[Sal Brisindi]

I knew one day I would own one of these, well that day happened, today.
I know some of you are not fans of this amplifier but pound for pound, I
don't think you can buy a better amplifier for the price. Photos at
http://www.tuberadios.com/temp/dynaco13.jpg

Regards,
Sal Brisindi

[WindsorFox]

Sal Brisindi wrote:
I knew one day I would own one of these, well that day happened, today.
I know some of you are not fans of this amplifier but pound for pound, I
don't think you can buy a better amplifier for the price. Photos at
http://www.tuberadios.com/temp/dynaco13.jpg

Regards,
Sal Brisindi


Where did you get it??

--
I used to have abs. Now, I've just got ab.
One big ol' Ab. - BigSkiff www.titanspot.com

Pyongyang sounds more like the sound effect an ACME catapult makes
as it goes off at precisely the wrong moment for Wile E. Coyote. -
Cadbury Moose

[Sal Brisindi]

WindsorFox wrote:
Sal Brisindi wrote:
I knew one day I would own one of these, well that day happened,
today. I know some of you are not fans of this amplifier but pound for
pound, I don't think you can buy a better amplifier for the price.
Photos at http://www.tuberadios.com/temp/dynaco13.jpg

Regards,
Sal Brisindi


Where did you get it??


I did a search on Craigslist.org state by state until I found this one.
Its almost all original, maybe only the 4 coupling capacitors were replaced.

[WindsorFox]

Sal Brisindi wrote:
WindsorFox wrote:
Sal Brisindi wrote:
I knew one day I would own one of these, well that day happened,
today. I know some of you are not fans of this amplifier but pound
for pound, I don't think you can buy a better amplifier for the
price. Photos at http://www.tuberadios.com/temp/dynaco13.jpg

Regards,
Sal Brisindi


Where did you get it??


I did a search on Craigslist.org state by state until I found this one.
Its almost all original, maybe only the 4 coupling capacitors were
replaced.

Ah, I'll have to try that. I've been sniffing around eBay but the
tube versions get rather expensive rather quickly. I almost fainted when
I saw some of the prices on old McIntosh stuff, especially compared to
what it was 4 years ago.

--
"One hard rule of sockpuppetry is that a sockpuppet
can't be smarter than its animator."
- Arny Krueger

[WindsorFox]

Bret Ludwig wrote:
Sal Brisindi wrote:
WindsorFox wrote:
Sal Brisindi wrote:
I knew one day I would own one of these, well that day happened,
today. I know some of you are not fans of this amplifier but pound for
pound, I don't think you can buy a better amplifier for the price.
Photos at http://www.tuberadios.com/temp/dynaco13.jpg


Provided you paid less than about $35 for it, that's true.



And far more people disagree with that opinion than agree with it I'm
afraid.

--
"One hard rule of sockpuppetry is that a sockpuppet
can't be smarter than its animator."
- Arny Krueger

[Sal Brisindi]

Bret Ludwig wrote:

Provided you paid less than about $35 for it, that's true.

Bret,
I will make you a deal,
For every working complete Dynaco ST-70 you can buy for $35.00, I will
pay you double for it, no questions asked. You seem to think that should
be going rate. While your at it, I will pay you $70 for any working
stereo tube amp you come across.

[WindsorFox]

Sal Brisindi wrote:
Bret Ludwig wrote:

Provided you paid less than about $35 for it, that's true.

Bret,
I will make you a deal,
For every working complete Dynaco ST-70 you can buy for $35.00, I will
pay you double for it, no questions asked. You seem to think that should
be going rate. While your at it, I will pay you $70 for any working
stereo tube amp you come across.

Hell, for that price put me down for two stereo or four mono amps of
35watts or up....

--
"One hard rule of sockpuppetry is that a sockpuppet
can't be smarter than its animator."
- Arny Krueger

[thomas]

Bret Ludwig wrote:
Sal Brisindi wrote:
Bret Ludwig wrote:

Provided you paid less than about $35 for it, that's true.

Bret,
I will make you a deal,
For every working complete Dynaco ST-70 you can buy for $35.00, I will
pay you double for it, no questions asked. You seem to think that should
be going rate. While your at it, I will pay you $70 for any working
stereo tube amp you come across.

Yes, but others will pay EVEN MORE. So I no longer look at ST-70s. Or
really any other old tube amp.

Starting with NEW transformers and chassis is cheaper and not that
difficult.

New trafos and chassis at $35? Please elaborate.

[Iain Churches]

"Bret Ludwig" wrote in message
oups.com...

Sal Brisindi wrote:
Bret Ludwig wrote:

Provided you paid less than about $35 for it, that's true.

Bret,
I will make you a deal,
For every working complete Dynaco ST-70 you can buy for $35.00, I will
pay you double for it, no questions asked. You seem to think that should
be going rate. While your at it, I will pay you $70 for any working
stereo tube amp you come across.

Yes, but others will pay EVEN MORE. So I no longer look at ST-70s. Or
really any other old tube amp.

Starting with NEW transformers and chassis is cheaper and not that
difficult.

Please post links to pics of your work, Bret
Iain

[Patrick Turner]

Bret Ludwig wrote:

WindsorFox wrote:
Bret Ludwig wrote:
Sal Brisindi wrote:
WindsorFox wrote:
Sal Brisindi wrote:
I knew one day I would own one of these, well that day happened,
today. I know some of you are not fans of this amplifier but pound for
pound, I don't think you can buy a better amplifier for the price.
Photos at http://www.tuberadios.com/temp/dynaco13.jpg


Provided you paid less than about $35 for it, that's true.



And far more people disagree with that opinion than agree with it I'm
afraid.


Yes, but they aren't buying it for quality of sound. It's a retro
style piece. That's all. It works, but most are only powered up
occasionally. Few run them all the time.

I want an amplifier to be really good, and I want to use it every day
for many hours. I want it not to eat tubes, crap up the sound, or give
off a level of heat that makes me think it will erupt in the near
future. Those things CAN be achieved with a Dynaco, but you wind up
spending several hundred dollars for a lot of stuff you are going to
throw most of in the trash.

Do we need to Air the Grievances against the ST70 again? I think so,
and I enjoy it even if we don't.

1. The pentode-triode circuit is no good. It uses the expensive and
crappy sounding 7199.

The trouble is that the pentode anode load is bootstrapped off the
following
concertina phase inverter so it has enough gain so that the amp
is still sensitive when NFB is applied. Pentodes have more distortions
than a dedicated
all triode input stage using say a pair of 6CG7 twin triodes.
But most PPL would never be able to tell the difference at the average 1
watt levels.


2. Said circuit is on a lame PCB that desperately needs to be smashed
and thrown in the recycle bin because it will cause a great amount of
trouble if used. I love busting them up. Sadly, I have approximately
196,300 boards yet to smash.

Yeah, I ain't a fan of the pcb used either; re-placing with a
sheet of Al with 4 x 9pin sockets for 6CG7 is better practice.


3. The power transformer is too small, leading to poor regulation and
high heat dissipation. Since its regulation stinks, they turned the
quiescent current (and the Class A power point) up, making it run even
hotter. And since the primary was wound for 110 volts nominal, all the
voltages are high, including the heaters. More heat yet!

The samples of ST70 I have seen do have hottish PTs, and highish B+,
especially when using solid state rectifiers, but there is room for a
larger tranny,
and one could do worse than use my schematic at
http://www.turneraudio.com.au/dynacost70mods.html

4. Bias circuit is sorely deficient, using a single odd value resistor
in the cathode circuit for a reason making no sense today. You cannot
individually bias each tube, meaning distortion can never be minimized.

Agreed!!!



5. About the best thing about the ST70 is the output transformers.
They are the one thing that's even adequate about it. But they are not
ideal: they achieve perfect AC balance at the expense of serious DC
unbalance. The copper losses will never be symmetrical.

I have found the OPTs are better overall than Quad or Leak,
but the circuit must be carefully damped to prevent oscillations,
and thse issues are addressed in my schematic.
If you want a naturally better amp than ST70, get an ST80.

But after removing the tube rectifier, a large variety of octal
output tubes can be used; even KT90 in triode, WOW!


Given all that where do you start the fix? When you could not buy
output transformers anywhere and used ST70s could be had for a few
dollars, the ST70 was a good place to start. Now, it's far better to
put one on ebay and use the funds to buy new stuff.

Fun is fun for sum I guess....

Real estate agents describe an old run down falling apart weatherboard
house
as a "renovator's delight filled with potential"

ST70 is a tinkerable old toy from which music may be had....

It looks just right on the bench inside the old weatherboard house
on a wet cold winter's day, and a cello can warm the cockles of your
heart.
Remember to turn the amps off when not in the room lest they burn down
the house
if you are so lazy to omit the active protection circuitry.

Patrick Turner.

[Sal Brisindi]

Bret Ludwig wrote:
Iain Churches wrote:
Starting with NEW transformers and chassis is cheaper and not that
difficult.
Please post links to pics of your work, Bret
Iain

No.

Why not?

[Peter Wieck]

On Jan 24, 7:37 am, Sal Brisindi wrote:
Bret Ludwig wrote:
Iain Churches wrote:
Starting with NEW transformers and chassis is cheaper and not that
difficult.
Please post links to pics of your work, Bret
Iain

No.Why not?

'Cause there isn't any (work) and aren't any (pictures).

Peter Wieck
Wyncote, PA

[Peter Wieck]

On Jan 21, 4:52 pm, WindsorFox wrote:

Ah, I'll have to try that. I've been sniffing around eBay but the
tube versions get rather expensive rather quickly. I almost fainted when
I saw some of the prices on old McIntosh stuff, especially compared to
what it was 4 years ago.

eBay still has the occasional bargain if you bottom-fish and/or have
the correct software. But they are getting fewer and further between.
You could do a bunch worse than a complete ST-70, I know of several
that have been in more-or-less continuous operation since-assembly (in
the 60s) to this day, one in particular that runs 56 hours per week (8
hours x 7 days) and another very nearly that. Neither has eaten a
transformer, speaker or melted down. One claims (which I would doubt
but all tubes read Dynaco) to have the OEM tubes. Neither is run at
very loud volumes, but they do run.

Others to keep in mind are various Eico, Scott and Fisher units. A
Scott LK-72 just went for $225 on eBay (mis-listed) and I have seen
several Eicos going under $200. But the best bargains are when you put
yourself in harm's way and get to swap-meets and radio shows. There is
one this weekend in Columbia, SC; I believe, and the various Kutztown
meets always have several good bargains in the tube-audio range from
direct experience.

If you do not object to flea-power, the Dynaco SCA-35 integrated amp
regularly goes for less than $200, and it is a sweet albeit low-powered
amp using "that awful" 7199 but also quite common 6BQ5/EL-84 output
tubes. It uses SS rectification and puts AC on the "heaters", but
manages to do it reasonably well.

7199s are not rare, and need not be expensive despite rumors to the
contrary. I have perhaps a dozen US-branded spares for my three
(SCA-35, ST-70, Scott LK-150) amps that use them, and I have yet to pay
more than $5 for one even from knowledgeable sellers. Yes, I do screen
them and no, they are not particularly noisy or microphonic if screened
correctly.

Peter Wieck
Wyncote, PA

[WindsorFox]

Peter Wieck wrote:

Others to keep in mind are various Eico, Scott and Fisher units. A
Scott LK-72 just went for $225 on eBay (mis-listed) and I have seen
several Eicos going under $200.

It seems everything with tubes the last few weeks went for $300+ I
keep kicking myself because I let a Citation 70 squeek past me for $147.

--
"One hard rule of sockpuppetry is that a sockpuppet
can't be smarter than its animator."
- Arny Krueger