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Old 2nd Feb 2019, 9:45 pm   #21
Argus25
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Default Re: Radionic Regen

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Originally Posted by Radio Wrangler View Post
THere is a snag to mumetal on CRTs... it can get permanently magnetised, just from getting a knock and being in the Earth's magnetic field, od from being worked. So you need to thermally anneal them after manufacture before they can be used.

David
I noticed on the Mu metal CRT shields for the VCR97 CRT that they can acquire a permanent magnetic field. It was easy to see the beam deflection when the two halves are assembled around the neck, with the CRT running. So I simply used a degaussing wand on it (well away from the CRT of course). That appeared to solve the problem, but I guess I could have heated it too.
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Old 2nd Feb 2019, 10:19 pm   #22
Argus25
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Default Re: Radionic Regen

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Originally Posted by VT FUSE View Post
Great stuff Tim

I have been thinking of a hybrid build as I have several of both pre TO3 types of OC16 stud mount Transistors of the type used by Argus25 and even predating the type he used.
Had thought of having the transformers specially wound but your iteration sounds very good.

Mike
On the transformers in mine as noted the driver was pre made for the task, according to the Mullard/Philips specs.

I wound my own butt stacked output choke. I had an 8R speaker, and the choke (autotransformer) was tapped to give an impedance ratio of 22:8. Also looking back at the circuit, the OC16's emitter current was 420mA, and I use a 3.3R emitter resistor dropping 1.38v. As I recall it could easily deliver 1.5 to 2W audio out which was plenty for a desk top radio. In a car they push it a bit harder to about 2.5W.

The OC16 is mounted on a 1/8" copper flange which is also thermally coupled to the steel chassis (The paint was removed under it, and heat conducting compound used). I did thermal stability tests on it at the time and the heat sinking was perfectly adequate for our sometimes 40 Deg C ambient temps, if not over killed. I also incorporated NFB from the speaker connection to the cathode of the EF98 driver valve, simply by adding a 75R resistor in the cathode and a 560R resistor to the speaker terminal. Also as I recall, the input sensitivity is such that about 1V or 2V rms at the EF98 grid, attains full output, but I would have to check that. I could attach the schematic of the radio if it is any help.
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Old 2nd Feb 2019, 11:35 pm   #23
astral highway
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Default Re: Radionic Regen

Tim, what a wonderful piece of work!

Love it! What are the dimensions?

It looks pretty expansive!
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Old 3rd Feb 2019, 12:04 am   #24
VT FUSE
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Default Re: Radionic Regen

Argus25

Thanks for the detailed info,I am impressed by your hybrid build and remember that you gave detail of the driver transformer designed for the task.It was not clear to me what you had used after the Transistor,however.

It is easy to find your posting on the forum therefore I appreciate your offer of a link but really have no personal need for it.

I have been messing around with the American space charge range of Tubes and the European 12V valves but have not settled yet on a Superhet or a Synchrodyne format.

Regards

Mike
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Old 3rd Feb 2019, 1:06 pm   #25
Hengist
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Default Re: Radionic Regen

Hello Al
The Radionic Perspex panels are 12" by 9" perforated with 1/8 inch holes at 3/4 inch pitch. The radio uses 3 panels so overall it's 36" by 9" .
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