Paramount v1.1 could not read plate voltage from 300K resistor

audioguy67 · 4826

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Offline audioguy67

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on: July 16, 2012, 05:45:29 PM
Hi All,
Just finished my Paramount monoblocks. Found one problem: voltage plate from 300K resistor showed 0 V.
I thought I did something wrong but then I checked voltage plate on tube socket leg and I was able to adjust it down to 175V.
Both amps were the same way.
Is this normal?
Besides that my amps are working lovely.
I'm thinking about getting iron upgrade already LOL.
Thanks,
Darius.
« Last Edit: July 16, 2012, 05:52:00 PM by audioguy67 »


Offline Grainger49

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Reply #1 on: July 17, 2012, 07:40:58 AM
The 300k RLd is in parallel with the plate.  If you get a reading on the tube pin 4 but not on the resistor recheck the soldering feeding the resistor (2 solder joints on the wire (B4 and OB) and 2 resistor solder pads). 

No, it is not normal. 

Great amps, have fun listening to all your old favorites!


Offline audioguy67

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Reply #2 on: July 17, 2012, 09:21:02 AM
Thanks Grainger,
I checked all soldering points and "heat" them up again but I have same problems on both amps.


Offline Paul Joppa

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Reply #3 on: July 17, 2012, 09:34:35 AM
If you have the same problem on both amps, then there is probably a wiring error that you have duplicated. Having done it twice, it will be very difficult to see it - us humans are like that - so take it slaw and careful.

The resistor makes the last trace of thump go away, and is very important for the direct coupled 2A3 version.

Paul Joppa

Offline audioguy67

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Reply #4 on: July 17, 2012, 09:43:26 AM
Thanks Paul, I will look at those boards again when I come back from vacation (next week).
Is it possible that I heat up 2N2907A transistors too much? It looks like I did cut their legs too short.


Offline audioguy67

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Reply #5 on: August 13, 2012, 04:09:00 PM
I checked all my soldering and everything looks correct.
I have voltage on other leg of 300K resistor about 450V  but nothing on OB side.


Offline Paul Joppa

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Reply #6 on: August 13, 2012, 06:21:28 PM
OK, something is very wrong here.

One end of the 300K resistor goes to -reg on the B side - it's on a corner of the board - and that point should be grounded - zero volts with respect to ground.

The other end goes to OB, where you can trim the voltage to 175v. It should never be greater than 300v, which is the regulated voltage. Even if the regulator is not working, the Zener diodes should prevent the "regulated" voltage from exceeding 340v+/-5%. If you have 450v at OB, then none of these things - the Zener string, the regulator, or the C4S feeding the driver plate - are working. In which case, the power transistors are probably fried, and possibly the Zeners as well. I'm sorry.

Fortunately, I gather that the rest of the test voltages are OK, so the circuit is probably working correctly except for the voltages on this resistor. It may simply be a measurement error, or the resistor may be installed incorrectly. Hard to tell at a distance.

There is 450v at IA on the other side of the board. Compare the pictures on pages 21 and 22 with your boards, being very careful to correctly identify the solder pads, especially on the back side where they are not marked.

Paul Joppa

Offline audioguy67

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Reply #7 on: August 13, 2012, 06:59:23 PM
OB does not have any voltage but other side has 450V so according to what you are saying I could adjust voltage on OB side to 176V with trimmer. I can still adjust that voltage on B4 leg of driver tube but nothing comes on resistor leg all other voltages on tubes are correct also resistor next to 300K shows 300V on OB side which I assume is correct.


Offline Paul Joppa

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Reply #8 on: August 25, 2012, 10:48:27 AM
Sorry, I was out of town and missed this. I think we are not talking about the same resistor. Unfortunately there's a typo in my last posr; I intended to refer to pages 32 and 33. At the bottom of page 32 there is a photograph of the PC board, whith an arrow pointing to the 300K resistor. The 300K resistor hangs just below the board in the photograph. Adjacent to the 300K resistor you can see the jumper #1. On page 60 of the manual, ithe same picture appears, with the jumper#1 labeled to go to B4; and the bottom of page 60 you are instructed to solder this to the B4 terminal.

Since B4 behaves correctly you must in fact have OB connected to B4. And you say that B4 is adjustable to 175v as desired. So it appears to me that either you are not measuring the 300K resistor - perhaps you are measuring the 330K 3Watt resistor at R2 on the A side?

Paul Joppa

Offline audioguy67

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Reply #9 on: January 27, 2014, 10:21:15 AM
OK guys just to close this topic I did take voltage from wrong resistor after all.
I'm just laughing at myself since I checked that board like 30 times before.
I went back to it since I put my BeePre together without any problems no hum or anything else.


Offline Reap

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Reply #10 on: January 29, 2014, 02:55:56 AM
What is this iron upgrade you speak of?


Offline audioguy67

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Reply #11 on: January 29, 2014, 03:30:29 AM
MagnaQuest upgradeds


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