SSS a Hartman Manning Affair

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dreric
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Re: SSS a Hartman Manning Affair

Post by dreric »

OK now to the power tube wiring. The ultra linear taps go to pins 3 and 4.

I've never done this before. Do I wire it the same as a 6L6? Can I use the same bias checking system as in Martin's diagram.

Standard 6L6 values?
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Eric
1949 Zenith, Zenith Toggle Recoil, Zenith 55 & 440
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martin manning
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Re: SSS a Hartman Manning Affair

Post by martin manning »

With minimal changes to the Hartman layout, this is how you would wire the power tubes. I would keep the 500R (or 470R) screen resistors, the 1k5 grid stoppers, and the 470k from grid to cathode (to limit the CF's cathode voltage on start-up). You'll have another 1R and test point to monitor the bias of each 6550. To switch back to standard p-p, all you have to do is disconnect the screen taps and connect all pin 6's to the screen node. Pin 1 is unused on 6550 so you can use that as a tie point. Some KT88 have pin 1 connected to the base shell, so if you want to run those it would be better to connect pin 1 to pin 8, relocate the 470k's (they could go on the CF socket), and stand the 1k5 grid stopper on end, Marshall style.
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stephenl
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Re: SSS a Hartman Manning Affair

Post by stephenl »

didit wrote: Mon Dec 11, 2017 11:51 pm
stephenl wrote: Mon Dec 11, 2017 11:17 pm You could add in a couple of small relays and make it switchable between UL and Pentode. I did this on one build but I always leave it in Pentode. To me, UL sounds kinda lifeless.
Did your setup disconnect the power amp NFB when UL was connected? Leaving both is definitely deadening.

Best .. Ian
No negative feedback on either of the UL builds.

I also had selectable cathode / fixed bias. I like both sounds but I pretty much left it in fixed bias. The setup I like the best was suggested by Gingertube - I implemented it on my latest build. It's fixed bias with a partial cathode bias. It uses an unbypassed, shared cathode resistor that is about 15% of what you'd normally use. The rest of the bias is supplied from the usual fixed bias supply...
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dreric
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Re: SSS a Hartman Manning Affair

Post by dreric »

Now that the holidays are over, back to the build.

Martin,

I'm having trouble understanding the UL wiring.

Your'e advocating, disconnecting the choke from the screens (pin 6) and disconnecting the screens from the Z node (453V), then connecting the choke to the Z node, correct? Connecting the screen taps from the OT to screens. Correct?

Then I don't understand where the screens are getting their voltage?

Thanks for your help!
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Eric
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Re: SSS a Hartman Manning Affair

Post by sluckey »

The UL screens get their voltage from the OT primary center tap the same as the plates.
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martin manning
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Re: SSS a Hartman Manning Affair

Post by martin manning »

dreric wrote: Sat Jan 06, 2018 7:08 pmYour'e advocating, disconnecting the choke from the screens (pin 6) and disconnecting the screens from the Z node (453V), then connecting the choke to the Z node, correct? Connecting the screen taps from the OT to screens. Correct?
Correct. I don't see a Z node, but yes the downstream side of the choke goes to the one marked 435V. The screen taps are just that, connections to the primary winding about 40% of the way out from the CT. The screen will therefore be at essentially the same voltage as the plate at idle (within a few volts), but when signal is applied and the plate voltage is pulled down, the screen voltage will come down too, but only about 40% as much. (edit: replaced snip with one from Sorado power amp)
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Last edited by martin manning on Fri Jan 12, 2018 2:46 pm, edited 1 time in total.
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dreric
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Re: SSS a Hartman Manning Affair

Post by dreric »

Thanks, this whole UL thing has me nervous, I wanted to be sure I understood.

Just waiting for the 500ohm resistors
Eric
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M Fowler
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Re: SSS a Hartman Manning Affair

Post by M Fowler »

You will be just fine and may like that UL clean.
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martin manning
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Re: SSS a Hartman Manning Affair

Post by martin manning »

500 or 470 ohm would be fine for the screen resistors. The only question I have is, will there be enough filtering in the power supply at the plate/screen. Sunn UL schematics have a high-current C-L-C ahead of the plate node, where here the choke will be ahead of the PI, but with a much larger reservoir cap. A bias balance or separate bias pots might help, or you can easily switch back to conventional plate-loaded push-pull.
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dreric
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Re: SSS a Hartman Manning Affair

Post by dreric »

All buttoned up! Double check tomorrow then the smoke test!
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Eric
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dreric
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Re: SSS a Hartman Manning Affair

Post by dreric »

It's even pretty!
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Eric
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martin manning
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Re: SSS a Hartman Manning Affair

Post by martin manning »

Looks fantastic, and that's a lot of work invested there too! For the smoke test, I'd power up with no tubes and check voltages, using a current limiter initially in case there are any shorts. Normally that is the point where you'd check the bias voltage and range. Here you'll have to put the CF tube in to get those measurements, so that's the first tube to install. If the bias voltage looks good, install the power tubes and see if you can set a good bias point.
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dreric
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Re: SSS a Hartman Manning Affair

Post by dreric »

No matter how many amps I build I'm always amazed when the thing works with the first try. No smoke!

Initial observations:

I've got some significant AC hum. I'll change out the 12AX7s and I think go with a 12AT7 to drive the reverb. Hopefully that will reduce the hum.

It is loud; but more than loud it's "punchy" and "crisp" much more authoritarian that my #002 build.

The reverb is fantastic, a little hot, I'll swap with a 12AT7.

I think I have the pot wired wrong for the FET but that a minor fix, dosen't track right. However, the FET is a great addition to this amp. With humbuckers it gives in a tasty-fuzzy-little-bit-of-break-up. The combination of the FET and the preamp gain gives outstanding sustain.

The presence pot doesn't seem to do anything, I'll check my wiring.

The filters..................

The Low is awesome big change in bass with each notch, very impressive and very usable.

The high doesn't seem to do anything, I'll double check my wiring.

For the first run through I'm very happy with the amp. Time to trouble shoot the hum, the wiring and measure voltages.

Personal thanks to Martin Manning for all of his expertise and help.
Eric
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martin manning
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Re: SSS a Hartman Manning Affair

Post by martin manning »

Great! Does the hum persist with the PI tube pulled? I’d want to rule out the power stage as the source right away.
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dreric
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Re: SSS a Hartman Manning Affair

Post by dreric »

martin manning wrote: Wed Jan 10, 2018 4:34 am Great! Does the hum persist with the PI tube pulled? I’d want to rule out the power stage as the source right away.
I pulled the PI tube (V5) and the hum stays the same. Turning the master volume has no affect on how loud the hum is.

The only thing different I did from your wiring on the power tubes was to install a bias check banana jack on pin, is this OK?
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Eric
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