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In Reply to: RE: Dynaco ST 70 Carpenter Mod posted by mark.korda@myfairpoint.net on October 04, 2024 at 19:02:31
Yup. Unbeknownst to Glass Audio, Roy Mottram, the author, owned/owns Tubes4hifi. When Ed Dell, the publisher, found out he printed a retraction/apology.
Follow Ups:
Hi Shovel, that was a great find but it's not the correct article.Thanks for looking that up.I'm going to save that. I emailed the guy who modded my amp to the Purist Audio mod Bob Gates. Bob and Jim Aud were in the Vietnam conflict working on and around Phantom jets, or the jets of that era.I kind of taunted them a little to join this forum and back up my story. Bob also modded my Dynaco PAS 2 following the Last PAS article by David Vorhis. I made a little square of brass covering the tone controls and gave him a stock PAS 2 to keep. We met thru the old Audiomart before the net. Recently I stripped down the PAS and made a new faceplate with wood and poly and my name covering the selector switch which is now on the bottom left.I have a gold plated switch there, cd or LP. I'll send a picture to see if you like it.I'm hoping Bob or Jim will get back to me on this before I enter The Audio Asylum...-take care...-Mark Korda
I recall us discussing this modded PAS once before, but I seem to remember you saying that he didn't regulate the B+ in yours. From your picture it looks like you don't have the external cap bank for the filament supply either, as called for in the build article.
Here's a section of the article regarding the heater supply. My 'Vorhis' has the regulated B+, and even so, I found impressive improvements to be had by adding large amounts of capacitance to the heater supply. If you've got room, I'd strongly suggest paralleling extra capacitance to yours.
The phono stage of the Last PAS always left me somewhat wanting, but I still find the line stage particularly good.
Hi Shovel, the guy who modded one of the PAS 2's I had took out the tone controls and added more caps.It worked and sounded great but he left more stuff in that I took out including the rotary control. You can see the extra caps he installed. The only components I took out were 2 resistors in the phono section.I put 2 5 position lugs to reinstall the phono resistors in the phono section. I have not retired it yet but have a picture of what my friend did inside on the circuit boards.I also will be putting in a Sheldon Stokes cap board which will replace the selenium rectifier area. Here is a picture...-..Mark
...actually reduces filament supply capacitance over even the stock PAS. Dynaco used two 2,000 uF caps, which the Stokes board reduces to 1,800 uF each, which is a step in the wrong direction. I'm going to assume the capacitance was reduced due to space constraints on the SDS board.Nichicon makes 12,000 uF @ 25 VDC caps (link below), which in my experience would be a sonic improvement, but you may have trouble making them fit on that board.
Another thing to note, the SDS board uses 1N4007 diodes, which is what I originally built my 'Vorhis' with. I later changed them to 31DQ10 Schottky diodes, and heard a distinct improvement over the 1N4007s [in the filament supply].
Edited to clarify that the 31DQ10 Schottky diodes are only to be used in the filament supply. I also upgraded the 1N4007s in the B+, using UF4007s per Eli Duttman, but there I heard no improvement.
Edits: 10/10/24
Hi Shovel, thanks for all that info. Even though I have had no problem in the past with the selenium rectifier rig wouldn't the Sheldon Stokes board best the old selenium set up? D Lab does an installation You Tube video on the Stokes board but he installs it upside down.Like Vinny Barbarino...-.I'm so confused! Thanks for taking the time writing that detailed letter. I had no clue about the quality of diodes...-take care...-Mark Korda
Hi Shovel, thanks for all that info. Even though I have had no problem in the past with the selenium rectifier rig wouldn't the Sheldon Stokes board best the old selenium set up? D Lab does an installation You Tube video on the Stokes board but he installs it upside down.Like Vinny Barbarino...-.I'm so confused! Thanks for taking the time writing that detailed letter. I had no clue about the quality of diodes...-take care...-Mark Korda
Yes, if for nothing else, a decreased voltage drop and more importantly, to potentially avoid the rancid fumes produced by the selenium rectifier when they 'go'.
I wasn't suggesting that you keep the selenium rectifier, but I would suggest using caps much greater in capacitance than the Stokes board's 1,800 uF. You have posted that you have a Last PAS, but if you still have the selenium rectifier, stock value caps in the heater supply, and are using the 12X4 rectifier tube instead of regulated B+, then you really don't have a 'Vorhis' Last PAS, in my opinion.
The improvement in adding significant capacitance to the heater supply is easy to hear. Using your current set-up, get yourself two 25 V or greater electrolytic caps of substantially higher capacitance than what is already in your heater supply, along with some alligator clip leads. With the preamp off, attach the caps in parallel to those already in place, being sure to observe proper polarity.
Turn the preamp on, and listen for a while. Then, without the need to power the preamp down, carefully disconnect the clip leads from the stock supply, and listen again. As long as you're careful not to discharge the external caps, you can reconnect and disconnect them at will. I think you'll like what you hear with the added capacitance.
All this already is detailed in The Last PAS article by Dave Vorhis. Email me through the Asylum if you don't have a copy.
Hi Shovel...-..
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