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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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5th Jul 2017, 12:57 pm | #41 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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Re: Audio amp on CV2799 ?
What was the PA? Another one?
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5th Jul 2017, 3:18 pm | #42 |
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Location: Solihull, West Midlands, UK.
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Re: Audio amp on CV2799 ?
Surely all top band rigs used a 6BW6 as PA?
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5th Jul 2017, 6:03 pm | #43 |
Nonode
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 2,039
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Re: Audio amp on CV2799 ?
Hi Al,
I'm not sure what you mean by High Side. Nothing special about the circuit, just the two tetrodes in push-pull, using an old HT mains transformer as the modulation transformer. The tetrodes were fed by an ECC83 as the phase splitter. Yes the PA valve was a 6BW6, but i nearly used a 5763. Cheers Aub
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5th Jul 2017, 6:28 pm | #44 |
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
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Re: Audio amp on CV2799 ?
Ah, I mean when the AF is power amplified to modulate the anode of the final in this case (via modulation xformer), or the drain of an MOSFET in class E amplifiers. From what you're saying, it is.
Maybe the high-side, low side distinction doesn't apply to valve transmitters. I know very little about it, it's only recently that my attention and knowledge have started to grow in this area...
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Al |
5th Jul 2017, 7:09 pm | #45 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,007
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Re: Audio amp on CV2799 ?
Some of us preferred to follow the mindset of the 62-set and use the squat little CV309/QV04-7 which was available dirt-cheap on the surplus market. An EF50 VFO, EF50 driver worked fine ahead of a QV04-7 PA.
The PL81 was also a popular choice [despite its odd heater-voltage]. At least it had a top-cap anode. |
5th Jul 2017, 9:29 pm | #46 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,899
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Re: Audio amp on CV2799 ?
The guy in our village used a 6L6 odulated by 6V6 and a great big Woden trnsformer. I think the crustal oscillator may have been a 6J5G.
I've just found a few unused 6BW6 sn 5763s while having a rootle, and I think I've got several YL11-somethings which are the directly heated double tetrodes. David
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5th Jul 2017, 9:35 pm | #47 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,007
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Re: Audio amp on CV2799 ?
Quote:
I doubt the YL1130 would be too sensible to use as an audio-amp. |
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5th Jul 2017, 11:36 pm | #48 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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Re: Audio amp on CV2799 ?
Somehow that's just the most evocative description of a home brewed lashup I've seen in a long while
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6th Jul 2017, 12:29 am | #49 |
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Location: Chard, South Somerset, UK.
Posts: 7,457
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Re: Audio amp on CV2799 ?
Would a '3-20A provide useful service as a pass-valve in a linear regulated H.V. PSU - possibly to power a '3-20A A.F. power amp.?
With the two halves strapped in parallel (perhaps with current-equalising resistors in the anodes), 400-v.d.c. input to them and a fixed 250-v.d.c. output, that puts a 150-v. drop across the valve. For an output current of no more that 100 mA, the combined anode dissipation will be 15-watts, which is within the rated Pa max. (combined) of 20-watts. Al. |
6th Jul 2017, 11:13 am | #50 | |
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
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Re: Audio amp on CV2799 ?
Quote:
Very obscure details available, (not even the heater voltage); appears to have two connections to a common grid, at 180 degrees to each-other radially laterally. Nice big anode, obviously designed for pulse application originally. How about that as a stylish audio amp in class A?, or a pair in push-pull?
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6th Jul 2017, 11:28 am | #51 |
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Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
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Re: Audio amp on CV2799 ?
The 5763 had a reputation for always wanting to be an oscillator, whatever the role intended for it by the circuit designer.
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6th Jul 2017, 12:33 pm | #52 | ||
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Audio amp on CV2799 ?
Quote:
If that's any use. Lawrence. |
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6th Jul 2017, 1:54 pm | #53 | |
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
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Re: Audio amp on CV2799 ?
Quote:
X-Ray specs, with that anode voltage! Cheers
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Al |
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6th Jul 2017, 8:41 pm | #54 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,007
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Re: Audio amp on CV2799 ?
Quote:
[Your regulator needs to have the same-if-not-better response-characteristics and bandwidth/slew-rate as the audio-amp it's feeding] Get it wrong (which you surely will) and the results will be an interesting mess of incompatible gain/bandwidth functions and negative-resistance effects at some point in the load cycle. If you're lucky the thing will take off and squeg/oscillate at some point, drawing your attention to just how poorly you understood the design requirements of this sotrt of thing. |
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7th Jul 2017, 1:53 pm | #55 | ||
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Join Date: Jun 2006
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Re: Audio amp on CV2799 ?
Quote:
Quote:
Al. |
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7th Jul 2017, 2:25 pm | #56 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,007
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Re: Audio amp on CV2799 ?
Yes!
The 'regulator' will still try to follow the audio component of the modulating waveform fed to the RF amplifier - so it would still need to have a response characteristic the same as an audio amplifier! This is a particular problem when trying to power amateur-radio 'field-day' transmitters from small portable generators: the generator's control/regulation circuitry tries to follow the transmitter's power demand - which is varying rapidly in response to the audio modulation or the on-off CW keying. Mechanical governors and systems with rotational inertia have difficulty responding to load demands that are varying millisecond by millisecond. The result is usually very bad ! The answer is to use a much bigger generator, and also to load it with something like a kettle or fan-heater so the transmitter's varying load is less significant. Plenty of really hot tea/coffee is always welcome on a Field Day or DXpedition anyway...! |
7th Jul 2017, 6:09 pm | #57 |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
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Re: Audio amp on CV2799 ?
But if that transmitter's modulation was F.M, then perhaps those problems would not arise?
Al |
7th Jul 2017, 8:33 pm | #59 |
Pentode
Join Date: Jul 2015
Location: Newbury, Berkshire, UK.
Posts: 243
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Re: Audio amp on CV2799 ?
Frank,
I saw that, thank you. I did my homework, read the posts and gave up the idea. I am no longer interested in building amp on cv2799. Thank you all. But I am still thinking about something different. The next candidate is rs1012L, or similar. My father worked here : http://old.radiopolska.pl/wykaz/poka...ja.php?pid=165 and used to keep one of the valves on a book shelf, so the books stayed straight. It was from about 15m long TV transmitter. The first rack was a power control for heaters, HV, etc , last one contained four huge output cavity filters, I was 11 or so at the time. Best regards, Jacek |