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Post subject: Re: PT question
Posted: Wed Aug 06, 2014 12:39 am
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BMW2002Ti wrote:
Maybe can use the PT for single-ended 6V6GT or EL84 amp. Like a simple early tweed amp era Champ. One that uses one 12AX7 and one output tube. The B+ maybe good enough for these simple circuit.


The 5E1 Champ needs about 340 VDC at the plate. But if the circuit were modified to run a 6K6GT, that mystery tranny's 260 volts would be more than adequate.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: PT question
Posted: Sat Aug 09, 2014 9:40 am
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Thanks for all the help on this transformer issue. The Hammond PT worked out good with the artificial CT. I also used coax cable to the volume and isolation washers on the inputs with a separate ground. It's basically hum-less (I don't think that's a word). Just installed the re-coned P12Q from Dusty and time to break it in.

Thanks again.

UN


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Post subject: Re: PT question
Posted: Sat Aug 09, 2014 11:06 am
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How's that P12Q sounding at the moment, UN?

Arjay

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Post subject: Re: PT question
Posted: Sat Aug 09, 2014 2:48 pm
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Sorry, I was gone for a while. It's pretty good for a fresh rebuild. A little thin but I only put about 10 minutes on it so far and that's to be expected until it loosens up some. He did a great job on it, I'm very happy with it. I'm really considering those two P12P's but I can't get to where he's at until next w-end. Could have them rebuilt by Dusty if needed and stash for later.

Edit: I need to recall my earlier statement on the P12Q. After I fully loaded it with RCA's it sounds great and I'm sure it will only get better. I would like to extend my sincere apologies to Fender and all the members of the forum for basing my judgement with new production tubes.

UN


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Post subject: Re: PT question
Posted: Sat Aug 09, 2014 5:30 pm
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No apologies necessary -- amp builds are a learning experience for all involved, even us "strap-hangers" who've not yet done it. Your analytical approach to the entire concept is nothing less than methodical IMO and whatever mistakes were made, you managed to isolate and correct them in an orderly, logical fashion.

Tip of the hat to you, sir!

8)

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: PT question
Posted: Sat Aug 09, 2014 5:53 pm
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Thanks Arjay, and a double +1 for the steering toward Dusty.


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Post subject: Re: PT question
Posted: Sun Aug 10, 2014 10:47 am
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He's always done right by me.

And he offers complete cosmetic restorations as well -- something that most of the other shops don't.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: PT question
Posted: Sun Aug 10, 2014 7:28 pm
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That low B+ PT got me thinking. A long time ago (early 1990's), I helped built a Matchless Hotbox clone. We used Tungsol 5687W tubes and not 12AX7. These are lower gain, but have dead quiet background noise. Very slow onset of OD.

Just a thought.


Here's one DIY site I found:

http://diy-fever.com/amps/tube-reactor-pre/

Demo's 1 & 2:

https://www.youtube.com/watch?v=KdFWfv02uMk

https://www.youtube.com/watch?v=q740Q_RKl7k


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Post subject: Re: PT question
Posted: Sun Aug 10, 2014 7:52 pm
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Interesting. Could evolve into a grab and go mini head with a line out.......somehow. :?: :idea:


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Post subject: Re: PT question
Posted: Mon Aug 11, 2014 3:05 am
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BMW2002Ti wrote:
That low B+ PT got me thinking. A long time ago (early 1990's), I helped built a Matchless Hotbox clone. We used Tungsol 5687W tubes and not 12AX7. These are lower gain, but have dead quiet background noise. Very slow onset of OD.

Just a thought.


Here's one DIY site I found:

http://diy-fever.com/amps/tube-reactor-pre/

Demo's 1 & 2:

https://www.youtube.com/watch?v=KdFWfv02uMk

https://www.youtube.com/watch?v=q740Q_RKl7k


That little amp is actually mighty impressive!

Even with the gain dialed up it's quieter than a typical contemporary amp with multiple cascaded stages, active EQ, buffered effects loop, and all the rest of the "modern" baggage that comes along for the ride.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: PT question
Posted: Mon Aug 11, 2014 5:51 pm
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Yeah, I've been toying with a 12AT7 output stage SET DIY amp. With high-efficiency speakers that are made today, anything is possible.

:D


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Post subject: Re: PT question
Posted: Wed Aug 13, 2014 1:32 pm
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I was thinking of trying a 5V4GA in this 5E3, I've got 2 NOS Sylvania's. Just wondering if it's necessary to increase the cathode resistor on the 6V6's first. I do have a 390 ohm 5w and a handful of 400 ohm 5w. I'm basically just experimenting with increasing the plate voltage a little and I can use some EH 6V6's. My plate voltage is about 330v's now, B+ is 382v.

Thanks for any advice.


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Post subject: Re: PT question
Posted: Wed Aug 13, 2014 4:48 pm
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If the plate voltages remain within 25% of each other (between the 5Y3GT and the 5V4GA), you should be ok, with same cathode resistor. Cathode bias has kind of a self-leveling effect, wrt the tube's idle bias. It's why you don't need to worry when swapping gain stage tubes (eg: 12AY7 for a 12AX7).

If you see that the 6V6GT's are red plating or running too "hot" (early onset of OD) --- you may need to adjust the cathode and/or grid-to-ground resistor value.

Good luck!

Here's the rectifier data chart:

-----

Image


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Post subject: Re: PT question
Posted: Wed Aug 13, 2014 5:14 pm
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Thanks. I did try it and also switched the resistor to a 390 ohm. My plate voltage ended up at 358v and the bias reading is 32mv with EH 6V6's (11.4w). With RCA 6V6GT's the plate is 353v and the bias reading is 30mv (10.6w). It seems a little different but I need to spend more playing time on it.


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Post subject: Re: PT question
Posted: Wed Aug 13, 2014 10:19 pm
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390-ohm is kinda lot of resistance for a shared cathode resistor in a 5E3 circuit (push-pull, 6V6GT). Should be closer to 250-ohms, with a 25mfd/50VDC bypass cap.

The plate voltage is a tad high from 6V6GT in Class "A" or hot AB1. Be better around 325VDC. Maybe, try removing a leg of the bypass cap and see how the amp sounds. Or drop the grid-to-ground resistor from 220k-ohms to 180k-ohms.

If the tone is fine with your current setup and you don't have problems with red plating or instability, at volume --- may want to let sleeping dogs lies.


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