High Voltage Transformer
 

I am looking at building an all tube television and have some questions about the high voltage supply. In looking at some of the early designs a 1b3 diode was used in conjunction with a beam pentode oscillator. My understanding is that the beam pentode would feed a high frequency into the primary transformer winding and thus creating the high voltage secondary to feed the 1b3. I am thinking of using an oscilloscope tube and will probably need 2-6kv depending on the tube.

My question: could I use a low frequency (60hz) high voltage transformer that are commonly used in ion fan generators, etc? My concern would be that there would be a high ripple voltage due to the low frequency.

http://www.ebay.com/itm/ACTOWN-ACME-...-/391001265597

http://www.aliexpress.com/item/Whole...380316397.html

Yes, something like that can probably be made to work, but as you have correctly surmised, you will need to use a much better filter to eliminate the ripple than what you see on the RF HV coil supplies. I would guess that something like 1 uF should be sufficient given the low current you need (something like 1mA).

Prewar sets did this, and used more like 0.03 to 0.1 uF.

Doug McDonald

Seems like a bit of overkill. I noticed the one one AliExpress is gone already, did you get it? The 1B3 is probably rated for the higher frequency and lower AC current. Note that the rectifier will have to pass higher ripple current because it will be charging the bigger capacitor even though the CRT current is very small.

No I didn't get the HV transformer. I am just getting started in scouting for parts. I might have better luck in stealing from a scraped chassis or looking for a NOS transformer. Is there some other source or option I could go with?

If you want to do a 60 cycle supply use a 2X2 or 2V3 as the rectifier, filter with a couple of .05uF to .1uF HV caps at 1.5-2X times your output voltage. This design was used for virtually every pre-war TV with a "brute-force" HV supply.

I have a transformer sitting here, 2.5KV, [email protected], [email protected] all the voltages you need for the HV section of your project. This transformer will work for a 2X2 not enough filament current for the 2V3

$25 plus shipping. Contact me off list if your interested.

Chuck

I don't know your background but designing a TV from scratch is a big project. Oscilloscope tubes generally don't need much more than 2 KV anode voltage even with post deflection acceleration. It might be better deciding on the CRT tube first (what you can find), then designing from there.
Too high an anode voltage could cause problems such as focusing.

"Brute force" High voltage supplies can also be quite dangerous. I would look for a more modern design.

Transformers from spent microwave ovens can often put out 2-4KV.

And with enough current to kill a HUNDRED people at ONE time !!!

But they are capable of putting out hundreds of milliamps of current. WAY more dangerous than the old time "brute force" supplies, which could deliver a few mA.

Of the two transformers you linked to above, I'd probably recommend the lower current one (8 mA max) because it would be safer. The 15 mA one has more shock danger. I would definitely stay away from a microwave oven transformer, especially since the transformers you found are only a few dollars each.

A major reason for using the horizontal deflection to make the high voltage is when the horiz fails, the high voltage also goes out, avoiding a burn spot dead center of the CRT. Also cheaper, you just use a bunch of fine wire on the horiz output transformer instead of a separate system. Also horiz derived high voltage is less unsafe than the old brute force 60Hz supplies were.

Even with those 'bug zapper" style transformers I STILL would NOT want to be shocked by the output from one after a couple of caps and diodes from it. While not as bad as a micorwave oven tranny...they STILL could be a killer likely...compared to a flyback...

Why a scope tube ? I would think retention would be
a problem with it.

73 Zeno:smoke: