Paraglow problem

[Bryon]

Hi Guys

I have a pair of Paraglow II's which I love dearly - problem right now is that one of them is making noises at me so I'm listening to mono again.

I've isolated the problem to the amp [switched inputs and the problem followed the amp].  It sounds like a tube problem - a gargling kind of interference - fairly loud at start-up and then quiets down a bit but still very obvious through my sensitive speakers, so I switched tubes and there was no difference.

I've visually checked the wiring and jiggled a few wires to make sure there were no shorts but to no avail.

Any suggestions where I should start?

thanks for your time and expertise.

Bryon

 

[Paul Joppa]

Voltages at the tube pins would help. The II designation indicates it has teh Tucker SR driver modification, I think? What is the driver tube now?

 

[Bryon]

Hi Paul

Yes, the Paraglow II's have the Tucker mod.  The driver is now a 6n1p.  I was hoping to avoid checking the voltages simply because I'm worried that the tubes are being damaged, but I guess if the voltages are necessary in order to help determine the problem, I'll check them.  I'll post my findings later tonight.

thanks

Bryon

 

[Grainger49]

I didn't see this, did you swap tubes from one amp to the other to see if it follows the tubes?

 

[Bryon]

Hi Grainger

I didn't actually switch tubes but I did put a new set of tubes [a new 6n1p and a 2A3 which had never exhibited any problems] into the affected amp without solving the problem. 

A better description of the sound might be an initial loud gargling interference with an occasional pop followed by relative quiet which is followed by a quieter motorboat type of interference as the tube warms up.

Bryon

 

[Bryon]

Phew - what a mess!

For what it's worth -

Terminal 1 - 385 vac  [should be 344]
            2 - 381 vac  [344]
            3 - 510 vdc  [425]
            6 - 505 vdc  [410]
            10 - 95 vdc [145]

Pins        A1- 95 vdc  [145]
              A2- 495 vdc [400]
              A3 - 5 vdc [100]
              A4 - 95 vdc  [145]

              B1 - 5.5 vdc [100]
              B2 - 0.65 vdc [0]
              B3 - 0.18 vdc [ 1.57]
              B6 - 0.5 vdc [225] - for Tucker's mod.

the leds on the sr boards don't light up

Any clues - looks like it might be in the board again

thanks for any help

Bryon

 

[Paul Joppa]

I see two problems right off. They are likely to be related ...

1) The power supply voltages are too high by 20%. This may or may not be a bad problem, it may just reflect a different power transformer than the one used for the manual voltage measurements. Two questions: Does the power transformer have flying leads or solder tabs? And what is your power line voltage?

2) The shunt reg board is toast. Well, at least I mean it's not working. You might inspect it carefully to see if there are signs of heat damage near the large power transistors - that could be a consequence of the excess voltage. The board is Tucker's product; we don't have the circuits, boards, or manuals, much less the expertise to provide much help. I would suggest you get the power supply voltage questions settled before fixing the board, to be sure the fix is not short-lived.

If you want a different board, the new Paramount part which is in the final stages of development could probably be adapted to work in this amp and provide similar performance. Between our experience with Tucker's board and previous iterations of our board, I believe that our lates will prove more reliable than previous versions.

 

[Bryon]

Hi Paul

Power line voltage is 119 vac, but strangely enough when I measure across the power switch of the Paraglow it is 219 vac.  Does this make sense to you?

The power transformer is the Magnequest PGP 8.1 with solder lugs.

I can't see any heat damage on the boards. 

I'd love to buy the new Paramount boards when they are available as I have run into some problems with the shunt reg boards that are in there. 

I'm thinking about rebuilding and maybe going back to the original design.

Any suggestions?

thanks

Bryon

 

[Bryon]

Still looking for some help - further to the post above - I found a record of voltages from a few earlier checks and the terminal 3 and 6 readings have been at least 500VDC right from the beginning and it has been making beautiful music for 7 years, so I'm not too worried about the voltage.

So that brings us to the sr board.  I replaced all the transistors and leds but without any improvement. 

The Tucker mod puts a 15kohm 3w wirewound resistor between terminal 6 and B6 which looks like it might have overheated as the surface has flaked off - is this just a symptom or could it be a cause?

any help would be really appreciated as I am becoming very frustrated.

thanks

Bryon

 

[Doc B]

I agree with PJ that the board is blown. At this point in the game the best bet would be to update it with the new Paramount II board which is under development and close to release. I'm not sure quite what you mean about measuring across the switch. To measure the primary voltage on a PGP 8.1 you want to measure from 1S to 1F on the power transformer itself.

 

[Bryon]

Hi Dan

Yeah, it's probably the board - but I don't understand how the board itself could fail - the traces on the pcb look fine and if I change all the components, shouldn't it work?

What I meant about across the switch was that I measured for voltage across the power switch thinking it would reflect the voltage coming from the wall.  It was way too high so then I checked the power line voltage directly and was surprised that there was 100 volts difference.  It doesn't make sense to me but then I don't really understand a lot about what is going on under the chassis plate.

I'd love to be able to put the Paramount II boards in - hopefully they'll be ready soon as I am an addict and withdrawl is painful.

What would be the expected value of IS to IF?  It should be VAC not VDC, right?  If there was a problem with the PGP 8.1 then I shouldn't be getting 385VAC on terminal 1 or 2, should I?

thanks again for your support

Bryon 

 

[Doc B]

Oops, my error. It has been some time since I worked with a PGP 8.1. The "1" terminals are the high voltage secondary, aren't they. I think it's 2S and 2F that are the primary, and that's what I should have said to measure, VAC. Measuring across the open power switch should give you the proper 120 ish reading too, but over the years we have seen quite a few instances where folks get screwy numbers when trying to measure AC with various meters. At any rate, measuring right at the power transformer primary with the power switch on should give you a good reading if the meter is cooperating.

When I said the board is blown, I did mean that some components on the board are blown, not necessarily a failure of the board itself. One can rework a PC board with replacement components, but sometimes it's pretty dicey to do without damaging it by lifting copper pads or traces. You would probably want to replace all of the semiconductors since it may have been running quite hot for 7 years. I would also measure the resistors to make sure they have maintained their value. IIRC John had a trimmer resistor on that board. If you replace that trimpot, be sure to set it to the middle of its range before you turn the amp on. If it is all the way to the 0 ohms end you can end up blowing transistors.

 

[Bryon]

Hi Dan

thanks for the quick response.

I just checked 2S to 2F and it was 119.7VAC so almost perfect.  But I still get 216VAC over the power switch when the power is on and 96VAC from the hot side of the switch to ground when the power switch is off.  This confuses me.

I have replaced all of the semiconductors and leds on the board but not the caps or resistors.  The board is still in really good shape so I guess those are next.

thanks again for your time

Bryon

 

[Doc B]

If you have the right voltage across the primary terminals forget about the switch. Measuring AC with respect to chassis ground won't give you a useful reading for what is on the primary. If you think about it, 216 - 96= 120.  So the reading is being floated up by 96V, perhaps it is some indication of your house wiring setup.

I don't think you necessarily need to replace caps and resistors on the PC board. I would suggest measuring the resistors just to be sure they have not drifted in value from being cooked over 7 years. The caps are probably OK unless they look really cooked or otherwise damaged.

On the other hand, after 7 years it might be prudent to replace electrolytics in the amps. The caps we used were marginally rated if a person had high AC mains voltage. It might be a worthwhile endeavor to uprate the 'lytics to 600V if you can find a suitable replacement at that value.