Kt66 for dirty shirley?

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Chance terrill

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Does any one know if I can put kt66s in my 40watt dirty shirley..... Maybe some gold Lion kt66s? Would I just have to bias it? And would it sound good? What differences sonically
 
Should work. The difference between sovtek 5881's, and GL kt66's, well I've tried both in an SLO 100, the kt66's were louder, more lows, and more scooped.
 
Oh never mind then lol u just named everything I dont want.... I had heard they are more midrangey like an el34..... If they are more scooped I definitely will stick with 58816l6wgc sovtek s.... Thanks
 
Chance terrill":14k4502o said:
I had heard they are more midrangey like an el34.....
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Yeah, not from my experience. They are more like a 6l6gc. I sent them back, and got GL KT77's. KT77's are more like el34 mids.

sovtek 5881's are a 6l6 type, but they lack the big lows of the 6l6gc's, and that allows the mids, and highs to shine.



If you had the screen resistors changed to 1k, and if they bias up (if not a resistor in the bias circuit can be changed) you can run el34's
Run it by Dave.
 
Im happy with the 5881s I was just wondering if the grass was greener is all.... If I gotta switch stuff then I'm good, i can bias it if I know what to bias it at..... I'm just not sure how to find out plate voltage for a specific tube.... How do u measure that? Or u just go by the manufacturers suggestions?
 
My DS40 has the 1 ohm resistor on the 3rd pin of tube etc. So I know to to measure that in mV since ma n mV r the same across 1 ohm resistance.....or something like that lol.... Basically I know how to bias it to 40mv (Dave's suggestion) for the 5881 sovteks with my 2019 shirley..... But if I were to try and put a different tube in it, I souk dnt know what number to bias it at.... My understanding is u can establish a bias number by measuring the p l ate voltage which idk how to do....... I've seen charts state what bias at what plate voltage for each tube n give options of 50 60 and 70 percent..... But how do u know what the plate voltage is on ur amp?
 
I'm just the type of person who has to know why things work and how to work on them.... I taught myself how to wire a house and side and shingle and lay tile etc..... Biasing an amp can't be that hard right? Well actually adjusting the bias isn't but I know if I didn't have that 1 ohm resistor it be alot trickier to measure...... I read something about measuring voltage drop across the pt which is the shit I want to stay away from.... Filter caps and transformers sketch me out cuz I don't know enough yet
 
Pin 3 is the plate. I would expect the 1 ohm resistor to be on pin 8. I usually put the 1 ohm shunt resistor between 8, and 1, then pin 1 goes to ground.

If Dave biases the 5881 around 40ma I would expect your plate voltage to be around 450vdc

Anyhow take a DC measurement on pin 3 (plate), other lead gnd to chassis. This will tell you your plate voltage. Now head over to http://www.tedweber.com/webervst/tubes1/calcbias.htm

At the top just select the tube type, and enter your plate voltage hit calculate bias. Done
 
It may be pins 8 and 1 because the resistor is going from Two pins next to each other and one has a black wire going to a bolt on the chassis grounding out.... If this is the case, to measure bias I would take one probe to chassis to ground out and the other probe to the side of the resistor that does not have the ground wire soldered to it correct? Which would be pin 8 with pin 1 going to ground like you said....
 
Pin 6 does nothing on EL34, or 6l6 type tubes, but it's usually used as a convenient spot to mount the screen resistor. If your screen resistors are not on the tube sockets then pin 6 would probably not be attached to anything.

As for Pin 1 (g3), this may, or may not be connected on 6l6/5881 types because it is internally connected to the cathode (pin 8). If pin 1 is not connected, and you want to used el34's you must connect it to ground.

 

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Based off what you're telling me I'm pretty sure the one ohm resistor is on pin 8 and 1 because that resistor is right by the notch in the center of the tube and I've been reading that that notches how do you tell where pin 1 and 8 is or are rather so that being the case when I go to measure my biased set it at 40 milliamps and take measurement with one probe going to ground and the other probe going to pin 8 on the resistor?
 
Then if I want to put a different type of 6l6gc in it and measure the plate voltage I would just measure pin 3 and ground to establish plate voltage then go to the Chart you sent me look at 6l6 tubes and go for a 60% bias?
 
Chance terrill":35ejjkht said:
Based off what you're telling me I'm pretty sure the one ohm resistor is on pin 8 and 1 because that resistor is right by the notch in the center of the tube and I've been reading that that notches how do you tell where pin 1 and 8 is or are rather so that being the case when I go to measure my biased set it at 40 milliamps and take measurement with one probe going to ground and the other probe going to pin 8 on the resistor?
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The viewing perspective of the pic I posted is from the bottom of the tube, so if you are looking inside your amp then that maps perfectly with the pic I posted, notch is between 1, and 8.

Yes probe on pin 8, and ground to measure MA.
 
Chance terrill":3gqrzqrh said:
Then if I want to put a different type of 6l6gc in it and measure the plate voltage I would just measure pin 3 and ground to establish plate voltage then go to the Chart you sent me look at 6l6 tubes and go for a 60% bias?
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Yes, measure the plate voltage on pin 3 first. write it down. Go do your calculations for your new tube type using the bias calc. Then pop your new tubes in, and bias them.

One thing to consider, when you put the new tubes in, the bias may initially be really low, really high, or somewhere in the middle. This is because the bias pot was set for the old tubes. This is not a big deal but you want to get the bias in range within a reasonable time, or else your tubes could red plate. Basically do not put the new tubes in, power up, and go make a sandwich before getting the bias in range. haha
 
Oh, and be cautious, dont kill yourself, and donot let the probe slip, it could touch other pins, and blow stuff.
 
So make sure I have a spoon in one hand touching the filter cap and then probe around the power transformer a whole bunch?....... Lol just kidding, thanks for all your help, I don't know that I want to swap out the 5881s because I love my amp through and through as is.... I just want to know how to do stuff myself, also if I was gonna put big money into really good tubes.... What tubes would have the biggest impact.... Power vs pre. And if preamp then I'm assuming v1 would have the biggest impact.... For example if I was gonna buy some gold Lion prep tubes, would they enhance my tone? And should I replace all 3 or just v1 and v2 or just v1 etc........ Thanks again btw
 
Chance terrill":3oup75n2 said:
What do you mean if they bias up? How do you know if they do or not?
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Different tube types need different amounts of negative voltage (bias voltage) you may not have enough range on the bias pot to satisfy this voltage requirement. If you max out the pot and you're only pulling 20ma current through the tube, then you know you can not bias it up. You'll have to then change a resistor in the bias circuit to give you more range. This happens sometimes even with tube that are exactly same type, and brand as you had in there.
 
Chance terrill":11u746y9 said:
So make sure I have a spoon in one hand touching the filter cap and then probe around the power transformer a whole bunch?....... Lol just kidding, thanks for all your help, I don't know that I want to swap out the 5881s because I love my amp through and through as is.... I just want to know how to do stuff myself, also if I was gonna put big money into really good tubes.... What tubes would have the biggest impact.... Power vs pre. And if preamp then I'm assuming v1 would have the biggest impact.... For example if I was gonna buy some gold Lion prep tubes, would they enhance my tone? And should I replace all 3 or just v1 and v2 or just v1 etc........ Thanks again btw
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Really big money does not always mean better. You'll have to experiment. As for Gold Lion, they sound nice in some amps, but I cant personally recommend the power tubes. From my own experience I dropped $200 on a quad of GL KT77's, and while I liked the sound in the amp I had them in, they started to rattle, go micrphonic, and get way out of match in a short period of time.

Here's something to consider, I think if Dave thought there was a better tube combo, he may have just used that (many amp builders initially voice their circuit around a set of tubes they plan on using. If those tubes go away they usually try to find something that sound similar) . Not to discourage you from experimenting, but keep in mind experiment comes with cost, and difficulty. If you're cool with trial & error then go for it. If you expect a guaranteed good result, well YMMV.
 
Well I'm not sure what he used in the pre amp cuz it's that branding company ars, just 12ax7 is all I know, so do u have a recommendation for good preamp tubes?
 
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