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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 8th Apr 2018, 8:11 pm   #81
G0HZU_JMR
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Location: Cheltenham, Gloucestershire, UK.
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Default Re: Testing unknown transistors for max frequency response

My application for a free webpage at qsl.net got approved today so I can upload some s2p data to it now.

I'm only going to upload the OC44N data for now as it is the most complete set of s2p data and also because I'm going to be playing around with my feeble attempt at creating a basic website. So data is likely to appear/move/disappear a lot.

But for now here is the folder for s2p data for the metal can OC44N.

http://www.qsl.net/g/g0hzu//RF%20Tra...rmanium/OC44N/

Hope the link works. I'm off to try it on my IPAD to see if it is really there
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Old 14th Apr 2018, 10:20 pm   #82
G0HZU_JMR
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Default Re: Testing unknown transistors for max frequency response

I managed to get a genuine (black) Mullard OC45 to play with and this device was quite interesting. It has a very low current gain of only 20 or so and the Ft is 3.8MHz at 6V 1mA. However, I googled for IF amplifier circuits and found a useful article on our forum here.

https://www.vintage-radio.com/repair...rf-stages.html

I tried simulating one of the IF amplifier stages shown in the 'Neutralisation' section of that link and managed to get 37dB gain when neutralised. But this was with a perfect lossless (tapped) transformer. When I put in a realistic loss factor for the transformer I managed 32dB gain per stage. Quite impressive considering the low Ft of this transistor.

See the image below. The orange trace in the graph is the reverse isolation which shows a deep null when neutralised. The neutralisation is very touchy and sensitive to the operating point of the transistor. I use s2p data for 6V 1mA here.

I also tried to make a hybrid model of this transistor at 1mA 6V and this is also shown below. I didn't spend much time on this but it seems to give results in the right ballpark when compared to the real transistor. It's also a very basic model so it can't compare well with the s2p model for accuracy.
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