Dynaco Stereo 80

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Meerkat 70

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Joined 2016
#1
Hello.. Anyone have any love for the Stereo 80.. I have the opportunity to pick one up for $30.. It distorts one channel after warm up but looks in good shape otherwise. Had a look at the schematic and pictorial and it looks easy to work on.. Any thoughts on this Thanks Wayne
 
#5
Good project. However Do buy and fit ALL the updatemydynaco.com parts. Good and affordable.
Anything less extensive is imo pointless.
That Dyna you are considering buying will contribute it's Case and potentially its' Transformer... no more, no less.
Have fun.
 
#7
Modern circuits should work fine with the 11 turns around a AA battery coils. This is for the RF feed in inhibition . zobel network they call it now. Peavey made their own coils too but on the PV1.3K they called them 0.8 mH. I'm still using the original coils on my ST120 but the capacitors are obviously much smaller these days. the old coilss stand there okay without the forms. I did do the Greg Dunn archived "TIP" mod to the output to lessen chance of oscillation from outside sources.
ST80 should be fine with the LM3886 boards, but I find peak power of that a bit cramped on the ST120. I'm doing an AX6 driver with NTE60 output transistors (MJ802 equiv) for more "music power". Not bass guitar power or disco power, high duty cycles overwhelm the heat sinks of dynaco ST80 & 120 quickly.
If you want serious heat sinks heatsinksamerica down in vendor forums has got some nice 3.0" high finned ones. 3.5" would fit. I melted the solder on the output cap in my ST120 after repair running about 10 watts PA in a 3.5 hour choir rehearsal.
The cool thing about the output cap, the output transistors were toasted after the wire shorted to the case, but the speakers weren't. Capacitor output amps are great for newbies, IMHO. My cheapest PA speakers cost $120 each, the expensive ones were $300 each. The ST120 cost me $50 toasted so good speaker protection is important imho.
 
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#8
Meerkat 70 said:
Thanks for the reply. Do you know the inductance of the wire coils around the output caps.. I want to replace them with torroid coils of the same values inductance and current.. Thanks Wayne
Click to expand...

Dunno What ? yer playing at.. Mate.
Buy and fit ALL the Updatemydynaco pieces.
Fairly simple and affordable.
The original Dynaco contraption is accurately described as Junk !
Rebuild it ..using the suggested V good available bits.. Or simply take it the trashbin.. now, thereby saving yourself pointless aggro.
Sad /classic example of: Horses, although led to water cannot be made to drink.. so they die.
 
#9
Bare said:
The original Dynaco contraption is accurately described as Junk !
Rebuild it ..using the suggested V good available bits.. Or simply take it the trashbin.. now, thereby saving yourself pointless aggro.
Sad /classic example of: Horses, although led to water cannot be made to drink.. so they die.
Click to expand...
In 1966 when transistor were $10 ea for power ones and $1 for little ones, it was quite amazing.
The difference between it and the successful Leak ST70 were the cheapo heatsinks.
But a lot of knowledge has has been learned since 1966, and some intense stupidity has also occurred.
In particular 99.9999% of the amps discussed on here directly connect the output transistors to the speaker, which in a diy project is very likely to toast the $150 speaker coil. 99% of the protection circuits people buy on e-bay have **** relays rated for AC current that won't break a DC arc into a short more than once, if that time. The $3 output capacitor of the dynaco is fool proof for the speaker, and doesn't sound bad.
Last I communicated with updatemydynaco he was pushing 3/8" solid bars for heat sinks. Okay ONLY if you use the amp for an hour or so then turn it off for 24 hours. I use my amp 18 hours a day sometimes, and have PCAT salvage fans on the original dynaco heatsinks. That worked reliably even with 250 ma idle bias current (see below)
There was a closed loop bias control addition board which allowed the PC15 to sound good, but it tends to blow up sense transistors and run the bias current up to 250 ma. I've abandoned that, but liked the sound and performance with that, the greg dunn TIP mod, and the fans.
The power transformer on dynaco equipment is stellar quality. I've had one take a lightning hit that arced across the power switch and vaporize the turn off pop capacitor.
 
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