[ARC5] BC-375 Re-Tube Project- Scratch Three

[Bruce Long]

I was in the precison osc business for years. We assumed osc must start up reliably both slow start from zero volts and also switch start. Slow start is usally the more demanding

Almost all osc without an agc loop run at least some

Sent from my iPhone

On Nov 19, 2013, at 2:50 PM, "Fuqua, Bill L" <wlfuqu00 at uky.edu> wrote:

 With a 60 Hz or dynamotor the supply is not applied very abruptly. Even with keying the click filter rise time is much less than
1/bandwidth of the tuned circuit. 
 73
Bill wa4lav

________________________________________
From: Dennis Monticelli [dennis.monticelli at gmail.com]
Sent: Tuesday, November 19, 2013 10:52 AM
To: Fuqua, Bill L
Cc: Geoff; kgordon2006 at frontier.com; David Stinson; ARC-5 List
Subject: Re: [ARC5] BC-375 Re-Tube Project- Scratch Three

It's been my experience that with most oscillators the sudden application of voltage (such as a switch or key closure) causes small displacement currents to flow as the capacitances of the circuit charge up.  These are usually much larger than the tube's noise mechanisms and so induce the start-up cycle.  If you slowly apply the voltages these displacement currents will fall below that of the inherent noise.

Dennis AE6C


On Mon, Nov 18, 2013 at 10:46 PM, Fuqua, Bill L <wlfuqu00 at uky.edu<mailto:wlfuqu00 at uky.edu>> wrote:
 I suspect that it is not the thermal noise that gets the power oscillators started up but
the electron shot noise.
73
Bill wa4lav

________________________________________
From: Fuqua, Bill L
Sent: Tuesday, November 19, 2013 1:44 AM
To: Geoff; kgordon2006 at frontier.com<mailto:kgordon2006 at frontier.com>; David Stinson; ARC-5 List
Subject: RE: [ARC5] BC-375 Re-Tube Project- Scratch Three

 what about a 812 or 812A. They are medium mu and probably sufficient plate dissipation.
Power oscillators usually use medium mu triodes so that there is sufficient plate current at low bias or zero bias to start up
oscillation.
 An  example is one used in a self-oscillation plasma generator that I recently got a tube from.
It had a 3-1000H. I have seen other power oscillators using 812 tubes as well.

73
Bill wa4lav

________________________________________
From: arc5-bounces at mailman.qth.net<mailto:arc5-bounces at mailman.qth.net> [arc5-bounces at mailman.qth.net<mailto:arc5-bounces at mailman.qth.net>] on behalf of Geoff [geoffrey at jeremy.mv.com<mailto:geoffrey at jeremy.mv.com>]
Sent: Monday, November 18, 2013 4:13 PM
To: kgordon2006 at frontier.com<mailto:kgordon2006 at frontier.com>; David Stinson; ARC-5 List
Subject: Re: [ARC5] BC-375 Re-Tube Project- Scratch Three

And then there is also the 809, T-40 and T-40Z, all of which are fairly
available.

Carl


----- Original Message -----
From: "Geoff" <geoffrey at jeremy.mv.com<mailto:geoffrey at jeremy.mv.com>>
To: <kgordon2006 at frontier.com<mailto:kgordon2006 at frontier.com>>; "David Stinson" <arc5 at ix.netcom.com<mailto:arc5 at ix.netcom.com>>; "ARC-5
List" <arc5 at mailman.qth.net<mailto:arc5 at mailman.qth.net>>
Sent: Monday, November 18, 2013 4:02 PM
Subject: Re: [ARC5] BC-375 Re-Tube Project- Scratch Three


What about an 811 or 812, A or non A?

Carl


----- Original Message -----
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com<mailto:kgordon2006 at frontier.com>>
To: "David Stinson" <arc5 at ix.netcom.com<mailto:arc5 at ix.netcom.com>>; "ARC-5 List"
<arc5 at mailman.qth.net<mailto:arc5 at mailman.qth.net>>
Sent: Monday, November 18, 2013 11:47 AM
Subject: Re: [ARC5] BC-375 Re-Tube Project- Scratch Three


On 18 Nov 2013 at 3:10, David Stinson wrote:

Three candidate tubes for the
"Cheap Tubes for the BC-375" project have disappointed.
1625, 837 and 7984 will not "hold up" in this service.
Once the screen voltages are dropped to spec,
the tubes lack the gain to oscillate reliably, even
with heavy "gimmick" cap coupling between grid
and plate in the OSC stage.

David: Have you yet tried connecting the screen to the GRID (G1). As I
said
earlier, this results in a HIGH-MU triode, which SHOULD work much better
as an oscillator.

Kenneth G. Gordon W7EKB

"Courage is being scared to death but saddling up anyway."--- John
Wayne

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