I have the SP 10 here, and I plan to remove the cam on my next day off, I can compare them and make sure they are the same, before installing the cam in the BC-779

So.. putting it back together, I ran into a slight problem, the variable caps do not have stops, so getting the frequency and bandspread lined up looks like a pain.
is the bandspread 100 fully meshed or fully open?
is the high side of the frequency scale fully meshed, or open?

IF nobody looks and comes up with it - I may be able to figure that out from a chassis that
is out of the radio... hopefully someone else comes up with that.

Look carefully at the manual, it may reveal this if read carefully, especially the alignment section.

                        _-_-bear

If I get desperate, I could take the covers off the SP-400, so many screws!
How did you do it? You had the dials off IIRC, or did you mark the shafts before removing the dials?

In the manual I found where the bandspread "0" is where the capacitor is fully meshed. But no reference to the tuning capacitor. Are they usually fully meshed at the low frequency point on the dial?
My Quad AM3 has the tuning cap meshed at the low frequency, so that is how I set it, we'll see when I get it powered up.

It is back together, I was able to accurately locate the dials by using my frequency counter to find the peak of when the capacitors were fully meshed, and used that for the end of the tuning scale / stop.
The bandswitch / tuning unit still has a problem, as the RF oscillator on one band does not run.
I am putting this in storage until fall / winter as I don't have time until then to work on it. The SP-10 cam fits perfectly, as do the slides.

Looks a lot better shined up!

It's the only Hammarlund besides my SP-10 that I have seen with a chromed chassis.(and the only one stamped with the tube numbers) The SP-10 looks so much like the Scott radios of their time, and about as complex mechanically.