New Clarinet...Help

Quicksilverproac · « **on:** 8 Jun 2013, 12:46 am »

I have been trying to get my recently built Clarinet to work. It did not smoke , or smell and everything seemed ok except it did not play music. I checked all the parts to make sure they are correct,, and went over all the solder joints...still no sound. there is a faint hum. All the voltages are close to the amounts printed on the PCB. I built a Cornet , however it did not have the switching...could that be the problem. I am out of ideas. Thanks , Allan

poty · « **Reply #1 on:** 8 Jun 2013, 08:45 pm »

1. Bad Tubes?
2. What voltages did you measure? Maybe some more info about that.
3. Try to touch by a bare metal wire (insulated from the grip end!!!) the wires of C303, C302. You should hear some hum on the corresponding channel output.

Quicksilverproac · « **Reply #2 on:** 9 Jun 2013, 02:56 am »

I have used 3 5y3's and 6 12au7,s...So the tubes should be ok. All the voltages checked out within 5 or 10 volts, however, I just rechecked and they are much higher....r314=340 volts r107 382 volts both sides and r311 287 volts. I am not sure what happened...I checked several times over the past 2 days and the voltages seemed, ok. I do hear a faint sound through one side. I will take a photo .... Thank You

Quicksilverproac · « **Reply #3 on:** 9 Jun 2013, 03:25 am »

poty · « **Reply #4 on:** 9 Jun 2013, 08:24 am »

It seems something wrong with the bottom tube (V300). Does the tube glow?
If yes: While the device is switched off and 1-2 minutes after - try to measure resistance between the following points (all tubes out):
- pins 1 and 6 of the middle tube (V301, 12AU7) to the pluses of corresponding C300s (one tester probe to the tube socket, the other - to the circuit) - should be around 220 Ohm.
- pins 2 to 3 and 7 to 8 of the V301 - should be around 900 Ohm.
- pins 3 of V301 to 1 of V300 (the 12AU7 at the front) and 8 of V301 to 6 of V300 - should be around 900 Ohm.
- pins 2 to ground (case) and 7 to ground of the V300 should be around 330kOhm.
- pins 3 to ground and 8 to ground of the V300 should be around 680 Ohm.

Quicksilverproac · « **Reply #5 on:** 9 Jun 2013, 02:11 pm »

pins 1 and 6 = 217 ohms pins 2 to 3 and 7 to 8 =884 & 890 ohms pins 3 of v301 and 8 of v301 =900 pins 2 to gnd & 7 to gnd 334 ohms pins 3 to gnd and 8 to gnd 680 ohms. I rechecked the voltages and the are still off. Can C300 be bad?

avahifi · « **Reply #6 on:** 9 Jun 2013, 04:54 pm »

POTY says - pins 2 to ground (case) and 7 to ground of the V300 should be around 330kOhm. (334000 ohms)

Your measurement report says 334 ohms!

This is off by a factor of 1000X.

Either a typo here or some resistor value is very wrong in your installation.

Frank Van Alstine

Quicksilverproac · « **Reply #7 on:** 9 Jun 2013, 05:07 pm »

Frank, I went back and checked...with the meter on the k ...its 0....the resister r303 is correct at 220 ohms

poty · « **Reply #8 on:** 9 Jun 2013, 06:02 pm »

C300 is out of question (I think).
The resistance from pins 2 and 7 of V300 to ground is incorrect. Check the value of R302. I'd also check the C302 and if the volume pot is soldered correctly (I remember your problems with finding the specified in the manual part).
I'm cautious about severe difference in test voltages, wrong R302 cannot be the source of the differences. You have not answered if the V300 is glowing when the device is on (it proves that the heating voltage is OK).

Quicksilverproac · « **Reply #9 on:** 9 Jun 2013, 06:19 pm »

All the tubes glow...c302 is jumpered wire..no cap. I used the volume pot as per Jim. I will check the soldering.

poty · « **Reply #10 on:** 9 Jun 2013, 07:03 pm »

If the C302 is jumpered then the resistance should depend on the volume pot position - something like from 220Ohm to around 50kOhm (input disconnected!). Anyway - check the R302. What is the source for the preamp? Is it possible that there is some DC at the output of the source (it can easily alter the voltages if there is no C302).

Quicksilverproac · « **Reply #11 on:** 9 Jun 2013, 07:08 pm »

I have been using a Benchmark DAC1 usb for the source.

poty · « **Reply #12 on:** 9 Jun 2013, 07:54 pm »

Try to measure the voltages with disconnected inputs. And check the resistances from pins 2 and 7 of V300 to ground!

Quicksilverproac · « **Reply #13 on:** 10 Jun 2013, 12:37 am »

2 & 7 of V3 to ground ... both 220 ohms r107... 392 volts r314... 350 & 351 volts r311 ...57 & 58 volts with nothing connected.

hagtech · « **Reply #14 on:** 10 Jun 2013, 04:30 am »

From your measurements it sounds like you have a short across R302, unless volume control was at minimum. It is C302 that is optional and can be replaced by a jumper.

Even with that, your operating voltages seem to be wrong. With power off, you can measure each individual resistor and get a reasonable reading. Find those that are obviously out of whack. Also note that left and right channels are not mirrored on the board (ie R306L is across from R308R).

R311 hot side should definitely be between 100V and 150V, depending on the bias resistors chosen.

jh

bregez · « **Reply #15 on:** 10 Jun 2013, 06:45 am »

Prior to installing the Vishay Z-FOIL resistors (I think that is what I see in your picture) did you double check the resistance values via multimeter or LCR meter? The Z-FOIL design is not very robust and you may have gotten a bad one in the bunch.

Brad

Quicksilverproac · « **Reply #16 on:** 10 Jun 2013, 03:14 pm »

The Vishays check out...However r105 reads 6 k... We have a surplus store in town. I will get some replacement resistors today. Thanks for all your help Allan

poty · « **Reply #17 on:** 10 Jun 2013, 08:10 pm »

R105 is not so important and can not be the source of your problems.

Quicksilverproac · « **Reply #18 on:** 10 Jun 2013, 08:40 pm »

Yeah I saw that it has to do with the led. I thought it could be something with the switch or the rca's ...a few days ago the voltages were correct.

Quicksilverproac · « **Reply #19 on:** 10 Jun 2013, 10:19 pm »

the 145 is 57 volts.... 280 is 336 375 is 380 this is close. all the resistor check out except the 10 k 104 If I have 380 volts at R107 would that mean that the power supply is ok. Would this have to be a sort if its not a resistor?