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In Reply to: RE: is that a DIY pre-amp? posted by kylealers@gmail.com on July 22, 2015 at 12:53:48
You'll need to experiment with the value. This depends a lot on how each stage is setup. Don't go crazy (like 250mfd) --- or you might get "farting" bad blocking distortion. That's a sign the bypass mfd value is too high.
I'd limit it to 100mfd/50VDC tops. See how the tone is like. 25mfd/50VDC maybe good, if you feel the very low notes are a bit muddy. IOW, you wish to get a cleaner bottom end.
Try to stay with 50VDC or higher voltage rated electrolytic caps.
Good luck! Tells us what bypass works the best.
Follow Ups:
I think I'm going to stay with 25v on the caps because all the original schematics on the web for a alembic F-2B is running 50uF 25v on the bypass caps I could only find 47uF 25v at our local electronics store I'll keep you guys posted on how its sounding
Most older amps and DIY kits were based on 112-118VAC outlet voltages. Today's outlet being ~125VAC can increase B+ significantly more (like 25-50VDC on the plates).
This leads to much greater voltage drawn across the cathode. Pushing the voltage near 25VDC, in some cases. 50VDC rated caps gives you a better range of safety.
I am from south africa our AC outlets are 250-260V some times at night it even goes as high as 280V I've even seen it go as high as 300V tested with my multi meter so I must try 25uF 50v for the bypass caps I have a few 100uF 50v caps will it be safe to try them?
If you tied two 100mfd/50VDC cap in SERIES --- (+) end of one to (-) of other --- you'll get resultant capacitance = 50mfd rated at 100VDC. This might be better for your application.
Like C1 and C2 in diagram.
I went and I got some 47uf 50v caps from the store it definitely improved on the low end a lot its sounding even better think I'm gona keep it just like this we tune down to drop A in my band so my bass has a lot of low end and this made a big difference thanks so much
Sounds good. You can try 100mfd/50VDC or 100/100 caps, but you may get blocking distortion.
Just use the 47mfd/50VDC for now.
BTW... what 5670 tubes are you using? GE black plate JAN-5670W or JG-5670 are nice and available.
I'm using the black plate GE JAN-5670W I'm thinking of experimenting and getting a pair of russian 6N3P's and maybe a pair of 2C51's and experimenting with different combinations of them. I was wondering If it might be possible using that other gain stage in channel the one that is un used to make an effects loop circuit with that has an effects blend as well?
if you might have a schematic of something like that?
You'd need a reverb driver tube. Fender amps usually use a 12AT7, both sections strapped together.-----
Not sure if the second half of that 5670 will have enough gain for the reverb unit.
Edits: 07/24/15
I don't really have any use for reverb I play bass I think I might build myself a effects loop pedal with a effects blend so I can use my tube screamer as well because I need it in a effects loop with a blend pot
But, this and other EFX can be emulated just fine with pedals.
Just disconnect the anode to the unused half.
is it a must to disconnect the anode to the unused halve? Because everything is put back together now
Disconnection just saves that one-half of the duo-triode. Don't worry about it. I'd get a few of those mil-spec GE 5670W tubes, for backup.Then, play the heck out of the amp. Enjoy!
Edit: meant "slap-back." But, you knew that.
8^)
Edits: 07/25/15
I wish I could get a couple of them for backup but its basically impossible finding them locally in south africa I have to get them shipped from the U.S and u.p.s shipping is about $150-$200 and using our local post service is useless it can take up to 6 months IF they arrive its a 50/50% chance the will arive or not.
Those bypass caps how exactly does it work? higer uF means more lows and lower uF means more highs? because those 47uf 50v caps I have in now has perfect low end but the high mids and high's are muddy now and I need them to be clear can I have different uF caps at different gain stages as long as the voltage stay the same?
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