Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rake on September 14, 2024, 10:34:04 pm
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Hey all,
The idea of a fairly lightweight amp intrigues me so my little brain came up with a 6V6 based idea. Sort of a Deluxe / Princeton hybrid with an extra preamp switchable boost. Reverb but no tremolo. (I never use tremolo) Figuring on a 25w - 35w single 12" speaker. Please give it a look and let me know it I missed or messed up anything!?!? :dontknow: :help: :w2: :l2:
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I think your amp will work as you've drawn it except for the PPIMV where the dual gang pots need a ground. Having said that, look at some of your cap values and make sure that's what you are intending or wanting? You have two .01 caps that are normally .1 cap values.
With respect, Tubenit
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Hi Rake,
Don't forget your 1R 1W on Pin 8 of output tubes. Makes life easy for checking O/P tube currents :icon_biggrin:
When you have completed the build, during testing you may need to adjust (down) 10k 3W dropping resistor for node C to achieve a "good" PS voltage for preamp. We look forward to your progress :m11
Regards
Mirek
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Thanks Guys! :worthy1:
And, YES, sometimes my fingers do out-type brain! :laugh:
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The master volume / output valve control grid circuit, needs a rethink, it's neither type 1, type 2 or LarMar, though has elements of each.
As it stands, the output valves will run super hot, maybe redplate unless the the bias supply voltage is upped.
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-bias diode is drawn wrong.
You show it as a shunt, should be series.
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-bias diode is drawn wrong.
You show it as a shunt, should be series.
Yep, another brain fart! Had it right on my hand drawn notes and did it wrong on the computer! :dontknow: :w2: :think1: :worthy1:
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I'm not great at finding errors on schematics - thankfully for you and me, others here are. But something you might consider
is a raw control. First attempt I tried a raw switch, but the change was too dramatic. Similar to the gain stage boost you are adding, a raw pot allows fine tuning the tone. Like many things, Sluckey has clear info on that.
Speaking of the gain stage boost. I love the way that works in the Plexi-6V6.
BTW, just a preference thing, but the 6G2 has the best Princeton tone IMO. Most of the tone caps are 0.02 I believe.
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Your phase inverter shows one plate resistor as 320k, I'm guessing that's a typo. There is also a missing connection to one of the coupling capacitors.
Get rid of the 47p between the plates -that was a fudge on early Marshalls that (barely) worked to stabilise their feedback loops; it usually makes things worse in any other amp.
Your PPIMV won't work as shown, as pdf64 noted, but you could do it as shown below.
Bias supply is wrong as Willabe noted.
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Consider a proven Bias Circuit as per attached :icon_biggrin:
Regards
Mirek
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it's neither type 1, type 2 or LarMar,
What do these terms mean?
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somewhere someone came up with 3 "distinct" types of master volume controls, those are the "common" labels used
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I don’t know if Fisher came up with the terms, but the nomenclature is delineated on the “Trainwreck Pages”:
https://robrobinette.com/The_Trainwreck_Pages.htm
About halfway down the page
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(https://el34world.com/Forum/index.php?action=dlattach;topic=32065.0;attach=115734;image)
That Is a Crossline MV
Franco