Daniel_Rai@ub.cc.umich.edu (03/04/91)
A Dyna Stereo 70 keeps blowing the main fuse
seconds after powering up. The tubes are fine,
and they all light up before the fuse blows. What
could be causing this? Is there troubleshooting
in the manual? (I've heard of a place in Ohio that
sells Dyna parts - I don't have a manual, but
think I can get one from them) If it is the input
board, I'm thinking about replacing it with one of
those solid state boards from Sutherland
Engineering, or from a few other companies. Has
anyone tried these things?
KUDOS: to Apogee, for including a new box, and
grill fabric without additional charge during a
bass ribbon replacement
to UPS, for cheap insurance rates (~10 cents
per $100 coverage?). The girl at the desk
chuckled, "We're much cheaper than US Mail because
we don't break things like they do - they *need*
their insurance." In my experience, everything I
have received with (in spite of?) UPS's handling
has arrived intact and unpunished.
Poo-Poos: to Roadway Express, and Roadway Package
System (RPS) for seriously damaging three separate
electronic and two speaker units during their
handling, then refusing to pay for *anything* by
writing it all off to "Inadequate Packing" (the
shipments were all in factory packing).
to Madrigal, for replacing an amplifier's
shipping box&foam during a repair then charging me
$100 for it on top of the $230 repair bill
(included $150 labor for replacing a cap, a
resistor, and a plastic washer). After this
repair, the amplifier still arrived with noise in
the repaired channel. This amplifier "blew" a
channel, while driving a pair of LS3/5a's at low
to moderate loudness levels (I didn't know 3/5a's
were such a difficult load ;)
The last Levinson amp I had, developed a buzzing
problem while connected to a pair of SMGa's. I
love the way Levinson amps sound and image, but am
curiously disappointed with their seemingly high
failure rate. These incidents occurred while
driving what I consider to be simple electronics
under undemanding circumstances. Tube stuff (CJ,
ARC, Dyna, and AVA) has never been this
unreliable. Has anyone had or heard of similar
failure rates with ML or other "high-end" gear?
Thanks,
(dan)JWB@SLACVM.SLAC.STANFORD.EDU (03/05/91)
In article <9903@uwm.edu>, Daniel_Rai@ub.cc.umich.edu says: > > A Dyna Stereo 70 keeps blowing the main fuse > seconds after powering up. The tubes are fine, > and they all light up before the fuse blows. What > could be causing this? (Much deleted) You say the tubes are fine, but are you sure? I had a similar problem with a Scott Amp after driving it to hard. Turned out to be the rectifier tube for the power supply. It too lit up prior to the fuse blowing. Just a thought... John Beach [The 5AR4 is allegedly notorious for heater-cathode shorts, according to a retired technician of my acquaintance. -tjk]
gap5444@lims03.lerc.nasa.gov (Greg Priddy) (03/05/91)
In article <9903@uwm.edu>, Daniel_Rai@ub.cc.umich.edu writes... > > A Dyna Stereo 70 keeps blowing the main fuse > seconds after powering up. The tubes are fine, > and they all light up before the fuse blows. What > could be causing this? Is there troubleshooting > in the manual? (I've heard of a place in Ohio that > sells Dyna parts - I don't have a manual, but > think I can get one from them) If it is the input > board, I'm thinking about replacing it with one of > those solid state boards from Sutherland > Engineering, or from a few other companies. Has > anyone tried these things? > As a long-time owner (and subsequent fixer) of a Dyna Stereo 70, I can say with some certainty that it is not your input board which is causing the blown fuses. If you are sure that your power rectifier tube (5AR4) is good then you probably have either a bad filter cap or bad bias cap(s). In any event, it is likely that something in the power supply section is awry. Stereo Cost Cutters of Dublin, OH does sell Dyna parts (including whole "new" amps), as does Audio by Van Alstine of Burnsville, MN. About all I have seen in the way of a manual is a schematic and parts list. There is also a place in Lakewood, OH (near Cleveland) called Play It Again Sam, which does excellent work on all sorts of stereo equipment, including Dyna's. As far as solid state input boards and other mods, there are as many opinions as there are experts. IMHO, unless you are dissatisfied with the way the amp sounds, I would try to stick to the original circuit topology. Replacing the old resistors and caps (which have probably drifted out of value) with new precision parts would be my recommendation. I have no affiliation with any of the places mention herein, and my opinions, for better or worse, are based on my experience and do not represent those of my employer or my employer's clients. Good Luck! -Greg
rmorss@uunet.UU.NET (Richard Morss) (03/08/91)
JWB@SLACVM.SLAC.STANFORD.EDU writes: >In article <9903@uwm.edu>, Daniel_Rai@ub.cc.umich.edu says: >> >> A Dyna Stereo 70 keeps blowing the main fuse >> seconds after powering up. The tubes are fine, >> and they all light up before the fuse blows. What >> could be causing this? >(Much deleted) >You say the tubes are fine, but are you sure? I had a similar problem >with a Scott Amp after driving it to hard. Turned out to be the rectifier >tube for the power supply. It too lit up prior to the fuse blowing. >Just a thought... >John Beach >[The 5AR4 is allegedly notorious for heater-cathode shorts, according to > a retired technician of my acquaintance. -tjk] If the replacement 5AR4 doesn't solve the problem, you need to start checking all the capacitors in the amp. A system this old probably has a leaky power supply filter cap at best. If you have the original assembly manual, there should be a very detailed checkout procedure right after the last assembly instruction. My memory doesn't go back that far, but, as I recall, they have you plug the thing in the wall with all the tubes removed to check for shorts. In any event, replacing the PS filter cap should do the job.