[Amps] QRO HF2000 tank coil Q question

Peter Voelpel dj7ww at t-online.de
Mon Mar 22 14:47:06 EDT 2021

Hi John,

With the Q of 7 to 8 you probably mean the pi network Q.
That is not the Q of the particular coil but that of the circuit, calculated
by tube Ra/Xc of anode capacitor.

Higher Q will produce even higher losses and more heat!

Losses can be reduced with larger cores or a separate coil for each band.


-----Original Message-----
From: John Keating [mailto:john.keating at outlook.com] 
Sent: Montag, 22. März 2021 19:06
To: Peter Voelpel; John Keating; Amps at contesting.com
Subject: RE: [Amps] QRO HF2000 tank coil Q question

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

73, John

-----Original Message-----
From: Peter Voelpel [mailto:dj7ww at t-online.de] 
Sent: Monday, March 22, 2021 10:52 AM
To: 'John Keating'; Amps at contesting.com
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 [mailto:amps-bounces at contesting.com] On Behalf Of John Keating
Sent: Montag, 22. März 2021 17:23
To: Amps at contesting.com
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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