[AMRadio] Home brew AM

Jim candela jcandela at prodigy.net
Tue Oct 5 07:38:52 EDT 2004


     That Altec amplifier sure is nice! I really like the 5R4 full wave
bridge rectifier with the extra filament taps off the HV windings. Never
seen that done before. Also the 6W6 triode connected cathode follower stage
is unique with the center tapped choke. I see negative feedback from the
output tranny all the way back to the first preamp stage. Without getting
too far into audio jargon, how do two of these beasts sound as a stereo
amplifier? The HV filter only has 6 uf as part of a LC filter, so how is the
bass response?

Got a few dozen of these lying around? :)

Jim Candela

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net]On Behalf Of Patrick Jankowiak
Sent: Monday, October 04, 2004 7:32 PM
To: amradio at mailman.qth.net; bcarling at cfl.rr.com
Subject: Re: [AMRadio] Home brew AM

I would say that the fidelity was pretty good compared to a
BC-610, mostly because the audio amplifier was of exceptional
quality and so lightly loaded.

The power at carrier was pretty low, only about 80 watts, and
when we were done tweeking, we were getting about a 340 watt PEP
signal out of it.

Running the power low, with low voltage and current allowed the
rare tube to stay cool.

As for power, I imagine the BC-610's carrier is much more powerful.

The modulator amplifier is rated at 175 watts and is an Altec
1570B, using two 811A's in class B push pull with the grids
driven directly from cathodes of some beam power tubes, the
schematic of this unit is here:


It has 10 tubes, and operates with 930VDC on the 811A's.

I use two of these amps in my stereo.

best regards,

From: "Brian Carling" <bcarling at cfl.rr.com>
Subject: Re: [AMRadio] Home brew AM

How does that compare to the performance of say the 250TH final
stage in a BC-610?
It sounds like you are running at lower power.
Also how many tubes do you use in the cathode modulator?

On 2 Oct 2004 at 20:12, Patrick Jankowiak wrote:
 >> Cathode mod works very well on a 250TH. We are getting 80-90
 >> watts carrier no problem at 2200V. For the details:
 >> http://www.montagar.com/~patj/cathmod01.htm
 >> Patrick
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