Please help me finish my PAS-2 upgrade

PeterCapo wrote:I think he meant for you to measure the filament supply output with the cap board loaded again.  The Triode PT specs at 12 volts for the filaments with 120 VAC mains.  Your readings unloaded were much higher.

Look, I think we have to distinguish between loaded and unloaded figures.  The unloaded figures will be higher than loaded figures, but we don't have specs for what unloaded B+ and filaments should actually measure.

At this point, I am in favor of:
1) going to whatever lengths necessary to verify the values and proper locations of the three resistors on the cap board and also the resistors on PC5 that I asked about in Post n°96
2) review the ground connections
3) if 1 & 2 above seem okay, then I vote for a new dynakitparts power transformer

That's it.  If anyone else has any other ideas, please speak up.

When I received the cap board R1/R2/R3 were all the same color code (brown/black/orange). This, according to the boards's schematic, is in error, since it gives R3 as 47K. Therefore, I replaced R3 with a previously measured and verified 47K resistor.  The resistor that I removed does indeed measure 9.94K.

As for verifying the resistors that you asked about in Post No.96 (those coming off pins 1 & 6 of the tubes on PC-5), here are photos of those resistors:

Pin 1 - Tube A:

Pin 1 - Tube A:

Pin 6 - Tube A:

Pin 6 - Tube B:


I have refurbished the ground connections so that there is one common ground point:

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The screw is going through the grounding tab.
I did the splice because the short black wire was already soldered to the grounding tab, and I didn't want to have to undue all of those connections to the tab just to get that red/orange wire in there. I'll drill a small hole in the tab in order to accommodate that transformer ground wire.

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PeterCapo wrote:
 Wait... were the mating surfaces of the chassis, ground tab, nut and tube socket collar clean before you screwed the ground tab down?

I think so (but I'm not certain). I'll separate and clean them with DeoxIT.

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Yes, there are five wires to the ground tab: one from PC-5 eyelet #8; one from PC-6 eyelet #11; one from PC-6 eyelet #4; one from the cap board GND connection, and one from the transformer (red/yellow wire).

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After reworking the red-yellow wire, with the variac putting out 120VAC into the preamp (measured both at the variac and at the preamp's rear unswitched outlet), I measure the following:

12X4 - pins 1&6: 325VAC; between pins 3&4: 10.8VAC; pin 7: 389 VDC  

PC-5 (tubes A/B) pin 1: 117/115 ; pin 3: 1.55/1.55;  pin 4: less than 1v;  pin 5: -12.5/13.8;  pin 6: 173/168;  pin 8: 1.20/1.20;  pin 9: 6.1/7.2

PC-6 (tubes A/B)  pin 1: 97/97;  pin 3: .66/.66;  pin 5: 12.4/13/8; pin 6: 123/118;  pin 8: .75/.72;  pin 9: 6.3/6.9

Working on the assumption that the readings taken below are *to the chassis*, except as it applies to the 12X4.

billinrio wrote:After reworking the red-yellow wire, with the variac putting out 120VAC into the preamp (measured both at the variac and at the preamp's rear unswitched outlet), I measure the following:

12X4 - pins 1&6: 325VAC; between pins 3&4: 10.8VAC; pin 7: 389 VDC  

PC-5 (tubes A/B) pin 1: 117/115 ; (should be +/- 175 VDC) pin 3: 1.55/1.55;  pin 4: less than 1v;  pin 5: -12.5/13.8;  pin 6: 173/168;  pin 8: 1.20/1.20;  pin 9: 6.1/7.2 (should be +/- 5.5 VDC

PC-6 (tubes A/B)  pin 1: 97/97; (should be +/- 115 VDC)  pin 3: .66/.66;  pin 5: 12.4/13/8 (should be +/- 5.5 VDC); pin 6: 123/118; (should be 135 VDC)  pin 8: .75/.72;  pin 9: 6.3/6.9 (should be +/- 5.5 VSC)

So - we have lift-off.

B+ is acceptable.
Filament winding voltage is acceptable.
Suggests that the power-transformer is good.

From the other readings (some I have put in bold), I would suggest that resistors on the new cap board were mixed up such that readings are alternately too high or too low. Note that this would cause differential loading, screwing up _all_ the voltages somewhat.

Anyone here remember Humphrey Bogart "Across the Pacific"  Should-a-be

Yes, all of the readings are "to the chassis" (the now common grounding point), except, of course, for the reading between pins 3&4 of the 12X4.

My manual indicates that the voltage reading at pins 5 on PC-6 should be +/- 11 V DC, (not the 5.5 in your comment above) whereas i'm getting a reading at those pins of 12.4 and 13.8 V DC.

As received, the cap board had one resistor (R3) at an incorrect value, which I corrected.  So, now the resistors on the board should be OK.  Or are you saying that they're still "mixed up"?

In regard to pins 1 on PC-5 and on PC-6, 115VDC is only 65% of 175VDC, and 97VDC is 84% of 115VDC.  Are 35% and 16% below target "acceptable"?

billinrio wrote:Yes, all of the readings are "to the chassis" (the now common grounding point), except, of course, for the reading between pins 3&4 of the 12X4.

My manual indicates that the voltage reading at pins 5 on PC-6 should be +/- 11 V DC, (not the 5.5 in your comment above) whereas i'm getting a reading at those pins of 12.4 and 13.8 V DC.

As received, the cap board had one resistor (R3) at an incorrect value, which I corrected.  So, now the resistors on the board should be OK.  Or are you saying that they're still "mixed up"?

My bad on PC6, Pin 5. But:

What I am suggesting is that the voltages from the power transformer are correct - that is, within acceptable tolerances and not excessive.

What is coming off the cap board is not acceptable or within tolerances. There are two possible failure points, which could also be simultaneous:

The new Cap Board.
The new Circuit Boards.

If it is the cap board, the most likely culprits would be resistors misplaced or out of tolerance.
Could also be a failed cap or caps.
Could be a cold-solder on the cap board.
Could be a broken trace on the cap board.
Could be a failed component on the cap board.

If it is the new circuit boards, the same as above.

Where resistance or an RC network is too low, voltages will be too high.
Where resistance or an RC network is too high, voltages will be too low.
Something could be drawing down the B+. Are there _ANY_ signs of excess heat anywhere on any of the board?

I do seriously suggest that you give yourself a 24-hour hiatus (48 is better), and come back with fresh eyes and a clear mind. I very often invoke the 24-hour rule before reacting to frustrating situations.

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PeterCapo wrote:Was planning to heed Peter W's 24-48 hour rule but then had a thought.  Bill, do you have the original PC5 and PC6 boards, and are they in working order?  If so, try swapping them back in one at a time starting with PC5 and see if the readings are any better.

Great idea. When I replace tube Dynaco boards, just for giggles, I will rebuild the OEMs to better-than-new, and consign them to the junk box. Dated and labeled. So, when the next whatsit comes along, I have drop in boards.

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I trashed those boards as soon as I got home with the new ones from Erhard - so clean and shiny, with beautiful traces, while the original ones were ugly, with a strange wax-like coating, and with some dubious traces. The original quad cap is still on the chassis (just to avoid having a hole there). I don't, of course, have the burnt-out original transformer, nor the selenium rectifier (the latter properly (read: environmentally) disposed of.

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Coconut and bamboo, for recharging the radio batteries   .
 
I've been thinking about that change I made to R3 from 10K to 47K on the cap board.  Could it be that the schematic  (see post number eight) is wrong in listing R3 as 47K?  All of the seller's photos of this board, including the one on his web site, show a 10K resistor at R3.  I wrote and asked, but the seller doesn't respond.  I've ended up filing a complaint (request for refund) with PayPal, which will hopefully shake the seller out of his lethargy.

Theoretically, what should be the effect of changing the value of that particular resistor?  Should I just change it back to 10K and see what happens?

Changing R3 to a lower value will raise the B+ on Pin 6 of the 12AX7s. The differential between 1 (the other plate) and 6 is managed on PC5 & 6, and need not be managed on the cap board. I suspect that the supplier figured that out in short order and made the change without modifying the board.

Without being snarky - it is generally not a good idea to modify anything without operational data or specific direction.

Peter W. wrote:Changing R3 to a lower value will raise the B+ on Pin 6 of the 12AX7s. The differential between 1 (the other plate) and 6 is managed on  PC5 & 6, and need not be managed on the cap board. I suspect that the supplier figured that out in short order and made the change without modifying the board.

Without being snarky - it is generally not a good idea to modify anything without operational data or specific direction.

Sorry, but I don't understand part of the above.  " ... made the change without modifying the board" refers to what change?
Is the board correct as I received it, with a 10K resistor at R3, or is the schematic of the board correct?

As for the change I made for R3, please see post number 32.

billinrio wrote:

Peter W. wrote:Changing R3 to a lower value will raise the B+ on Pin 6 of the 12AX7s. The differential between 1 (the other plate) and 6 is managed on  PC5 & 6, and need not be managed on the cap board. I suspect that the supplier figured that out in short order and made the change without modifying the board.

Without being snarky - it is generally not a good idea to modify anything without operational data or specific direction.

Sorry, but I don't understand part of the above.  " ... made the change without modifying the board" refers to what change?
Is the board correct as I received it, with a 10K resistor at R3, or is the schematic of the board correct?

As for the change I made for R3, please see post number 32.

Look at the purveyor of this board as a cottage industry. He buys parts-and-pieces from various suppliers per his specification.
In the midst of all this, he makes a change for any number of reasons. Meanwhile, he has received parts-and-pieces based on the original design.
He has two choices. Scrap what he has and start over, or make a flying change and keep going.
Given that these are plug-and-play boards, he is not going to expect the receiver to cross-check what is received.
You, being one of the few that did became a victim of flying change.

Note that the likes of Zenith, Crosley, RCA and many others made such flying changes pretty much all the time back in the day, and in some very few cases modified the published schematics after the fact. But not always. Those of us in that hobby are constantly on the lookout for such changes and have to accommodate them when doing electronic restorations. And when we do see changes, we try to discern whether they are pre or post first-sale.

And therefore R3 should be 47K?

billinrio wrote:And therefore R3 should be 47K?

Oy Gevalt!

Try putting it back to whatever it was when you received it.
Irrespective of the schematic, your opinion or any communications or lack thereof from the supplier.
You are forcing me to recall my NYC neighbors and their Yiddish.

Please report back after restoring the board to its as-received condition and then doing the tests.

PLEASE, PRETTY PLEASE!!! TAKE THE HIATUS FIRST! IT WILL CLEAR YOUR MIND!

No doubt good times, about which I'm happy to remind you.
Right. I'll put back the 10K resistor. Many thanks!

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