PAS-2 woes

billinrio wrote:This is my first post to this forum.  A little background:  I'm an American who for many years has lived in Brazil.  When I came here, I brought much vintage tube equipment with me, including Dynaco (PAS-2, MKIV, FM3 and Heathkit (WM-4's, WM-5's) that usually drive AR2a's and AR4ax's.  Tech assistance is pretty much impossible where I live.
To give you an idea, no electronic stores in the city (of more than 3 million) where I live sell caps that are appropriate for tube equipment. This besides the question I get from them, "tubes, what are they?".
My concern right now is in regard to my PAS2.  About 3 years ago the transformer burned out, and I bought a regulated power supply from Roy Mottram.  Once it arrived, Roy and I exchanged a good number of e-mails, many of which involved my complaining about the scant nature of his written instructions, and him expressing amazement at my lack of basic technical know-how.  In any case, I finally got the unit to function, and have used it for a couple of years.  Last week, I turned it on, and only the rectifier tube lit up.  The unit's power has always been derived from a variac set at 117vac (the power from the wall is 128vac).  I checked the tube pin-outs and got the following:

Tube     12X4      PC5 12AX7 (1)    PC5 12AX& (2)    PC6 12AX7 (1)    PC6 12AX& (2)

Pin 1     273          190                     190                      243                    243
Pin 2  
Pin 3    13.3ac
Pin 4    13.3ac
Pin 5
Pin 6    273           254                     254                      254                     254
Pin 7    364
Pin 8
Pin 9

Pin values not indicated read 0.

Once again I emphasize that there's no tech capable of working on this unit within thousands of miles of me.
Shipping it off internationally is also not an option, due to high shipping costs and high duties i would have to
pay upon its re-entry into the country.
I would much appreciate recommendations on how to proceed.  Many thanks for your attention.

billinrio wrote:Many thanks for the very prompt replies.  The line voltage at the wallplate here is 132VAC, 60Hz, but I'm powering my equipment from a variac which is set at 117VAC.  
Suggestion (a):  I assume you refer to the filament pins of all of the 5 tubes. I will check all tube pin connections for broken wires/ cold solders / poor connections.
Suggestion (b):  there is no longer a selenium device, since I removed it when installing Roy's regulated power supply board.  Roy's board has four diodes (D1-D4). There are also two other diodes, one running off pin 1 and one running off pin 6 of the 12X4 tube. How do I check them?
Suggestion (c): The 12AX7 tubes I'm using all read as good on my tube checker.  Just to be sure, I tried replacing them with other 12AX7 tubes, to no effect.
Suggestion (d):  Roy's board has no 2,000 caps.  The two larger ones on his board (C4 & C5) are 3300 uF 25v.  How do I check if they're open/shorted?
Suggestion (e):  I'm not sure about a regulator chip on the mod board; whether there is one, and if so, where it would be.
I've scanned the schematic and drawing of the PS board, but see no way to include attachments in this message.  Apparently, because I'm new to this forum I'm not yet allowed to include attachments or links in my messages.  i've uploaded the two scans to my Photobucket account, and tried to give you the links but that doesn't work either.

billinrio wrote:Many thanks for the very prompt replies.  The line voltage at the wallplate here is 132VAC, 60Hz, but I'm powering my equipment from a variac which is set at 117VAC.  
Suggestion (a):  I assume you refer to the filament pins of all of the 5 tubes. I will check all tube pin connections for broken wires/ cold solders / poor connections.
Suggestion (b):  there is no longer a selenium device, since I removed it when installing Roy's regulated power supply board.  Roy's board has four diodes (D1-D4). There are also two other diodes, one running off pin 1 and one running off pin 6 of the 12X4 tube. How do I check them?
Suggestion (c): The 12AX7 tubes I'm using all read as normal on my tube checker.  Just to be sure, I tried replacing them with other 12AX7 tubes, to no effect.
Suggestion (d):  Roy's board has no 2,000 caps.  The two larger ones on his board (C4 & C5) are 3300 uF 25v.  How do I check if they're open/shorted?
Suggestion (e):  I'm not sure about a regulator chip on the mod board; whether there is one, and if so, where it would be.
I've scanned the schematic and drawing of the PS board, but see no way to include attachments in this message.  Apparently, because I'm new to this forum I'm not yet allowed to include attachments in my messages.  i've uploaded the two scans to my Photobucket account, and tried to give you the links but that doesn't work either.

PeterCapo wrote:

billinrio wrote:The line voltage at the wallplate here is 132VAC, 60Hz, but I'm powering my equipment from a variac which is set at 117VAC.

How do you set your variac to 117VAC output?  Don't rely on the scale or meter built onto/into the variac.  They are calibrated for only one assumed level of AC mains from your wall socket that cannot be predicted by the variac's manufacturer.

The output of the variac must be set with an external measuring device like a handheld meter, and under the load of actual operating conditions.  A power strip comes in handy for this - plug power strip into variac's output, adjust variac output with handheld meter reading one of the sockets on the same power strip.

corndog71 wrote:Sadly, unless you're willing to pay, photobucket is no longer useful for linking pics.

Peter W. wrote:OK - I am going to issue, unilaterally, a STOP WORK order until we get to the bottom of the 30% higher voltages than stock. If I had to diagnose from several thousand miles, I would expect that the modified power-supply is DOA and is passing what would be expected when running wide open.

ebay dot com/itm/HV-B-And-Heater-Capacitor-Power-Supply-Board-For-DYNACO-PAS2-PAS3-Pre-Amplifier/391736076646?hash=item5b354a2966:g:uhYAAOSwZQRYfb2q  

While not endorsing this option, I am presently running it in my "extra" PAS-3X - which is the one I use to test various options and configurations. It runs cool, provides spot-on down-line voltages (118 at the wallplate) and has caused me no regret to date. It also eliminates the 12X4, taking that load off the filament winding. I pick this of several options as it all comes from Hong Kong, and shipping is irrespective of destination country.

With all that in mind and a potential cure a short time away, let's figure out why those voltages are so high before going any further. This will be a tubes-out testing regimen until the cause/culprit is discerned.

Starting with verifying your VOM/DVM against a known voltage to eliminate it as the source of bad readings. I admit to being spoiled with all sorts of meters right-to-hand including an ESR meter. But, you can test capacitors with a VOM in the resistance setting, however, they must be out-of-circuit.

What will happen is that the meter will go to low resistance, then slowly climb to infinity, or something in excess of several megs. If it does not, the cap is leaky, full stop. This is not a 100% reliable test, just an indicator-test. But it does separate the wheat from the chaff at least.

Diodes can be tested, more-or-less in circuit with the diode setting on your meter. High in one direction, not so high in the other. Look for parallel resistors as that will be the reading in one direction.

How do "gifts" work via your customs service? Were something sent to you with a 'no-value' or 'gift' declaration, are their duties or tariffs?

peterh wrote:You have  "utsource dot net"  ( located in brazil ) for components.
Also see .usadobrasil dot com.br/dynaco] .usadobrasil dot com.br/dynaco for some dynaco related ads