[AMRadio] Re: AMRadio Digest, Vol 9, Issue 6

Patrick Jankowiak recycler at swbell.net
Wed Oct 6 20:41:01 EDT 2004


As a hi-fi amp, it is extremely clean and very flat from 20Hz to 
20KHz up to about 80-100 watts.

Above that, despite what the specs may say, heavy bass causes 
distortion due to the smallish size of the output transformer. As 
the point is approached, hum increases due to the transformer 

It is a first rate public address amp and a super modulator.

I have looked into getting (having made)  larger transformers to 
hadle 20-20K at 200W, but finding one with a 6500 ohm CT primary 
that will take the 930 volts DC is difficult. If I were to have 
them made, I would go for a 10K or 12K primary and change the 
power supply to solid state, add about 200uF of capacitors (mount 
where the 5R4's are), and eliminate the choke input (and the 
choke, to make room for the big transformer) for 1100-1200V on 
the plates. I have been quoted $400 each for such.

I did experiment, simply bypassing the choke to get higher volts 
on the tubes, and got 240 watts, but the 'KLIXON' popped after a 
couple minutes, not from heat, but it also responds to current. I 
would not run them that way unless replacing the OPT's.

I have only three, one is reserved for parts but is actually in 
working order less perhaps the tubes.


From: "Jim candela" <jcandela at prodigy.net>
Subject: RE: [AMRadio] Home brew AM


      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 
too far into audio jargon, how do two of these beasts sound as a 
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

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