Bass amp- raspy-hashy sound only when played through

[pbman1953]

My Traynor YBA-3 Custom has been great. Its gone through cap updates with help here, from the forum. Recently , when played through there's a raspy/hashy sound. Power wise, the amp is still all there.
 
What's the first thing to check?


Thanks

[tubenit]

If you know how to work on amps safely ..............

Check tubes with known good tubes.   Check plate and cathode voltages.  Check the soldering of the caps you changed out. Try a different speaker, guitar, guitar cable.  Don't use any effects.  Guitar into amp only.


If none of those reveal a problem. Using a non-conductive chopstick tap on PCB board and other places to see if there is a crackling noise.



with respect, Tubenit

[tubeswell]

Measure all the HT voltage nodes in the power rail. You want to see voltages dropping as you move along the rail. If two nodes measure the same, it’s an indication that one of the filter caps isn’t decoupling the supply.

[pbman1953]

If you know how to work on amps safely ..............

Check tubes with known good tubes.   Check plate and cathode voltages.  Check the soldering of the caps you changed out. Try a different speaker, guitar, guitar cable.  Don't use any effects.  Guitar into amp only.


If none of those reveal a problem. Using a non-conductive chopstick tap on PCB board and other places to see if there is a crackling noise.



with respect, Tubenit

I can check the cap connections and probe with a wooden Chopstick. Please layout how to check the plate (pin 3) and cathode (pin 8) voltages and what they should measure at

Thanks

[pbman1953]

Measure all the HT voltage nodes in the power rail. You want to see voltages dropping as you move along the rail. If two nodes measure the same, it’s an indication that one of the filter caps isn’t decoupling the supply.

As far as the "HT", the High Tension/B+, do you want the voltages from each filter cap point?

[tubeswell]

Measure all the HT voltage nodes in the power rail. You want to see voltages dropping as you move along the rail. If two nodes measure the same, it’s an indication that one of the filter caps isn’t decoupling the supply.

As far as the "HT", the High Tension/B+, do you want the voltages from each filter cap point?

Yes

[pbman1953]

Measure all the HT voltage nodes in the power rail. You want to see voltages dropping as you move along the rail. If two nodes measure the same, it’s an indication that one of the filter caps isn’t decoupling the supply.

As far as the "HT", the High Tension/B+, do you want the voltages from each filter cap point?

Ok to confirm off the schematic-


1st stage should be  +540v
2nd-   +536v
3rd stage , to the preamp- +250v

Yes

[passaloutre]

There's also a 355V node for the phase inverter

[tubeswell]

Regardless of what the schematic voltages say, what are the voltages in your amp?

[pbman1953]

Findings-




1st stage- 549
2nd- 555
3rd- 273
Phase- 373

[tubeswell]

Findings-

1st stage- 549
2nd- 555
3rd- 273
Phase- 373

Looks like the rail is dropping as it should so the caps are all working.


However, the voltages are highish. Assuming the heaters are putting out around 6.3VAC, the raspy sound could be the output tubes are biased way too cold.


What is the cathode current on (each of) the output tubes?

[pbman1953]

Findings-

1st stage- 549
2nd- 555
3rd- 273
Phase- 373

Looks like the rail is dropping as it should so the caps are all working.

However, the voltages are highish. Assuming the heaters are putting out around 6.3VAC, the raspy sound could be the output tubes are biased way too cold.

What is the cathode current on (each of) the output tubes?

The filament measurement is 6.3.

I have a list of questions-

There's an old Traynor fan page that goes down a list of each Traynor YBA series amp-  http://www.0rigami.com/vb/models.html#customspecialyba-3

This should lead you to the YBA-3 Custom, the amp I have.

There a couple of mods that people suggest and I'd like to your take on them.

1- "Original input resistor was 100k and I changed it for 5.6meg like my Ampeg."- 
Which resistor is that R23? Would you suggest to change to the 5.6meg?

2- "The last two caps at the phase inverter(bias feed) are .1 change these two caps to .33 or.47 mfd 600volts"

Are these c18 &19? would you suggest to change those to the .33 or .47 value?

3- back when I did the upgrade this is how I have the stages-

1- 550MF/ 385 v and 550MF/385v in series 
2-  same as #2
c29 is 50mf/500v
c32 is a 50mf/500v

Do these larger values have adverse effects or are they simply overkill?
Also #8 (cathode) is grounded. What's the best way to measure it?

4- I think someone in the forum, years back, told about this next one-

   a) add a 1k 5w resistor , to each tube, on pin 4.
    Run the resistor from 4 to 6, the used pin. Then tie all the 6's together so the +536V signal runs through each 1k resistor. 

[tubeswell]

The filament measurement is 6.3.

Good

The filament measurement is 6.3.Side question- back when I did the upgrade this is how I have the stages-1- 550MF/ 385 v and 550MF/385v in series  2-  same as #2c29 is 50mf/500vc32 is a 50mf/500v Do these larger values have adverse effects or are they simply overkill?

Filter cap capacitance and voltage rating are important for ensuring the components can handle the working conditions, but they do not fundamentally make the amp voltages higher - only the power source can do that.

Also #8 (cathode) is grounded. What's the best way to measure it?

Either by using an expensive bias measuring adaptor, or break the cathode-to-ground connection at Pin 8 on each socket and install a permanent 1 ohm 1% tolerant resistor between the cathode and the ground, and set your V-meter to the 'mV' setting and measure the millivoltage drop across each resistor. Ohms Law tells us that 1V = 1R x 1A so 1mV/1R = 1mA

Measuring cathode current is a relatively easy (and safe) way to enable estimation of plate power dissipation.

[pbman1953]

"Either by an expensive bias measuring adaptor that you can use, or break the cathode-to-ground connection at Pin 8 on each socket and install a permanent 1 ohm 1% tolerant resistor between the cathode and the ground, and set your V-meter to the 'mV' setting and measure the millivoltage drop across each resistor. Ohms Law tells us that 1V = 1R x 1A so 1mV/1R = 1mAMeasuring cathode current is a relatively easy (and safe) way to enable estimation of plate power dissipation."




I have a Bias Rite that can easily measure cathode current. I'll have readings back tomorrow.


Thanks for helping!

[pbman1953]

First set of readings


Tubes             A           B         C           D


Voltage         547       545      547        547


Cathode-       42.8      45.2     46.5      48.6


Watts-          23.4       24.6     25.4      26.6


At first I had 4 Tung Sols, more recent not NOS. 3 were close but one was hotter at 32 watts. I have a couple GE's that I tried. One was close to the TS's and the other was hotter in the low 60's cathode wise. The readings above are with 1 GE & 3 TS's.


Looks like I may need another tube to be close or raise it to bring up A closer to at least 25 watts. But D will be running in the high 20's.

[pbman1953]

Filter cap capacitance and voltage rating are important for ensuring the components can handle the working conditions, but they do not fundamentally make the amp voltages higher - only the power source can do that.


 


So even if the values are higher, away from the stock schematic, the sound will be fine?

[tubeswell]

First set of readings


Tubes             A           B         C           D


Voltage         547       545      547        547


Cathode-       42.8      45.2     46.5      48.6


Watts-          23.4       24.6     25.4      26.6


At first I had 4 Tung Sols, more recent not NOS. 3 were close but one was hotter at 32 watts. I have a couple GE's that I tried. One was close to the TS's and the other was hotter in the low 60's cathode wise. The readings above are with 1 GE & 3 TS's.


Looks like I may need another tube to be close or raise it to bring up A closer to at least 25 watts. But D will be running in the high 20's.

6550s?

[pbman1953]

Yes, all 4

[tubeswell]

For a 42W tube, 23-26w is a little on the cold side. Try warming them up a bit.

[pbman1953]

What number should I go f for?

[tubeswell]

What number should I go f for?

Try 65-70%

[pbman1953]

What number should I go f for?

Try 65-70%

Tubes             A           B         C           D
Voltage         544       542      551        543
Cathode-       49.6      51.8     52.4      47.8
Watts-          26.9       28.1     28.8      26

[tubeswell]

How's the sound? Any improvement?

[tubeswell]

Tubes             A           B         C           D
Voltage         544       542      551        543
Cathode-       49.6      51.8     52.4      47.8
Watts-          26.9       28.1     28.8      26

At this point you could also try swapping the combinations of tubes around a bit to see if you can get them to balance more evenly. It's not immediately obvious as to how to get there - it's a matter of trial and error. e.g., if you put both '28's on one* side and both '26's on the other side, you might actually find they're all '27's etc.


* e.g., try both 28s on the side of the primary that measures the highest DC resistance and both 26s on the side the measures the lowest DC resistance or vice-versa

[tubeswell]

How's the sound? Any improvement?

Note that if it isn't any better, then we start looking at something else

[pbman1953]

Tubes             A           B         C           D
Voltage         533       533      534        536
Cathode-       45          49     47.7       48.3
Watts-          24          26      25.4        25.7

One side 28's and the other 26's. I have run out of bias control it's maxed. There's a bias resistor I need to increase to increase the cathode

[pbman1953]

For R38/39, it's hard to tell if its 38 or 39, but it's the on coming direct off T1 from the PT.
The stock resistor is 150k, but there was a 100k in there. Since I needed more , being that the bias pot (20K) was maxed I tried different values. The first was a 130k, which was way to much, then 120k , still higher than I needed. I ended with 110k. The pot is on its lowest setting.


Tubes             A           B         C           D
Voltage         551       551      549        548
Cathode-       49.7      55        54         52.7
Watts-          27.4      30.3     29.6        28.8

If you feel that (B) is too high at 30.3, I'd need to see if I can configure  a 105K value

[tubeswell]

What about the sound? Any improvement?

[pbman1953]

What about the sound? Any improvement?

Sounds great, thanks! I found issue that could of been the noise problem. One of the 1k 5w resistor's on one tube, (pin 4 connection) had a cold solder joint.


Couple questions-


I have room for a balance pot. Would you suggest to install one?


From reply #11- I wrote-  The last two caps at the phase inverter(bias feed) are .1 change these two caps to .33 or.47 mfd 600volts.

Do you suggest that or leave them?


Thanks!

[tubeswell]

Balance pot is up to you.


Coupling cap capacitance on output tube grids affects the band pass. If 0.1uF isn’t bassy enough you could experiment with increasing capacitance (again up to you), but if it starts to introduce blocking distortion, you’ll know you’ve gone too far.

[pbman1953]

I think I'm done.




Thanks soo much!