Birmingham - - - G3UPA - - - IO92dm

Heard on the Air

The writer does not necessarily endorse any modifications mentioned here.

160m - "I've fitted 4 x 1N5408's in place of the 7.5v zener in dozens of 922's and they work fine"

I think that there is a lot of confusion regarding the replacement of the 7.5 volt Bias Zener diode with 4 x 1N5408 diodes. ( 4 x 0.7v = 2.8v ! ) "Why is my anode current 500mA? and what's that funny smell ?" oooooops
I have also seen one internet article that stated "I used 10 x 1N5408 diodes", which is much nearer to the specified voltage. 11 might be even better, plus you can easily change the actual level by shorting out a few diodes.
In the UK we are, mostly, fortunate in that the mains supply voltage is fairly consistent at around 245 volts. Many of the articles on changing the bias voltage are from individuals who are not so lucky. Since the 922 has only 220v or 240v mains input taps, then those people having a 230v supply are lumbered.
If they use the 240v tap then their heater voltage will be lower than specified and the anode current will be lower, hence the need to reduce the bias voltage to increase the standing current.
If they use the 220v tap then their heater voltage will be higher than specified and the anode current will be higher so they need to increase the bias voltage to reduce the standing current.
Since the gain is proportional to the temperature of the heater then a variation in heater voltage will cause a variation in standing current.
Having said all of that, the standing current vs. bias voltage is not the same for all makes of 3-500Z anyway.
Conclusion: Make sure you know the Spec of the valves fitted Before you start modifying the bias, just because "G3??? told me it would work ok"!!!
Of course these statements assume that your 3-500z's are absolutely 100% to spec. If their emission is anything less than 100% then the bias voltage vs anode current will also be below spec.
Maybe many of these internet articles are from operators who need to replace the bottles.

Note: 3-500Z anodes should be made to glow Red regularly since this is how the 'Getter' keeps the internal gases at a minimum level. Leave them lying around for months/years and they will probably go Bang the next time you apply 3kv. due to a build up of gas inside the bottle.
3-500Z's have a less than perfect vacuum seal and are prone to ingress of impurities.

P.S. I am currently revising the TL-922 pdf service manual to correct the error regarding S3 shorting out the 7.5v zener, which it does Not, according to the circuit diagram. S3 simply changes the high voltage supply. If anyone has a schematic showing how S3 reduces the bias I would be pleased to see it.

   "Reducing the filament voltage of a thoriated-tungsten heated tube by 3% will double the tube life" Eimac said that!

Here is a link to the 3-500Z data sheets.

And here is a link to some interesting TL-922 mods"

160m - "The hairpin anti parasitic anode chokes mod to the 922 don't make a halfpenny worth of difference."
Well unless you have a spectrum analyser that works up to about 10 Gig, like wot the makers have, then I personally, cannot agree with this one. Just because it seems to work ok on the HF bands doesn't necessarily mean it's not producing sprogs all the way to 'Infinity and beyonddddd'. And self oscillation could easily cause a rise in standing current.

160 - "My 126ft inverted L works great on 160 with a 9:1 un-un at the bottom and it works on all the harmonically related bands."
How many bands are harmonically related to 1.9MHz ?. 5.7MHz, 9.5MHz or maybe 13.3MHz. Which ones do you use ? ......

Heard on 3.757 - from he who knows All - "How can a slinky made from high carbon content steel possibly work as an antenna".
Call me on 160 and I'll demonstrate. (G3UPA said that)

All bands "QSL". No thanks, I don't need a qsl card- - - .
True meaning:- 'can you acknowledge receipt ?' / 'I am acknowledging receipt'.

All bands "QSK" . In my case yes because I use full break-in cw. In ALL other cases NO. I can't listen between transmissions unless I drop the PTT between words. (unless of course you have an extremely fast respone vox system that drops between words ! )

Things that are best kept to 27MHz ------

My working conditions are - . If you want to describe your station then do so. As "The radio is.... My aerial is... etc. Thank you.

"Over over" - Just 'over' is all that is required, unless of course you stick to convention and give callsigns.

"M0AAA M0BBB call" - ? What the hell is that supposed to mean?.

"The name would be Fred" if my parents hadn't called me Michael... Come on..... Please Keep the CB stuff on 27MHz....

G3UPA said (some of) that !