LPAM Transmitter suggestions

[Bow/KD5KZN]

Hey All you Tube AM Gurus...

I got this schematic and I want to build it, but de-rate it for LPAM use and possibily QRP 160 Meter.

I have thought of running 12AX7's in place of the 6C5's and I want to use lower power output tubes instead of the 5881. Any suggestions?



Also, the carbon mic circuit will be removed for something more... modern.

Any chances this thing will sound good on the air?

I am wide open for suggestions.

Thanks,

[K1JJ]

Hi Bow,

Well, at first glance, you cud probably sub 6AQ5's in there
and bring it down to the 5-10W area. Maybe diddle with resistor
values a little to get the recommended screen and grid currents.

Also, that carbon mike has LOTS of gain. If you go wid a different
mike, you will need another stage in there. Maybe cornsider a dual
stage pentode/ triode or something from one of the handbooks for
a low output mike.


Expect that series modulated Heising modulator tube to run MUCH
hotter than the final, as it is in class A vs: class C for the final.

Another thing to consider is add two components and make the xtal
osc a VXO to pull the xtals down 3-4kc, variable. Check out my
6AQ5 PW series modulated rig on the AM Window under tech section
for details. Or click:

http://www.amwindow.org/tech/htm/series.htm

Being a series modulated rig, it shud sound good on the air
once you get everything adjusted. The bottleneck will be how
good you process your audio at the input or simply use a direct
mike in w/o an EQ.  Do a full audio sweep proof test to find
out. [Check "Sweeping Your Rig", under the Handbook section
or in East coast Sound on this site for more details.]



Maybe some of the other guys will have comments before you
begin.

73,
Tom, K1JJ

[Bow/KD5KZN]

Hi Bow,

Well, at first glance, you cud probably sub 6AQ5's in there
and bring it down to the 5-10W area.
[/qoute]

Ok Cool.. that is closer to what I am looking for.

Also, that carbon mike has LOTS of gain. If you go wid a different
mike, you will need another stage in there. Maybe cornsider a dual
stage pentode/ triode or something from one of the handbooks for
a low output mike.

I was thinking of a 12AX7 preamp with one triode feeding the next... think that would do it?

Expect that series modulated Heising modulator tube to run MUCH
hotter than the final, as it is in class A vs: class C for the final.

hmmm.. ok.. this is why I hate being a newb... lack of knowledge... I got over my tube project fears by building a few low power tube guitar amps... now I am getting brave enough to try a radio project!

Another thing to consider is add two components and make the xtal
osc a VXO to pull the xtals down 3-4kc, variable. Check out my
6AQ5 PW series modulated rig on the AM Window under tech section
for details. Or click:

http://www.amwindow.org/tech/htm/series.htm

OK, Thanks.. I have looked at that schematic a few times!

Being a series modulated rig, it shud sound good on the air
once you get everything adjusted. The bottleneck will be how
good you process your audio at the input or simply use a direct
mike in w/o an EQ.  Do a full audio sweep proof test to find
out. [Check "Sweeping Your Rig", under the Handbook section
or in East coast Sound on this site for more details.]

I'll check that out now!

Maybe some of the other guys will have comments before you
begin.

73,
Tom, K1JJ

Thank you for your input!