Problem with Paramount v1.1

[Roger]

Hi,

I've just finished soldering my Paramounts. All resistance measurements taken and found to be ok. Plugged one of the amps to AC, and took the voltage measurements, and everything was ok (284 volts on pin B6 after reg had kicked in and 445 volts on pin A2). I know this is a bit low, but I use a 240 volt power transformer on a 230 volt power grid. Plugged the other amp to AC, and the LEDs on the B side of the regulator don't light up. Measure 350 volts on B6 and 496 volts at A2 (on the four pin socket). I have checked all my solder joints and reflowed a couple of them.
How do I proceed with the amp that doesn't light up on the B reg side? Any ideas?
Roger

 

[Roger]

By the way, I got the hum down to 1mV on the amp that works properly. Is that acceptable with 2A3 as the output tube (and to be used with Avantgarde Duo Grosso with a sensitivity of 107 dB)?
Roger

 

[Grainger49]

I have Paramours (2A3) and I get them down to 1mV and 1.7mV.  The Paramour is less sophisticated than the Paramount.

As for your problem with the second amp.  Verify the orientation of the LEDs.  If backward they won't turn on.  Voltage in that part of the circuit, B side, would be high because of the lack of conduction.  The schematic doesn't say if the B side feeds the diode string or if the B side is the plate load for the driver half of the tube.  So I'm not sure either.

496V is less than 10% high for the A2 expected of 464; that shouldn't be a problem.  350V on B6 is not regulating, and the LEDs would indicate that.

Your problem is somewhere on the board.  You might need to lift it to see if you missed any solder pads.

 

[Doc B]

Sounds like the regulator half (B6) is working. Without the manual in front of me, my guess is the gain stage half (B1) is not. Check your connections to B1, B2 and B3 from the PC board and check the jumpers on the PC board to be sure they are connecting the correct pads.

 

[Roger]

Thanks to both of you. I'm in Norway and it's already saturday evening. I'm half way through a six-pack, so I'll check again tomorrow.
Roger

 

[Roger]

Doc B, is it possible to have connections wrong (ref. your comment above), and correct resistance measurements?
Roger

 

[Doc B]

Yes there are probably some points in the measurements where a good reading won't necessarily point out every flaw. Have you tried replacing the tubes tubes with the ones from good amp? That might be an easy test to start with. I do need to correct my previous comment about pin B1. That was the plate of the second triode of the 12AT7 used in the old Paramount. The plates of the 5670 triodes are B6 and B4.

I am working from the photo of the soft start board on the web site. The C4S load on the B side is the load for the shunt regulator. So what is happening right now is the Zener string is regulating to 350V, but the C4S loading the shunt reg and hybrid shunt reg are not working. The Zener string will give that 350V reading even if the tube is not working - that is why it is there, to regulate until the tube warms up and the hybrid reg takes over. Check to see if the tube is heating up, and if you have around 6.3 volts DC across pin B1 and B9. If the tube is heating up, check the jumper connections on the PC board next. It's fairly common to forget one or miswire one.

 

[Roger]

Yes there are probably some points in the measurements where a good reading won't necessarily point out every flaw. Have you tried replacing the tubes tubes with the ones from good amp? That might be an easy test to start with. I do need to correct my previous comment about pin B1. That was the plate of the second triode of the 12AT7 used in the old Paramount. The plates of the 5670 triodes are B6 and B4.

I am working from the photo of the soft start board on the web site. The C4S load on the B side is the load for the shunt regulator. So what is happening right now is the Zener string is regulating to 350V, but the C4S loading the shunt reg and hybrid shunt reg are not working. The Zener string will give that 350V reading even if the tube is not working - that is why it is there, to regulate until the tube warms up and the hybrid reg takes over. Check to see if the tube is heating up, and if you have around 6.3 volts DC across pin B1 and B9. If the tube is heating up, check the jumper connections on the PC board next. It's fairly common to forget one or miswire one.

I'll check it tomorrow. Thanks.
Roger

 

[Doc B]

By the way this is unrelated to the issue at hand, but I believe there may also be a typo in the voltage measurements regarding terminal 13, which I believe is actually connected to ground and should be 0.

You might also check the transistors on the B end of the board for shorts, by measuring across each possible pairing of the transistor leads, left to center, left to right, right to center. With the test leads one way you should see a very high reading and with the test leads swapped on the transistor leads the other way should be maybe around 700-1500 ohms. If you see a very low reading like 50 ohms the transistor is shorted and needs to be replaced. I doubt this is the problem, but it's worth checking.

Argh, without the schematic in front of me I am losing track of which end is which on the PC board. Looks in the photo like the B end is actually the load on the gain stage, not the load on the shunt reg. That doesn't really change any of my suggestions for sorting it out. You might try adjusting the blue trimpot to about the same value as the one on the good amp and see if that changes anything. The amp should work no matter how the trimmer is set, but again, it is something easy to try.

 

[Roger]

By the way this is unrelated to the issue at hand, but I believe there may also be a typo in the voltage measurements regarding terminal 13, which I believe is actually connected to ground and should be 0.

You might also check the transistors on the B end of the board for shorts, by measuring across each possible pairing of the transistor leads, left to center, left to right, right to center. With the test leads one way you should see a very high reading and with the test leads swapped on the transistor leads the other way should be maybe around 700-1500 ohms. If you see a very low reading like 50 ohms the transistor is shorted and needs to be replaced. I doubt this is the problem, but it's worth checking.

Argh, without the schematic in front of me I am losing track of which end is which on the PC board. Looks in the photo like the B end is actually the load on the gain stage, not the load on the shunt reg. That doesn't really change any of my suggestions for sorting it out. You might try adjusting the blue trimpot to about the same value as the one on the good amp and see if that changes anything. The amp should work no matter how the trimmer is set, but again, it is something easy to try.

I have switched to the tube from the working amp. No change. The A side of the reg is for the driver, and the B side is for the regulating half of the 5670. It is the B side of the reg that doesn't work.
Roger

 

[Roger]

Found the problem, I think. Had forgotten to solder the wire from the reg board to pin B8 on the nine pin socket. Will do that tomorrow and check again. Wonder how I missed that. Just hope I haven't damaged anything because of this.
Roger

 

[Roger]

Found the problem, I think. Had forgotten to solder the wire from the reg board to pin B8 on the nine pin socket. Will do that tomorrow and check again. Wonder how I missed that. Just hope I haven't damaged anything because of this.
Roger

Couldn't wait. Did the soldering with a beer and a cognac beside me. Everything lit up nicely. Music tomorrow?
Roger

 

[Roger]

The amps are up and playing, and they sound good. It sounds a little on the bright side of neutral, but I guess they need some hours to open up. The amps are dead quite. In a few weeks it will be time to starts some tube rolling.
The system is VPI Classic with AT OC9/MLII, Trigon Advance phono pre, Electrocompaniet EMC1 Up CD player (which I haven't used for years. I prefer vinyl), BorderPatrol Line 1 and Avantgarde Duo Grosso horn speakers.
Roger

 

[Doc B]

Good job, glad you got it sorted out. Yes the amps are a bit bright at first. They will come into better balance as they break in.

 

[Roger]

Good job, glad you got it sorted out. Yes the amps are a bit bright at first. They will come into better balance as they break in.

Here in Norway, we are already at sunday evening (9 hours time difference). I have played for about 8 hours today, and the amps are already much better than right after the first power up. Looking forward to more music from my system. It sounds great now. What amazes me is that they are dead quite on 107dB horns.
Roger

 

[Roger]

By the way this is unrelated to the issue at hand, but I believe there may also be a typo in the voltage measurements regarding terminal 13, which I believe is actually connected to ground and should be 0.

You might also check the transistors on the B end of the board for shorts, by measuring across each possible pairing of the transistor leads, left to center, left to right, right to center. With the test leads one way you should see a very high reading and with the test leads swapped on the transistor leads the other way should be maybe around 700-1500 ohms. If you see a very low reading like 50 ohms the transistor is shorted and needs to be replaced. I doubt this is the problem, but it's worth checking.

Argh, without the schematic in front of me I am losing track of which end is which on the PC board. Looks in the photo like the B end is actually the load on the gain stage, not the load on the shunt reg. That doesn't really change any of my suggestions for sorting it out. You might try adjusting the blue trimpot to about the same value as the one on the good amp and see if that changes anything. The amp should work no matter how the trimmer is set, but again, it is something easy to try.

Is there a typo in the manual. It says that terminal 10 should read 233V. Terminal 10 is the negative side of the 47uF/450V cap (which is connected to ground on the schematic). I measure 0V in my amps.

A new problem arose yesterday. I had played with the stock tubes for about a week and everything has been working fine. Changed the driver to Bendix 6385 and the output to NOS (1959) RCA 2A3. I cleaned the tube pins before plugging them in, and inserted the tube a couple of times to ensure good contact. No sound out of the amp. Measured the voltages (only the B+ and the input to the 2A3), and the voltages on the output of the 6385 were high (on both amps), so I adjusted down. I was not able to get them low enough to achieve 2A3/3. Changed back to the stock tube. No sound out of one of the amps.
Any idea how to troubleshoot this problem?
Roger

 

[Grainger49]

Yes, every terminal in Paramount ending in 3 or 8 is screwed to the top plate.  And again, yes, the negative side of the cathode bypass cap is grounded... somewhere I don't see it on the picture in the manual.  So you are spot on with both measurements.

Biasing is specific to the driver tube.  So that might be a problem.  Did you change the driver before the output tube?  Did you leave the same drivers in when going back to your stock tubes?  I think you see where this line of questioning goes.  You are troubleshooting pretty well so far.

 

[Doc B]

If everything is showing proper voltages LEDs are lighting up, etc., and you have no sound it indicates that there is an open in the signal path. Suggest you trace the signal path, looking most closely at what was disturbed when tubes were changed. It could be a loose tube socket, or something may have worked loose that is attached to one of the sockets. If the amp was going back and forth between the bench and the listening room there might be a connection that became loose when connecting and disconnecting interconnects or speaker cables.

What usually happens to me is it turns out to be the interconnect cable rather than the amp...

 

[Roger]

Yes, every terminal in Paramount ending in 3 or 8 is screwed to the top plate.  And again, yes, the negative side of the cathode bypass cap is grounded... somewhere I don't see it on the picture in the manual.  So you are spot on with both measurements.

Biasing is specific to the driver tube.  So that might be a problem.  Did you change the driver before the output tube?  Did you leave the same drivers in when going back to your stock tubes?  I think you see where this line of questioning goes.  You are troubleshooting pretty well so far.

I changed both the driver and the output tubes at the same time. Changed back to the 5670 and the Sovtek 2A3 supplied with the kit. No sound out of the right channel amp. Muffled sound out of the left channel amp.
Roger

 

[Roger]

If everything is showing proper voltages LEDs are lighting up, etc., and you have no sound it indicates that there is an open in the signal path. Suggest you trace the signal path, looking most closely at what was disturbed when tubes were changed. It could be a loose tube socket, or something may have worked loose that is attached to one of the sockets. If the amp was going back and forth between the bench and the listening room there might be a connection that became loose when connecting and disconnecting interconnects or speaker cables.

What usually happens to me is it turns out to be the interconnect cable rather than the amp...

I have been over both amps several times, and I can not find anything being loose, but I'll check again and again and again....until everything is working.
Plugged in an SS amp in my system, and everything works fine (same cables, same preamp etc.)