Re: Parafeed line stage design questions

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Posted by Paul Joppa (P) on October 4, 2006 at 19:13:10

In Reply to: Parafeed line stage design questions posted by drsx on October 2, 2006 at 11:55:38:

I started to post an answer last week, but it got too complex and I gave up. Here's another try:

>> Is there an advantage to the coupling cap connecting between the cathode and the transformer as opposed to the transformer connecting directly to the cathode and being AC coupled to the plate?

Some people think so; others disagree. Only your ears can tell for sure.

>> Second question, is there a good rule of thumb for determining the size of the coupling cap?

No, there isn't.

There are analyses, but they require knowledge of the transformer inductance, resistance, eddy current losses, and hysteresis losses. All except wire resistance are strong functions of frequency and signal level, and depend on the actual construction (e.g. how close the E-lams are butted up to the I-lams...). A huge amount of work, and still gives just a theoretical answer.

Best bet is to pick a "large" cap so any resonance is very low in frequency, and then measure to confirm that any resonance is well damped. A large enough cap will ensure well damped performance - it's just hard to predict how large is large enough.

>> Third, I have some old cheapie edcor 10K:600 transformers, and i am wondering if they will be suitable for experimentation. That is, they are intended to have DC on them. Will they give decent enough performance to try to get the circuit basically correct before upgrading to the MQ iron ...

Sure. They may not be rated for DC, so the cap would have to go in the plate side, and of course they will tell you nothing of the desireable cap value for other transformers.

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Follow Ups Full Thread

Topic - Parafeed line stage design questions - drsx 11:55:38 10/02/06 (11)

Re: Parafeed line stage design questions - Paul Joppa 19:13:10 10/04/06 (2)

Re: Parafeed line stage design questions - drsx 23:27:46 10/04/06 (1)

Yes (nt) - Paul Joppa 00:01:51 10/05/06 (0)

Spreadsheet for showing the low freq -3db down - Bas Horneman 02:55:41 10/04/06 (5)

Re: Spreadsheet for showing the low freq -3db down - drsx 10:18:13 10/04/06 (3)

Re: Spreadsheet for showing the low freq -3db down - mqracing 11:44:58 10/04/06 (2)

Re: Spreadsheet for showing the low freq -3db down - drsx 13:14:19 10/04/06 (1)

Mike, do you accept Monopoly money now? - Mike Spence 16:54:27 10/04/06 (0)

Oeps..only works if you have a google account...nt - Bas Horneman 02:58:12 10/04/06 (0)

Re: Parafeed line stage design questions - fred76 10:04:23 10/03/06 (0)

Re: Parafeed line stage design questions - Auratus 02:49:01 10/03/06 (0)

Follow Ups

Re: Parafeed line stage design questions - Paul Joppa 19:13:10 10/04/06 (2)

Re: Parafeed line stage design questions - drsx 23:27:46 10/04/06 (1)

Yes (nt) - Paul Joppa 00:01:51 10/05/06 (0)

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