The Dynaco (Panor) ST-80 and ST-160 tube amps of the mid '90's

I had the Panor PAS 4 and stupidly sold it........

I Have the 2 model Dynaco PS-4 And The Ampli Stereo 80 that's realy good sound It,s Realy Différent construction and Sounds of Qualité Or the Model Fabrication 70' ,,,it'S Sound More better .

j'ai les 2 pièces depuis plus de 20 ans

Just purchased one. It has some PCB issues. It was bought knowing that the bias indicator was not working on one channel. Looking at the PCB there is a burn through hole by one of the triode/ultra linear relays and some heat discolor by the other (like the VTA 120 and 70 these can be run in triode or ultra linear mode. However, the switching is done via relay)

My guess is that the relay is generating heat when the coil is engaged (triode mode). Of course in troubleshooting I damaged a resistor on the bias control board (which looks like it was replaced once before). The bias monitoring trace on the PCB is adjacent to the relay, so it looks like it shorted in the past, went and is now open.

The only real way to fix is to remove the relays, remove the carbonized PCB area and then fix any traces removed with point to point wiring. Else the carbonized area is going to start conducting.

I’ve ordered new relays and resistors as well as the comparator IC for the bias. Hope to have it all fixed soon

A little update... and perhaps some questions..

So, had the amp apart (again) tonight to fix the issues with it. As I mentioned earlier, the initial problem was that the V8 bias LED was stuck on red. When I opened it, I found that the PC board under the triode / ultralinear relay had burned. I had probed the damaged area of the PCB, and then when I repowered the amp, arcs and sparks. So, tonight I took to removing the relay and looking real hard. The sense line for the bias runs under the relay, then goes through a plated through hole, and then to the edge of the PCB so it can connect to the bias control board. What appears to have happened is that this line ended up shorting against the output of the relay.

Repair wasn't too bad. I cleaned up the area of the damage, and inspected the lands. Sealed the edges of the pcb with expoxy. Where the lands looked questionable, tacked point-to-point wire to bypass the lands.

When the arcs flew, a resistor on the bias board smoked (though it still tested good). Decided to replace that with new. The circuit that drives the LED is a LM339 comparator IC. Removed the existing one and installed a socket and new chip.

Once reassembled, it all worked. Now to the listening.

My usual system is either my original ST-70 or my VTA board ST-70 (the original one is in use now), with a PAS-3 and Klipsch Heresy speakers. Put the ST-80 in its place. After re-biasing, amp is definitely clear. It's definitely a different sound than the ST-70. The one thing I noticed is that I could here distortion, not on the main musical notes, but seemingly underneath them (sort of like rattling piano strings). Switched back to the ST-70, not really the same. Also the ST-80 seems to be a lot more 'flat' than the ST-70, and while I'd never accuse the Heresy's and the ST-70 of being bass machines, it seemed there was much more base there than with the ST-80.

Kind of wondering if both the distortion and the seeming lack of base is perhaps a mis-match between the PAS-3 and the ST-80?

I'll play with the amp for a while, but right now, have to say I prefer the ST-70.

Comments? Suggestions? Questions?

I was using ST-80 Stereo Valve amp since 2000. It's powerful and easy matching with other brand's preamp. In recent years, I encounter an issue - a popping sound from speakers when I switch it off (just the time to turn the rocker switch to "off").

I turn off the amp the speakers would make a loud pop. Even after turning the volume all the way down it still made a pop.

Any hints or experience about this?

Thanks Bob.
I tried the cap replacement this morning. Before the replacement, I did some measurements on existing cap and switch, they are in good condition actually.  Both caps (for L+N double pole switch terminals) were replaced however, the pop is still there.

I also tried the EL34 tube replacement but the pop is still there.

As Bob says "...If you still get a loud pop, it could mean that the power switch is bad."
Even though the switch measures ok there could still be a mechanical fault with the contacts, corrosion, oxidation, etc.

I can't tell but, it doesn't look like you measured those caps out of circuit. If you do, you may get a more accurate reading.

I have a question for anyone that may be able to help. I am in the midst of a second generation of a rebuild of a Dynaco PAS4 tube preamp. This is NOT a PAT model or an upgraded PAS 3. This was a very limited production preamp which I think was the last tube preamp that Dynaco produced. It was way overbuilt as far as power supply and sounds fantastic. Dissappears in the system.

My problem is that the 50Kohm stereo balance control (original) has developed noise and needs to be replaced. Tried cleaning it - no joy - lots of noise. It seems that there are two choices - cheap or unaffordable.

So my question is this: Can I use a good quality stereo volume control (linear) and just wire one channel in reverse of the other s on o that at center positon both channels have equal settings? Would I have to add any additional components?

I have read a lot of posts that say this should work fine as long as it is a linear (not logrithmic) volume control. However, no one has ever said they have actually tried it.

Any help would be greatly appreciated....all comments welcome!

Thanks in advance.

Thx1326 wrote:I have a question for anyone that may be able to help.  I am in the midst of a second generation of a rebuild of a Dynaco PAS4 tube preamp.  This is NOT a PAT model or an upgraded PAS 3.  This was a very limited production preamp which I think was the last tube preamp that Dynaco produced.  It was way overbuilt as far as power supply and sounds fantastic.  Dissappears in the system.

My problem is that the 50Kohm stereo balance control (original) has developed noise and needs to be replaced.  Tried cleaning it - no joy - lots of noise.  It seems that there are two choices - cheap or unaffordable.

So my question is this:  Can I use a good quality stereo volume control (linear) and just wire one channel in reverse of the other s on o that at center positon both channels have equal settings?  Would I have to add any additional components?

I have read a lot of posts that say this should work fine as long as it is a linear (not logrithmic) volume control.  However, no one has ever said they have actually tried it.

Any help would be greatly appreciated....all comments welcome!

Thanks in advance.

Yes you can. That is even as the original is made according to my notes.

Thanks for the reply.  Would you need any further information to confirm this.  I have schematics if it would help.

The parts list in the manual actually indicates two seperate parts. One labeled as:

Dual Volume Control Potentiometer
Dual Balance Potentiometer

Thanks again.