OK, lots of useful information so far BUT NOBODY HAS ANSWERED THE QUESTION!!

My heatsink is large enough, I am using enough (large) power transistors for the application and they are correctly mounted.

What I am looking for are suggestions for the trip point on the temperature controlled fan, anyone prepared to step up to the plate and give a figure?

HA5RXZ

It's called the Icom X3 and it's a commercial rig intended for rack mount use. They were displaying it at a show in Japan recently.

Post your email and I'll send you some pictures.

HA5RXZ

Happy memories.

Way back in the mists of time I transmitted and received SSTV. This was not done using a computer, we received the image on a surplus radar tube with a seven second long persistance phosphor. No color unless you wanted orange.

This explains the 'slow' part of SSTV. The hardware took 1/60th of a second to paint a line on the screen but seven seconds to paint a full frame. By sitting in a darkened shack you could see the picture slowly develop before your eyes.

The folk with lots of cash had a box made by a company called Robot. This received the SSTV signal, stored it digitally, and then displayed it on a standard monitor or TV.

HA5RXZ

A small UK company based in NE England but willing to ship orders worldwide if required. The accounts and order system seems very well organized and they are willing to help source more unusual items.

Website http://www.users.zetnet.co.uk/esr/index.html

Telephone 0044 191 251 4363

Fax 0044 191 252 2296

Good folk to do business with. Their main trade is data comms and all the cabling that comes with it but they also stock a good range of cable management supplies that could come in useful in the shack.

The main reason I have dealt with them twice so far is their amazing range of heatshrink. 2:1, 3:1 and 4:1 shrink ratios are available in long lengths and up to ten colors.

Website is http://cableorganizer.com/

Toll Free Phone (866) 222 0030

Well, here's where it gets interesting.

According to the datasheet for the 2N3771 I am supposed to start derating the device once the transistor gets above 25 degrees centigrade. This Summer the air temperature in Hungary hit 37 degrees C in the shade so, in theory, the fan would be on 100% of the time.

Having said that, it may not be so bad. A single device can pass 150 watts if the temperature is 25C and 125 watts if the temperature is 50C.

So, would anybody like to make a guess at what temperature I should set my fan control?

HA5RXZ

I have just finished a homebrew power supply which is fitted with a fan on the heatsink. To reduce noise levels in the shack the fan only switches on when the heatsink gets too hot.

How warm is too hot?? I have found various opinions which vary from 40C (104F) to 70C (158F).

HA5RXZ

Ice lolly sticks. Give a small bounty to each local kid for a bunch of ten sticks and you will soon have enough. They then need to be soaked in varnish to waterproof them.

HA5RXZ

I'd love to buy one but the price is a bit of a showstopper, especially when you add the 25% Hungarian VAT on top. Good luck in your search.

HA5RXZ

The topic describing a hams troubles with Vertex Standard / Yaesu is now up to 30 contributions. The topic describing another hams troubles with an LDG autotuner has been removed and I can't find it even when I enter the article number.

I wonder if this is because LDG are a regular advertiser on the Eham site?

Waiting for this post to vanish as well. 3  2  1  ..............

HA5RXZ

Not really an amplifier question, but as most amps generate heat I'm hoping that some of you can help.

If I install a fan to cool a cabinet should the fan:

a) Draw cold air into the cabinet.

or

b) Extract hot air from the cabinet

Assume adequate ventilation holes to equalize air pressure and give reasons for your answer :-)

HA5RXZ

Now you see how I've been struggling for the last two days. My skills are in digital design and all of this op amp stuff makes my knees sweat 8-(

If I altered the input circuit so that it varied from 0 to 100mV would that make things easier? I could do this by applying a DC bias to the input.

HA5RXZ

I have been playing around with this for a couple of days and got nowhere. After a second blown op amp I've decided to ask for help. The required specification of the circuit is as follows:

1) Op amp with single +13.8 volt supply. Negative supply pin of op amp is tied to ground.

2) Op amp input will be 100mV audio signal via a DC blocking capacitor. Input is therefore assumed to be +/- 50mV with reference to ground.

3) Required op amp output is +5V with no signal applied. With the 100mV signal applied to the input the output should vary between 5V and OV.

Can anyone help me out here?

HA5RXZ

See http://www.cumbriadesigns.co.uk/t-1.htm

Add a VFO and a bit of amplification and you will be good to go.

HA5RXZ

There's an FT-9000 users group on Yahoo! Ask there and I'm sure that someone will know.

As for opening up the transmit range I can think of a number of reasons:

1) Transverter driving. You now have the option of the best frequency, not just a choice of those available.

2) Wideband high-power signal generator. Useful for testing antennas and filters.

3) HF Marine band, MARS operation, lots of HF work which may be legal in the USA but I'm not sure as I don't know American regs.

HA5RXZ