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KB2VXA > TECH 23.07.03 08:58l 66 Lines 3088 Bytes #999 (0) @ WW
BID : 10779_WT3V
Read: DB0FHN GUEST OE7FMI
Subj: Re: KB9ALN > P-P AF amp
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Sent: 030723/0501 10779@WT3V.#CNJ.NJ.USA.NOAM $:10779_WT3V
From: KB2VXA@WT3V.#CNJ.NJ.USA.NOAM
To : TECH@WW
Hi Andy and readers,
I have heard of bridged amplifiers used in the old Western Electric
telephone repeaters, but there's a lot more to it than push pull. The
amplifier(s) use push pull triode outputs, but there are balance
transformers also which make them bidirectional, full duplex. Sorry, I
don't understand how that is applied to hi-fi work.
There are all sorts of wiring and tone control arrangements in juke
boxes, too much to go into great detail. The ones I was talking about
were made by Rowe and used in the Rowe-AMI boxes. In addition to the push
pull configuration for the woofer they had a three channel switched tone
control and DC remote volume control. One interesting feature is a long
time constant volume compressor/mute which eliminates the thump of the
needle engaging the disc and keeps the volume constant from record to
record. I suppose they have somthing similar in the new CD models.
Having access to a vast array of junk box items I reconstructed and
experimented with several versions of the amps at home, one was used as a
120W guitar amp which cracked a window pane. Never mid my ears, I'm half
deaf anyway. (;->)
Now if you look at a solid state power output stage using discreet
components, you'll notice that there are two in series connected across
B+ and B- with a capacitor coupled output between them. Whether put in
paralell with another or the whole thing operated push pull push pull
nothing will burn out because of the DC blocking capacitor. This is the
output arrangement of those Rowe amps and they also had a massive
tapped autotransformer for determining the wattage output. In this manner
the overall speaker balance could be achieved.
Another feature was the 70V line output which fed satellite speakers used
as fill in for large halls. Each speaker used a tapped line to voice coil
transformer, the input taps were marked in watts so the total did not
exceed the amplifier output when all was said and done.
BTW, I learned all this while repairing those amps for a major NJ based
distributor, one of the Rowe International subsidiaries which also
includes Thorn/EMI, Musak, MTV and lots more.
Those Darlington transistors I mentioned are two devices connected in
series just like the discreet outputs I mentioned, only they're etched on
a single substrate and for all outward appearances are single
transistors. Sorry about the confusion, still I don't understand how
you're using that term "bridged".
Like they say, draw me a picture, one is worth a thousand words. You can
do exactly that, scan the image and attatch it to an e-mail message. Send
it to my address below and it will surely help if I know what I'm looking
at. Thanks a whole bunch in advance, I just might learn something!
73 de Warren, KB2VXA@WT3V.#CNJ.NJ.USA.NOAM
E-MAIL: kb2vxa@juno.com
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Message timed: 05:08 on 2003-Jul-23 GMT
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