Problem with Paramour + C4S

[yage]

Hi,

Complete newbie here. I recently decided to finish an original Paramour kit that I started building in 2003. I've read some Paramour related forum posts since I had to troubleshoot one amp so I rewired both amps to have the 270k resistor span T14 and T17 instead of A3 and T17.

Now I have a problem with the C4S board on the other amp. The LED farthest away from the MJE 350 transistor doesn't light when I power up the amp. Here are the voltages I get at the test points:

T15 - 383 V
Left most term - 249 V
B6 - 245 V
B8 - 3.45 V

Here are the voltages for the rest of the amp:

T1 - 321 VAC
T2 - 321 VAC
T5 - 398 V
A1 - 60.8 V
A2 - 369 V
A4 - 60 V

I've been testing for continuity all over the C4S board and the input tube socket and everything seems to check out fine. Not sure what's going on here. I read in a post that I might need to swap out one of the 499 ohm resistors on the C4S board to 750 ohm. Could this be the issue?

Thanks in advance for all your help!

[Paul Birkeland]

There are three terminals on the C4S board.  One goes to ground, so the voltage there isn't too important, but what do you get at the other two terminals?

I think 2003 would be the Paramour I but with our custom power transformer, but if you have Paramour IIs let us know.

On the 9 pin socket, one pin connects to the center pin o the RCA jack through a resistor (this will be pin 2 or pin 7), one pin connects to the C4S board (this will be pin 1 or pin 6), and another will go to ground through a resistor (pin 3 or pin .  I would be very interested in knowing the voltage at this pin that goes to ground through the little resistor.

These three voltages will give some useful info on how your C4S is functioning.  If you have those older square yellow-ish/white PC boards, give the center leg of the MJE350 some more heat to be sure it's well soldered.

[yage]

Hi Paul,

It's the Paramour I with the Hammond mains transformer and Speco output transformer. I reflowed the solder joint between the middle pin of the MJE transistor and the PC board just in case.

Here are the voltages on the C4S pins (using the RCA input ground tab):

Pin nearest MJE transistor (connected to B6) - 267 V
Pin to left most terminal - 270 V
B8 (pin to RCA ground through 499 ohm resistor) - 2.7 V

Does this make sense?

[Paul Birkeland]

My Paramour I C4S upgrade manual is buried at the moment.  There's a big resistor that is probably 200K-500K, then the current set resistor that's under 1K.  What value is in that position? 

2.7V across 499 ohms is 5.4mA.
267V and 5.4mA on the 12AT7 plate curves cross at 4V of bias.

My conclusion would be that either the grid of your 12AT7 is not properly grounded (I think in the Parmaour I there is a resistor between the center pin and ground tab of the RCA jack) or you have a damaged 12AT7.

A very easy step to diagnose whether you actually have a C4S issue is to exchange boards between amps. 

[yage]

Ok - just switched boards into the working amp... and the LED still remained dark. Put the working board back into the same amp and both LEDs light.

[Paul Birkeland]

Check the LED orientation and look for solder bridges on the bottom of the PC board. 

[yage]

I pulled the LED out of the circuit and the diode test shows an open line in both directions. I guess I must have fried the LED when trying to remove it. Any good replacements to be had?

[Paul Birkeland]

These are what we currently use:
https://bottlehead.com/product/hlmp-6000-leds/

The striped end of the current LED is equivalent to the flat side of the old ones.

The LEDs in your kit may have just sat around long enough that they absorbed too much moisture to be soldered without popping.

[yage]

Thanks. Should I go ahead and replace all the LEDs with the new version?

[Paul Birkeland]

Yes, I'd do the pair on that board.

[yage]

Got it - thanks for all the help!

[yage]

Ok - fixed both boards with the new LEDs and the voltages around the input tube on both amps are almost in line with the manual except for B6 which is about 10% high (171 V instead of 155 V). I decided that was good enough tested them with some music and they sound good.

One amp, however, has a very light buzz. After reading some posts I think I'll double check the wiring and reflow some solder joints around the power supply terminals. Is this a good plan? Should I focus on anything else?

Thanks again!

[Paul Birkeland]

Buzz coming through your speakers is often a loose or unsoldered power supply capacitor.

Buzz coming from the amp itself is usually loose power transformer hardware.

[patrickamory]

These are what we currently use:
https://bottlehead.com/product/hlmp-6000-leds/

The striped end of the current LED is equivalent to the flat side of the old ones.

I just got some of the current HLMP-6000 LEDs for my broken Paramour (one of the C4S LEDs is open).

Is the striped end of the current LED equivalent to the longer lead of my ancient ones? These original C4S LEDs had one longer lead, not one flat side, to indicate the positive.

Thanks!

[patrickamory]

I just got some of the current HLMP-6000 LEDs for my broken Paramour (one of the C4S LEDs is open).

Is the striped end of the current LED equivalent to the longer lead of my ancient ones? These original C4S LEDs had one longer lead, not one flat side, to indicate the positive.

Thanks!

I think I figured this out by using my multimeter on the diode setting. The new LED lights up when the positive probe is applied to the non-striped end, so that is the anode? Which means that the non-striped end is equivalent to the longer lead in the original LED?