Dynaco Stereo 80 test results

[w1vtp]

I did a little fixin of this really nice Dynaco Stereo 80 amp.*  Before I got this, I never realized there was such a thing. - Knew of the Stereo 120 (which I also have) but not the Stereo 80

Anyway, here are some pics of the beauty.  I had to mount the caps horizontally so they would fit.  I bought some replacement output LC units.  The original 'lytics were swollen and had to be replaced.

I'll attach some pics

Here are the THD results. In most cases an order of magnitude better than spec.

http://homepage.fcgnetworks.net/w1vtp/DYNACO_ST80_TESTS/

I have another one just like it that works fine too.

Al
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Actually, my friend Paul SKC was a major player in this exercise

[Pete, WA2CWA]

Dynaco made a number of tube and solid-state amps. They generally went by the "Stereo" and "ST" prefix. Both prefixes were used interchangeably. Besides the ST-120 and 80, there was the Stereo 70 and 70 Series II, Stereo 150, Stereo 35, Stereo 416, SCA-35, Mark 2, 3, and 4, and probably a few more.

[WA3VJB]

Nice amp.
I bought one new from a place that was going out of business.
Also bought the matching AM/FM stereo tuner, with variable AM selectivity.
Actually, if you wanted to put it with the amp I'd consider selling it.

It's just sittin'

[Fred k2dx]

There are modern versions of the Dynaco tube amps available in kit form: reproduction chassis (stainless steel I think), pc boards, iron etc. The iron is supposed to be faithful to the originals too.

[w1vtp]

There are modern versions of the Dynaco tube amps available in kit form: reproduction chassis (stainless steel I think), pc boards, iron etc. The iron is supposed to be faithful to the originals too.

This is a solid state amp.  I have several tube amps including a Dynaco MKIV, an Eico St70 and a Bogen M60.  I think I'm going to like this amp a lot.  I don't know why they designed it this way but the freq resp goes out to 150 KC

Al

[ke7trp]

Pretty neat.. Good job!   I have never seen the 80.  We have had the 70s and the mono blocks. 

I rebuilt the 70 and upgraded it.  I got it from a local gentleman for $60 out of an add in the paper. Sold the Mallard tubes off for $400 to a guy in japan:) Got a new set of matched Russians for $70. I ran it for a few years in my home theater.  Then I got a Carver Cube amp that blew it away, made no heat and had many times the power. I sold the 70 off to the guy that owns Vibe records for a pretty sum. 

I have two monoblocks on the storage rack. Maybe one day I will get to them. I thought about using one for a modulator a few times    

C

[N8LGU]

I had two Mark III's with a PAS-3X for my stereo system. My neighbor bought a Stereo 80 and a PAT-4 and had me build them for him. I thought the tube system sounded much better, but then again, I was biased. I remember on the St-80 I had to wind hookup wire chokes around the output electrolytics. Dyna made very high quality stuff for the little they cost. I wish we could still get kits like that!

[flintstone mop]

Was there a fella named Hafler that was able to modify a Dynaco amp to give it the tube sound?  How did Dynaco come up with model numbers?? The ST80 is a 30W RMS per chan amp,. @ 10-50kc at 1 watt
AL are you sure about 150KHZ?? Flat out to 150KHZ? I was always aware of McIntosh going flat out to 100kc on their tube amps, but not Dynaco.

Fred

[Pete, WA2CWA]

Was there a fella named Hafler that was able to modify a Dynaco amp to give it the tube sound?  How did Dynaco come up with model numbers?? The ST80 is a 30W RMS per chan amp,. @ 10-50kc at 1 watt
AL are you sure about 150KHZ?? Flat out to 150KHZ? I was always aware of McIntosh going flat out to 100kc on their tube amps, but not Dynaco.

Fred

Dave Hafler owned Dynaco. Sold it to Tyco in 1968. He was also the founder of Acrosound, and the company that bears his name, Hafler.
http://www.stereophile.com/news/11661/
Lots of stuff on the web about him.

[KD6VXI]

Was there a fella named Hafler that was able to modify a Dynaco amp to give it the tube sound? 

Fred,

This may or may not be the same instance you are talking about, BBBUUUTTT:

Bob Carver did that.  He answered a challenge Sharper Image and some 'audiophool' rag put up in the mid to late 80s, IIRC, that they couldn't make a solid state amp emulate a tube amps 'sound and warmth'.

Bobs answer, putting a big resistor in the collector circuit.  I believe he showed that the impedance transformation caused the 'warmth' and tonal quality of the tubes...  He was able to 'vary' the quality of reproduction by changing the value of the resistor.

I wish I still had the article around here...  It was interesting reading.

--Shane

[w1vtp]

Was there a fella named Hafler that was able to modify a Dynaco amp to give it the tube sound?  How did Dynaco come up with model numbers?? The ST80 is a 30W RMS per chan amp,. @ 10-50kc at 1 watt
AL are you sure about 150KHZ?? Flat out to 150KHZ? I was always aware of McIntosh going flat out to 100kc on their tube amps, but not Dynaco.

Fred

Fred

As measured on lab equipment.  That frequency point was measured at 1 watt level - a level encountered at most modest listening levels - at least by me.  Points at 40 watts were at 50 Hz, 1000 Hz and 10,000 Hz.  The link to my homepage shows the THD results.  ~18 volts was set across the 8 ohms thus establishing the 40 watt level.  Those data points were were measured using a HP 3585A spectrum analyzer and entered into a THD calculator spreadsheet that I ginned up.  The amplifier was loaded by a 150 watt rated non-inductive load.  I only went to 10 KHz at 40 watts.  I saw no point in going any higher because at that point the second harmonic would have been 20 KHz - way past my hearing capabilities.

The numbers are amazing but I can't deny what I saw on the Spec Analyzer.