NRTD: 6P3S matched quad

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Re: NRTD: 6P3S matched quad

Post by MikeC »

The tech in me sees a possible issue, can't help myself!! Sorry for going on about it. Cheers.
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Re: NRTD: 6P3S matched quad

Post by NippleWrestler »

MikeC wrote: Thu Aug 12, 2021 7:39 pm The tech in me sees a possible issue, can't help myself!! Sorry for going on about it. Cheers.
No it's fair. What's the problem? I was playing for about 2 hours nonstop with no issues but if there's an issue, how do we resolve it? Bias pot?

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Re: NRTD: 6P3S matched quad

Post by MikeC »

NippleWrestler wrote: Thu Aug 12, 2021 7:43 pm
MikeC wrote: Thu Aug 12, 2021 7:39 pm The tech in me sees a possible issue, can't help myself!! Sorry for going on about it. Cheers.
No it's fair. What's the problem? I was playing for about 2 hours nonstop with no issues but if there's an issue, how do we resolve it? Bias pot?
Techy answer.... You might be fine (I'd bet that you're not) but I would check the plate dissipation to know for sure. You won't be able to do anything about your plate V (which might also kill the 6P3S & the amp) but anecdotally it seems that they can take it. The 6P3S is a different tube than the 6L6-GC and according to the specs I've checked online, has 50% less "max-plate-dissipation" (20W v 30W) and much lower plate & screen grid max voltages than the 6L6-GC. Mesa amps use a fixed "grid bias" biasing arrangement on the power tubes - the idea is that you put in Mesa spec'd 6L6GC tubes and the bias will be fine (and Mesa sells lots of tubes)! I would say that you're risking those 6P3S tubes and any damage that red plating or screen grid shorts could cause to the amp. And you may well get better tone if you bias them correctly. So you would need your variable biasing mod to achieve correct bias or install the correct value bias resistor for the tubes you install. But you have to check the plate dissipation to know. Downside to modding - future owners can't just buy Mesa spec'd tubes and KNOW they are biased correctly. Upside of mod - any 6L6 type tube can be installed and biased correctly!
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Re: NRTD: 6P3S matched quad

Post by NippleWrestler »

Yeah I was just talking tk my amp tech mate about checking the pv and bias in this amp. It's not fun. Something to do with testing the ground tap of the transformer and pin 3, then measuring something else and equating one with the other. He warned me to stay sharp and keep a hand in my back pocket.

I think I'll pass.

Anecdotally. The tung sols were in there for 4 years gigging and whatnot and were awesome. Granted those are 6l6gc tubes.

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Re: NRTD: 6P3S matched quad

Post by MikeC »

My bias probes eliminate all of that and are accurate :)
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Re: NRTD: 6P3S matched quad

Post by NippleWrestler »

MikeC wrote: Thu Aug 12, 2021 8:35 pm My bias probes eliminate all of that and are accurate :)
I'm guessing they're also less lethal.

What can I do to convince you to check my bias with your probe... If you know what I mean.

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Re: NRTD: 6P3S matched quad

Post by MikeC »

I'm always happy to apply my probe. You just might have to come in my basement for some IScream!!!!
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Re: NRTD: 6P3S matched quad

Post by jeremyb »

MikeC wrote: Thu Aug 12, 2021 8:49 pm I'm always happy to apply my probe. You just might have to come in my basement for some IScream!!!!
Aroused.
Slowy wrote: That's the problem; everything rewarding is just such hard work. Regret takes much less effort.

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Re: NRTD: 6P3S matched quad

Post by MikeC »

jeremyb wrote: Thu Aug 12, 2021 8:55 pm
MikeC wrote: Thu Aug 12, 2021 8:49 pm I'm always happy to apply my probe. You just might have to come in my basement for some IScream!!!!
Aroused.
Uh oh...
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Re: NRTD: 6P3S matched quad

Post by murky »

NippleWrestler wrote: Thu Aug 12, 2021 2:53 pm
murky wrote: Thu Aug 12, 2021 2:41 pm Have been wondering about those. Did you get them from Gary?

Edit: https://www.trademe.co.nz/a/marketplace ... D5D018568A
"Got a matched quad of these guys for $45 shipped off the ebay."
Ha ha. Doh.

But was his name Gary?

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Re: NRTD: 6P3S matched quad

Post by NippleWrestler »

Good ol" Gary from Ukraine.

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Re: NRTD: 6P3S matched quad

Post by sizzlingbadger »

Mesa amps are biased very cold, its practically impossible to overdrive the output section too on the high gain amps. The original tubes will probably last a life time too. Unless you are overdriving the output tubes colder bias will sound fine. Biasing the output tubes hotter to say 70% changes the overdrive characteristics which is pointless in these amps.

My Lonestar bias info - 100W Setting Full Voltage Mode with diode rectifier.

Code: Select all

Mesa 6L6STR (30W)
		Vp		Ik mA		W
V6		435		20		8.7
V7		435		12		5.2
V8		435		16		7.0
V9		435		21		9.1

TungSol 6L6STR (30W)
		Vp		Ik mA		W
V6		430		28		12.0
V7		430		32		13.7
V8		430		29		12.5
V9		430		27		11.6

It would be good to run the probe on the 6P3S's at some point for peace of mind though.
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Re: NRTD: 6P3S matched quad

Post by NippleWrestler »

sizzlingbadger wrote: Fri Aug 13, 2021 10:27 am Mesa amps are biased very cold, its practically impossible to overdrive the output section too on the high gain amps. The original tubes will probably last a life time too. Unless you are overdriving the output tubes colder bias will sound fine. Biasing the output tubes hotter to say 70% changes the overdrive characteristics which is pointless in these amps.

My Lonestar bias info - 100W Setting Full Voltage Mode with diode rectifier.

Code: Select all

Mesa 6L6STR (30W)
		Vp		Ik mA		W
V6		435		20		8.7
V7		435		12		5.2
V8		435		16		7.0
V9		435		21		9.1

TungSol 6L6STR (30W)
		Vp		Ik mA		W
V6		430		28		12.0
V7		430		32		13.7
V8		430		29		12.5
V9		430		27		11.6

It would be good to run the probe on the 6P3S's at some point for peace of mind though.
Good info. Thanks for that. I'll arrange a probing session and see what we get.

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Re: NRTD: 6P3S matched quad

Post by jeremyb »

NippleWrestler wrote: Fri Aug 13, 2021 10:36 amI'll arrange a probing session and see what we get.
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Slowy wrote: That's the problem; everything rewarding is just such hard work. Regret takes much less effort.

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Re: NRTD: 6P3S matched quad

Post by MikeC »

sizzlingbadger wrote: Fri Aug 13, 2021 10:27 am Mesa amps are biased very cold, its practically impossible to overdrive the output section too on the high gain amps. The original tubes will probably last a life time too. Unless you are overdriving the output tubes colder bias will sound fine. Biasing the output tubes hotter to say 70% changes the overdrive characteristics which is pointless in these amps.

My Lonestar bias info - 100W Setting Full Voltage Mode with diode rectifier.

Code: Select all

Mesa 6L6STR (30W)
		Vp		Ik mA		W
V6		435		20		8.7
V7		435		12		5.2
V8		435		16		7.0
V9		435		21		9.1

TungSol 6L6STR (30W)
		Vp		Ik mA		W
V6		430		28		12.0
V7		430		32		13.7
V8		430		29		12.5
V9		430		27		11.6

It would be good to run the probe on the 6P3S's at some point for peace of mind though.
Good info, thanks. I didn't know that they biased 6L6's THAT cold - and those Mesa tubes are practically freezing!
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