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Dynaco 400 Power Amp

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Anonymous
April 25, 2005 11:27:13 PM

Archived from groups: rec.audio.tech (More info?)

I just purchased a used Dyna 400 and need some help. I don't have a
parts list or even a schematic. So, my problems are compounded. But
here goes. There is a small circuitboard mounted on the front side of
the huge transformer. On this board a 2 large power resistors, R307 &
R308. I need to know what the resistance values and watt ratings are
for these 2 resistors. Can anyone help??

Chicago Pete

More about : dynaco 400 power amp

Anonymous
April 26, 2005 10:54:03 AM

Archived from groups: rec.audio.tech (More info?)

Pete, I would be interested in hearing more about your Dyna 400 after
you get it working. Also, if anybody else has any comments about the
400, I would like to hear them. That's one Dyna amp that I don't have
any experience with. Please let me know how you like its sound
compared to a tube amp. Thanks. Bill Crowell
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Anonymous
April 26, 2005 8:02:02 PM

Archived from groups: rec.audio.tech (More info?)

bcrowell@excite.com wrote:
> Pete, I would be interested in hearing more about your Dyna 400
after
> you get it working. Also, if anybody else has any comments about
the
> 400, I would like to hear them. That's one Dyna amp that I don't
have
> any experience with. Please let me know how you like its sound
> compared to a tube amp. Thanks. Bill Crowell

I have 2 Dyna 400s that have been maintained over the years, and were
still working fine (for Dyna 400s) the last time I powered them up
which was a couple of years ago.

One of my Dynas has MJE 15002x outputs, and recalibrated SOA circuits,
because without mods, these amps are not the best choice for driving
very reactive loads. Hence the 416.
Anonymous
April 27, 2005 12:26:12 AM

Archived from groups: rec.audio.tech (More info?)

I think there was a conversion kit, or the equivalent, from Sound
Values. They were a difficult bunch to deal with though.
Anonymous
April 27, 2005 1:51:11 AM

Archived from groups: rec.audio.tech (More info?)

I already did. That site doesn't answer my question - in fact there's
nothing there regarding PC Board #30 or the 2 resistors I'm interested
in.

Can you/anyone tell me the wattage and resistance values for R307 and
R308???

Chicago Pete
Anonymous
April 27, 2005 11:03:11 AM

Archived from groups: rec.audio.tech (More info?)

calcerise@hotmail.com wrote:

> I think there was a conversion kit, or the equivalent, from Sound
> Values. They were a difficult bunch to deal with though.

Their kit was crude - it slavishly doubled the number of output
devices, requiring a redrilled heat sink.

The easy, just as effective route was to sub in some modern output
devices with twice the SOA of the stock devices, and recalibrate the
SOA circuits.
Anonymous
April 27, 2005 11:17:47 AM

Archived from groups: rec.audio.tech (More info?)

kafer77@ameritech.net wrote:
> I already did. That site doesn't answer my question - in fact
there's
> nothing there regarding PC Board #30 or the 2 resistors I'm
interested
> in.
>
> Can you/anyone tell me the wattage and resistance values for R307
and
> R308???


You're right. The parts list at

http://home.indy.net/~gregdunn/dynaco/components/ST400/...

is highly incomplete. The markings on mine are indistinct. They run
fairly hot.

They provide the regulated power for the op amps on the input boards,
the input buffers & etc.

I believe that they drop about 70 volts. Current through them seems
to be about 10-20 mA. Resistance is probably about 3,500 ohms. They
probably dissipate less than 2 watts, so 20 watt parts should be
pretty good. If they are too low of a resistance the zener diodes will
run hot. If they are too high of a resistance, the zener diodes will
break regulation and not have enough voltage drop across them. I
think the zeners are 13 or 15 volt parts.
Anonymous
April 29, 2005 11:31:46 PM

Archived from groups: rec.audio.tech (More info?)

I checked the owners manual I have for a St-400 and it lists R307, r308 as
850 ohms 10watts

Barry Streets

<calcerise@hotmail.com> wrote in message
news:1114572372.925724.228700@l41g2000cwc.googlegroups.com...
> I think there was a conversion kit, or the equivalent, from Sound
> Values. They were a difficult bunch to deal with though.
>
!