Quote:
Originally Posted by Ed_Dinning
Hi Richard, thanks for all the work on the PSU and the details from the AP's.
The DC heaters are a must, I'm told, when using the transmitter to reduce the 50Kz mod.
I've used a FET for the 1155 filter and made it adjustable as it is easily done. This is more of an active filter for hum reduction than a true compensated regulator. I'm told the limited range adjustment (200 to 240V) makes it easier to find a low drift point for the 1155 oscillator.
The EHT supply seems to benefit from an LCL filter where the first choke is a swinging type. It is also possible with some of the transformers available to have hi/lo EHT switching
There is a significant noise reduction if the HT an EHT negative rails are bypassed to ground with a 0.1uF paralleled with a 1Meg.
Ed
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Ed,
I would agree with you on the need for DC when the T1154 is being powered. The keying relay alone dictates it - unless you are going to make internal mods to the Tx - and that's regardless of any problems with the direct heaters of the PA valves (PT15s). I've not heard of a problem with feeding the R1155 heaters with AC though - and as far as I recall when I had the bits in my hands it all worked fine.
Of course, its possible to make semiconductor regulators using BJTs, MOSFETS etc. I had a rather negative experience of them as I described - too easily destroyed - and we happened to have the inductor winding facility that made the production of a choke very easy. Of course not true for all!
With reference to the 1200V EHT supply - which is strictly speaking outside the scope of this thread - I did in fact stick to the original recipe in AP1186E - except that I adopted the same strategy of a single L-C stage filter. I used the same amount of L, and loads more C as I recall. Simulating it gave similar results as the original achieves. its important to use a filter that gives a stable output voltage, because of course the load current varies from 0 to 100mA (or so) rather rapidly in CW mode - and the T1154 really doesn't need any encouragement to makes its chirp any worse!!
I am not familiar with an L-C-L filter, which will be essentially the same as I had but with an extra choke, and as you say, the first choke swinging. What benefit does that offer? It would appear to have the obvious drawback of even more lumps of iron - more weight, and more money!
Richard