Not in mine they don't, Gary, OM ;>) I'm talking fairly extensive mods here:
(1) Change screen grid voltage to ~450V, preferably regulated. (plate V is
about 550 - 600). Change control grid bias to ~ -50V for proper operating
point (~35 - 40mA/tube quiescent). This allows up to 50V of audio on each
grid (100V P-P) before going into grid current.
(2) Replace adio driver transformer with resistance-coupled phase inverter.
I've used the split-load circuit, as well as others, with good results.
(3) Feedback from mod xfmr secondary to phase inverter input. Roll off highs
in the feedback network so that phase shift don't getcha!
(4) Increase 1st audio input resistor, beef up audio coupling & decoupling
caps, replace .02 mfd accross mod xfmr secondary with 0.002, yada, yada...
Works for me - I did it for my Viking I, and a friends Viking II. Able to
modulate the things at 100% cleanly at full rated input. Can't argue with
the results!
73,
-Larry/NE1S
Gary Schafer writes:
The 807's in the Viking and DX-100 run in AB2. In AB1 you wont get more than
around 45 to 50 watts of audio before they start drawing grid current. In
AB2 they will produce 120 watts of audio.
73
Gary K4FMX
-----Original Message-----
From: ne1s [mailto:[EMAIL PROTECTED]
Sent: Monday, March 27, 2006 1:06 PM
To: [EMAIL PROTECTED]; Discussion of AM Radio
Subject: Re: Modulator design needed
While other tubes may do better, I've had good luck using AB1 807s in
VikingI/II/DX-100 class transmitters - they'll do 100% cleanly.
-Larry/NE1S
Gary Schafer writes:
> Just remember if you are going to use a tube phase inverter rather than
a
> driver transformer the modulator tubes need to be run in AB1 and not
AB2.
> You can't run any grid current without a driver transformer.
> This leaves out 807's as modulators as you can't get very much power out
of
> them in AB1 but they are fine in AB2 as they are used in most rigs.
Dx100
> etc.
>
> 73
> Gary K4FMX
>
>
>> -----Original Message-----
>> From: [EMAIL PROTECTED] [mailto:amradio-
>> [EMAIL PROTECTED] On Behalf Of Peter Markavage
>> Sent: Sunday, March 26, 2006 1:34 PM
>> To: amradio@mailman.qth.net
>> Subject: Re: [AMRadio] Modulator design needed
>>
>> 12BY7 drives the driver transformer which, in turn drives the EL-34's.
>>
>> Build a phase inverter, like many of the Hi-Fi amps that don't use a
>> driver transformer to drive the EL-34's.
>>
>> Pete, wa2cwa
>>
>> On Sun, 26 Mar 2006 13:19:06 -0500 "Mike Sawyer" <[EMAIL PROTECTED]>
>> writes:
>> > Bob,
>> > I suggest you look at the schematics again. The output of the
>> > 5763 goes
>> > no where near the modulator. I don't have the schematics in front
>> > of me but
>> > I have done some extensive work in the audio section.
>> > Mod-U-Lator,
>> > Mike(y)
>> > W3SLK
>> > ----- Original Message -----
>> > From: <[EMAIL PROTECTED]>
>> > To: <[EMAIL PROTECTED]>; "Discussion of AM Radio"
>> > <amradio@mailman.qth.net>;
>> > "Discussion of AM Radio" <amradio@mailman.qth.net>
>> > Sent: Sunday, March 26, 2006 12:59 PM
>> > Subject: Re: [AMRadio] Modulator design needed
>> >
>> >
>> > Mark,
>> >
>> > Take a look at a Heathkit Apache schematic, (TX-1), for ideas.
>> >
>> > There is NO driver transformer. The 5763 driver goes to the Mod
>> > transformer
>> > and the EL-34s feed it for audio.
>> >
>> > Bob - N0DGN
>> >
>> > -------------- Original message ----------------------
>> > From: "W1EOF" <[EMAIL PROTECTED]>
>> > >
>> > > I've been gifted a nice mod transformer so I can build a modulator
>> > for my
>> > > Johnson 6N2. I don't have a driver transformer so I'm looking for
>> > a design
>> > > which doesn't need one. I'm sure the schematics are out there, but
>> > I keep
>> > > finding ones with the driver transformer. Same with all my old
>> > radio books
>> > > that I've looked at so far. Can someone point me in the direction
>> > of a
>> > > good
>> > > design that is online, or one that you can share with me via
>> > email?
>> > > Thanks!
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>
>
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