[Amps] Amps Digest, Vol 87, Issue 117

Carl km1h at jeremy.mv.com
Wed Mar 31 15:16:58 PDT 2010




> Carl, I didn't build the Tyler output modification, as the tube 
> manufacturer in France doesn't recommend 'efficiency improvements' via 
> plate current waveform modification. Although i did notice a copper slug
> in their own test cavity amplifier that was said to help minimize second 
> harmonic power in the output. I am sticking to class AB2 - to B. I was 
> referring to the effects on plate current waveshape (and measured
> DC to RF conversion efficiency) that MIGHT happen if a quarter wave stub 
> was placed at the wrong place, distance from the plate to the stub. 
> However, it would effect even harmonics and not odd ones, so it might
> have zero net effect. I hoped to hear someone's experimental evidence of 
> this before I make big mechanical design changes.


I think I'll play with the Tyler 3rd harmonic tuning at low power and see if 
it works in Class AB2 or B GG up on VHF. I would love to get 15-20% 
improvement.


>
> In some of the medium wave b'dcast transmitters with tubes, though, I've 
> seen that circuit in use. The Collins 5 kW power rock did it. RCA had a 
> nice app note on it, Power Tube Engineering Note IEN-4. They
> talked about the 5762/7C24 being overdriven with flat topped grid voltage 
> in the BTA5U, and having third harmonic parallel resonant traps in the 
> cathode and the plate leads to the tube.
> Its tricky to try and design these same equivalent resonators into a 
> coaxial line circuit (a cavity). I can scan and email the app note, dated 
> 1964.


I already have the 1960 RCA Broadcast News #107 info for the BTA-5T John. 
The comparison with the 5R is an eye opener. If your -5U App note is 
additional data Id appreciate a copy.

Carl
KM1H


>
> John
> K5PRO
>
>> Date: Wed, 31 Mar 2010 09:40:32 -0400
>> From: "Carl" <km1h at jeremy.mv.com>
>> Subject: Re: [Amps] gg feedthru power
>> To: <jtml at vla.com>, <amps at contesting.com>
>
>> Thats how I remember it also John but its been a long while since I read 
>> it!
>>
>> BTW, when you mentioned the Tyler circuit in that 500KW amp what 
>> efficiency
>> improvement were you getting?  What class and how is it driven?
>>
>> Carl
>> KM1H
>
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