Amp gurus... step inside

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SFW

SFW

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Ok. So I now have had two new quads of tubes that are running extremely hot in my amp. Hot as in I cannot get the idle bias mA below 60mA. I realize that with current tube stock the Rubys that I used to love are probably not coming back. So its deal with what is available. The current bias resistor is a 27K ohm. What value can I replace it with to get me into the 32mA range? Thanks in advance for the assistance!
 
SFW said:
Ok. So I now have had two new quads of tubes that are running extremely hot in my amp. Hot as in I cannot get the idle bias mA below 60mA. I realize that with current tube stock the Rubys that I used to love are probably not coming back. So its deal with what is available. The current bias resistor is a 27K ohm. What value can I replace it with to get me into the 32mA range? Thanks in advance for the assistance!
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What amp? What’s the plate voltage? How are you measuring?
 
You need more negative voltage so lower your bias resistor. Piggyback a 100k on top which will give you 21k. See if that is enough. It might be too much. If I remember correctly a little is a lot when making these changes Hopefully I have this correct as it's been a while since I needed to do this. Last time I did this I had to go higher in value. I think you need to go lower so you are good as you can just piggyback rather than having to replace the resistor because you cannot go to a higher value by piggybacking.
 
Is this your Splawn amp that you were having problems with? Did you have a tech looks at it? What did they end up finding?

They could just be a high current draw tube set.
 
harddriver said:
Is this your Splawn amp that you were having problems with? Did you have a tech looks at it? What did they end up finding?

They could just be a high current draw tube set.
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Yes this is my Splawn. The amp tested ok. The last two sets of tubes I have purchased are very high draw. So I'm just trying to get them under control.
 
Buy some tubes that are matched closer to what you want. Give them the plate voltage and dissipation % or just say I'd like to try some tubes biased closer to xx. :dunno:
 
Are these the tube sets that were crackling. popping, whistling and seemed to arcing and making noises from your earlier thread? Did you ever find out what was causing this? You never updated us, last we heard the Splawn was going to a tech thinking it was a output transformer, I think I remember you saying the amp was accidently played with no speaker connected then after that you started having issues with the amp.. Your video was removed.

https://www.rig-talk.com/forum/threads/tube-amp-gurus-need-help.245395/
SFW said:
So last week I plugged in my Splawn for the first time in a few weeks and was greeted by silence. While attempting to troubleshoot the issue, I noticed that I'm getting a weird high pitch whistle when signal goes to the amp. And its coming from the actual tubes! Which are only a month old. Video below shows the issue. DO you think its just bad tubes?
 
harddriver said:
Are these the tube sets that were crackling. popping, whistling and seemed to arcing and making noises from your earlier thread? Did you ever find out what was causing this? You never updated us, last we heard the Splawn was going to a tech thinking it was a output transformer, I think I remember you saying the amp was accidently played with no speaker connected then after that you started having issues with the amp.. Your video was removed.

https://www.rig-talk.com/forum/threads/tube-amp-gurus-need-help.245395/
SFW said:
So last week I plugged in my Splawn for the first time in a few weeks and was greeted by silence. While attempting to troubleshoot the issue, I noticed that I'm getting a weird high pitch whistle when signal goes to the amp. And its coming from the actual tubes! Which are only a month old. Video below shows the issue. DO you think its just bad tubes?
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The amp check out fine. Bad set of tubes. I ordered two more sets of EL34s. They are both wanting to run extremely hot. I spoke with Scott Splawn yesterday. He said to change the bias resistor from 27K ohms to 22K ohms and it should fix the issue. I stopped and picked up a few this morning and will knock it out when I get home this evening. Hopefully it will get things back to normal.
 
UPDATE:

Got the old 27k resistor out and installed the new 22k resistor. Fired up the amp and let it sit for a while. When I took the amp off of standby the voltage read 30mA. A slight turn got me to 32mA. Let it sit idle for 30 minutes and it never drifted off of 32mA. So I am back in business!
 
That's great that you got the bias issue sorted out SFW! And it's a plus that your output transformer in your Splawn tested good!

It's a WIN WIN.............:2thumbsup:
 
Sounds like an extremely hot set of tubes, not the amp. Splawns have a narrow sweep, so it's important to get measured/graded tubes in the range you need. Most reputable dealers can accommodate. Those tubes are just plain hot.
 
SFW said:
UPDATE:

Got the old 27k resistor out and installed the new 22k resistor. Fired up the amp and let it sit for a while. When I took the amp off of standby the voltage read 30mA. A slight turn got me to 32mA. Let it sit idle for 30 minutes and it never drifted off of 32mA. So I am back in business!
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Thats why I suggested 21k by piggybacking the 100K on top. Beats lifting the board up
 
glip22 said:
Thats why I suggested 21k by piggybacking the 100K on top. Beats lifting the board up
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Yeah I know, but I'm a stickler for neat wiring. After years as a low voltage field tech, I like it to look good. :)
 
SFW said:
Yeah I know, but I'm a stickler for neat wiring. After years as a low voltage field tech, I like it to look good. :)
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I'm exactly the same way. It's called anal, or slightly OCD 123.....
 
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