Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Paramount => Topic started by: Paully on April 09, 2011, 11:41:21 AM
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There was a pop in my speaker while it was playing, wasn't turning it off or on. Then I noticed that the sound sounded muffled, like there was little treble or the speaker was playing through a heavy wet blanket. I swapped all the tubes, changed sources, and even changed preamps. No luck. I did change the speaker cables and the problem followed. So I seem to be down to the left channel Paramount. It still plays and the tubes light up, but there is occasional static and constant muffled sound. Seems like this is the one where I had the problem with the short before and changed the diodes which fixed it at that time. Any thoughts on where to begin?
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Some voltages. The amps are configured for 45 so I took voltages on both. The first is the one with the difficulty.
1 453 459
5 226 198
6 226 198
9 188 152
10 0 0
11 120 233
12 50 162
14 0 93
15 0 24
16 465 470
17 0 0
18 0 0
19 188 152
20 0 0
Looks like the zener diodes went bad, sound right? If so, would anything have caused them to go bad that I should go ahead and replace as well (or is it something else alltogether).
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"The amps are configured for 45..." Tell us how - I'm sorry but I don't remember all the modifications we've discussed, and which ones have been adopted. Does it have the soft-start board?
Some of the voltages (in the manual I have) don't make sense, so I'll have to go through the manual and determine which terminal is where in the circuit, and what voltage should be there. This will take me some time since I haven't done it yet for the soft-start board, but it will eventually save me time once I write it all down... :^)
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Put in the 3K cathode resistors in paralel seemed like the main thing. And it does have the new soft start board. My memory is a lot worse than yours (migraines). I am actually looking at the bottom of the amps trying to figure out if there is anything else I have done of significance. I don't think so.
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Hi Paully - you meant to say two cathode resistors in series right? I'm sure you must have. I actually just converted my Paramounts to use 45's a few days ago. I've listened to them for a bunch of hours so far and I was going to recheck my voltages and bias tomorrow. I'll post them in the forum post I had started about my own swap ("Converting to 2a3 mode"). I hope they could be of some use for comparison's sake.
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We talked on the telephone right after Paul (Paully) posted the voltages above. The first odd voltage is a high voltage on terminal 5. If I am reading the manual right that is attached to the top of the cathode resistors (wiper of the hum balance pot). I don't much like high voltage there.
Terminal 12 also jumps out. It has 50V in the bad amp and 162 in the good one. That is in the Zener string and that is what brought us to the idea that there is a problem with the Zener diodes. And maybe the voltage coming from the power supply is low.
I'll be driving the four hours to Paul's house on Wednesday. While I'm there he will be putting in the resistors, tube sockets and 10 turn pots so the soft start on the amps can be adjusted without flipping them. I just look over his shoulder and give guidance.
Hopefully he will know what is wrong with the amp and have parts available before I start the drive. We can fix this if we know what it is.
Is there a way to test the Zener diodes? I mean, they should read infinity in the reverse direction to a multimeter unless it puts out over 60V DC (I don't know of one that does). And a Zener should be a low resistance, or small voltage drop, in the forward direction like a normal diode. Right?
Are there any other things that should be checked.
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Yes I meant in series (and I meant to spell parallel properly too). We are going to install a 680 ohm resister in series with the cathode resisters also to get the resistance up a bit. Paul Joppa posted on another thread replying to some of the voltages I had on the 45 and where they should be given what my line voltage are. That post is worth reading. Do post your resistances if you can, I would like to have the comparison.
Thanks for the post Grainger. If we aren't able to figure out what is wrong for sure today I will go ahead and order the Zeners today so we will have them by Tuesday. Might as well. Hopefully it isn't something else causing the problem.
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Ok, so I went ahead and changed the diodes. Didn't work. Not sure where to go from here. Maybe I should take some more voltages on other areas on the amplifier.
Edit: Interesting symptom that I hadn't noticed that might help. The amp works perfectly for about 5-7 seconds and then suddenly becomes what I am calling muffled.
Edit 2: Still plays fine for a few seconds but second thing I see is that the LED on the soft start board at D2 is not lighting up. I changed that to a new one which also doesn't light up. It is the LED nearest the big black capacitor and the letter B.
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Thank you Grainger!!!!!!!!!!!!! We re-wet the solder joints on the silver transistor between the two LEDs on the B side and the blue 147K resistor and the LED in question now lights up and everything is working. Apparently just a bad solder joint. Hopefully it stays working. Thanks again!
Paul
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Hurray Paully! I got to reading the soft start instructions when I rechecked my voltages and noticed it states something to the effecct of: the zeners will handle the voltage until the shunt regulator takes over. This doesn't mention however if the zeners can regulate on their own indefinitely with the shunt regulator offline? That's beyond my current understanding of the paramounts design. I would be interested with seeing your new voltage readings. Did you install the extra cathode resistance?
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I don't know about your first question. Well beyond my understanding as well.
I am going to install the additional resistor between the cathode resistors today and tomorrow. At the moment the plan is just to put a 680 ohm 25 watt resistor in. I will be taking readings of the four pin socket at a minimum and will repost.
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I don't know about your first question. Well beyond my understanding as well.
I am going to install the additional resistor between the cathode resistors today and tomorrow. At the moment the plan is just to put a 680 ohm 25 watt resistor in. I will be taking readings of the four pin socket at a minimum and will repost.
5 watts or more is fine, up to 1000 ohms with 45s.
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Ok, problem has resurfaced. Pop in one speaker then muffled sound. LED at D2 on the B side is out again. This is the third time. I can go back and re-wet the solder joints in question and see if that corrects the problem once again but I don't understand how a solder joint goes bad three times. I suppose I can re-wet solder joints one at a time and see if I can isolate the specific location but I don't understand what is happening and why. Any help?
Paul
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Ok, problem has resurfaced. Pop in one speaker then muffled sound. LED at D2 on the B side is out again. This is the third time. I can go back and re-wet the solder joints in question and see if that corrects the problem once again but I don't understand how a solder joint goes bad three times. I suppose I can re-wet solder joints one at a time and see if I can isolate the specific location but I don't understand what is happening and why. Any help?
Paul
As silly as this sounds I went through the exact same thing with my seduction, re wetted three times, swapped this, changed that till I was friggin going mad!!! I decided to try and move every single piece ( resistor/cap wire end, tighten all the screws down for good contact, etc etc) turns out it was a wire inside the Teflon covering that had snapped and was only buggering up once and a while, it looked perfect till I gave it a wiggle to find the wire inside had actually snapped in two about a half inch from the terminal strip, worth a try anyways.....
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Certainly will look. Thanks for the heads up.
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Meanwhile, back at the ranch ...
I finally marked up my schematic and checked the voltages.
Terminals 11 through 15 are the Zeners, which are inactive after the shunt regulator kicks in - so there's not much point in measuring the voltages there. Since the board is misbehaving, it's only T16 and T19 that have anything useful. But the tube driver voltages are critically important to determining what's wrong.
The LEDs on the board are part of the C4S (not the shunt regulator) and the B side C4S feeds plate voltage to the driver. So - without knowing the tube voltages - I can only guess that the connection from OB on the board to B4 on the tube is the problem. If you did not remove the heat sink before re-heating the solder joint at OB, which goes to the middle lead of the large transistor on the B side, you may not have gotten that joint hot enough. That middle lead is connected to the metal flange which clips to the heat sink.
If that's not the problem, then we need voltages.
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Ok, I will measure voltages tomorrow. We didn't resolder anything with a heat sink. Just the resistor we mentioned, 147K, and the 2N2907A transistor. Though the second time I did reheat a bunch of other resistors for good measure. But the first time I just reheated those two. Regardless, I will get you the voltages tomorrow and also take a look at the spots you mentioned.
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Sounds to me like you have bad connection that by luck got a bit better while you were poking around nearby.Time to tug on the wires, poke at the connections. Look for a cracked resistor, or something like that...John
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I want to point out that the problem appeared after the installation of the soft start board. It has continued through the installation of the new iron and the pot & 2 resistors for top plate bias adjustment (associated with the soft start).
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Thanks for the suggestions everyone, they give me some great places to start. I am at work now but I will take a look at the connections and the voltages today and post them. Just turning it upside down to resolder might have been enough to make something shaky reconnect that disconnects shortly after I turn it back over. Will post back soon. Thanks!
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These are the voltages I was able to get:
Pins
1 0
2 3.5
3 0
4 192
5 0
6 194
7 Can't get to
8 6.6
9 0
Terminals
16 495
17 0
18 0
19 192
20 0
I am of course looking for questionable solder joints and loose connections. I will go back and search again. And I will start getting into the actual wires as suggested if nothing obvious jumps out.
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This one is a puzzler.
When LED D2 does not light, but D1 does, that usually means there is no load on the C4S - which would indicate that the driver section of the 5670 is not connected to the board OB. But the voltages on pins 2, 3, and 4 indicate that the driver is drawing all the available current, limited only by the other C4S (A side) which feeds the shunt reg. That would at least explain why the shunt reg is not regulating (pin 6 should be 300v, regulated) - there's no current left to shunt, the driver side is hogging it all.
So the B side C4S is getting bias power (D1 lights up) but is dumping too much current, meaning the 215 ohm current set resistor is not doing its job. My best guess right now is that Q1 (2N2907) has been damaged, possibly by an intermittent connection to D2. If D2 opens up, you could easily apply too much voltage to Q1. I would at the least replace D1, D2, Q1, and Q2 on the B side of the board.
However, I can't make sense of seeing only 6.6v on the cathode of the shunt regulator, pin 8. I would expect it to be higher, if in fact it is not regulating at all. So there may be something wrong with one of the 149K resistors, or the B side 431 chip - or something else.
You can try replacing parts, but at this point I recommend that you simply get a new board and components, build it up carefully, and install it. The old board can become an object lesson on display, if you want to keep it out of the landfill (it's only other application). :^)
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I replaced Q1 and it is playing now without incident for a little while. But we have been there before. So I will look into replacing the board. If one of the things you suspect fails, will the failure be catastrophic, i.e. is it going to take something expensive with it so I shouldn't play my amplifier until I replace the board?
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While I can't predict EVERY possible failure mode, it's the solid state parts that are easy to damage. Tubes are tough!
A failure of everything could drive the 45 grid pretty high, and might damage that tube. Don't use the pricey ones until you are confident that everything is running well.
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I was more worried about having to replace a (Magnequest) transformer or some such. Anyway, I am going to see how it goes for a little bit then. I suppose I should actually check the voltages now that it is running. Thanks for the help as always!
Paul
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Let's remember that rewetting solder has helped 3 times before for only hours then a failure. We can't declare it fixed till Paul gets through the weekend and it works for a week. I'm thinking there is something we are overlooking. I hope I'm wrong.
While I can't predict EVERY possible failure mode, it's the solid state parts that are easy to damage. Tubes are tough!
A failure of everything could drive the 45 grid pretty high, and might damage that tube. Don't use the pricey ones until you are confident that everything is running well.
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The Queen is getting a board together for me so I think I am just going to heed the Man's advice and replace the one that is in there. We have spent so much on other tweaks that it is probably the wise thing to do so we know we have an amp that is operating properly.
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Ok, so I went in and replaced some parts on the driver board two months ago and at the same time ordered a new board just in case. The amp decided to work perfectly for the next two months until yesterday wen the problem resurfaced. Sound is fine for a few seconds then goes bad. Flipping it over and watching I can see that two sets of LEDS light up instantly, the last two never do. So I went ahead and put in the new board and all new parts. Didn't fix the problem. I suppose I can replace all of the wires on and into the board in case one of them is bad. Any other thoughts? Very frustrating.
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I wouldn't necessarily pull all those wires, but it might be worth touching up the connections at both ends of each wire and checking their continuity. If the board itself is good then the problem must lie in one of the connections to it. You might try monitoring the plate voltage of each half of the 5670 as the amp goes thru the "Sound is fine for a few seconds then goes bad. Flipping it over and watching I can see that two sets of LEDS light up instantly, the last two never do" cycle. That might help to understand what is going on.
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I did just check continuity, that was fine. But it wouldn't hurt to touch up the solder joints to be sure. Will do that tonight and see what I can figure out on the 5670 while I am at it. Thanks Doc!
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I just talked to Paul, Paully. He did the chop stick test while I was talking to him. He tried both ends of all the connections/wires to the soft start board as well as every component on the board. There was no change in the sound. I think he rewet all the terminations on both ends also.
What is happening is that after some delay the sound comes on and is beautiful. Then after 4-5 seconds of music it gets extremely muffled. It is like the B+ has dropped but it is still playing, just not right.
Is there a chance that the delay circuit is at fault? I'm guessing that the initial delay is the circuit doing its job. But then the poor sound comes in.
Paul will check the 5670 high voltage tomorrow and post.
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Two different PC boards, two different delay circuits, same problem. So I still think the problem is off the board. Paul, I'm guessing you have tried a different 5670?
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I am positive that I swapped all of the tubes, wouldn't hurt to try again. Will do tomorrow. Thanks!
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Just as a reminder, I do have 45's as the output tubes. Reading at IB and OB on the board, which should give the reading on the 5670 for pins 4 and 6 I get 150V DC. I went ahead and checked pin 4 just to be sure and got basically the same reading. Last time, before replacing the board, I got 192 on both pin 4 and 6. Also swapped the 5670 just to be sure. Re-wet multiple solder joints leading into the board. It has to be whatever powers the last two LEDs on the B-side of the board shouldn't it?
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Did you replace the zener diodes when you replaced the PC board? If not, that may be what is pulling the regulated voltage down. It would be worth checking the diodes with a diode checker or ohmmeter to see if any of them are reading shorted (very low ohms in both directions).
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The diodes were the first thing I replaced a few months ago before I put in a new board. So those are new. But I will go look at resistance readings on them anyway just to be sure.
Edit: All read 25 to 35 Mega-ohms when measured in the same direction.
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Remembering this is a 45 output...
Paul is measuring the voltages now. He reads 476V incoming from the power supply (IA). The schematic for the SS board says 450V, sounds good. But at OA, the schematic shows 300V and he is reading 148V. That is about 1/2 of what it should be.
Any help here? I'm guessing a connection because it sounded sooo good when we finished last time. But it is driving both of us to distraction, well me remotely but Paul directly.
Some voltages:
IA 476V
bA 1.6V (remember there is a resistor in parallel with a Zener diode on this connection to ground)
OA/IB/+reg (B) 148V
OB 146V
bB/breg (B) 74V
Kreg (B)/driver tube pin 8 1.9V
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When the amplifier is first turned on the voltage at OA should be what the zener string pulls it down to. That should be something a little over 300V, like maybe 325. Then as the 5670 heater warms up the voltage at OA should drop to 300V as the 5670/431 shunt regulator begins to draw current. What I would like you to do is attach the voltage probe to OA or IB, whatever is easiest attach to, and monitor that regulated voltage as the amp starts up and goes through the heater warm up period of the 5670. We need to see if the 148V shows up immediately upon startup or if it starts out at something around 325 for a few seconds as the zener string properly regulates it and then drops to 148V as the 5670 begins to conduct.
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At IB it started out at 350V or thereabouts. It seems about the same time as the sound cuts out and it goes muffled it started to plummet to 150V.
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R3(B) should be 2.49K, ans R3(A) should be 4.99K. Are they backwards?
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They aren't reversed but the one in R3 (b) appears to be 249K ohms not 2.49. I will go to work on this and see what happens. Thanks!
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I replaced the 249K resistor incorrectly in R3(B) with a 2.56K resistor I fashioned together. Close enough I assume. Amp comes up and IB settles out at 290V and the amp plays and the second set of LEDs light up. So that appears to have been the problem. Not sure what happened. I checked all of the resistors before I put them in.
Here is the odd thing. I went back and checked the board we replaced and the resistor in that board was 2.49K ohms as it should be. So I replaced a bad board with some problem somewhere that was causing muffled sound and non-lighting LEDs. I put in a new board and didn't notice I had the wrong resistor which caused the same muffled sound and non-lighting LEDs even though the original board had the proper resistor. Go figure.
I suppose at this point I will just be thankful for the help and let it play.