help with noise at startup volume turned down

[Paul Birkeland]

The 5998 does not have the high strength heater to cathode insulation that the 6080 and 6AS7 do.  Consequently, when you exceed the 100V heater to cathode voltage limitation, there is the possibility that the tube will make some noise while operating.

One way to check to see if this is an issue is to plug a 12BH7 into the amp with the stock circuit.  This will drop the grid bias on the 5998 significantly, and lower the cathode voltage at the same time.  If this solves the noise issue, then there are approaches that can be implemented to account for this.

-PB

[Paul Joppa]

PB is exactly right. Remember, the circuit was designed for the 6080 or 6AS7, which have unusually high heater-cathode voltage ratings of +/-300v. Most tubes, including the 5998, are at most +/-100v.

[tdubl07]

Hi guys, I was following this thread today because I as well got a 5998 in the other night, and had the loud hum going on as well. This is with the stock 12au7 also. So I'm very glad it's something as simple as a different tube up front. With my 6080 in, no humming at all and the amp sounds glorious with the speedball. Thanks for the helpful insight PB and Paul.

[ghost_rider]

The 5998 does not have the high strength heater to cathode insulation that the 6080 and 6AS7 do.  Consequently, when you exceed the 100V heater to cathode voltage limitation, there is the possibility that the tube will make some noise while operating.

One way to check to see if this is an issue is to plug a 12BH7 into the amp with the stock circuit.  This will drop the grid bias on the 5998 significantly, and lower the cathode voltage at the same time.  If this solves the noise issue, then there are approaches that can be implemented to account for this.

-PB

PB is exactly right. Remember, the circuit was designed for the 6080 or 6AS7, which have unusually high heater-cathode voltage ratings of +/-300v. Most tubes, including the 5998, are at most +/-100v.

Thanks PB and Paul. But the thing is I cant check with a 12BH7 now

Let me explain my situation a little. I am from Bangladesh and I study in the UK. I was at home now for easter and in here i got the crack and built it. The problem is I cant find any tubes within few thousand miles of my home country and the post office is not very delicate so getting off ebay is also not an option. Therefore what I did was when coming back to home from UK,I bought 3 5998s,2 mazda 12au7,1 westingstone 12au7 and a Svetlana 6H5C. The reason I got so many of them is cause getting a tube in uk is alot easier than getting one in bangladesh. I am leaving in 3 days for 4 months (another semester). The crack will be left home because of its size and weight.

I can bring some 12BH7s next time when I come back home but I was thinking is there any other problems that might have happened here? Like if I have soldered something wrong in the board (which is highly unlikely cause I double checked everything) Or any errors from my end? Because from I have read is that the 5998 is a very very common and proffered tube for the crack and also with speedball. So many people is running a 5998 in there crack+speedball system. Are all of them using the 12BH7s? Do they also face the same problem with 12au7s? Or is it just me and "Hornet900"?

I guess im getting too worried about the speedball but see I was really really excited about it. So much excited that I already started saving up for the S.E.X or Stereomour for a small speaker setup for my room So you can understand when this bad hum comes with all 3 tubes,how i feel 

I will order some 12BH7s in a week but in the meantime do let me know if there are anything els I can check? Just to be sure that there is no problems/errors/mis-solders from my side and the amp is built right,now all it will need is a 12BH7.

Thanks everybody for the help.

Ghost_rider

[Paul Birkeland]

It's just a matter of how lucky you are.  A lot of 5998's work fine, some do not, and this operation will depend a bit on how strong the 12AU7 is that's used in conjunction with the 5998.

If the amp works well with your Svetlana tube, but not with the 5998, that would point to an insulation issue in the tubes themselves.

[ghost_rider]

It's just a matter of how lucky you are.  A lot of 5998's work fine, some do not, and this operation will depend a bit on how strong the 12AU7 is that's used in conjunction with the 5998.

If the amp works well with your Svetlana tube, but not with the 5998, that would point to an insulation issue in the tubes themselves.

I just found something very stupid that i think I did. I was looking at speedball update guide and i noticed a 270k Ohm resister at the terminal 12U and 13U. But I remember I only attached the capacitor there. On my inspection I saw that I really dont have a resistor installed on my 12U and 13U. I was shocked as how did i miss it and it never came up in my volt checks.

Anyways the wierd thing is I have holes on both the terminal 12U and 13U but no resistor there (I usually filled the holes with solder.)

I am gona get a 270k Ohm 1W resistor first thing tomorrow and try to connect it and pray it works 

It feels like a beacon of hope cause a wire is going from terminal 13 to power tubes 2 ports and then to terminal 2. And when I connected my Volt checker to terminal 12 and 2,the noise did vanish for a while.

Do you think it might work? 

[Hornet900]

One way to check to see if this is an issue is to plug a 12BH7 into the amp with the stock circuit.  This will drop the grid bias on the 5998 significantly, and lower the cathode voltage at the same time.  If this solves the noise issue, then there are approaches that can be implemented to account for this.

-PB

Hello
I'm going to buy some more tubes so I'll get a 12BH7 now

What are the changes to the amp you are talking about Paul to make it work with 5998 ?

[fullheadofnothing]

The 270KΩ resistor is there to bleed off the voltage from the power supply. DO NOT RUN YOUR AMPLIFIER WITHOUT IT!!!!!!

[ghost_rider]

The 270KΩ resistor is there to bleed off the voltage from the power supply. DO NOT RUN YOUR AMPLIFIER WITHOUT IT!!!!!!

I totaly forgot to put that one in. I dont know how it happened. 

I will get one tomorrow and install it. Do you think it might solve my problem?

[ghost_rider]

I just installed the 270K 1W resistor on the terminal 12U and 13U. Sadly nothing changed

There is still the warm up noise/hum when using the 6080WA for first 5mins at 0 Volume and Noise/hum on all volume levels with Tung Sol 5998 There are still some pop sounds when I increase volume from 0 to 5mm. The Noise/hum is louder on the left side than the right side.

What should I do now??

[Paul Birkeland]

at about 4mm travel point it makes a pop sound and the noise goes away. But the noise goes away after about 3 minutes.

Is this still the case when running a 6080?

[ghost_rider]

at about 4mm travel point it makes a pop sound and the noise goes away. But the noise goes away after about 3 minutes.

Is this still the case when running a 6080?

Yes. its with 6080WA.

The only change i got from installing the register is the voltage on terminal 22 droped from 203 to 196.

[ghost_rider]

Did I make a mistake somewhere or is this normal?

Everything was fine without the speedball installed both tubes were working fine.

If i did everything right then is there anyway I can mod the crack+speedball to run better (optimized) with the Tung Sol 5998? Cause for now I plan on running my amp on this tube alone for  a while, with different input tubes i suppose.

[Paul Birkeland]

It's just a matter of how lucky you are.  A lot of 5998's work fine, some do not, and this operation will depend a bit on how strong the 12AU7 is that's used in conjunction with the 5998.

If the amp works well with your Svetlana tube, but not with the 5998, that would point to an insulation issue in the tubes themselves.

This would be the applicable if the 6080 works at the 5998 does not.

[ghost_rider]

It's just a matter of how lucky you are.  A lot of 5998's work fine, some do not, and this operation will depend a bit on how strong the 12AU7 is that's used in conjunction with the 5998.

If the amp works well with your Svetlana tube, but not with the 5998, that would point to an insulation issue in the tubes themselves.

This would be the applicable if the 6080 works at the 5998 does not.

What should I do now then?