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Post by gtrjunior on Oct 16, 2017 8:59:09 GMT -5
I wonder if that’s a possible reason you’re having trouble getting into the bias range?
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Post by cvogue on Oct 16, 2017 14:06:35 GMT -5
I'd call Scott vice emailing. He can take a little while to respond to an email... he's a busy guy!
This sounds bad... I wouldn't do anything with that amp until you hear from him. I'll bet you have it on half power mode so it "works". When it's in this mode the two outside tubes are "disconnected" according to the manual but I'd think there's still going to be some bias there.... and it definitely shouldn't be 0 if the other outside tube is 29!
Let us know what Scott says.
Edit: Also, be aware that you need to adjust the output impedance when going to half power mode (should be half the speaker impedance per the manual). Maybe the previous owner didn't do that and damaged something?
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tjdjr1
Junior Member
Posts: 70 
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Post by tjdjr1 on Oct 16, 2017 18:07:04 GMT -5
I am puzzled too I talked to my old tech who is retired and does not repair anymore and he told me how to check a few things. He had me check the Srcn grid resistors and they are the 1k 5w variety. I checked them after work and this is where I am completely stumped. The S G resistors 3 of them measure in spec and one does not register, BUT the one that does not register is not the one that is on the cold R outside tube ! So I wonder if the other L outside tube has a bad S G resistor and effecting the other (R) side? Anyone know any good tech around the Erie, pa area, I am willing to drive Cleveland, Buffalo, Pittsburgh to get this right, I have heard its potential..
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Post by gtrjunior on Oct 16, 2017 18:47:12 GMT -5
I suppose the bad SG resistor could be affecting the right side since they work in conjunction. Honestly, idk. Not sure if this helps but I tried googling an amp tech in your area.... www.google.com/search?q=guitar+amp+tech+erie,+pa&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari Here in New England I have 2 excellent techs nearby. I’m pretty sure you could ship it to Scott for repair .... Not sure why that link isn’t working. I tried 3x. I just googled “Guitar amp tech Erie, PA” And a handful of places came up...no idea if they are any good. |
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tjdjr1
Junior Member
Posts: 70
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Post by tjdjr1 on Oct 16, 2017 20:45:23 GMT -5
Checking things again after taking in some football and I got to thinking that the locating pin on the one tube is missing and I bet at one time someone may have put the tube in wrong and blew the screen grid resistor. In my explanation I got things twisted in my head and the truth is the cool tube has the blown screen grid resistor, so that would explain the cool tube. I ordered some 5w 1k resistors and when I get it installed gonna try the bias again with these el34 II's, so I could have a bad tube in the mix after all.
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tjdjr1
Junior Member
Posts: 70
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Post by tjdjr1 on Oct 21, 2017 7:54:21 GMT -5
Ok got the screen grid resistor changed and re-biased the old JJ EL34 II's and highest I can get within 1mA is 25, which is higher than when first checked at 15mA. Put in the new EH EL34's and I am up to 29 mA +/- 1mA, better, but what would be the reason bias still a bit cold?. I did buy the EH El34 Red tubes for quicker break-up fairly close matched quad. thanks for any suggestions, still have to pick Scott's brain, but will try that this week..
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Post by gtrjunior on Oct 21, 2017 8:55:23 GMT -5
Do a search on power tubes here in the forum. You’ll find that a LOT of people have had this issue. One solution, iirc is some people changed a resistor to get the bias right.
That’s why, for me I just go through Scott. The numbered set will always work in my particular amp. If there is a way to definitively match other brands to be correct in any given amp, Scott would know how to tell you to determine the right ones so you can order on your own. Or if you email someone like the Valve Queen, she can help you. From what I understand she also has a Quickrod. And she knows her sh!t.
Now that you replaced the grid resistor is the 4th tube powering up properly?
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tjdjr1
Junior Member
Posts: 70
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Post by tjdjr1 on Oct 21, 2017 17:59:00 GMT -5
yes all 4 working as they should even at the 29mA the amp is the amp I had in my mind when I bought this thing. Now I have a loud tone monster ! The EH tubes are a good sounding tube kinda smooth out the trademark mids of the Splawn. I had to turn the bass down and mids and treble up since the swap. I will find out what I have to do to get the bias adjustment fixed. thanks for the help, Tom
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