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Old 5th Jul 2017, 12:57 pm   #41
Herald1360
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Default Re: Audio amp on CV2799 ?

What was the PA? Another one?
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Old 5th Jul 2017, 3:18 pm   #42
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Default Re: Audio amp on CV2799 ?

Surely all top band rigs used a 6BW6 as PA?
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Old 5th Jul 2017, 6:03 pm   #43
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Default 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

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Old 5th Jul 2017, 6:28 pm   #44
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Default Re: Audio amp on CV2799 ?

Quote:
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I'm not sure what you mean by High Side...
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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Old 5th Jul 2017, 7:09 pm   #45
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Default Re: Audio amp on CV2799 ?

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Originally Posted by G8HQP Dave View Post
Surely all top band rigs used a 6BW6 as PA?
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.
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Old 5th Jul 2017, 9:29 pm   #46
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Default 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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Old 5th Jul 2017, 9:35 pm   #47
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Default Re: Audio amp on CV2799 ?

Quote:
I think I've got several YL11-somethings which are the directly heated double tetrodes.
YL1130? I remember them being used in some 1960s/1970s AM mobile gear, if only because PC Plod didn't understand he had to wait a second between keying the mic and speaking otherwise his first few words didn't make it to "YK" [or whatever his area base-station was].

I doubt the YL1130 would be too sensible to use as an audio-amp.
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Old 5th Jul 2017, 11:36 pm   #48
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Default Re: Audio amp on CV2799 ?

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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.

David
Somehow that's just the most evocative description of a home brewed lashup I've seen in a long while
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Old 6th Jul 2017, 12:29 am   #49
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Question 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.
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Old 6th Jul 2017, 11:13 am   #50
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Default Re: Audio amp on CV2799 ?

Quote:
Originally Posted by Radio Wrangler View Post
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.
Ok, another candidate that was built for UHF + service...I've just found in my stocks here a remarkably good-looking CWL 327-A, ex US Navy, WW2.

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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Old 6th Jul 2017, 11:28 am   #51
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Default 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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Old 6th Jul 2017, 12:33 pm   #52
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Default Re: Audio amp on CV2799 ?

Quote:
Originally Posted by astral highway View Post
Quote:
Originally Posted by Radio Wrangler View Post
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.
Ok, another candidate that was built for UHF + service...I've just found in my stocks here a remarkably good-looking CWL 327-A, ex US Navy, WW2.

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?
There's a 327A listed in Babani's International Radio Tube Encyclopedia, say's filament = 10.5V at 10.6A, Plate = 15,000V, no other electrical data given.

If that's any use.

Lawrence.
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Old 6th Jul 2017, 1:54 pm   #53
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Default Re: Audio amp on CV2799 ?

Quote:
Originally Posted by ms660 View Post
There's a 327A listed in Babani's International Radio Tube Encyclopedia, say's filament = 10.5V at 10.6A, Plate = 15,000V, no other electrical data given.

If that's any use...
Thank you , Lawrence! Very helpful! But I think I'll stay clear unless I have
X-Ray specs, with that anode voltage!

Cheers ��
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Old 6th Jul 2017, 8:41 pm   #54
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Default Re: Audio amp on CV2799 ?

Quote:
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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.?
Trying to regulate the supply to an audio-frequency power-amplifier is a fool's errand: you're basically connecting two audio amplifiers in series, with interesting effects!

[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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Old 7th Jul 2017, 1:53 pm   #55
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Question Re: Audio amp on CV2799 ?

Quote:
Originally Posted by Skywave View Post
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.?
Quote:
Originally Posted by G6Tanuki View Post
Trying to regulate the supply to an audio-frequency power-amplifier is a fool's errand.
I see. So if a '3-20A was used in this way, but with that A.F. power amplifier replaced by an R.F. power amplifier, would that still be an unwise thing to do?

Al.
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Old 7th Jul 2017, 2:25 pm   #56
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Default 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...!
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Old 7th Jul 2017, 6:09 pm   #57
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Question Re: Audio amp on CV2799 ?

But if that transmitter's modulation was F.M, then perhaps those problems would not arise?

Al
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Old 7th Jul 2017, 8:00 pm   #58
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Default Re: Audio amp on CV2799 ?

Ah, Jacek. Someone beat you to it! Here

You could probably beat him/her on build standard, though!

Cheers,

Frank
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Old 7th Jul 2017, 8:33 pm   #59
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Default 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
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