I have one of those and two Dynaco ST-70's What I did with my ST-70's is run the filiment voltage through a full wave bridge rectifier to eliminate the AC hum that they had, works fantastic now!
Nice video Terry, I particularly thought that your mentioning about ground loops being introduced by connecting a chassis to a buildings equipment ground worth further consideration. Particularly on receivers with transformer isolated the power supplies then one can have external ground and antenna connection results in better reception. 73
If you are going to restore a Dynakit PAS preamp, you need to be sure that, no matter what model you begin with, you use a PAS-3X assembly manual for the restoration because there are a couple of modifications Dynakit made to the circuit that are important. One is to increase the value of the interstage coupling capacitor in the output section, and the other, and the more important, is to add a capacitor at the output of the preamp. This is located between the bass controls and the circuit board and replaces a direct wire at that point. This is a 1 ufd capacitor and serves to block a sneak path for DC through the negative feedback circuit for the Baxandall tone controls. If this cap isn't there, the bias from the first stage cathode in the line amp appears on the output jack. It is about plus 1.5 volts. Dynakit vacuum tube power amplifiers -- and some others -- do not have DC blocking capacitors on the input and this positive voltage appears on the grid of the voltage amplifier, essentially canceling the contact potential bias on that stage bringing it down to zero. This is not an after-market "improvement," but a production change made by Dynakit documented in the 3X manual. Another difference in the later PAS preamps is that all the tone control potentiometers are custom pots that have a dead zone in the center of rotation. Swapping pots around between units of different vintages, you need to keep this in mind. Note too, that the paper sticker on the back of the PAS-3X is the same as the one on the back of the PAS-3, there is no way to know what version of the preamp you have without checking the circuit for the up-sized and added capacitors and the action of the tone control pots. You can feel the dead detent if you adjust the pots carefully.
I had one of these few years ago. At first i remplace the power supply by one similar and finally put new boards with new parts. After it sounded a lot better but my 4S with cathode follower is superior so i sold the PAS.
Terry, take care of the switches as they are highly delicate, and are likely not available any longer. If the switch for the various modes is still OK, then I would give it back to the customer and let him know how valuable it is. Just a heads up Terry. Cheers
I have had people argue that modern SS(digital) sound equipment sounds the best, well I say “bull crap”! The preamp part of any amp is the part that defines the tone of the amp. Sure the power amp section does effect the tone, but the preamp is where it all starts and if you begin great it makes a hugh difference in what your eras hear! Vacuum tubes have pleasing harmonics that enhances the tone. ICs don’t. These preamps are gold when serviced right and Terry you know how to bring them back to life! I had a Marantz tube preamp that sounded so good I swapped out for a SS one in a radio station I engineered at back in the 70s and the difference in the way the music sounded over the air was fantastic! The owner of the station gave me a healthy bonus. I’m looking to build a new home theater using hifi tube amps. Since vinyl records are coming back to audiophiles, a great turntable with a magnetic cartridge and some strong speakers and you have it! I’m glad I still have my vinyl record collection. Great video Terry! Love from your buddy in NW Colorado. Thanxz
Did you ever work with or make something with subminuiture tubes like the ones they used in hearing aids and other circiutes.and used small round ones too.
Just wanted to point out the wild coincidence that one of those preamps seems to be the same one this person used in their review. th-cam.com/video/ooD2wMC0cnw/w-d-xo.html They must have decided to get rid of it!
Dissing your competitor like that is pretty immature, and does not necessarily inspire confidence in your work. If it was a kit, you don't know who did the mods.
My initial thought was that the filter cap may have been re-stuffed. Beautiful work Terry!
I have one of those and two Dynaco ST-70's
What I did with my ST-70's is run the filiment voltage through a full wave bridge rectifier to eliminate the AC hum that they had, works fantastic now!
Thank you very much Terry. I can’t wait to hear it. 🎶🎼🎵🎧🎹
Really nice job Terry !! Makes you wonder what people try to do for mods... crazy stuff..
Nice video Terry, I particularly thought that your mentioning about ground loops being introduced by connecting a chassis to a buildings equipment ground worth further consideration. Particularly on receivers with transformer isolated the power supplies then one can have external ground and antenna connection results in better reception. 73
If you are going to restore a Dynakit PAS preamp, you need to be sure that, no matter what model you begin with, you use a PAS-3X assembly manual for the restoration because there are a couple of modifications Dynakit made to the circuit that are important. One is to increase the value of the interstage coupling capacitor in the output section, and the other, and the more important, is to add a capacitor at the output of the preamp. This is located between the bass controls and the circuit board and replaces a direct wire at that point. This is a 1 ufd capacitor and serves to block a sneak path for DC through the negative feedback circuit for the Baxandall tone controls. If this cap isn't there, the bias from the first stage cathode in the line amp appears on the output jack. It is about plus 1.5 volts. Dynakit vacuum tube power amplifiers -- and some others -- do not have DC blocking capacitors on the input and this positive voltage appears on the grid of the voltage amplifier, essentially canceling the contact potential bias on that stage bringing it down to zero. This is not an after-market "improvement," but a production change made by Dynakit documented in the 3X manual. Another difference in the later PAS preamps is that all the tone control potentiometers are custom pots that have a dead zone in the center of rotation. Swapping pots around between units of different vintages, you need to keep this in mind. Note too, that the paper sticker on the back of the PAS-3X is the same as the one on the back of the PAS-3, there is no way to know what version of the preamp you have without checking the circuit for the up-sized and added capacitors and the action of the tone control pots. You can feel the dead detent if you adjust the pots carefully.
I had one of these few years ago. At first i remplace the power supply by one similar and finally put new boards with new parts. After it sounded a lot better but my 4S with cathode follower is superior so i sold the PAS.
I can remember seeing the dynaco with the yellow board and missing a bunch of stuff on ebay. I wondered who bought it :)
Very nice Terry! Oh no!!! I see a restuffed RME converter lurking in the background... 73, Mike
Yep, That is now a Push pull 2E26 amp. It will be featured soon
Terry, take care of the switches as they are highly delicate, and are likely not available any longer. If the switch for the various modes is still OK, then I would give it back to the customer and let him know how valuable it is. Just a heads up Terry. Cheers
D lab Electronics this cool good dynaco pas. Home streo preamp from tow band to one
I have had people argue that modern SS(digital) sound equipment sounds the best, well I say “bull crap”! The preamp part of any amp is the part that defines the tone of the amp. Sure the power amp section does effect the tone, but the preamp is where it all starts and if you begin great it makes a hugh difference in what your eras hear! Vacuum tubes have pleasing harmonics that enhances the tone. ICs don’t. These preamps are gold when serviced right and Terry you know how to bring them back to life! I had a Marantz tube preamp that sounded so good I swapped out for a SS one in a radio station I engineered at back in the 70s and the difference in the way the music sounded over the air was fantastic! The owner of the station gave me a healthy bonus. I’m looking to build a new home theater using hifi tube amps. Since vinyl records are coming back to audiophiles, a great turntable with a magnetic cartridge and some strong speakers and you have it! I’m glad I still have my vinyl record collection. Great video Terry! Love from your buddy in NW Colorado. Thanxz
Did you ever work with or make something with subminuiture tubes like the ones they used in hearing aids and other circiutes.and used small round ones too.
Fantastic!
Hi Terry, just wondering if you have a schematic for your power supply module with the relay circuit avlable? Thank you.
Any comments on the sonic difference from the change from the stock filter can values to the 47uf?
I thought the knobs on the donor amp looked better.
Where are you located ? I need the caps replaced in my fender Deluxe reverb.
Battle Creek, MI see d-labelectronics.com for contact info
I think they mistook the O for an A when they named these units 😂
Nice Terry. Is D-Lab Dyna-MIte power supply board available for sale? Does it include a fuse?
Hello, Yes I have the boards, Yes they have an on board fuse. E-mail me, info is on d-labelectronics.com
What is wrong with the re-issue boards? Out of interest
These are not re-issues, they are a creation all their own. All I can tell you is they did not work on this installation
Just wanted to point out the wild coincidence that one of those preamps seems to be the same one this person used in their review.
th-cam.com/video/ooD2wMC0cnw/w-d-xo.html
They must have decided to get rid of it!
Dissing your competitor like that is pretty immature, and does not necessarily inspire confidence in your work. If it was a kit, you don't know who did the mods.