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Post by flem on Oct 1, 2005 12:22:36 GMT -7
Does anyone know if the trimpot for the bias on the 6545 is for balancing the bias between the power tubes only or also setting the current?
Is there a resistor in the circuit that sets the plate current that I also have to adjust?
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Post by DRZ on Oct 1, 2005 13:09:04 GMT -7
No just a bias pot , like an old marshall I guess. One pot sets the plate currant for both tubes so used matched ones.
Z
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Post by Lefty on Oct 1, 2005 19:43:29 GMT -7
Ahhhhh, the ol "balance"...The curse of the SF Fenders. My '68 Super had that stupid thing. It actually had a bit of both balance and bias, more balance. Luckily they did'nt change much, the fiber board was the same layout...all I had to do was pull out a few resistors and rewire it like it's BF counter parts. Engineers...go figure.
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Post by jackson on Nov 2, 2005 9:06:23 GMT -7
so, how do you measure the bias current on each tube?
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Post by prowler on Nov 14, 2005 5:38:52 GMT -7
I'm interested in knowing where to take the measurement as well. I'd like to bias my 6545 without having to rely on someone else.
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Post by Paul (TRANE) on Nov 15, 2005 8:26:14 GMT -7
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Post by myles on Nov 21, 2005 21:42:41 GMT -7
I personally prefer using a bias tool over the shunt method. They are fast and easy to use and I have used the GT one long before I ever came to GT.
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Post by terryg on Dec 1, 2005 7:03:18 GMT -7
I second that - I'm using the Weber adapter thing with whatever DMM I happen to grab, muy conveniente. It's paid for itself so many times over it's not even funny. Last time I checked, my 6545 w/ a 5AR4 was measuring 410V, and I set the current bias to 28mA. I'm using GTE34LS #6 power tubes. Shame on me, I didn't write down when I checked that. Guess I'll check again....ding, saved another $50 (or more) right there!
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Post by myles on Dec 6, 2005 18:30:33 GMT -7
I second that - I'm using the Weber adapter thing with whatever DMM I happen to grab, muy conveniente. It's paid for itself so many times over it's not even funny. Last time I checked, my 6545 w/ a 5AR4 was measuring 410V, and I set the current bias to 28mA. I'm using GTE34LS #6 power tubes. Shame on me, I didn't write down when I checked that. Guess I'll check again....ding, saved another $50 (or more) right there! Terry .... At 410 B+ with the E34LS (which is a 30 watt tube and not a 25 watter as the other EL34's) bring the bias up a bit. Here is the range at 410 B+ 410 V 30 W 40% 50% 60% 70% 29 37 44 51 So 38-40mA would be pretty great. Make sure your B+ is REALLY 410 off pin 3 of a loaded output tube socket from the bottom of the amp. If it is higher rerun the program. I always thought these amps showed higher B+ but if you are tube rectified and have a slacker rectifier this could be what is going on. When you are out here next time a new rectifier will be on me..... Now if you really want to dial in to the "green range", on my website is a little sort of hidden area. At the top of the main page near the right hand corner, there is a little red sort of button looking thing. I put this here so I could be anywhere there was a PC and have access to this for others. It was originally written by the folks at Duncan amps but I modded it with a lot of text and tube data so I would have it on the road. In any case .... there is a place to plug in your plate voltage and another place for the tube dissapation (such as "25" for an EL34 or "30" for an E34LS etc). It will then show you what to bias at in mA across the scale. I usually bias between 50 and 60%. Hope it's not getting too cold back where you are! By the way .... I should update that xls program and add the Mesa color codes.... Mesa tubes are and the GT rating is Yellow 4 Red 4 Green 5 Gray 5 Blue 6 White 6 Not really a Z issue but I thought I'd sort of toss that in since I mentioned the program.
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Post by terryg on Dec 6, 2005 22:22:01 GMT -7
Hi Myles! That spreadsheet is excellent, definitely. I used it extensively when I was biasing the Z28. I think it's really great news that I'm on the cold side. I have a recollection from when I set it where it's at now, and thinking "wow, this is so much better." My math must have been all goofy or something because I think I usually try to go in for 50% ID at a minimum. Either that or ... this may in fact be the case ... my DMM was messed up. I actually have replaced the DMM that I was using back then! Are you recommending that I take measurement straight from pin 3 on the [socket/pin/male end] instead of relying on the handy Weber adapter? You're the BOSS, and I'll do that....zzzzzzzzzzzt...Shazbot! Aah, the rectifier. I'm using one of these from Mike K. All my 5AR4 amps have one, in fact. kcanostubes.com/content/estore_details.asp?product=149It is becoming frigid out here. No question about it - 18F excites me now. I'm waiting for some approvals to get time off to go to California for Christmas - it's been too long!
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Post by myles on Dec 12, 2005 13:13:50 GMT -7
Hi Myles! That spreadsheet is excellent, definitely. I used it extensively when I was biasing the Z28. I think it's really great news that I'm on the cold side. I have a recollection from when I set it where it's at now, and thinking "wow, this is so much better." My math must have been all goofy or something because I think I usually try to go in for 50% ID at a minimum. Either that or ... this may in fact be the case ... my DMM was messed up. I actually have replaced the DMM that I was using back then! Are you recommending that I take measurement straight from pin 3 on the [socket/pin/male end] instead of relying on the handy Weber adapter? You're the BOSS, and I'll do that....zzzzzzzzzzzt...Shazbot! Aah, the rectifier. I'm using one of these from Mike K. All my 5AR4 amps have one, in fact. kcanostubes.com/content/estore_details.asp?product=149It is becoming frigid out here. No question about it - 18F excites me now. I'm waiting for some approvals to get time off to go to California for Christmas - it's been too long! Terry .... The spreadsheet is also on my website from the little red secret button tha is at the upper right hand corner on the main first page of my website. I like 50%-60% most of the time. Sometime even as high as 70% for some uses in some amps. The Weber tool is fine and dandy. What I do not like is when folks pull one of the output tubes to get to pin 3. You can do that safely but you get a false higher reading as the tube is not there to pull down the power supply. I don't think it has been all that long since you were last out.... you were here for Natalie's new table and I don't feel I have been staring at it all that long. Then again, maybe time flies. You know that you are always welcome to our place anytime you are here, even with no notice. Actually ... unless I am confused ... Wasn't it about early October that you were here. We were going to do something Saturday but I was called at the last minute for the Brad Paisley / Sara Evans concert and was going to work with them Saturday and Sunday so you came over Friday night?
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Post by terryg on Dec 13, 2005 23:18:04 GMT -7
That's a really nice table. I was indeed there in early October, and regrettably was *not* able to get over to Universal to see Erik or Brad that Saturday. You graciously did allow some time with me on Friday, that's right. We spent the time looking at the very special Pierson amp. If the fates are smiling, I'll be back out over Christmas!
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Post by jwr on Dec 30, 2005 23:50:06 GMT -7
Myles, that Mesa color code made my Trem-O-Verb a keeper. Not even the same amp anymore. I talked to you through e-mail a couple of times, and retubed it front to back, your a life saver brother!!!!
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