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Re: [Amps] QRO HF2000 tank coil Q question

To: John Keating <>, Peter Voelpel <>, "" <>
Subject: Re: [Amps] QRO HF2000 tank coil Q question
From: gudguyham via Amps <>
Reply-to: gudguyham <>
Date: Tue, 23 Mar 2021 01:24:38 +0000 (UTC)
List-post: <>
Have you guys taken into consideration that the tank circuit in these amps only 
transform down to 200 ohms, not 50 ohms from the plate impedance?  After the 
tank circuit it passes through a 4 to 1 balun which brings it down to 50 ohms.

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On Monday, March 22, 2021, 2:05 PM, John Keating <> 

Thanks Peter. I calculate a Q of 7 to 8 for the stock design mentioned in the 
previous email.

There are still a fair number of these amps in use, I wondered if others had 
similar experience.

I considered redesigning for higher Q but the modifications to the entire tank 
circuit would be extensive. Again, I wondered if anyone had done such a thing.

73, John

-----Original Message-----
From: Peter Voelpel [] 
Sent: Monday, March 22, 2021 10:52 AM
To: 'John Keating';
Subject: RE: [Amps] QRO HF2000 tank coil Q question

I used stacks of T225-2 for a mobile antenna loading coil on 40m.
Measured Q was around 400.
Toroid coils with taps, which no good idea anyway, will have much lower Q.
As part of a pi network for 160m in the 2KW out class only T400 was not
getting too hot, stacks of T300 still overheated in RTTY.


-----Original Message-----
From: Amps [] On Behalf Of John Keating
Sent: Montag, 22. März 2021 17:23
Subject: [Amps] QRO HF2000 tank coil Q question

Wondering if anyone can provide the specs on the low band tank coil for a
QRO HF2000.

It appears to be a stack of two red-mix T225A-2 iron powder toroids, with a
total of 25 turns, and taps for 40M at the 7th turn, and for 80M at the 13th

Also wondering if anyone else notices how hot it gets on 160m.

73, John

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