Jump to content

Dynaco ST70 help


hogwylde09

Recommended Posts

Anybody know what the miniature sockets are? Bias points? 1/8 input jacks? I know nothing about Dynaco stuff. Other than the tubes in this thing alone are probably worth what I gave for the whole amp.4418c151b2c7d4db356f6bb0d0f730a0.jpg

 

Sent from my SM-N900V using Tapatalk

 

 

Link to comment
Share on other sites

I know jack about them as well but with the two blue pots in the back the red points bias points makes sense with common ground in the middle; black would have made it more intuitive if that is the case.

Link to comment
Share on other sites

Probably should. Really want all electrons hitting the plates. At the speed of sound. Front & back. Narrowed down to the Belle's and CF4'S. I'll let the kg5.5 and JBL L200T rest comfortably numb. While I'm the same.

Sent from my SM-N900V using Tapatalk

Link to comment
Share on other sites

That's not a Dynaco driver board. The ST-70 used two 7199 tubes, but yes, the pots with the blue shafts on the original ST-70 would be to set the bias for the output tubes.

 

The red jacks on the front were added to make it easier to use your meter probes. The must have added those when the took out the octal sockets that were on the front. They were used to power the Dynaco preamp. Also used one of the socket pins and ground to measure for stting the bias.

 

Bruce

Link to comment
Share on other sites

Bruce could you enlighten me on the updated driver board? I am assuming the two mesh plate preamp tubes have been converted to something other than what wa originally in it. Is it 7199? I know I have a lot of research to do on mods. But maybe you could tell me what the factory used in those 2 positions, and what their recommendations were for it?

 

Sent from my SM-N900V using Tapatalk

 

 

 

 

Link to comment
Share on other sites

The 7199 contained a pentode and triode in one tube. The pentode was the input stage and the triode used as a phase splitter/inverter.

 

There are various all triode boards available as upgrades. Craig (nosvalves) used a modified version one on an early version of his VRD amps (although I believe he used point to point wiring).

 

The 7199 is no longer in production, and hasn't been for quite some time, and remaing ones are getting costly. The upgrade boards usually provide more features, such as individual bias settings for each output tube, etc.

 

Bruce

Link to comment
Share on other sites

That's definitely not a tubes4hifi VTA driver board as it has no bias adjustments on the board itself. That one of the other brands that slips my mind at the moment. I'll see if I can find it. I believe it goes with those front bias adjustments in place of the original sockets where the probes would normally go. Looks like a single adjustment per pair versus separate for each tube. 

Link to comment
Share on other sites

It's never good to assume that circuit changes are what you think they should be based on what you would have done!  Direct examination of the circuit is the only way to proceed when dealing with an unknown of any type.  Trust me on this.  I have encountered some really nasty things in home built/modified equipment over the years.

 

Maynard

Link to comment
Share on other sites

7 hours ago, Marvel said:

That's not a Dynaco driver board. The ST-70 used two 7199 tubes, but yes, the pots with the blue shafts on the original ST-70 would be to set the bias for the output tubes.

 

The red jacks on the front were added to make it easier to use your meter probes. The must have added those when the took out the octal sockets that were on the front. They were used to power the Dynaco preamp. Also used one of the socket pins and ground to measure for stting the bias.

 

Bruce

+1. That's the ever popular dynaco mod kit in there. Populrly installed by every hamfisted clown with delusions of "ability" and "knowledge". I know, cos I got one too. Thankfully, it does work, however some things in it are bypasses. By design ... yea right, the manufacturer intende to not be able to do 1/2 the functions they install. Yea sure.

Cool.

Srinath.

Link to comment
Share on other sites

1 hour ago, tube fanatic said:

Direct examination of the circuit is the only way to proceed when dealing with an unknown of any type.  Trust me on this.  I have encountered some really nasty things in home built/modified equipment over the years.

 

Here's a good example. I bought this for 25 bucks from the retired EE friend.

Masco "Audiosphere 100" 6550 PP PA amplifier. A guy would think no problem, check over the circuit, replace what is necessary and power it up. But unfortunately, some slob hacked on the amplifier and the wiring is a mess. Which makes things really difficult to trace through the circuit and figure out.

 

A guy figures okay, it's hacked so maybe there is a online schematic or a Sams...nope...

I dunno if this unit is a one off, or they were manufactured in really low numbers. It's like it doesn't exist.

One of these days, I'll sit back down and try to trace through it again. It uses a 6V6 or some such for a voltage regulator...not really the most simple of circuits to chase through.

 

Searched online for Masco "Audiosphere 100" to no avail. The older and lower power Masco PA amplifiers are popular with Blues Harp players, and there is a lower power smaller sized Masco PA amp which looks the same with the grey cover, brushed aluminum faceplate, and white knobs.

 

The Audiosphere 100 must be a misfit.

While it's not really an amp for fidelity audio, it would make a rather nice guitar head.

 

Mike

 

post-6643-13819330144128_thumb.jpg

 

Link to comment
Share on other sites

There are many ST-70 driver board options:

 

Curcio Audio (I have one of these but am replacing with another)

http://www.curcioaudio.com/dynadr_3.htm#DYNACO STEREO 70 POWER AMPLIFIER

 

Tubes4hifi board (what I'm wiring up now)

http://www.tubes4hifi.com/ST70.htm

 

And on and on...

http://www.kta-hifi.net/projects/amp_page/st70amp/st70.html

 

http://triodeelectronics.com/st70buildkit.html

 

Take your pick

  • Like 1
Link to comment
Share on other sites

53 minutes ago, Marvel said:

There are many ST-70 driver board options:

 

Curcio Audio (I have one of these but am replacing with another)

http://www.curcioaudio.com/dynadr_3.htm#DYNACO STEREO 70 POWER AMPLIFIER

 

Tubes4hifi board (what I'm wiring up now)

http://www.tubes4hifi.com/ST70.htm

 

And on and on...

http://www.kta-hifi.net/projects/amp_page/st70amp/st70.html

 

http://triodeelectronics.com/st70buildkit.html

 

Take your pick

 

I have an ST70 with a Curcio Audio mod and thought about changing it as well. I am not real impressed with it. What are you going to replace yours with? 

 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...