The Amp Garage

Don’t put too much into that particular spec ..

bcmatt wrote: ↑Mon Mar 18, 2024 4:11 pm So, I'll put the dropping resisters back to stock for now and see if I can get close to schematic voltages through some tube swaps.

Maybe hold off with your soldering iron until you’ve tested with a full set of known good tubes?

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Hammond 154G?

Fits and has the basic correct specs.

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What is the ‘D’ node voltage with V1/V2 & V4 pulled? While sockets are empty can you add a static load temporarily to ‘D’ with 5W resistor at reasonable value (Ohm’s law) to hit a current target of ~10mA? What’s the voltage loaded? The goal being, 100% confirm "load" weakness somewhere in and around...

cbass wrote: ↑Fri Mar 15, 2024 10:14 pm BBQ chicken pizza

Awesome ..

Hello Guy -- Recommend you get set up to run simulation using http://www.duncanamps.com/psud2/ . A bit of learning effort. However, in my experience quite accurate and much easier to learn than Spice or other similar general tools. And yes, it's possible to both reduce voltage and improve B+ stabili...

Doubtless touch and go off topic for this spot, but no other alternative seemed obviously better.



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Perhaps a read through of this semi-related thread would help 1974 Deluxe Reverb Restoration.

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martin manning wrote: ↑Tue Mar 12, 2024 8:59 am Still don't understand why the preamp voltages are so high when the OT C voltage is pretty much spot-on. Is the value of the dropping resistor between B and C ok? C is also quite a bit high.

Exactly so ..

What’s the story between B & C? Seems the elevated potential begins there ..

Hello -- A pair of mil-spec quality 6AQ5/6005 ($10-15 at most) will work durably in a Princeton circuit with a 330VDC B+. Keep plate current within max dissipation using a sensible bias. Data sheet value for 6V6 "max voltage" spec is 315VDC, and yet Fender's Deluxe Reverb run between 410-450VDC work...

Hello —

Depending on guitar pickups somewhere round 4 to 5 is that obvious edge threshold. This was consistent within one notch across half dozen examples I had here at one time. Martin, as expected, has the guidance for you. Check preamp plate voltages too, if you haven’t already.

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Mmmmm --

Reeltarded wrote: ↑Thu Feb 29, 2024 11:17 pm QUAD CORTEX AWAY!!

Jumpin' the SHARC.

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Hello --

I have had good experiences with both 6CA7EH and JJ KT77 as stand-ins for EL34 in the few amps here with aggressively high plate voltages. Small sample as it's just my personal collection, plus family and friends.

Best ..

Hello -- Another solid (perhaps better) option from the Hammond catalog is the 378CX ; with slightly higher secondary, bunch more current, and no winding wasted on 5V rectifier. .. Nice . Bias winding is only 6A instead of 8A…probably works fine still , we all know 183 Twin PT can handle the extra ...