Thursday, December 11, 2008

Panda Cub - a boatanchor for the shack

The Panda Cub transmitter survived a 900Km trip in the boot of the car. Despite the rough handling and a bit of accumulated rust, it fired up just fine.

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I used a 240V 50W lightbulb as a dummy load, (it has a cold resistance of 70 ohms, no idea what it goes to when hot), and it certainly puts out a little power.

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There's not a lot of information available on the internet about the Panda Cub. There are a few mentions and mostly information about the larger sibling by the English Panda Radio corporation.

A circuit in my bad handwriting is available in the scans of the old Contronics humour magazine here, and here.

It's a very simple design with a single 807 in the final. If anyone could point me to a user manual I would be most grateful.

Over the years the built in modulation circuitry has been decommissioned and the unit must be modulated by plugging in a 30W audio amplifier drive through a socket in the back.

Also, the frequency multiplier that made this a multi-band transmitter isn't there anymore so this is now a 160m AM transmitter which is fine by me.

Dallas tells me that the metal covered 6AG7 valve has an "N" on it because it belongs to Nigel - let me know if you need it.

I'm modulating it with a 100W RMS amplifier (way more than enough) and it's looking good:

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The trapizoid (audio on the X axis, RF on the Y axis) shows a phase problem, not sure how serious that is.

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Would you believe I purchased this in the 80s for $10 at an auction. I count myself very lucky.

The next challenge is an antenna for 160m...

Antenna update

I've hammered an earth stake into the ground at the base of the neighbour's gum tree and run up an inverted L with a 10m vertical and 12m horizontal part.

A test transmission over the weekend sounds terrific on a transistor radio while I walk around the block but I don't think I'm getting out much more than that - no one responded to my calls during the Sunday morning VK2WI 160m callback.

No doubt more inductance is needed to make this work a bit better.

8 comments:

AM Audio said...

Great to see the panda cub I have its big brother the Panda 120V a great British Am Cw Transmitter of the early 1950s used on our Am nett on Wednesdays on 7.125 it has loverly audio,Great to see another Panda like the bear they are rare.

Peter B Marks said...

Wow, you found the post quickly!

I'm experimenting with modulation now, seems capable of full modulation. I'll post some CRO shots soon.

AM Audio said...

Hello Peter,
The Panda Cub is the smaller brother to the 120V it has 160m the big brother has not mine is in good condition unfortunatley the Lv power transformer burnout not long after I bought it had to have it rewound but did away with the 866juniors 8amp filament current and horror for the purists replaced them with Si Diodes works well now.

geo said...

steampunk radio, I love it.

Nigel said...

...so that's where my 6AG7 went to... Good to hear the Panda Cub is still emitting rf. It's been used in some odd places & carried NYE once didn't it?

Peter B Marks said...

It was an exciter for the 'Stu for some years.

Ipanda App said...

Always have been a great fan of those

Anonymous said...

I have drilled holes in the front panel for two leds and a small incandescent lamp.
The leds indicate grid and screen currents , the bulb shows rf current out , fed from a 1:8 ferrite tranny on the output lead.
Silicon rects. Choke input . 6L6M modulators.
20 watts good AM out , 27 watts on cw.
G3TSA