Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Balticnoiseforge on September 18, 2024, 03:49:58 am
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I have managed to build a really big ampeg v4/V4b that iam really happy with, but the master volume ive used isnt really that good - it is the basic one ampeg used between fx loop.
Sadly i cant use PPIMV since all x6 powertubes have invidual bias which means alot of coupling caps.
Would there be any other position that a master volume could be placed with good results in a early 70 based ampeg?
Maybe after last triode before the floating paraphase? But unsure how to do that without disturbing phase inverter or loading it down with a pot.
Or could it be done by making 0.01uF slightly bigger, add 1meg pot with a 0.01uF at wiper?
Also thought about having it alot earlier, ie after tonestack - but suppose that could make the active mid not work that well :/
Any suggestions appreciated!
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2 or 4 or 6 power tubes need the same PPIMV wiring.
Individual bias are of no importance and make no difference to the wiring.
Look at my next answer:
Use this MV wiring I often built ; great.
Put pots after the 0.047 mfd caps and add new caps on pots wiper C3 and C4 on the scketch
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The MV I use to mod few amp , it work great. I try some other too ; From the first book The Ultimate Tone written by Kevin O'Connor page 5-9
A must to learn and work on amps.
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Oh its a old style ampeg V4, so not SVT.
And dont understand how i could hook up a ppimv when using x6 invidual bias? Ie x6 grid leak resistors being fed on their own by a bias pot, each having a coupling cap before them.
Pretty much like this but with 2 additional tubes.
( Edit missunderdtood your second message at first read, that ppimv could actually work, what values would you recommend prior the ppimv? Since using 0.33uF for coupling after - also thanks for book recommendation !
I usually prefer pre phase inverter MV though, but maybe using a ppimv is the better way )
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I'll same caps value ; 0.047
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I'll same caps value ; 0.047
C3, C4. - 10x - C2, C1
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I'll same caps value ; 0.047
C3, C4. - 10x - C2, C1
:w2:
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I'll same caps value ; 0.047
C3, C4. - 10x - C2, C1
So basically 3.3uF if using a500k stereo?
Or is that with a1m?
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I have managed to build a really big ampeg v4/V4b that iam really happy with, but the master volume ive used isnt really that good - it is the basic one ampeg used between fx loop.
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What don't you like about it?
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I'll same caps value ; 0.047
C3, C4. - 10x - C2, C1
So basically 3.3uF if using a500k stereo?
Or is that with a1m?
What for 3.3uf ?
Follow the K. O'Connor sketch and add 0.047mf with existing 0,047 mf
Pots ; both values are good.
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What for 3.3uf ?
Follow the K. O'Connor sketch and add 0.047mf with existing 0,047 mf
Read the rest of the story.
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I'll same caps value ; 0.047
C3, C4. - 10x - C2, C1
Follow the K. O'Connor sketch and add 0.047mf with existing 0,047 mf
Latole, coupling caps C1 and C2 are supposed to be 10X the value of C3 and C4.
It is to keep the bass from being cut out. And you know it.
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What don't you like about it?
Oh that is really hard to explain in words, it has quite a weird curve of dB, and it wont let you press preamp and still let it sound good without having lots of volume on the master.
I suppose it is abit by design, since without alot poweramp volume it kinda looses its growl.
But still believe it might be a better mV for it out there, will probably try one mentioned here in thread even if i usually prefer pre phase inverter MV that ppimv could probably work good on this amp, and it really needs a master since x6 7027a is quite loud.
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What don't you like about it?
Oh that is really hard to explain in words, it has quite a weird curve of dB, and it wont let you press preamp and still let it sound good without having lots of volume on the master.
I suppose it is abit by design, since without alot poweramp volume it kinda looses its growl.
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Well, if you took the 500k lin master volume spec from the circuit snippet in post 1, the taper (dB curve?) will be, err, linear, so perhaps not user friendly in achieving your goal.
I suggest to try a 100k or 220k audio pot there before you give up on a type 4 master volume.
But there may not be sufficient preamp gain for a useful degree of preamp overdrive. It's usually feasible to tweak things for a bit more gain though.
The type 1 master volume being suggested will provide more gain hence depth of overdrive, though not as much as would normally be the case, due to the 12AU7 phase splitter.
Also the shared cathodes of the floating (self balancing) phase splitter may cause unpleasant sonic artefacts, as there's a positive feedback loop. If so consider splitting the cathodes.
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[quote author=pdf64
Perhaps that is worth a try, not sure it doesnt have enough preamp gain.
But if having master volume on half it sounds like the preamp drive pot stops acting above 60% then it is all the same up to 100%.
But if disengaging the MV pot the preamp drive pots acts on full rotation.
But trying audio pots instead of linear may be a better start to see if that works better.
Barely have any experience with floating paraphase so good to know ppimv could cause issues.
But may it also be worth trying a different tube in the placement? It is basically a early high voltage ampeg from the early 70s, but with altered power amp section - ie two more tubes and invidual bias.
Perhaps another tube type could work better? Even if it may alter the sound slightly, perhaps ecc81 or even a ecc99?
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Tried changing phase inverter tube between ecc81 to ecc83.
Ecc83 worked alot better for preamp gain ( ie rock sound ) at lower MV, while ecc82-81 kept the amp clean for longer and more stable, but ecc83 also made preamp drive more interactive even at lower MV, while ecc81/82 needed more master volume % for that.
Which i suppose shouldnt be a surprise, will continue and try audio taper etc
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Bypassing 2nd stage cathodes at R14&15 would help with preamp gain https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_v4_vt22.pdf
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Yeah it does, iam having so i can bypass those already with a switch, adds quite abit of gain. 👍