• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Balanced Audio Technology VK-D5SE

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#61
ErikdeBest said:
You are welcome. After you did the above, did the CD player work and produce sound from both channels? If yes, how the did the output levels compare?

It sounds as if the bad channel was pulling to much current, interacting with the supply to the good channel. 55V over the resistors on the good channel sounds a bit too high, but more reasonable then 12V. Can you check if on the good channel all plate resistors are still good, and that the effective resistance there is around 1k275?

Today I had a look again at the working of the Q15 and Q14, which I incorrectly described as a constant current source, it is actually a constant current sink. Anyway, the Q15 has a constant voltage between base and emitter of ~0.7V. A fixed voltage over a fixed resistor (the 10R of R157) defines a constant current of circa 70mA. This 70mA is split over the two legs, so 35mA per leg. As each leg has an effective 1k275 resistor in the plate, the voltage drop is indeed about 45V, which is closer to your 55V than the previous 12V. Can you measure the vlaue over R121 (110 ohm resistor in the left channel)? This should give a good indication of the target current BAT had in mind for this circuit.

So you measure 12V over the resistors in the bad channel. This was the expected result with the 1k2 resistor between pin 2&3 of Q14. Lets get the bad channel to pull around 70mA through the tubes now. Doing the same calculation as before: cathodes at circa 3V, negative supply of -15V, give a span of 18V. To get 70mA, we need 18V/0,07A = 257R. You already have 120R, so you need another 137R. So replace the 1k2 resistor between pin 2&3 with something around 140R, power rating shoud be around 2W.
Click to expand...
I'm going to take out the 1K and put in a 140 and see what happens. I never did test the sound yet. I'm ok with leaving the resistor in place. But do you think its worth it for me to continue to track down the "real" issue? Before using the resistor to test I did replace both Q14 and Q15. So in that circuit it just leaves like three resistors, correct? They physically look ok and I think I compared their ohm value to the other side in circuit and they were the same. Or do I say screw it and just leave the 140 ohm resistor in place and call it a day. Assuming a good sound test??? Oh and did you want a voltage reading across R121?
 
#62
Ok, so now we have on the working side 52v and the "bad" side is now 40v. I need to hook it up and check the sound. But back to my last post, is try to find out the issue or be done and leave the 140 resistor in place? But it appears, after replacing Q14 and Q15, its just 4 resistors? I suppose one could be off value but would that casue this?
 
#63
Values more or less according to expectation, let's see if it plays... I destroyed a number of SS components due to electrostatic discharge of my soldering iron, so now I always check if the tip is still connected to ground, and no more dead components. So it could be that when replacing you already killed the new components, hard to say. Also difficult to troubleshoot, as you can't leave the CD player on too long because of the heat.

Well, let's see if it works first!
 
#64
Well, that could be, so maybe I killed the new Q14 and Q15? Because since visually those 4 resistors attached to Q14 and Q15 look fine and measure the same, I kinda doubt its them. But, I am wrong at least 1 time every 10 min. I'll hook it up later today and see what it sounds like.
 
#67
Well . . . So we have output. Interesting enough, the bad side with the "test" resistor has normal sound output, maybe a tad on the low output side. But the left channel or working channel is way low. So the working side is low, non-working side is about normal. But a huge variance in output. It is a brand-new set of tubes on each side.
 
#70
I know you said you replaced the heater regulators, are they both putting out the exact same voltages to the tube heaters? What you are describing is the exact same issue I had with my BAT VK-30 preamp when the one side was lower in sound and I noticed the heaters on the bad channel tubes look more dim than the good side. I measured the output of the regulator on the low side and the regulator was measuring low. Maybe double check them again to see if nothing has change?

If possible, some pics will be nice to help out troubleshooting. Have to double checked the output coupling caps, Jensen Copper Foil PIO are know for going bad/leaky
 
#71
I did replace those. Both tubes sets 6v on the heater, or 6.1. I can't remember. Replaced the jensen caps. I like the BAT gang, but those Jensen caps, that was bad. I understand they didn't know at the time, but that was a bad deal. I think its probably something with this circuit that Erikdebest has been having me isolate. The only reason I've tried this hard to fix it is I've acquired possibly the last known new philips transport for this thing in the known universe. I wanted to put it in and restore this to full glory. But at this point, I'm about ready to throw in the towel and sell it for parts on audiogon.
 
#72
Now that the circuit seems to be stable from a DC point of view, I would get (burn) a CD with eg 100Hz tone on both channels, play it and compare AC voltages throughout the player. At certain point you will find they are different, and we troubleshoot further.
 
#73
Thank you again for all the help. Yes, I have a test CD around here somewhere or can make one. Couple questions. One - Would you leave that other side (working side) as is or remove Q12 and put in a resistor, so it matches the other side? Could that possibly fix the output difference? Next, when looking for the output issue with a test CD, it looks like the Grid circuit is the input for the signal (comes in from SH9), would you start there?

jim
 
#74
jimmyp11 said:
I did replace those. Both tubes sets 6v on the heater, or 6.1. I can't remember. Replaced the jensen caps. I like the BAT gang, but those Jensen caps, that was bad. I understand they didn't know at the time, but that was a bad deal. I think its probably something with this circuit that Erikdebest has been having me isolate. The only reason I've tried this hard to fix it is I've acquired possibly the last known new philips transport for this thing in the known universe. I wanted to put it in and restore this to full glory. But at this point, I'm about ready to throw in the towel and sell it for parts on audiogon.
Click to expand...
I know this can be frustrating but don't give up, you may be very close to finding the issue. Just keep a log of all the things you have done like replacement of parts and voltage readings for certain points so you can go back and compare. It can get to where it seems like a constant circle going around and around but just hang in there. I wish I had a schematic of this CD player to try to help you out as well.

What gets me upset from this whole thing is the non support, that was an expensive CD player and should still be supported.
 
#76
Oh ok, I guess I missed that. 🙂

I remember this CD player and I hearing back in the 2000's. It was connected to a VK-5i preamp and a VK-200 power amp with Vandersteen 3A's. Still one the best sounding setup I have heard til this day.

I got rid of my BAT VK-30 preamp because I didn't want to deal with anymore issues. First was High DC Offset on outputs due to bad output Coupling caps, retubing all matched, then the bad heater voltage regulator I ended up replacing both. After that, I just said goodbye and haven't looked back. I love the sound but I was starting to get a picture of the durability side I didn't like. Tubes is just part of the game in tube gear but still it was expensive for 6 matched.

I'm really surprised that Victor doesn't want to help.
 
#77
Yeah, his help was sending the schematics. Which, yes, was helpful. They can't get the transport which is a lot of issues and it was a combo deal with them and another company for the digital domain pieces. Notice they never made another . . .
 
#78
Just to confirm, on the left channel (with the low output), you have about 55V over the plate resistors in both legs of the circuit, and in the right channel you have about 40V over the plate resistors in both legs?

55V over the plate resistors is a good value, but it creates about 2.3W of heat, and the resistors should support 2W only. Also the CCS value suggests rather about 44V over the plates, so maybe there is something fishy there. Therefore I ask if there is indeed 55V over the plate resistors in both legs (maybe one is less, would explain the lower output). You can indeed replace Q12 with a resistor between pin 2 and pin 3, just as Q14.

Lets check if both channels have good DC conditions. With a test tone at circa 100Hz one can measure AC well with a DVM. Please measure voltages at (all) grids, at all plates. Maybe somehow a tube is not connected correctly and disbalancing the circuit.
 
#80
I have checked all the tube sockets, all seem good and pins connected well. I'll have to do the test tone later today or tomorrow. I am going to put the same value resistor in Q12 as the other channel and see what the plate voltage does.
 
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