Tube Amp Archive

Well after weeks of testing and chasing a fault the amp is finally fixed! 😃 The new tubes have solved the issue. The only terrible noise coming out of it now is when i play through it! 😂 I really should have taken heed of my gut instinct. I suspected the tubes initially and its even in the title of ...

Thanks again guys for all your input. The first thing i did was to resolder the tube sockets but with no improvement. As for the V-B+E Phil, i have already probed to the B+ side of the resistors and there was no interference there... I was on the same train of thought as you but, with absence of int...

No not yet, that may well be the next step as every other thing seems to check out ok.... I did a few tests previously that i thought did not point to a single tube. The interference was on both outputs from the power tubes. I thought it would be unlikely to have the same failure at the exact same t...

Pdf - you were correct! Diode is not the fault. I measured the voltage and it did not waver when the noise occured... I understood what you were saying in the previous post about the common mode cancelling out. Of course it would! Thats what the phase inverter is for! 🤦🏻‍♂️ I do however have the fau...

Thanks Pdf - good to see the failings in my knowledge highlighted as that is the only way you learn. You are correct about the cap polarity. My theory seems good to me but in practice may not hold true... My testing will prove that to be the case anyhow. However the noise is in hiding today... I am ...

I have already tested the other side of R14 (82k plate resistor) which feeds pin 6 which is also connected through the 100k. There was no interference on the B+E side but there was on the pin/plate side. Everything is still a possibility but i want to test again with both probes on pins 1 & 6 of the...

So tonight the noise was back - 2 probes, one on the pre amp the other to PI. Only interference on PI probe. So i pulled that tube and the noise stopped, then about 5 seconds later came back with interference on pin 1 of the tube socket! This kinda rules out the PI tube, presence circuit and feedbac...

Thanks for your input Phil. As you suggest my next strategy was to pull the tubes. Its a long winded task as the amp seems to have to be left a long time for the fault to re-occur! I may get 1 shot per night! The volume has no control over the fault and that corresponds to the fault occuring after t...

Pages 8 - 9 are the pages of interest. Ignoring the 4 way tube arrangement, the rest is identical.

https://manualzz.com/doc/6276119/spider-valve-service-manual?__cf_chl_jschl_tk__=8606da4a930d94c727a4bc6b1ad4a0608611dc72-1617387996-0-ARlKmG_Z3M1_8s8nAbTapwSH74IF5cCXCj6WBZ_xr8gHCCa250lxUmHRN6Sqhr9Pk2RTRnClU3VIAd1Aze0Z08xj7ydvboXIKuYu-1xUA9rlrkFy2kgvSpiEW447D8V5sBqt9vJ4Ql4dkqNE2tQv629FnHmmAggVTy2d...

Hi Phil, Yes you are correct the input from guitar plugs into the digital “solid state” side as i called it, and this in turn plugs into the tube main board. I have completely disconnected this and still have the noise. There is no input and yet i have interference present at the PI stage (not at th...

Ha no need to apologise, its good to get some help. The standby switch plugs into the main board. I removed the plug and fitted another same type plug but with the wire are soldered together. Does that make sense? So basically the switch has been taken out of the equation and i still have the noise....

Yes the guitar is completely disconnected. The input of this amp goes through a solid state section for the effects before being run into the main tube board. I have completely disconnected this from the tube board and still have the noise. Thus far I have probed the output of the Pre amp which has ...

Hi Phil, excellent advice. I am a complete newby to amps but have repaired a lot of welding gear so not completely new to electronics. As to why i have never done it - i did not think the amp would work with the tubes out and therefor would be pointless. But thanks for the heads up! That is a great ...

Ok guys thanks for the info. I will revisit the switch again... I managed to get the scope across the output of the inverter tube when the fault occured which also had interference on both channels. I dont believe its the switch as the worst the sound has been was when the switch was completely remo...