What you need to remember is SIDE.

S witch off the amp.
I solate the amp by removing the power cord and putting it in your pocket.
D ump the high voltage to chassis using a grounding rod through a 100K 5W resistor
E arth the anode caps to ground using clip-on leads.

Now, some other tips.................

1) If you ever watch a TV engineer he will probably work with his left hand in his pocket. It stops you grabbing on with both hands and getting an electric shock across the heart.

2) Never work alone.

3) Some safety gear such as protective goggles or glasses might be a good idea.

4) If you have a variable transformer handy then use this to bring the linear back up the first time.

HA6SST

500mW is 27dBm and 80mW (to give you a degree of safety) is 19dBm, you therefore need an 8dB attenuator.

A pi attenuator will have 869 ohms across the input and output and 5.77 ohms in series. Nearest 1% values are 866 ohms and 2 11.3 ohm resistors in parallel for the 5.77 ohm resistor. You could probably get away with half watt resistors in this application.

My favorite attenuator calculator is at http://www.microwaves101.com/encyclopedia/calcattenuator.cfm

HA6SST

Web site address is http://www.therfc.com/

HA6SST

OK, please let me rephrase the question.

Would it be possible to use a tube power amplifier as a high IP3 receive pre-amplifier by reversing the connections and inverting the PTT signal which controls it? There would also (theoreticaly) be some preselection as the tank circuit on the output would need to be tuned to the frequency of operation.

Thanks to HA5RXZ for helping me with my English.

HA6SST

OK, here's a crazy question, please think carefully before you answer.

There has been various research conducted on the subject of receiver front ends with high IP3 figures. Some of this work involves large devices with higher than normal power supply voltages. If I connect the input of a power amplifier to an antenna and the output of a power amplifier to the receiver input will I

a) Find myself with a high performance preselector that has world beating IP3 figures?

or

b) Blow up the front end of my receiver and probably let the magic smoke out of other components as well?

HA6SST

The alarm tape is certainly difficult to obtain but adhesive copper tape in various widths is available from Mouser.

HA6SST

Two hours of the Book of Revelations sent using CW would be wonderful code practice. When life gives you lemons make lemonade.

HA6SST

Sorry, my math was wrong. The Digikey total should be $114 but Mouser still win.

HA6SST

I am building a low pass filter set and to ensure that the filter will operate at 100 watts without problems I decided to use 500 volt silver mica capacitors. After spending two hours with each catalog these are my results.

Digikey
Managed to make up all values required but some positions will require three capacitors in parallel.

Components                     $87
International surcharge   $6
Shipping                           $21
TOTAL                                $168


Mouser
Bigger range of silver mica capacitors which meant that most of the positions on the circuit were filled by a single capacitor. Set against this is a slightly higher cost for the larger values.

Components                     $52
International Surcharge    none
Shipping                           $17
TOTAL                                $69


It looks like Mouser get the business but I really hope that someone from Digikey sees this. Digikey have an amazing product range but they really need to improve some of their prices and company policies.

HA6SST

Add another vote for Mouser, these guys are good.

HA6SST

For tubes you can use Collins Y-400 or 4CX-250R devices. I cannot find any information for you on the power cord.

HA6SST

See http://www.ab4oj.com/pwrmeas.html for some good ideas.

HA6SST

Horrible TVI problems. Hungary still has a TV service on 50 MHz and a lot of the TV sets are very old. If I transmit more than 15W on any HF band my neighbors start banging on my front door.

HA6SST

Now I think you see my problem ;-( I examined the device under a microscope and the part number is correct (Oscar Foxtrot Seven Zero Two) but there is no manufacturers information.

HA6SST

I'm looking for any information on the OF702 VHF varicap diode. A Google search has failed to find a datasheet.

Please email information to edwardalmos@gmail.com.

Thanks.

HA6SST